How to Track a Vampire (Bat)

Posted on October 31, 2012 by TMartin

The arrival of Halloween reminds us to celebrate mythical creatures that frighten yet also intrigue us, although recent popular crazes have made this less of an annual event and more year-round. Along those lines, probably the top three of such imaginary beings are zombies, werewolves, and vampires. All of these can be classified as changelings of a sort, with two of them dead, but not really. Here in Georgia, public fascination with zombies has even provided employment opportunities, as many people compete for coveted slots as shuffling extras on the TV series The Walking Dead.

Among these inspirations for Halloween costumes, short stories, novels, musicals, TV shows, and movies, which would be the toughest for an aspiring Van Hesling to track down using ichnological methods? Zombies would be far too easy, considering their slow-moving, foot dragging, bipedal locomotion; their trackways would also commonly intersect as they bump into one another in their search for cranial sustenance. In other words, zombie trackway patterns would closely match those of people texting.

As a result, we have many modern analogs for zombie traces, which would also make their recognition in the fossil record that much easier. Traces made by the zombie-like characters portrayed in 28 Days Later, however, would be far different, showing greater distances between tracks and reflecting more rapid movement. (And all kidding aside, we actually do have trace fossil evidence of zombie ants from about 50 million years ago, an example of reality trumping fiction.)

Similarly, tracking werewolves would be straightforward, in that trackway patterns should show normal human bipedal locomotion followed by abrupt changes to quadrupedal patterns that would range from a trot to full gallop, gaits that are comparatively rare in humans. Anatomical details of tracks would also include a transition from five-toed plantigrade tracks to four-toed digitigrade ones, and metatarsal impressions would be replaced by heel-pad impressions. Additional traces to expect from a werewolf would be the direct effects of successful predation, such as blood spatters, scattering of prey body parts, toothmarks, and so on. (Don’t ask me about werewolf scat, though. I don’t even want to think about some of the things that would show up in that, especially if they started consuming suburbanites.)

Mixed assemblage of wolf and human tracks, which no doubt proves the existence of werewolves. Or not. Your choice. (Photograph by Anthony Martin, taken in Yellowstone National Park, Wyoming: scale = 10 cm (4 in).)

A closer look at those supposed “wolf” tracks. Yes, I know, they’re in the same area of Yellowstone National Park where a successful wolf-release program took place. But my doubt means you have to consider the impossible as equally valid.

A gorgeous “wolf” track with evidence of skidding to a halt and turning to the right. Could this have been made immediately after a human transformed into a wolf? My Magic 8-ball says, “Ask again later.”

Scene from some movie I’ll never see, in which one of the characters undergoes a mid-air transformation from a human to a werewolf (Canis lupus hormonensis), abruptly changing his tracks from a more plantigrade bipedal running to digitigrade quadrupedal movement. Sorry, I don’t know if any evidence of teen angst would preserve in such a trackway, nor do I care.

In contrast to zombies and werewolves, vampires would be the most challenging to track, considering their occasional aerial phases of movement, as depicted in Bram Stoker’s novel Dracula (1897) and various popular adaptations. Traces made during a pre-transformation phase – while still in human form – would be indistinguishable from those of a non-undead human, texting or not, and once in the air, no evidence of its movement would be recorded.

A large bat (megachiropteran) in flight, leaving no traces of its passing when traveling in a substrate of air.

So just to leave vampires for a moment, let’s talk about bats, which are real and do leave traces of their activities. Knowing that bats are among the most diverse and abundant of mammals (more than 1,200 species), I made sure to discuss their traces in my upcoming book, Life Traces of the Georgia Coast. Although I personally have not yet seen any of their traces on the Georgia barrier islands, these are predictable and identifiable, so I hold out hope that I or someone else will find them some day.

Probably the most likely traces made by bats that one could encounter on the Georgia barrier islands are their feces, which in other places, through the right geology (think caves) and collective action, can form economic resources (more on that later). About 75% of bat species are insectivores, and because they catch their meals on the fly, their scat will mostly contain winged insect parts. However, the geology of the Georgia barrier islands lacks limestone, and thus precludes the formation of caves or other environments serving as roosting spots for bat colonies. Thus bat feces, such as those dropped by the common brown bat (Myotis lucifugus), will be hard to find unless you look in the right place, such as below a favorite roosting spot. If you are lucky enough to notice these, though, these traces are dark 2-3 mm (0.1 in) wide and 5-15 mm (0.2-0.6 in) long cylinders and filled with parts of flying insects.

Two small samples of bat poop for you. You’re welcome. (Image from Internet Center for Wildlife Damage Management.)

Most other bats are fruit-eaters; this means these bats, like many birds, are also important seed dispersers through their excreting indigestible seeds covered in fertilizer. Speaking of fertilizers, massive deposits of bat feces (guano) also accumulate in caves and other places where millions of bats have roosted. These nitrogen- and phosphorous-rich deposits have been mined for fertilizers used in agriculture, an example of feeding traces helping to feed people.

Do bats come to the ground and leave tracks? Yes, once in a while they do, where they might forage and walk on all fours. When they do this, they make diagonal walking patterns, contacting with the thumbs on the tips of their wings – which are skin membranes connected to their other, elongated fingers – and their rear feet.

OK, now back to vampires, or rather, vampire bats. There are only three species of parasitic bats, all of which subsist on the blood of other mammals. For feeding, they slice skin with their sharp teeth, which leaves a small (several centimeters long, millimeters thin) incision. They then lap up whatever blood comes out, and the victim often isn’t aware of its blood loss. These wounds also heal, but leave visible scars.

What about other traces left by vampire bats? Surprisingly, scientists have actually asked themselves, “Hey, I wonder how vampire bats get around on the ground?”, and conducted experiments on terrestrial movement of the common vampire-bat (Desmodus rotundus), as well as the short-tailed bat of New Zealand (Mystacina tuberculata).

Just in case you needed another reason why science is cool, these scientists constructed bat-sized treadmills and placed these bats on them. This experiment confirmed that bats, including the common vampire bat, perform an alternating-walking movement in which the rear foot (pes) registers just behind the thumb, which also bears a claw. (This claw comes in handy as a sort of grappling hook at they climb onto their blood sources.)

Walking on Wings from Science News on Vimeo.

Based on this video, here is what I would hypothesize as the trackway pattern of a walking vampire bat. Note that the rear foot has five digits, nearly equal in length, and that the feet point away from the midline of the trackway.

But then they found out something most people didn’t expect. When they increased treadmill speeds, the bats bound and almost gallop, in which their rear feet nearly move past their wings. While bounding, these bats land on one of the digits on their wings, then push off with their rear feet, causing a suspension phase, reaching maximum speeds of 1.2 m/s. (Which, incidentally, is about the same speed as most people walking while texting, or slow zombies.) The resulting trackway patterns would be in sets of four – rear feet paired behind thumb impressions – separated from one another by about a body length. Based on my viewing of the videos, the trackways would show both half-bound and full-bound patterns, in which the rear feet are either offset or parallel, respectively.

Vampire Running from Science News on Vimeo.

And here is the hypothesized trackway pattern for a running vampire bat, which is almost like a gallop pattern, but more like a half-bound or full-bound. The feet actually should point a little more inward than during walking, and depending on the substrate, deformation structures might be associated with track exteriors.

Just to insert a little paleontology into this consideration of bat traces: has anyone found a trackway, feces, or other traces made by bast in the fossil record? No, unless you count old guano deposits as trace fossils (which I would if they exceed 10,000 years old). The body fossil record for bats extends back to the Eocene Epoch, about 50 million years ago, but such fossils are rare, too. Far more impressive than a bat body fossil, though, would be a fossil bat trackway would be the discovery of a lifetime, almost as noteworthy as finding an actual vampire. And if you found a fossil bat trackway where it was running? Time to start playing the lottery.

More readily available in ancient strata, though, are pterosaur tracks, whose makers likely walked in a manner similar to bats when on land. Hence bats, although not directly related to these flying reptiles, may provide analogues for how some small pterosaurs moved about when on the ground. Despite their long study and many pterosaur fossils, though, a few people are still arguing about how pterosaurs moved on the ground. So hopefully more studies of bat locomotion will help us to better understand the earthbound behaviors of pterosaurs.

The take-home message of the preceding is that even though zombies, werewolves, and vampires still garner plenty of attention from the public, the truth is that real animals of the past and present – like bats and pterosaurs – are actually more fantastic than we sometimes know. Sure, let’s continue to have fun with our mythical creatures, but in the meantime, also keep an eye out for traces left by the marvelous animals of today and yesteryear.

Further Reading

Elbroch, M. 2003. Mammal Tracks and Sign: A Guide to North American Species. Stackpole Books, Mechanicsburg, Pennsylvania: 778 p.

Mazin, J.-M., Billon-Bruyat, J.-P., and Padian, K. 2009. First record of a pterosaur landing trackway. Proceedings of the Royal Society of London, B, 276: 3881-3886.

Padian, K., and Fallon, B. 2012. Meta-analysis of reported pterosaur trackways: testing the corrspondence between skeletal and footprint records. Journal of Vertebrate Paleontology, 32 [Supplement to 3]: 153.

Riskin, D.K. et al. 2006. Terrestrial locomotion of the New Zealand short-tailed bat Mystacina tuberculata and the common vampire bat Desmodus rotundus. Journal of Experimental Biology, 209: 1725-1736.

Different Coastlines, Same Traces, and Time

Posted on October 25, 2012 by TMartin

This past week, I visited North Carolina for varied reasons, but all related to paleontology and geology. First, I gave a well-attended evening lecture about polar dinosaurs, graciously invited and hosted by the Department of Geography and Geology at the University of North Carolina-Wilmington (UNCW). Later in the week, I presented a poster at the Society of Vertebrate Paleontology (SVP) meeting in Raleigh (covered last week here), while also taking in a couple of days of talks, posters, and enjoyably catching up with paleo-friends while meeting neo-friends. Regrettably, I had to leave the meeting early, but with good reason, which was for a field trip to look at fossils in a Pleistocene outcrop near Wilmington with faculty and students from UNCW. Overall, it was a fulfilling week, teeming with paleontological and social variety.

This pithy summary, though, omits lots of details (and if it didn’t, then it wouldn’t be pithy). But one item worth explaining a bit more here was a brief trip to Wrightsville Beach, which is a barrier island was just east of Wilmington. Dr. Doug Gamble, a geography professor in the UNCW Department of Geography and Geology, offered to take me there just before my talk, which I eagerly accepted. Considering all of the field work I had done on the Georgia barrier islands to the south of there, and that I would be teaching a course on barrier islands next semester, going to this beach was an opportunity to learn more about the similarities and differences between Georgia and North Carolina beaches.

Panorama of Wrightsville Beach on the coast of North Carolina, replete with human locomotion traces and dwelling structures. These features make it very different from most beaches in Georgia. But what about other traces? Don’t you just love rhetorical questions? Including this one? (Photograph by Anthony Martin.)

Many North Carolina beaches are famous (or infamous) as examples of what can go wrong with unrestrained development of barrier islands. Many such case studies have been explored through the research, writings, and activism of geologist Dr. Orrin Pilkey of Duke University, as well as other coastal geologists who have looked at the effects of human alterations of these habitats. Wrightsville Beach is such a barrier-island beach, having been heavily modified by human activities during the past 150 years or so. When comparing it in my mind to the Georgia barrier islands, it most resembled Tybee Island, which is also next to a relatively large city (Savannah), easily accessible by a bridge, and developed as a sort of “vacation destination” for people who like beaches, but also want them to have all of the amenities of the places they left behind. Otherwise, it held little resemblance to the mostly uninhabited and undeveloped beaches I prefer to peruse on the Georgia barrier islands.

After driving over the bridge to the island, we walked onto the beach in several places, and I began looking for traces. At first there was little to see, which was a direct result of there being too much to see. Because it was a pleasant day and we were visiting in the afternoon, much of the beach had been heavily trampled by humans, with more than a few of these people aided in their bioturbation by canine companions. Obvious restructuring of the beach included a jetty at the north end that combined a concrete wall and boulders, and pilings of concrete blocks at the south end. Dunes were modest, low-profile, and capped by sparse stands of sea oats (Uniola paniculata), and behind these were hotels, condominiums, and houses, all chock-a-block. It would be too strong to say this beach was alien to me, let alone post-apocalyptic, but it did seem like an altered reality compared to my experiences in Georgia.

A jetty at Wrightsville Beach (North Carolina) composed of concrete and rocks, intended to preserve sand on the beach, which it is doing here, but also results in an imbalanced distribution of sand along it. Note the abundant human and canine tracks on the right, shouting out any other animal traces that might have been in the sand. (Photograph by Anthony Martin.)

Another view of the jetty at Wrightsville Beach, sharply contrasting sand deposition and erosion on either side of it. (Photograph by Anthony Martin.)

A pile of broken concrete being used as rip-rap at the south end of Wrightsville Beach in an attempt to slow erosion there. Or something. (Photograph by Anthony Martin.)

Only with more walking toward the south end of the beach did we see less of an overwhelming human-dog ichnoassemblage and start noticing signs of the native fauna. With this, I became comforted by the familiar. These traces included some I had seen many times on Georgia beaches, including: the soda-straw-like burrows of parchment worms (Onuphis microcephala); the volcano-like sand mounds and chocolate-sprinkle-like feces of callianassid shrimp (either Biffarius biformis and Callichirus major); the soft-serve-ice-cream-like fecal mound of acorn worms (Balanoglossus aurantiactus); and the hole-in-the-ground-like burrows of ghost crabs (Ocypode quadrata). (OK, so I ran out of metaphors.) Seagull tracks abounded as well, lending more of a dinosaurian flavor to the trace assemblage.

Two burrows of parchment worms (Onuphis microcephala) on Wrightsville Beach, exposed by a little bit of erosion, with tiny fecal pellets at their bases. Scale in millimeters. (Photograph by Anthony Martin.)

Burrow aperture and fecal pellets of a ghost shrimp (either Biffarius biformis or Callichirus major) on Wrightsville Beach. Scale in millimeters again. (Photograph by Anthony Martin.)

Fecal casting of an acorn worm, and probably that of a golden acorn worm (Balanoglossus aurantiactus) on Wriightsville Beach. One end of its burrow is underneath this pile, and that would be its anal end, which is sensibly located in a different place from its oral end. And I think you know the scale by now. (Photograph by Anthony Martin.)

Ghost crab (Ocypode quadrata) burrow and tracks, out of the intertidal zone and more into the dunes on Wrightsville Beach. (Photograph by Anthony Martin.)

These traces thus showed us that this North Carolina beach, one majorly changed by humankind during the past 150 years, actually was more biodiverse than one might think at first glance. In my mind, then, it became just a bit more wild through these signs of life hinting at what laid beneath our feet.

At this point, I could depress everyone by listing what traces and biota were not there, but that’s not the point, so I won’t. In a more progressive sense, what traces we saw represented traces of hope, of life hanging on despite environmental change, living almost invisibly beneath our feet. So as human development continues on beaches like these, and sea level rises through the rest of this century, I felt assured of their being survivors of this change, and of their traces outlasting our humanity. The trace fossils of the future are now, and recording our effects on the life that makes these traces. How many will wink out with our species, and how many of their marks will outlast us?

An intergenerational stroll – a grandmother and grandson? – alongside the pier on Wrightsville Beach in North Carolina. Did she have memories of this beach in her childhood? How do these compare to what she sees there now? What memories will this child have of it in the future, especially as the sea continues to rise? If these memories are not recorded, what will be left behind? (Photograph by Anthony Martin.)

Further Reading

Pilkey, O., and Fraser, M.E. 2005. A Celebration of the World’s Barrier Islands. Columbia University Press, New York: 309 p.

Thieler, E.R., Pilkey, O., Cleary, W.J., and Schwab, W.C. 2001. Modern sedimentation on the shoreface and inner continental shelf at Wrightsville Beach, North Carolina, U.S.A. Journal of Sedimentary Research, 71: 958-970.

Deconstructing an Ichnology Abstract, with Alligators

Posted on October 19, 2012 by TMartin

Many people from outside of the realm of academia (or is it a fiefdom?) prefer to get the latest scoops on new paleontological or geological research directly from the source, rather than just reading a press release or news article about it. As someone looking from the inside out, I’m pleased to see so many non-scientists try to probe one layer deeper with their understanding of a beloved scientific topic that interests them, and I try to encourage it through my own blogging, speaking, teaching, and other forms of outreach.

An alligator den on St. Catherines Island, (Georgia), with baby alligator and “big momma” alligator for scale. This week, I presented a poster with about these big burrows and their makers at the Society of Vertebrate Paleontology meeting in Raleigh, North Carolina. The original field work we did for this research was reported back in March here, and now we’re ready to share more of what we found out. (Photograph by Anthony Martin.)

Unfortunately, many of the original research articles that become subjects of media attention are behind paywalls, requiring a reader to pay for access to read those articles, even if the research was publicly funded. This practice is especially common if the research is published in one of those glamorous journals that seemingly make or break academic careers in science, regardless of the lasting quality of the research. (I won’t name them directly, but let’s just say that’s the nature of science nowadays.)

So one option for these curious folks is to read abstracts from proceedings volumes of professional meetings. Abstracts, which ideally are succinct summaries highlighting the most significant findings of a given study, can thus serve as a way for the public to at least get a few insights on the latest scientific research happening in their favorite disciplines.

Want to get below the surface with this research? Oh, sorry, I was just being metaphorical. You really don’t want to go below the surface of an alligator den, which is why we mostly studied abandoned ones, mapped them, and otherwise tried to use methods that didn’t bother the alligators or otherwise have uncomfortable encounters with them.

Along those lines, the annual meeting of the Society of Vertebrate Paleontology (SVP) has been taking place this week in Raleigh, North Carolina, and it has an abstract volume associated with the meeting. Regrettably, though, the general public does not have access to these abstracts, only SVP members and people who have registered for the meeting. The Society of Vertebrate Paleontology also has a policy regarding researchers who publicly share their research results based on these abstracts, muddied by the word “embargo.” In short, this policy holds that people working for the media, which include reporters and bloggers (the latter of whom are also sometimes reporters), cannot write about and otherwise publicize research results presented at the meeting. That is, unless the researchers have given their permission to do so, or the results have been freely distributed by the researchers through a press release, blog, or other forms of outreach.

So in the spirit of the public having easier access to this primary scientific information, the following is our SVP abstract, which I presented as a poster at the meeting yesterday. The abstract is co-authored with Michael Page (Emory University), Sheldon Skaggs (Georgia Southern University), and R. Kelly Vance (also Georgia Southern University), and we worked together on the research, writing, and editing of the abstract. Because this abstract also includes a lot of scientific shorthand (charitably referred to as “jargon”), I also included a sentence-by-sentence explanation of it, in which the abstract text is in italics and my explanation is in formal typeface. So I hope you, the gentle reader, get something from this exercise in explanation, and we look forward to sharing more of this research with you as it continues to evolve and we publish it sometime next year as a peer-reviewed paper.

DENS OF THE AMERICAN ALLIGATOR (ALLIGATOR MISSISSIPPIENSIS) AS TRACES AND THEIR PREDICTIVE VALUE FOR FINDING LARGE ARCHOSAUR BURROWS IN THE GEOLOGIC RECORD

MARTIN, Anthony J., Emory University, Atlanta, GA, United States; PAGE, Michael, Emory University, Atlanta, GA, United States; SKAGGS, Sheldon, Georgia Southern University, Statesboro, GA, United States; VANCE, Robert K., Georgia Southern University, Statesboro, GA, United States

Large archosaur burrows are rarely interpreted from the geologic record, a circumstance that may be attributable to a lack of search images based on modern examples, rather than actual rarity.

Archosaurs make up an evolutionarily related group of vertebrates that include crocodilians (alligators and crocodiles), dinosaurs (the non-bird ones, that is), birds, and their extinct relatives. A few of the larger extinct archosaurs may have dug burrows, but paleontologists have reported very few of these, with one exception being the small Cretaceous ornithopod dinosaur Oryctodromeus cubicularis, found in its burrow with two juveniles of the same species. The authors are proposing here that this “rarity” of archosaur burrows in the fossil record might be more attributable to paleontologists not knowing what modern archosaur burrows look like. So they don’t recognize the fossil ones, leading to a perceived rarity rather than an actual one.

To test this idea, we measured, imaged, and mapped den structures of the American alligator (Alligator mississippiensis) on St. Catherines Island (Georgia, USA).

By “measured,” I mean that my colleagues and I used a low-tech instrument known as a “tape measure” to assess the width and height of an alligator den entrance. By “imaged,” we used a much more technologically complex instruments and method, called ground-penetrating radar (GPR) in combination with computers to figure out what these dens looked like below the surface. By “mapped,” I mean that we looked for alligator dens on St. Catherines Island (Georgia) and recorded their locations using a handheld GPS (global positioning system) unit, then plotted the distribution of these points to see if any patterns emerged.

St. Catherines is an undeveloped barrier island on the Georgia coast, consisting of Pleistocene and Holocene sediments.

St. Catherines Island is undeveloped in the sense that very few buildings or people live on the island year-round. It is privately owned and reserved for researchers’ uses under the direction of the St. Catherines Island Foundation. Like most of the Georgia barrier islands on the southern part of its coast, St. Catherines also has a geologically complex history. Its northwestern end is made of sediments deposited about 40,000 years ago – during the Pleistocene Epoch – whereas its southeastern end is made of much more recent sediments from the Holocene Epoch.

Alligators dug most dens along the edges of freshwater ponds in loosely consolidated Holocene or Pleistocene sand.

This sentence doesn’t need much more explanation other than to reemphasize that alligators gravitate to freshwater ecosystems to dig their dens (pictured below), not saltwater ecosystems, like salt marshes or coastal dunes.

Adult female alligators use dens to protect offspring, but burrows also aid in thermoregulation or serve as refugia for alligators during droughts and fires.

This is probably the neatest insight we gained from doing the research, is that the dens aren’t just used by big momma ‘gators for raising baby ‘gators, but also to make sure alligators of all ages are cozy during winters, stay wet during droughts, and are safe from fires. For instance, because southern Georgia has been going through a drought the past few years, some of the occupied dens we saw were in places that were high-and-dry, but the dens themselves intersected the local water table (seen in one photo above).

Some dens are evidently reused and modified by different alligators after initial construction.

This is an important point for paleontologists to know, and probably shouldn’t have been buried so far into the abstract, but we couldn’t very well put it at the beginning, either. Dens, like other homes, get used again, and probably by generations of alligators. This means that once a den is dug, stays open, and has a wetland nearby, alligators may just move into an abandoned den and modify it if needed, an alligator form of “home improvement.”

Drought conditions along the Georgia coast have exposed many abandoned dens, thus better allowing for their study while increasing researcher safety.

The drought is bad for alligators but was good for us when we did our field work, because so many dens were abandoned and exposed on dry land. This also eased any concerns we had about bothering the alligators, but especially alleviated worries we might have had about close encounters with protective parents near occupied dens. To be sure, we ran into a few of those, but not as many as we would have if conditions had been wetter.

Den entrances have half-moon cross-sections, and based on one sample (n = 20), these range from 22-115 cm wide (mean = 63 + 23 cm) and 14-55 cm high (23 + 9 cm).

I like throwing numbers into ichnology, just to remind people that this is a part of it as a science. Although our sample size is small compared to other studies of traces and trace fossils, it gives people an idea of the range of sizes of these dens, or at least their entrances. As an exercise in the imagination, think about whether you could squeeze into one of these. You know, if you were crazy enough to do such a thing.

In addition to field descriptions, we applied geographic information systems (GIS) and ground-penetrating radar (GPR) to help define the ecological context and subsurface geometry of these structures, respectively.

Computer-aided mapping methods like GIS helped us to test how alligators decided to make dens as a function of the landscape. For instance, we found most of their dens were in lower-elevation areas, which made sense when you think about water accumulating in those places. And the GPR served the dual purpose of not bothering the alligators if they were in their dens, while also keeping us away from their, um, denizens. (Sorry.)

GIS gave spatial data relatable to alligator territoriality, substrate conditions, and proximity to potential nest sites. GPR produced subsurface images of active dens, which were compared to abandoned dens for a sense of taphonomic history.

Big alligators tend to stay away from other big alligators. They also tend to burrow in sediments that don’t take too much effort for them. Female alligators also make their nests close to water bodies and dens, so their little tykes don’t have to travel so far to the water. Newer, active dens were also compared to those no longer being used to see what happens to them over time with neglect, kind of like how an old, abandoned house tends to fall apart and collapse on itself over time.

Most den entrances are southerly facing, with tunnels dipping to the northwest or northeast.

This is pretty self-explanatory, but I’ll just ask readers to think about why these dens are oriented like this.

From entrances, tunnels slope at about 10-15°, turn right or left within a meter, and lead to enlarged turn-around chambers.

Pure description here too, but by “turn-around chamber,” that means the den has enough room inside the den for a big adult alligator to go in head-first and turn around so that it’s head is right at the entrance. (See the photo of “big momma” at the top for an example of that.)

Collapsed dens in formerly ponded areas (secondary-succession maritime forests) provided further insights into subsurface forms of these structures.

Dens left high-and-dry from years ago and taken over by forests collapsed in a way that we could see the full outline of the den and measure these.

These features are: 3.1-4.6 m long; 30-40 cm deep, relatively narrow at either end (35-60 cm), and 1.2-1.6 m wide in their middles.

Dude. Those are big burrows. Dude.

Expansive areas were probable turn-around chambers, and total volumes of collapsed dens accordingly reflect maximum body sizes of their former occupants.

The bigger the den, the easier it was for a large occupant to turn around in it. And although smaller, younger alligators could have lived in these dens, some of the dens were too small to allow the really big alligators from moving into them.

One sampled area (8,100 m²), an almost dry former pond, had 30 abandoned dens, showing how multiple generations of alligators and fluctuating water levels can result in dense concentrations of alligator burrows over time.

Think of an area about the size of an American football field, and put 30 alligator dens in that area. (Now that would make for an interesting game, wouldn’t it?) These dens weren’t all made at the same time, though, and were constructed or abandoned as the pond filled or dried out, respectively.

In summary, the sheer abundance, distinctive traits, and sizes of these structures on St. Catherines and elsewhere in the Georgia barrier islands give paleontologists excellent search images for seeking similar trace fossils made by large semi-aquatic archosaurs.

That’s the big take-home message here for vertebrate paleontologists. All of the information we gathered about these alligator dens from the Georgia barrier islands, especially what they look like, can be applied to test the fossil record of archosaurs. In other words, did archosaurs actually leave lots of dens for us to find, but we just didn’t know what to look for? Hopefully we’ll find out because of this research.

Later, denning ‘gator. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)

(Special thanks to Ruth Schowalter for assisting with the field work, and to the St. Catherines Island Foundation for funding some of the research.)

Source of Abstract (Reference):

Martin, A.J., Page, M., Vance, R.K., and Skaggs, S. 2012. Dens of the American alligator (Alligator mississippiensis) as traces and their predictive value for finding large archosaur burrows in the geologic record. Journal of Vertebrate Paleontology, 32 [Suppl. to No. 3]: 136.

Descent with Modification

Posted on October 9, 2012 by TMartin

At this time last year, Fernbank Museum of Natural History was hosting the Darwin exhibit. On loan from the American Museum of Natural History, this exhibit was a major coup for the museum and the Atlanta area, which has enjoyed a growing culture of celebrating science during the past few years. Along with this exhibit, the museum also planned and concurrently displayed an evolution-themed art show, appropriately titled Selections, which I wrote about then here.*

Descent with Modification (2011), mixed media (colored pencils and ink) on paper, 24″ X 36.” Although this artwork might at first look like a tentacled creature infested with crustaceans and living on a sea bottom, its main form actually mimics a typical burrow system made by ten-legged crustaceans (decapods). Yet it’s also an evolutionary hypothesis. Intrigued? If so, please read on. If not, there are plenty of funny cat-themed Web sites that otherwise require your attention. (Artwork and photograph of the artwork by Anthony Martin.)

One unusual feature of this art show was that five of the eight artists were also scientists (full confession: I was one of them). Furthemore, one of the other artists was married to a scientist (fuller confession: that would be my wife Ruth). The show stayed up for more than three months, which was also as long as the Darwin exhibit resided at Fernbank. Thus we like to think it successfully exposed thousands of museum visitors to the concept that scientists, like many other humans, have artistic inspirations and abilities, neatly refuting the stereotype that not all of us are joyless, left-brained automatons and misanthropes.

Last week I was reminded of this anniversary and further connections between science and art during a campus visit last week by marine biologist and crustacean expert Joel Martin (no relation). Dr. Martin was invited to Emory University to give a public lecture with the provocative title God or Darwin? A Marine Biologist’s Take on the Compatibility of Faith and Evolution. His lecture was the first of several on campus this year about the intersections between matters of faith and science, the Nature of Knowledge Seminar Series. This series was organized as a direct response to the university inviting a commencement speaker this past May who held decidedly strong and publicly expressed anti-science views.

Dr. Martin, who is also an ordained elder in his Presbyterian church and has taught Sunday school to teenagers in his church for more than 20 years, gave an informative, organized, congenial, and otherwise well-delivered presentation to an audience of more than 200 students, staff, faculty, and other people from the Atlanta community. In his talk, Martin effectively explored the false “either-or” choice often presented to Americans who are challenged by those who unknowingly misunderstand or deliberately misrepresent evolutionary theory in favor of their beliefs. Much of what he mentioned, he said, is summarized in a book he wrote for teenagers and their parents, titled The Prism and the Rainbow: A Christian Explains Why Evolution is Not a Threat.

I purposefully won’t mention any of the labels that have been applied to the people and organizations who promote this divisiveness between evolutionary theory and faith. After all, words have power, especially when backed up by Internet search engines. Moreover, it is an old and tired subject, of which I grow weary discussing when there is so much more to learn from the natural world. Better to just say that Martin persuasively conveyed his personal wonder for the insights provided by evolutionary theory, how science informs and melds with his faith, and otherwise showed how science and faith are completely compatible with one another. You know, kind of like science and art.

Previous to his arrival, his host in the Department of Biology asked Emory science faculty via e-mail if any of us would like to have a one-on-one meeting with Dr. Martin during his time here. I leaped at the chance, and was lucky enough to secure a half-hour slot in his schedule. When he and I met in my office, we had an enjoyable chat on a wide range of topics, but mostly on our shared enthusiasm for the evolution of burrowing crustaceans, and particularly marine crustaceans.

Ophiomorpha nodosa, a burrow network in a Pleistocene limestone of San Salvador, Bahamas. In this instance, the burrows were probably made by callianassid shrimp, otherwise known as “ghost shrimp,” and are preserved in what was a sandy patch next to a once-thriving reef from 125,000 years ago. (Photograph by Anthony Martin.)

Interestingly, during this conversation we also touched on on how art and science work together, and I was pleasantly surprised to find out that Dr. Martin is a talented artist, too. It turns out he has illustrated many of his articles with exquisite line drawings of his beloved subjects, marine crustaceans. Yes, I realize that some artists like to draw a line (get it?) between being an “artist” and an “illustrator,” with the latter being held in some sort of disdain for merely “copying” what is seen in nature. If you’re one of those, sorry, I don’t have the time or inclination to argue about this with you. (Now go back to putting a red dot on a white canvas and leave us alone.)

Cover art of branchiopod Lepidurus packardi from California, drawn by Joel W. Martin, for An Updated Classification of the Recent Crustacea, also co-authored by Joel W. Martin and George E. Davis: No. 39, Science Series, Natural History Museum of Los Angeles County, Los Angeles, California.

During our discussion in my office, I pointed out a enlarged reproduction of a drawing of mine depicting the burrow complex of an Atlantic mud crab (Panopeus herbstii). He immediately recognized it as a crustacean burrow, for which I was glad, because it is an illustration of just that in my upcoming book, Life Traces of the Georgia Coast.

Burrow complex made by Atlantic mud crab (Panopeus herbstii), originally credited to a snapping shrimp (Alpheus heterochaelis). Scale = 5 cm (2 in). (Illustration by Anthony Martin, based on epoxy resin cast figured by Basan and Frey (1977).

After his campus visit, though, I realized that an even more appropriate artistic work to have shown him was the following one made for the Selections art exhibit last fall, titled Descent with Modification. This title in honor of the phrase used by Charles Darwin to describe the evolutionary process, but also is a play on words connecting to the evolution of burrowing crustaceans.

Descent with Modification again, but this time look at it as an evolutionary chart, where the burrow junctions in the burrow system reflect divergence points (nodes) from common ancestors. For example, from left to right, the ghost shrimp is more closely related to a mud shrimp, and both of these are more closely related to the ghost crab (middle) than they are to the lobster and freshwater crayfish (right). The main vertical burrow shaft represents their common ancestry from a “first decapod,” which may have been as far back as the Ordovician Period, about 450 million years ago.

The image shows five burrowing crustaceans, or to be more specific, ten-legged crustaceans called decapods. Along with these is a structure, which has a burrow entrance surrounded by a conical mound of excavated and pelleted sediment, a vertical shaft connecting to the main burrow network, and branching tunnels that lead to terminal chambers. A burrowing crustacean occupies each chamber, and these are, from left to right: a ghost shrimp (Callichirus major), a mud shrimp (Upogebia pusilla), a ghost crab (Ocypode quadrata), a marine lobster (Homarus gammarus), and a freshwater crayfish (Procambarus clarkii).

Here’s the cool part (or at least I think so): this burrow system also serves as an evolutionary chart – kind of a cladogram – depicting the ancestral relationships of these modern burrowing decapods. For example, lobsters and crayfish are more closely related to one another (share a more recent common ancestor) than lobsters are related to crabs. Mud shrimp are more closely related to crabs than ghost shrimp. Accordingly, the burrow junctions show where these decapod lineages diverged. So the title of the artwork is a double entendre with reference to Darwin’s phrase describing evolution as a process of “descent with modification,” along with burrowing decapods undergoing change through time as they descend in the sediment.

Modern decapod burrows and trace fossils of probable decapod burrows support both the science and the artwork, too. Here are a few examples to whet your ichnological and aesthetic appetites:

Thalassinoides, a trace fossil of horizontally oriented and branching burrow systems made by decapods in Early Cretaceous rocks (about 115 mya) of Victoria, Australia. In this case, these burrows were likely by freshwater decapods, such as crayfish, which had probably diverged from a common ancestor with marine lobsters more than 100 million years before then. Scale = 10 cm (4 in). (Photograph by Anthony Martin.)

Thalassinoides again, but this time in limestones formed originally in marine environments, from the Miocene of Argentina. Note the convergence in forms of the burrows with those of the freshwater crayfish ones in Australia. Think that might be related to some sort of evolutionary heritage? Scale = 15 cm (6 in). (Photograph by Anthony Martin.)

Horizontally oriented burrow junction of a modern ghost shrimp – probably made by a Carolina ghost shrimp (Callichirus major) – exposed along the shoreline of Sapelo Island, Georgia. Note the pelleted exterior, which is also visible on the burrow networks of the fossil ones in the Bahamas, pictured earlier. So if fossilized, this would be classified as the trace fossil Ophiomorpha nodosa. Scale in centimeters. (Photograph by Anthony Martin.)

Two ghost-shrimp burrow entrances on a beach of Sapelo Island, Georgia, with the one on the right showing evidence of its occupant expelling water from its burrow. No scale, but burrow mound on right is about 5 cm (2 in) wide. (Photograph by Anthony Martin.)

Burrow entrance and conical, pelleted mound made by a freshwater crayfish (probably a species of Procambarus) in the interior of Jekyll Island, Georgia. Scale = 1 cm (0.4 in). (Photograph by Anthony Martin.)

So the take-away message of all of these musings and visual depictions is that evolution, faith, science, art, trace fossils, modern burrows, and burrowing decapods can all co-exist and be celebrated, regardless of whether we sing Kumbaya or not. So let’s stop dividing one another, get out there, and learn.

*I’m also proud to say that my post from October 17, 2011, Georgia Life Traces as Art and Science, was nominated for possible inclusion in Open Laboratory 2013. Thank you!

Further Reading

Basan, P.B., and Frey, R.W. 1977. Actual-palaeontology and neoichnology of salt marshes near Sapelo Island, Georgia. In Crimes, T.P., and Harper, J.C. (editors), Trace Fossils 2. Liverpool, Seel House Press: 41-70.

Martin, A.J. In press. Life Traces of the Georgia Coast: Revealing the Unseen Lives of Plants and Animals. Indiana University Press, Bloomington, IN: 680 p.

Martin, A.J., Rich, T.H., Poore, G.C.B., Schultz, M.B., Austin, C.M., Kool, L., and Vickers-Rich, P. 2008. Fossil evidence from Australia for oldest known freshwater crayfish in Gondwana. Gondwana Research, 14: 287-296.

Martin, J.W. 2010. The Prism and the Rainbow: A Christian Explains Why Evolution is Not a Threat. Johns Hopkins University Press, Baltimore, MD: 192 p.

Martin, J.W., and Davis. G.E. 2001. An Updated Classification of the Recent Crustacea, No. 39, Science Series, Natural History Museum of Los Angeles County, Los Angeles, California: 132 p.

The Traces We Leave Behind: A Tribute to Jordi Maria de Gibert

Posted on September 28, 2012 by TMartin

Paleontologists have an odd relationship with death. We often joke about how our livelihoods depend on what has died before us, or we experience great delight when we find an exquisite fossil, which probably was buried alive for it to be so well preserved. We also blithely talk about “death assemblages” and happily explain this gruesome term to non-paleontologically inclined students, friends, spouses, and partners without much thought about how it sounds to people outside of our field.

For ichnologists, who mostly study the tracks, burrows, and other vestiges of these lives that preceded us, our perspectives become even more skewed. Once-live animals, through their behavior, made trace fossils. Yet we almost never see what made them. Hence we also spend much of our time among the living, watching them make traces that we can use as analogs for those trace fossils left by their ancestors. Sometimes we find ourselves identifying with modern animals, developing empathy for what they experience as they form traces, a sensitivity that can extend to their trace-fossil equivalents. Hence for ichnologists, these parts of the fossil record become just a bit less removed from death, and we end up feeling for our tracemakers, both long gone and extant.

Jordi Maria de Gibert, contemplating and lamenting the loss of dinosaurian tracemakers from mass extinctions. The window display was in Basel, Switzerland, one of many places visited by Jordi in his quest to learn all things ichnological. (Photograph by Anthony Martin, who is also pictured in the reflection, along with ichnologists Luis Buatois and Gabriela Mángano, taken in 2003.)

In this sense, our small and close-knit international community of ichnologists was shocked to learn about the sudden loss of one of our own “tracemakers” this past weekend, Jordi Maria de Gibert. His death was unexpected and its impact accentuated because he and the rest of us had just gathered together only last month for the International Congress of Ichnology (Ichnia) in St. Johns, Newfoundland. We also anticipated seeing him again in his home city of Barcelona in 2016, where he died on Sunday. None of us had prepared ourselves to reflect on his legacy, let alone contemplate the possibility that his cognitive traces would cease any time soon.

The aftermath of the first Ichnia football match (sometimes known as “soccer” to you Yanks) between ichnologists of Team Gondwana and Team Laurasia, which took place on a pitch near Trelew, Argentina. Jordi, in the middle of the back row, is either signaling “Peace,” “Victory,” or, most likely, ordering two beers: one for him, and one for you so he can sit down to argue about trace fossils with you. (Photograph by Anthony Martin, taken in 2004.)

Most of our dismay about Jordi’s departure is because we loved him as a person, but it is also surely connected to our witnessing an ascendancy cut short. For instance, at the end of the meeting in St. Johns, Jordi addressed all of us as the newly elected president of the International Ichnological Association, and he had volunteered to serve as the main organizer for the next Ichnia meeting four years from now. His larger-than-life personality was on full display during his informal and impromptu speech: enthusiastic, cheerful, witty, earnest. In the days before then, he delivered multiple presentations on ongoing research projects, most of which revolved around his continuing interests in crustaceans and their traces, as well as those of marine bioeroders, animals that make a living by boring into rocks. Jordi was a prolific publisher of peer-reviewed papers on these topics, and was well known for his cooperative spirit, coauthoring with many ichnologists and other types of paleontologists on these papers.

Jordi (right, seated), in his preferred life habit, talking about fossils with colleagues (and friends) at an outcrop. And this wasn’t just any outcrop, but was at Mistaken Point, Newfoundland, which has one of the most spectacular Ediacaran fossil assemblages in the world. This had to have been a dream come true for him, as it was for many of us.

Jordi showing off his “Bama booties,” required footwear for the sacred ground of Mistaken Point, as some other ichnologist vainly attempts to “photobomb” him with his own blue-footed bootie. (Photograph by Ruth Schowalter.)

I had known Jordi since 1995, having first met in Bornholm, Denmark at a small ichnological meeting there. He and I were still new to our discipline (we were about the same age) and quite green, but eager to learn from our elders. As is typical with many academic friendships, over the next 17 years we would see each other at various meetings, and by my count we saw trace fossils and toasted one another in six countries (Denmark, U.S., U.K., Switzerland, Poland, Canada). Each time together, I grew more impressed with his intense and tenacious will to seek out more knowledge, digest it, and pass it on to others. He was a fierce intellectual who relished the debating of ideas, and was never satisfied with a conversation if he did not leave it wiser. This, of course, benefited all who were brave enough (and lucky enough) to enter into such discussions with him.

A happy time at the Ichnia 2004 banquet in Trelew, Argentina, with (from left to right) Renata Guimarães Netto, Jordi, and Ludvig Loewemark, where the exchange of ideas and good cheer flowed nearly as fast as the wine.

Jordi was young as far as ichnologists go, and as I argued in my previous post, the best ichnologists are the most experienced ones. So he knew as well as any of us that gaining more experience in the field was essential, and traveled to many places and studied traces of all ages – from the Ediacaran to the present – and traces of all kinds, from plant roots to dinosaur tracks. Accordingly, because of his dedication and broad interests, he had already become one of our best. In this vein, one of the metaphorical jokes ichnologists tell is how our academic success can be measured by how deeply we can burrow: shallow tiers are the least successful, whereas the deepst tiers are the most successful. Jordi was assuredly well on his way to the deepest tier, but we are all saddened about his unexpectedly reaching the historical layer before so many of us.

Los quatros amigos, posing happily toward the end of an ichnology field trip in Switzerland in 2003: from left to right, ichnologists Noelia Carmona, Gabriela Mángano, Luis Buatois, and Jordi, sporting some distinctive headgear and proudly flouting conformity. (Photograph by Anthony Martin.)

I learned about Jordi’s death on Sunday through our mutual ichnologist friend, Renata Guimarães Netto, who had likewise known Jordi for more nearly 20 years. Quickly the word spread through social media, e-mails, and phone calls, our sadness multiplying and magnifying worldwide. Only last month, we had celebrated with him, and now we mourned him, and expressed our sorrow to his family members, and close friends.

To ease some of this pain and enjoy an otherwise beautiful Sunday in Decatur, Georgia, my wife Ruth and I went for a walk. Without thinking, I suggested that we meander in one of the largest, quietest green spaces in Decatur, which turned out to be its cemetery. (Yes, I know. All I can say is that the subconscious is more powerful than we know.) While we strolled, I thought about times spent with Jordi on field trips and in conferences, while also recalling papers he had written and discoveries he had made. As mentioned earlier, Jordi’s interests were varied, but perhaps his favorite research topic was crustacean burrows, especially the burrows of crabs, shrimp, lobsters, and other 10-legged crustaceans. Too bad we were nowhere near the Georgia coast, I thought, as it would have been a fitting and comforting homage for Ruth and I to take in the many decapod burrows of the Georgia beaches and salt marshes, which Jordi had never seen in person.

That’s when an eerie coincidence happened. During our walk, we spotted a former pond on the cemetery grounds, now drained for dredging. There’s something about a big pit of mud that appeals to every ichnologist, so I excitedly suggested that we go take a look to see what traces were there. We expected to find lots of tracks, such as those of birds, raccoons, squirrels, and coyotes, and maybe a few other urban fauna. Instead, though, the muddy surface was perforated by decapod tracks and burrows.

Need to see some crustacean traces, but you live in the landlocked part of Georgia? Just go to a dried pond and look for tracks like these.

These were the traces of crayfish, decapods that diverged from a common ancestor to modern lobsters more than 250 million years ago to live in freshwater environments as their brethren dispersed throughout the seas. A few years back, I studied Cretaceous crayfish and their burrows in Australia, but had never seen a live crayfish in its burrow here in Georgia, let alone seen so many of their tracks in one place. We even saw some crayfish (probably a species of Procambarus) poking their heads and claws out of their burrows, or walking around on the mudflat. So it turned out we did not need to go to the Georgia coast after all to see traces reminding us of Jordi: they had been right here with us the whole time.

A crayfish at its burrow entrance in the mudpit now in Decatur Cemetery, either defending its territory, or waving goodbye to people who study its kind and their traces. Your choice, but I know which one I’m picking.

In April, Jordi began writing about ichnology and invertebrate zoology for a more public audience through his cleverly titled blog, Infaunal Epiphany. His first entry was titled First Post, Hope Not Last!, in which he expressed a growing aspiration to connect with more than just his academic colleagues:

We scientists produce science. We scientists consume science. Most of us do that. We do our research, we publish it and other scientists read it. We are keeping all the fun for ourselves!!! It is true that there are scientists, journalists and writers who devote an effort to popularize science results. They are the ones building a bridge to society and I think it is fair to do that as many of us are investigating on public money.

Jordi wanted to share the fun of science, and in that respect, field trips with him were always a delight. These are probably what I will miss most about him, a pang that becomes particularly acute when I realize that one of our last conversations was about his some day visiting the Georgia coast to see its modern traces with me and our like-minded friends.

Lastly, in the light of his most recent life departing us, perhaps Jordi’s most poignant post on his nascent blog was Seven Reasons to Reincarnate as a Cephalopod. I won’t spoil it for anyone who hasn’t read this wonderful piece, but will just say that this post alone showcases how Jordi’s fine sense of humor blended readily with his science.

We will never know whether Jordi’s wish came true, let alone which cephalopod he might have become, or whether some element of his considerable spirit is now somehow connected to one of his beloved crustacean tracemakers or bioeroders in the past or present. But we can be assured that he will continue to live with us through his works and our memories of him. When our ichnological community meets again in his home town of Barcelona four years from now, his traces will all around us, continuing to inspire us to learn and live more.

Salud y un abrazo grande, mi amigo Jordi. Vaya con las trazas.

Correction: Someone pointed out to me that the newly elected International Ichnological Association (IIA) president is actually Alfred Uchman, not Jord. Jordi only seemed presidential to me because of his inspiring report given at Ichnia 2012 as outgoing secretary of the IIA and his agreement to host Ichnia 2016. (I am pleased to report that Alfred likewise gave an excellent speech to those gathered.) Apologies for the mistake, and thanks (as always) to anyone who points them out to me.

A Mirror Less Distant in Time

Posted on September 17, 2012 by TMartin

(This post is the third in a series about my recent field experiences in Newfoundland, Canada in association with the International Congress on Ichnology meeting (Ichnia 2012) in August, 2012. The first dealt with the unusualness of the Ediacaran Period and the second was about the transition from the Ediacaran to the Cambrian Period for burrowing animals.)

The Ordovician Period, a time represented by rocks from 488-443 million years ago, is an old (and I mean, really old) friend of mine. In my master’s thesis, I studied Ordovician fossils from southwestern Ohio, and for my Ph.D. dissertation, I described and interpreted Ordovician trace fossils and strata in Georgia and Tennessee. Thus for the formative years of my academic career, the Ordovician had a strong presence in my life, overshadowing most other geologically inspired opportunities in my adopted home state of Georgia.

Nice outcrop, eh? It’s composed of Lower Ordovician sedimentary rocks, formed more than 450 million years ago, and is on Bell Island, just offshore from St. Johns, Newfoundland (Canada). It’s a place I had never visited before last month, but its trace fossils took me back to Georgia. How? Guess you’ll have to read some more to find out. (Photograph by Anthony Martin.)

This Ordovician-dominated worldview contrasted with a much later focus on the present-day Georgia barrier islands. Between when I first arrived in Georgia, in 1985 through 1998, my only foray to its coast was a three-day field trip as a graduate student to Sapelo Island in 1988. Fortunately, I’ve been a more regular visitor to Sapelo and other Georgia barrier islands throughout the past 14 years or so, and my geologic perspective has accordingly traveled more than 400 million years forward to study modern plant and animal traces.

However, as I’ve embraced the present and the lessons it offers, what also happened over those years was a personal distancing from the Ordovician. This separation was unfortunate for several reasons. One is that Ordovician body and trace fossils are a mere 1.5-2 hour drive from where I live in the metropolitan Atlanta area, just south of Chattanooga, Tennessee. In contrast, the Georgia coast takes a minimum of four hours to reach by car.

Granted, northwest Georgia was part of my dissertation field area, so my leaving behind a place already prospected, poked, prodded, and otherwise inspected thoroughly more than 20 years ago is understandable and forgivable. Yet a day trip there with a colleague last spring (March 2011), along with a recent field trip to view Ordovician rocks in Newfoundland, Canada last month, reminded me of what was in my geological backyard, while also provoking new thoughts about the intersections between the Ordovician and the Georgia coast.

So what happened during those 20+ years of not studying the Ordovician rocks close to me in Georgia? Well, I gained lots more experience, went to many places with rocks and trace fossils of varying ages, and thus – I like to think – became a better ichnologist. So that leads to an imperiously pronounced statement, so please read it, take it in, and revel in its truth: Ichnology is a skill-based science.

People who study the earth sciences have an old saying, often stated during field trips to students: “The best geologist is the one who’s seen the most rocks.” The same sentiment might be applied to ichnologists. To excel as an ichnologist, it’s not your publication record (let alone impact factors of journals publishing your work), the number or size of your grants, accolades of your peers, “big-idea” review papers, erudite tomes, or any number of trappings imposed by academia that matter. What really matters in becoming a better ichnologist is how many traces you’ve seen, measured, sketched, journaled, photographed, pondered, argued over, and folded into your consciousness.

Hey, look – it’s ichnologists, trying to learn more by studying trace fossils in the field! (Photograph by Ruth Schowalter, taken on Bell Island, Newfoundland, Canada.)

Sure, peer review from your colleagues is still an important part of this learning process. Otherwise, as a tracking instructor once told me and other nascent trackers, “When you always track by yourself, you’re always right.” You don’t want to be that ichnologist who gets things wrong, then insists every other ichnologist is wrong, while also imagining that they’re teeming with jealousy over your brilliance. You know, the “they laughed at Galileo, too” fallacy.

Behold my genius! Only I can clearly see these are the tracks of an eight-legged river otter. Oh, so you think they’re from two four-legged otters, with one following the other? Dolt! Don’t you know who I am?

So am I the best ichnologist? Not just no, but hell no. The acknowledged master of ichnology is Dolf Seilacher. And the main reason I enthusiastically bestow Dr. Seilacher with a crown of back-filled and spreiten-laden burrows is because of the extraordinary amount of experience he has as an ichnologist. Granted, he’s also done all of that academic-type stuff that persuades far less-accomplished members of tenure-review committees to nod their heads with utmost seriousness and say, “Well, I suppose we can make an exception in this case.” But he also has seen, measured, sketched, journaled, photographed, pondered, argued over many, many trace fossils during his 87 years on this planet. Dolf knows traces.

Dolf Seilacher, the widely hailed master of ichnology in the world. Even when he’s wrong, he’s really good at it. (Photograph by Anthony Martin, taken in Krakow, Poland.)

So let’s go back to the Ordovician, and how it relates to Dolf and my claim about the importance of experience in ichnology. In 1997, I invited Dolf to visit Emory University as a distinguished speaker in an evolutionary biology lecture series we had then (since gone defunct, like many things at Emory). Because he had never before visited Georgia, he insisted that we also arrange a field trip for him to see some trace fossils here. So with my friend and colleague, Andy Rindsberg, we organized a day trip to an outcrop near Ringgold, Georgia to look at the Ordovician trace fossils there. Andy had done his master’s thesis on the Ordovician and Silurian trace fossils in that area, and as mentioned earlier, I had done my Ph.D. dissertation about the Ordovician rocks, in which I interpreted them mostly through an ichnological lens.

Dolf Seilacher in Georgia (USA) for the first time in November 1997, coffee in one hand and a trilobite burrow in the other. See all of those Ordovician rocks in the background? Even though he’d never been there before, he noticed trace fossils in them in less time than most of us take to read a Huffington Post headline. Gee, you think it had anything to do with his experience? (Photograph by Anthony Martin, taken near Ringgold, Georgia. And just so you know, no paleontologists were “Dolfed” in this photo.)

Andy and I knew the rocks and their trace fossils at this outcrop better than anyone in the world. Yet within five minutes of arriving at the outcrop, Dolf laid his hand on a large slab of Ordovician rock and began talking matter-of-factly about the trilobite burrows in it. Andy and I looked at each other, and said (almost simultaneously), “Trilobite burrows?”

Dolf was right. This rock and many others there were filled with circular, back-filled burrows, which were made by small trilobites that burrowed into mudflats more than 400 million years ago. During a futile attempt to disprove him the following year, Andy and I found these burrows connected to trackways, and one even ended in a resting trace, perfectly outlining the body of a small trilobite. (Did I mention Dolf was right?)

Burrow (upper right, circular structure) connected to tracks made by little legs from a little trilobite. Trace fossils are on the bottom of a sandstone from the Upper Ordovician Sequatchie Formation of northwest Georgia. Scale in centimeters. (Photograph by Anthony Martin.)

Later on that same day, we looked more carefully at some other fossil burrows at the outcrop. These broad, banana-shaped trace fossils were ones that Andy and I had noted in our respective studies, called Trichophycus. Dolf continued his trilobite–tracemaker theme, insisting that these were also trilobite burrows. This idea was supported by scratchmarks on the burrow walls, which linked the burrows to the small legs of whichever arthropod lived in the burrows. Again, trilobites made sense as the tracemakers, and we haven’t yet found a reason why this would be wrong.

Trusted field assistant Paleontologist Barbie, pointing to a cluster of Trichophycus (interpreted as trilobite burrows) in the Sequatchie Formation of northwest Georgia. She is pointing to some scratchmarks on the burrow walls, which are preserved in natural casts of the burrows. (Photograph by Anthony Martin.)

Almost 13 years later, in March 2011, Andy and I went back to this same Ringgold outcrop to re-study the trace fossils there, done in preparation for a presentation he gave the next month at a regional Geological Society of America meeting (abstract here). He and I were surprised at how much the outcrop had changed since we last visited. Vegetation, particularly of the thorny variety, covered the ground and impeded our progress. Nonetheless, we found many excellent examples of trilobite burrows (Trichophycus), a beautiful trilobite resting trace (Rusophycus), and, for the first time for either of us, a sea-star resting trace.

Resting trace of a trilobite (Rusophycus), with a small part of its trackway leading to the trace, in the Upper Ordovician Sequatchie Formation of northwest Georgia. These trace fossils are preserved as natural casts on the bottom of a sandstone, so you’re seeing the underside of where the trilobite hunkered down more than 400 million years ago. (Photograph by Anthony Martin.)

Resting trace of a sea star (Asteriacites) in the Upper Ordovician Sequatchie Formation of northwest Georgia. This trace fossil, like that of the trilobite resting trace, is also preserved as natural casts on the bottom of a sandstone, so you’re looking underneath where the sea star moved into the mud. (Photograph by Anthony Martin.)

Our discovery of the latter two trace fossils – the trilobite and sea-star resting traces – took me from the Ordovician to the Georgia coast and back again. Throughout the late 1980s, I recall my Ph.D. advisor, Robert (“Bob”) Frey placing many of his articles in my graduate-student mailbox, all of which dealt with the traces of the modern Georgia coast. That’s odd, I thought. What did the traces of the modern Georgia coast have to do with these 440-million-year-old rocks?

In my limited worldview at the time, I did not see that the Georgia barrier islands and their traces composed a mirror, however removed by time, for looking into that Ordovician past. But eventually, given enough articles read, field work done, and trace fossils examined at these Ordovician outcrops, I slowly realized these 440-million-year-old rocks had been formed in estuaries, similar to those along the Georgia coast. When I first published an article about these rocks and their trace fossils in 1993 (link here), these strata represented the oldest known estuary deposits in the world, and some of the trace fossils could be readily compared to those on the Georgia coast. The beauty of this realization was that Frey, a master ichnologist in his own right and a contemporary of Seilacher, had allowed me to discover it for myself: he just provided the clues.

Remember that small, circular trilobite burrow with tracks connecting to it? Now compare it to the same sort of traces made by a modern beach mole crab (Albunea paretii), which left its burrow on the right, walked to the left, and is here rapidly burying itself in the sand. Scale in centimeters. (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)

Resting trace and attached trackway of a juvenile horseshoe crab (or limulid, specifically Limulus polyphemus). So think about a similarly sized trilobite making this, and what the bottom of the trace would like like, then compare it to the Ordovician trilobite resting trace fossil shown earlier. Scale in centimeters. (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)

Resting trace of a lined sea star (Luidia clathrata), with the original tracemaker just below its trace. This sea star was stuck above the high tide mark, burrowed into the underlying moist sand, but then tried to move to a better place once its spot started to dry out. Now compare this resting trace to the Ordovician trace fossil shown before. No scale, but sea star is about 8-10 cm wide. (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)

The following year and only a month ago (August 2012), Andy and I had another Ordovician learning opportunity presented to us, but this time in Newfoundland, Canada. A day trip to see Ordovician rocks and trace fossils on Bell Island, just a 30-minute ferry ride from St. Johns, Newfoundland, was a welcome break from the butt-numbing sessions of the previous two days of the Ichnia 2012 conference at Memorial University.

In our first few minutes at the outcrop and its numerous boulders – spoil piles from an iron-ore mine – we realized that one of the dislodged slabs in front of me was loaded with specimens of Trichophycus. It was a pleasant surprise to get reacquainted with this trace fossil, and in a place far away both geographically and experientially from Georgia.

Multiple specimens of Trichophycus in Lower Ordovician rocks of Newfoundland, Canada, preserved as natural casts of the burrows. See all of those scratchmarks on the burrow walls? These were also made by trilobites, but probably different ones from those in Georgia. Scale in centimeters (and that ain’t no real maple leaf.) (Photograph by Anthony Martin.)

Multiple specimens of Trichophycus in the Upper Ordovician Sequatchie Formation of Georgia, USA, also preserved as natural casts of the burrows and showing some scratchmarks on the walls. Do they look familiar to you, too? If so, welcome to the Ordovician. (Photograph by Anthony Martin.)

Here’s that trilobite resting trace (Rusophycus) from Georgia that I showed earlier. Now take a gander at the one below…

Why, that seems to be a trilobite resting trace (Rusophycus), too, but in Lower Ordovician rocks of Newfoundland. Surprise, surprise, surprise! Scale in centimeters. (Photograph by Anthony Martin.)

Suddenly, much of Andy’s and my previous experience with the Ordovician rocks of Georgia came back to us. We were, paradoxically, home, only in this instance, “home” was a time, not a place. Ichnological colleagues who had no idea Andy and I had worked with Ordovician trace fossils stared at us quizzically (and skeptically) as we excitedly discussed the burrows. But once we informed them that we had seen these trace fossils before, our experience was recognized, egos were set aside, and learning was enhanced. Funny how that works sometimes.

So with our trip to Newfoundland, we went from the alien world of the Ediacaran Period, with its trace fossils unlike anything I had seen before, to the more familiar and accommodating Ordovician Period rocks and their trace fossils. What I learned from this trip, combined with many others to Ordovician rocks elsewhere, as well as the modern sediments of the Georgia coast, was that the mirror was not so foggy after all, and that more field experiences can only further clarify these connections between life traces from the present and the not-so-distant past.

Further Reading

Buatois, L.A., Gingras, M.K., MacEachern, J., Mángano, M.G., Zonneveld, J.-P, Pemberton, S.G., Netto, R.G., and Martin, A.J. 2005. Colonization of brackish-water systems through time: Evidence from the trace-fossil record. Palaios, 20: 321-347.

Eldredge, N., 1970. Observations on burrowing behavior in Limulus polyphemus (Chelicerata, Merostomata), with implications on the functional anatomy of trilobites. American Museum Novitates, 2436: 17 p.

Fillion, D. and Pickerill, R.K. 1990. Ichnology of the Lower Ordovician Bell Island and Wabana Groups of eastern Newfoundland. Palaeontographica Canadiana, 7: 1-119.

Martin, A.J. 1993. Semiquantitative and statistical analysis of bioturbate textures, sequatchie formation (upper ordovician), Georgia and Tennessee, USA. Ichnos, 2: 117-136.

Seilacher, A. 2007. Trace Fossil Analysis. Springer, Berlin: 240 p.

Tracking Bookzilla

Posted on August 31, 2012 by TMartin

The AJC-Decatur Book Festival, an annual event held on Labor Day weekend in my hometown of Decatur, Georgia, begins tonight with a poetry reading from Natasha Trethewey, the new U.S. Poet Laureate and a colleague of mine at Emory University. The festival is one of the largest independent book fairs in the U.S., featuring readings by hundreds of fiction and non-fiction authors, poets, illustrators, spoken-word artists, and other people interested in all things literary, as well as having lots of books for sale.

But along with the authors and other written-word enthusiasts will be an elusive figure, one you may or may not notice among the 80,000 or so people, but whose visage will preside over activities as an iconic talisman. Known as Bookzilla, he – or she, as its gender is uncertain – is apparently the result of a genetic experiment gone awry, mixing the traits of a near-sighted human, theropod dinosaur, and book (pre-Kindle version).

A rare photo of Bookzilla, making a rare appearance in downtown Decatur, Georgia this past June. Note the physical characteristics denoting a voraciously studious consumer of words, and one that doesn’t care whether a book is fiction, non-fiction, new, or used.

Fortunately, as an ichnologist, I don’t have to rely on sightings to know where Bookzilla might be or what he/she was doing at the festival. Bookzilla, much like other cryptozoological beings who are infrequently observed in nature, leaves many traces from his/her behavior. So when I spotted Bookzilla in downtown Decatur earlier this year, I made sure to observe his/her behavior very carefully and take several photos of him/her to aid in my ichnological predictions of Bookzilla traces. After all, every trace is a function of what I often call the “Holy Trinity” of ichnology: an tracemaker’s anatomy, its behavior, and the substrate preserving its traces.

Another view of Bookzilla, giving an overall view of its form and behavior, thus lending to a better appraisal of its tracemaking abilities. An especially important feature to keep in mind is his/her large, forward-leaning, rectangular head, which should cause deeper impressions in the front halves of his/her tracks. Also note the small child cowering nearby, yet being reassured by her father that Bookzilla, and by default books and the knowledge they contain, are to be embraced, not feared.

Close-up view of the foot morphology of Bookzilla. Note the unusual blend of a plantigrade mode, with metatarsals in contact with the walking surface, combined with a trapezoidal (but symmetrical) outline to his/her foot, as well as three sharp unguals (claws) elevated well above the surface by excessive padding in the foot. Such feet, particularly when moved by a vertically oriented biped such as Bookzilla, will result in distinctive trackways that could never be confused with, say, those of a person wearing a clumsy costume.

Based on this admittedly limited sample of Bookzilla’s anatomy and behavior, I can nonetheless reasonably hypothesize what sorts of tracks and trackway patterns Bookzilla would form during normal activities. In a firm substrate, such as moist sand, Bookzilla’s tracks would only register only a vague trapzoidal outline of his/her feet, and claws would not register. However, in a softer substrate, such as a saturated mud or wet cement, Bookzilla would impart shallow impressions of three claws directly in front of the trapezoidal outlines.

Hypothesized Bookzilla tracks, which could be from either the right or left feet owing to bilateral symmetry of the foot structure. (Left) Track outline formed in relatively firm substrate, such as a moist sand, with no claws showing and with the deepest part of the track in the front half because of its weighty, tome-like head. (Right) Track outline formed in soft substrate with finer grain size and higher water content, such as mud. In this instance, claw marks will register, and the track outline will be accompanied by numerous pressure-release structures from the tracemaker deforming the sediment with application and release of foot pressure caused by forward movement. Footprint length (minus claws) = 30-35 cm (12-14 in).

A typical trackway pattern for Bookzilla should show mostly diagonal walking (right-left-right diagonal to one another), but will be punctuated by many side-by-side tracks, representing long periods of stopping and standing while reading books.

Hypothesized Bookzilla trackway pattern, indicating alternate (diagonal) walking, typical of a biped, but also interrupted by frequent stops to look at books and read. Note claw impressions are only visible in parts of the trackway, depending on local variations in substrate conditions; in this instance, stepping into wet cement.

Considering how Bookzilla is well known as an insatiable reader and is constantly hunting for books, no sitting traces, such as those interpreted for some theropod dinosaurs, are known, nor expected. I also cannot yet speculate about about additional traces made by Bookzilla, such as dwelling structures, toothmarks, or scat. Remarkably, his/her consumption of books does not actually result in digestive products, but instead seems to cause increased levels of cognitive pleasure.

So if you are in the Decatur-Atlanta area this weekend and attending the book festival, maybe you’ll be lucky enough to actually see Bookzilla, but you’re much more likely to spot his tracks. In the meantime, take a look at some books and enjoy all of the literary traces that are offered there.

(The AJC-Decatur Book Festival will take place in downtown Decatur, Georgia from September 1-2. The full schedule is here, and it will feature appearances and talks by well-established and emerging authors and illustrators, the latter including my wife Ruth Schowalter. If you can’t make this year’s festival, it is held on Labor Day weekend every year, so plan to make next year’s. And many thanks to Daren Wang for suggesting this several months ago as a blog post!)

Out of One’s Depth in the Ediacaran

Posted on August 27, 2012 by TMartin

In my previous post, which followed a field trip to see a spectacular assemblage of 565-million-year-old Ediacaran body and trace fossils at Mistaken Point in Newfoundland, I made an awkward confession. This admission was that the stock phrase “the present is the key to the past,” used by geologists and paleontologists to describe actualism (also known as uniformitarianism) really depends on which past you’re talking about. As it turns out, when it comes to earth history, there are a lot of pasts.

Looking from afar onto the world standard for rocks recording the transition from life that lived superficially to life that, well, went a little deeper. (Photograph by Ruth Schowalter, taken at Fortune Head, Newfoundland (Canada).)

For instance, if you mean to apply that aphorism while referring to the last 12% of earth history, then for the most part you’ll be OK, although some of it will fall completely flat (more on that later).

But if you think it can be said blithely when referring to a time when all of the lifeforms looked like aliens from a bad Star Trek episode (TOS, of course), or when global oxygen levels were significantly lower than today, or the ozone layer protecting us from UV radiation was mostly absent, or deep-burrowing predators were completely unknown from every ecosystem, or the geochemistry of bottom sediments in the world oceans were radically different, then that’s not going to work so well for you. The world was vastly different at the Precambrian-Cambrian transition about 550 million years ago, and no amount of studying modern geological and biological processes or, say, modern traces of the Georgia barrier islands, is going to close that factual gap.

Underneath the intertidal sandflats of the Georgia barrier islands lurks the common moon snail (Neverita duplicata), detected through its burrow (left); and it radiates malevolence once exhumed from the burrow end (right, arrow). It is the top predator, the lion of the tidal flat, one might say, burrowing under sandflat surfaces to stalk its prey (other mollusks, including its own species), enveloping them with its muscular foot, and drilling into their shells to eat them alive. Simple, effective, and deadly. Was there anything like this moon snail in the Ediacaran Period, 635-542 million years ago? Nope. (Photographs by Anthony Martin, taken on Jekyll Island, Georgia.)

So let’s say you took a common moon snail from the Georgia coast and sent it back to the Ediacaran. You would think its evolutionarily advanced status, placed among such primitives, means that it would suddenly become the gastropod equivalent of a Terminator (the Summer Glau version, of course), wiping out every Ediacaran challenger in its mucus-lined path. Instead, it would die and quick and messy death from a combination of low oxygen levels, excessive biomats getting in its way, a lack of desirable prey, and excessive UV radiation. So you can stop building that gastropod-sized Tardis, and just face up to two realities: (1) the present is not always the key to the past; and (2) there is no such thing as time travel.

Oh yeah, back to the field trip. During the same excursion that included a stop at Mistaken Point, we also went to Fortune Head. Fortune Head is the place where the International Commission on Stratigraphy established the standard stratigraphic boundary for the switch from the Precambrian to the Cambrian. Called a Global Boundary Stratotype Section and Point (GSSP), or simply “stratotype,” this is a section of rock with the most nearly complete transition of rock units representing one time unit to the next.

A plaque at Fortune Head Ecological Reserve, informing visitors about the scientific importance of this site to geologists and paleontologists.

For example, the outcrop at Fortune Head is the stratotype for the transition from the Ediacaran Period (635-542 mya) to the Cambrian Period (542-488 mya). Sometimes geologists nickname this system of picking an exact boundary “the golden spike,” invoking images of a geologist hammering such a gaudy implement into the outcrop to imperiously announce its precise location. Lacking such geo-bling, though, we settled for one of the field trip leaders simply pointing with his walking stick to the boundary.

While we stayed safely on the hillside, the graduate students risked their lives to climb down onto the section and point at the Ediacaran-Cambrian boundary at Fortune Head, Newfoundland. For me, this brought back fond memories of Marlin Perkins, Jim Fowler, and Wild Kingdom. (Spoiler: the graduate students made it back OK.) (Photograph by Anthony Martin.)

So how would you know for yourself where, er, when you are – geologically speaking – in a section that has the youngest rocks of the Ediacaran Period and the oldest rocks of the Cambrian Period? That’s where the awesome power of ichnology comes into play, and it’s really simple to wield. If you look at the rocks and see the following trace fossil – Treptichnus pedum – you’re in the Cambrian Period. But if you don’t, you’re in the Ediacaran.

Whoa, check out that beautiful trace fossil! It’s Treptichnus pedum, a burrow made by a deposit-feeding animal, which was probably a worm-like animal, but also could have been an arthropod. Regardless of who made it, it’s a burrow reflecting a new behavior that evidently didn’t exist only a few million years before it was made. And that, boys and girls, makes this trace fossil a distinctive one. Scale in centimeters. (Photograph by Anthony Martin, taken at Grand Bank, Newfoundland.)

This trace fossil, a feeding burrow made by an invertebrate animal living in the seafloor 542 mya, is one of the few trace fossils used as an index fossil. Index fossils (also called guide fossils) tell you the age of the rocks you’re viewing. A good index fossil should have the following traits:

Abundant
Easily identifiable
Stratigraphically restricted
Geographically widespread

Treptichnus pedum indicates a behavior very different from every other trace fossil seen in Ediacaran rocks. It shows that the burrowing animal – probably a type of worm or arthropod – systematically probed into the sediment to ingest some of it, withdrew back into the main part of its burrow, then moved forward to probe again. Furthermore, over the course of making its burrow, its pathway may make loops, which increased the likelihood of it getting lots of goodies (organics) from the sediment. This behavior was totally different, and if it had been allowed to happen in the Ediacaran, no doubt would have led to laughter and ostracizing by other epifaunal and infaunal invertebrates. That is, if they could laugh or ostracize. (Hey, like I said, it was really different back then.)

But here’s the really strange dimension of the Ediacaran Period: as far as burrowers were concerned, it was mostly two-dimensional. Animal movement seemed restricted to horizontal planes, in which animals (worm-like or otherwise) squirmed, crawled, anchored and pulled, or whatever they did to get around, but stayed mainly in the plane.

Vertical movement, such as daring to burrow up or down in the sediment, was forbidden by either the rules of the marine ecosystems at that time, or by the bodies of the animals themselves. What kept animals from digging a little deeper? Part of the problem was that the seafloor was ruled by microbial mats, which covered sediment surfaces like plastic coverings on furniture at your grandma’s home.

This wrinkled surface on a Lower Cambrian sandstone just above the Ediacaran-Cambrian boundary at Fortune Head, Newfoundland is evidence of a probable microbial mat, or “biomat” These biomats were really common in the Ediacaran, became less common in the Cambrian, then after the Cambrian became more rare than a modest politician in an election year. Scale in centimeters. (Photograph by Anthony Martin.)

So if you were an animal then, you had no choice: you could adapt to being under these mats or on top of them. To make matters worse, all animal life apparently lacked the right hard parts, limbs, or other anatomical traits that could have pierced those mats or excavated the sediment underneath them. So no amount of rugged individualism in those invertebrates was going to change their horizontal movement to vertical.

A horizontal trail, probably made by an invertebrate animal, preserved on a 565-million-year-old bedding plane at Mistaken Point, Newfoundland. So you thought you could burrow vertically? Forget it, Jake – it’s Ediacaratown!

Of course, eventually the earth changed, the tyranny of the microbial mats was overcome by new evolutionary innovations in animals, and other adaptive paths took life into a third dimension. Consequently, the animals living on the seafloor started acting more like the ones we see today: not just living on or just underneath that seafloor, but also going down into it. This change was huge in an ecological sense, sometimes dubbed by paleontologists as the agronomic revolution, which accompanied the Cambrian explosion. This is not to say that revolutions must involve explosions, though. On the contrary, this was a quiet and slow sort of revolt, in which as earth environments changed, natural selection favored the burrowers, and the burrowers changed their environment. ¡Viva la revolución!

Here’s a little musical lesson about the increased biodiversity of the Cambrian Period. Professors, assign it to your students. Students, tell you professors about it, so they can look like they’re almost hip when they assign it. And for American viewers: the song has some sort of subversive subliminal message toward the end, praising some country other than the U.S. You’ve been warned.

In this respect, what was most meaningful about our visit to Fortune Head was seeing evidence of this ecological shift at the very same outcrop holding the stratotype for the Ediacaran-Cambrian boundary. Small, thin burrows preserved in the rocks from the earliest part of the Cambrian Period, spoke of this difference in the way life related to the seafloor. Vertically oriented they were, having gone into the sediment at a depth only the width of my fingernail. Nonetheless, it was a start, and an important one, heralding the evolution of ecosystems that more closely approach those of today.

See that little U-shaped burrow just below that thin sandstone? It only goes about a centimeter down, but that’s deeper than nearly any other burrow you would see in rocks from the Ediacaran Period. This sort of simple U-shaped burrow is given the ichnogenus name Arenicolites by ichnologists. Canadian-themed scale is in centimeters. (Photograph by Anthony Martin, taken at Fortune Head, Newfoundland.)

Same goes for this burrow, which is a spiral – cut on its side – and named Gyrolithes. Scale bar = 1 cm (0.4 in). (Photograph by Anthony Martin, taken at Fortune Head, Newfoundland.)

Life has moved further downward since, from worms to arthropods in marine environments, then later from millipedes to dinosaurs to gopher tortoises in continental environments, looking to places well below the surface that they could call home. So it was a awe-inspiring privilege to see a sample from the geologic record of when this first started, one centimeter at a time.

What was next stage for burrowing animals in the world’s oceans during the next 100 million years or so? To answer that question, we’ll jump ahead to the Ordovician Period, shuttling between rocks and trace fossils of that age in both Newfoundland and Georgia (USA, y’all). But while doing this, we’ll also look for glimpses of how these Ordovician trace fossils get just a little bit closer to the traces we being made in the modern sediments of the Georgia coast, and thus more like the actualism we all know and love.

Further Reading

Bottjer,D.J., Hagadorn, J.W., and Dornbos, S.Q. 2000. The Cambrian substrate revolution. GSA Today, 10(9): 1-7.

Canfield, D.E., and Farquhar, J. 2009. Animal evolution, bioturbation, and the sulfate concentration of the oceans. Proceedings of the National Academy of Sciences, 106: 8123-8127.

Gingras, M., et al. 2011. Possible evolution of mobile animals in association with microbial mats. Nature Geoscience, 4: 372-375.

Seilacher, A. 1999.Biomat-related lifestyles in the Precambrian. Palaios, 14: 86-93.

Vickers-Rich, P., and Komarower, P. (editors). 2007 The Rise and Fall of the Ediacaran Biota. Geological Society of London, Special Publication 286: 448 p.

Mistaken Point and the Limits of Actualism

Posted on August 23, 2012 by TMartin

Sometimes we paleontologists, especially those who also study modern organisms and their behaviors, get a little too sure of ourselves, thinking we have a clear vision of life during the pre-human past. So it’s good to have that confidence shaken a little, made uneasy by a glimpse at a much deeper past, one that preceded the bulk of fossils that shape our accepted norms and basic expectations in paleontology.

Welcome to the Ediacaran Period, the span of earth history from 635-542 million years ago, and a time when actualism – the precept that the present is the key to the past – becomes a naïve, idealistic dream, a glib summary of a world that has only existed for a mere 12% of earth history.

What are these? They’re fossils, but otherwise I’m not sure what else to tell you: guess I’ve been spending too much time in the present. But for for those people who have studied them and know better than me, they’re called Charniodiscus, and they’re frond-like fossils with holdfasts (those circular parts connected to their stems) that kept them attached to the seafloor about 565 million years ago. All you have to do to see these fossils is go to Newfoundland, Mistaken Point Ecological Reserve in Newfoundland, Canada, get permission from the Reserve to visit them, have a guide accompany you, and walk 40-45 minutes to the site from a car park. Incidentally, there will be absolutely no cafes or toilets on the way there. You know, just like how it was in the Precambrian. (Photograph by Anthony Martin; scale in centimeters.)

These discomforting realizations started a little less than two weeks ago, inspired by a field trip to the Ediacaran-Cambrian rocks of eastern Newfoundland, Canada. Why was I in cool, temperate Newfoundland, instead of sweating it out on the summertime Georgia coast? The occasion was a pre-meeting trip associated with the International Congress on Ichnology, simply known among ichnologists as Ichnia. This was the third such meeting, a once-every-four-years event (coinciding with years of the summer Olympics). The previous two were in Krakow, Poland (2008) and Trelew, Argentina (2004), and thus far these meetings also include fabulous field trips.

For Ichnia 2012, upon seeing an announcement of a field trip to Mistaken Point and other localities associated with the Precambrian-Cambrian boundary, I eagerly signed up for it. You see, Mistaken Point is world famous for its extraordinary preservation of more than 1,000 body fossils of those weird and wonderful fossils known as the Ediacaran fauna, Ediacaran biota, Vendian fauna, or Vendobionts (take your pick). This was the main reason why my fellow ichnologists on the field trip – 16 of us from 9 countries – were along for the ride, despite the trip’s clear emphasis on body fossils.

A rare photo of ichnologists getting really excited about seeing body fossils, which is totally understandable when we’re talking about the Ediacaran fossils at Mistaken Point, Newfoundland. Eventually, though, they later became unruly and started demanding, “Show me your trace fossils!” Fortunately for the sake of international ichnological relations, the field-trip leaders happily obliged that same day. (Photograph by Ruth Schowalter.)

These rare fossils, which are strange enough to even cause paleontologists to question whether or not they are animals (hence the cautious use of the more inclusive term “biota” instead of “fauna”), are abundantly exposed on broad bedding planes in Mistaken Point Ecological Reserve on the southeastern coast of Newfoundland. Discovered in 1967, these fossils have since proved to be one of the best examples of easily visible body fossils from more than 542 million years ago, and the Newfoundland fossils comprise the only such assemblage that originally lived in deep-marine environments. They evidently died in place when suffocated by a layer of volcanic ash that settled onto the seafloor, hence the fossils reflect a probable sample of their original ecosystem. This ash layer neatly preserved the fossils, and its minerals provided a means to calculate absolute age dates for the assemblage, which is from 565 +/- 3 mya (million years ago).

Bedding-plane exposure at Mistaken Point with many frond-like fossils, broadly referred to as rangeomorphs. (Photograph by Anthony Martin, Canadian-themed scale is in centimeters.)

A close-up of one of the more exquisitely preserved rangeomorphs, which I think is Fractofusus misrai. But you really shouldn’t trust this ichnologist with that identification, so it’d be wise to double-check that with a real expert. (Photograph by Anthony Martin.)

Just a few years ago, though, Mistaken Point became paleontologically famous again, and this time for its trace fossils. Researchers from Memorial University in Newfoundland and Oxford University looked at bedding planes near those holding the the body fossils, and were surprised to find a few trails there. At that time, it was the oldest evidence of animal movement from the fossil record, and although these finds have been disputed and others have tried to stake this claim for trace fossils elsewhere, it is still holding up fairly well.

A surface trail, probably made by a < 1 cm wide animal moving along the seafloor about 565 mya. The animal moved from left to right, which is indicated by the crescentic ridges inside the trail, which open in the direction of movement. (Photograph by Anthony Martin, taken at Mistaken Point, Newfoundland.)

Another surface trail, but this one without the internal structure of the other one, and with levees on either side of the central furrow. (Photograph by Anthony Martin, taken at Mistaken Point, Newfoundland.)What’s this? Don’t have a clue. It looks like a series of overlapping trails, some looping, but would have taken me several hours to unravel. Anyway, it generated some good discussion at the outcrop, and they’re probably trace fossils, which made us ichnologists both happy and perplexed. (Photograph by Anthony Martin, taken at Mistaken Point, Newfoundland; scale in centimeters.)

What made these trace fossils? It’s hard to say, and that’s a humbling statement for me to make. In public talks I’ve given about my upcoming book, and in a presentation I gave the following week at Ichnia on the Memorial University campus, I’ve assured how the actualism of the Georgia barrier islands and its traces can reliably serve as models for interpreting many trace fossils formed in different environments, and trace fossils of various geologic ages from around the world. But in this instance, I didn’t have a inkling of what made the Mistaken Point trace fossils. These trace fossils were also made in deep-marine environments, which are lacking from the Georgia coast, and I haven’t learned much about deep-marine trace fossils from elsewhere.

In short, my ignorance was showing, and these trace fossils were completely out of my realm of experience. The only feeble hypothesis I could conjure on the basis of what I’ve seen in modern sediments of the Georgia barrier islands are small marine gastropod trails. Sorry, that’s all I got.

Oooo, look, it’s snail! Making a trail! Isn’t that neat? And if you squint really hard and have a couple of beers, you might agree that it almost resembles one of the fossil trails from Mistaken Point. Don’t see it yet? Here, have another beer. (Photograph by Anthony Martin, taken at Sapelo Island, Georgia; scale in millimeters. )

But if ignorance loves company, I can feel good in knowing that others have grasped at the same straw of actualism and found it far too short. I could tell a few of my ichnological colleagues were likewise a little challenged by what they saw at Mistaken Point, and I knew that for some of them – like me – they normally deal with trace fossils in much younger rocks. But hey, that’s what geology field trips are supposed to do: challenge us with what’s really there in the rock record, right there in front of us, rather than what we wish were there.

Fortunately, a little more information provided during the meeting after the field trip helped my understanding of the trace fossils we saw at Mistaken Point, and actually connected to modern tracemakers. Alexander Liu, the primary author of the paper that first reported the trace fossils, gave a talk that reviewed the evidence for Precambrian trace fossils, including those from Mistaken Point. In experiments he and his coauthors did with living anemones in a laboratory setting, they were able to reproduce trails similar to the Mistaken Point trace fossil with the internal structure. Thus these researchers were able to use actualism to assist in their interpretation, which also meant that neoichnology was not so useless after all when applied to the Ediacaran. That made me feel a little better.

Let’s take a look at that first surface trail again, but this time with the help of my trustworthy colleague Paleontologist Barbie, who was along for the field trip. The crecentic ridges in the interior of the trail may represent marks where the basal disc of a anemone-like animal pushed against the surface as it moved. Even more interesting, the arrow points to an oval impression, which may be a resting trace that shows the approximate basal diameter of the tracemaker. What was the tracemaker? It’s currently identified as a small anemone, which is based on modern traces. Neoichnology rules! (Photograph by Anthony Martin.)

Ediacaran trace fossils still engender debate, though, and especially with people who don’t necessarily accept that animals made trails during the Ediacaran. For instance, about four years ago, some scuba-diving researchers observed a giant protozoan making a trail on a sediment surface in the Bahamas. Accordingly, they proposed that one-celled organisms – not animals – could have made similar trails during the Ediacaran Period. Interestingly, this shows how actualism can produce conflicting results when applied to Ediacaran fossils. After all, it’s still a big world out there, and we humans haven’t really observed everything in it yet.

So I’ll make one last point about Ediacaran fossils here, then will move on to more recent times. If you think that at the very least we paleontologists should be able to tell the difference between trace fossils and body fossils in Ediacaran rocks, you’re also in for some confusion. In the only research article I have ever attempted on Ediacaran fossils, which were much closer to Georgia – coming from the Carolina Slate Belt of North Carolina – my coauthors and I struggled with exactly that question with some fossils found in that area. In the end, we said they were body fossils, not trace fossils. And as everyone knows, I love trace fossils, and I really wanted these to be trace fossils. But they were not. That’s science for you: denying your deepest desires in the face of reality.

So surely the Cambrian would be easier to interpret, right? I meanl, after 542 mya, animals started burrowing merrily, to and fro, hither and tither, with uninhibited and orgiastic abandon, and, well, you get the idea. But, not really. Another part of the field trip involved looking at what happened with the departure of the relatively unbioturbated alien world of the Ediacaran, pre-542 mya, to the more familiar sediment mixing of the Cambrian and Ordovician Periods, post-542 mya. Yet even these rocks and their trace fossils were still not quite like what we see today.

This will be the subject of my next post, which will again explore the theme of how we should approach strict actualism like any scientifically based idea: with a mixture of astonished wonder, but also with a hard-edged look at what is really there.

As we bid adieu to Mistaken Point and began our walk back to the car park, we could swear we saw lifeforms emerging from the mist-covered rocks, resurrected from the deep time and deep water of the Avalonian Precambrian. Then we realized those were just some of our group behind us. Oh well. Maybe next time. (Photograph by Anthony Martin.)

(Acknowledgements: Much appreciation is extended to the field trip leaders – Liam Herringshaw, Jack Matthews, and Duncan McIlroy – for their organization and execution of a fantastic three-day field trip; to Valerie and Richard of the Mistaken Point Ecological Reserve for guiding us to the site; to my ichnological colleagues for their cheery and knowledge-broadening company; and my wife Ruth for being with me and providing an artist’s perspective about her experiences with us crazy ichnologists, shared here and here.)

Further Reading

Fedonkin, M., Vickers-Rich, P. Grey, K., and Narbonne, G. 2007.The Rise of Animals: Evolution and Diversification of the Animalia. Johns Hopkins Press, Washington: 320 p.

Liu, A.G., McIlroy, D., and Brasier, M.D. 2010. First evidence for locomotion in the Ediacaran biota from the 565Ma Mistaken Point Formation, Newfoundland. Geology, 38: 123-126.

Matz, M.V., Frank. T.M., Marshall, N.J., Widder, E.A., and Johnsen, S. 2008. Giant deep-sea protest produces bilaterian-like traces. Current Biology, 18: 1-6

Tacker, R.C., Martin, A.J., Weaver, P.G., and Lawver, D.R. 2010. Trace vs. body fossil: Oldhamia recta revisited. Precambrian Research, 178: 43-50.

Vickers-Rich, P., and Komarower, P. (editors). 2007 The Rise and Fall of the Ediacaran Biota. Geological Society of London, Special Publication 286: 448 p.

Deep in the Dinosaur Tracks of Texas

Posted on August 6, 2012 by TMartin

Given the continuing public mania over dinosaurs, and recent important discoveries of yet more exquisite specimens of feathered theropod dinosaurs discovered in countries far away from the U.S. (here and here), it is sometimes easy to forget what has long been known about these animals, and right here in my own “backyard” (globally speaking).

Need to see some of the best dinosaur tracks in the world, and you live in the southeastern U.S.? Guess what: you can seen them in Glen Rose, Texas. Not China, Mongolia, Canada, Utah, or some other far-off land inhabited by strange people with unusual customs, but Texas. Saddle up! (Photograph by Michael Blair, taken in Dinosaur Valley State Park, Texas.)

So on July 22, just to jog my memory a bit, I flew from Atlanta, Georgia to the Dallas-Ft. Worth (Texas) airport, and only a few hours later was gazing upon dinosaur tracks accompanied by the burrows of invertebrate animals, both trace fossils having been made more than 100 million years ago. It was a fitting welcome to Glen Rose, Texas, a place famous for its dinosaur trace fossils since the 1930s, and where dinosaurs were an integral part of its culture long before it was cool, hip, and contemporary elsewhere.

In Glen Rose, Texas, the dinosaur tracks are so abundant, you can choose whether to see these just outside of your hotel room, or go to the hotel jacuzzi and pool. Naturally, I chose both. (Photograph by Anthony Martin, taken in Glen Rose, Texas.)

So just how did I end up in Glen Rose, Texas, looking at Cretaceous dinosaur tracks and invertebrate burrows? I was lucky enough to be there as an invited participant in an expedition sponsored by the National Geographic Society. I say “lucky” because luck was certainly a part of it, a fortuitous connection made through my writing a book about the modern traces of the Georgia coast. James (Jim) Farlow, a paleontologist at Indiana-Purdue University Fort Wayne (IPFW) and an associate editor with Indiana University Press, reviewed the first draft of my book, but he was also in charge of this dinosaur-track expedition to Glen Rose. Evidently he was impressed enough about what I knew about invertebrate burrows (or at least what I wrote about them) that he considered me as a possible member for his team of scientists, field assistants, and teachers on this expedition.

Dr. Jim Farlow, the world expert on the Glen Rose dinosaur tracks, having a reflective moment at Dinosaur Valley State Park near Glen Rose, Texas. What’s with the broom? He and other people in the expedition used these to sweep river sediment out of dinosaur tracks submerged in the river. In 100° F (38° C) temperatures. On the other hand, I just described invertebrate trace fossils, which was more of a job, not work. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

Thus when Jim asked me last fall if I would be interested in joining them to describe and interpret the Cretaceous invertebrate burrows that occur with the dinosaur tracks there, I jumped at the opportunity. The Glen Rose dinosaur tracksites, most of which crop out in the Paluxy River bed in Dinosaur Valley State Park, are world famous for their quantity and quality, and they connect with an important part of the history of dinosaur studies. Going there, experiencing these tracks for myself, and better understanding their paleoecological and geological context would be of great benefit to me, my students, and of course, you, gentle readers.

Just to back up a bit, and clarify for anyone who doesn’t know why these tracks are so darned important, here’s a brief background. In November 1938, Roland T. Bird, an employee of the American Museum of Natural History and a field assistant to flamboyant paleontologist Barnum Brown (the guy who named Tyrannosaurus rex), saw large, isolated limestone slabs with theropod dinosaur tracks in a Native American trading post in Gallup, New Mexico. Upon inquiring about the origin of these tracks, Bird was told they came from Glen Rose, Texas. So he set out in his Buick for Glen Rose to see for himself whether these tracks were real or not, and whether there were any more to see in the rocks around Glen Rose. The theropod track set in the town bandstand – pictured below – was one of the first sites that greeted him, and Glen Rose locals told him about the tracks in the Paluxy River.

Glen Rose, Texas, the only place in the world where the town bandstand has an Early Cretaceous theropod dinosaur track on display. Wish I could also tell you about all of those little holes in the rock with that track, but I can’t right now. Nonetheless, rumor has it they are burrows made by small, marine invertebrates that lived at the same time as the dinosaurs. (Photograph by Anthony Martin, taken in Glen Rose, Texas.)

Bird had hit the jackpot, the motherlode, the bonanza, the surfeit, the, well, you get the point. Not only did the Paluxy River outcrops contain hundreds of theropod dinosaur tracks – many as continuous trackways – but also the first known evidence of sauropod dinosaur tracks.

A couple of beautifully preserved theropod tracks under shallow water in the Paluxy River. Note that the track at the bottom also has a partial metatarsal (“heel”) impression, and look closely for the digit I (“thumb”) imprint on the right. Scale is about 20 cm (8 in) long. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

Funny how those “potholes” in the limestone bedrock of the Paluxy River have oblong outlines and form regular alternating patterns, isn’t it? Well, them ain’t no potholes, y’all. They’re sauropod tracks, and were among the hundreds recognized as the first know =n such tracks from the geologic record. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

The discovery of sauropod tracks was as huge as the tracks. Up until then, sauropods were assumed to have been so large that they could not support their weights on land and spent most of their time in water bodies. These tracks said otherwise, that these sauropods were walking along mudflats along with the theropods. In short, the trace fossil evidence contradicted the assumed story about how these massive animals moved. After all, trace fossils are direct records of animal behavior, and if interpreted correctly, can tell paleontologists more about what an animal was doing on a given day than any amount of shells, bones, and yes, even feathers.

Sauropod tracks from the main tracksite in Dinosaur Valley State Park, Texas. The sauropod was moving away in this view, and the trackway pattern is a typical diagonal-walking one, right-left-right. In parts of this trackway, both the manus (front foot) and pes) rear foot registered, something Bird noticed in 1938, his observation accompanied by more than a little bit of excitement. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

The details preserved in these sauropod tracks are also astounding. Most sauropod tracks I have seen elsewhere, in Jurassic and Cretaceous rocks of the American West, Europe, and Western Australia, are only evident as large, rounded depressions that you would only know are tracks because they form diagonal-walking patterns. In contrast, the Glen Rose tracks include all five toe and claw impressions on the rear feet (pes) and full outlines of the front feet (manus). The original calcium-carbonate mud in the shoreline environments where the sauropods walked, similar to mudflats I’ve seen in the modern-day Bahamas, is what made this exquisite preservation possible. The mud had to be firm enough to preserve these specific details of the sauropods’ feet, but not so soft that the mud would collapse into the tracks after the sauropods extracted their feet.

Beautifully preserved tracks, manus (top) and pes (bottom). Note the five toe impressions in the pes, which along with its size confirms that these were made by a large sauropod. Meter stick for scale. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

One sauropod trackway, preserved with a theropod trackway paralleling and intersecting it, was actually quarried out of the river and taken to the American Museum. Once there, its pieces stay disassembled for years, before Bird helped with putting the puzzle pieces back together so that it could be used as part of a display there.

Archival video footage of Roland Bird and his field crew working on the dinosaur tracks in the Paluxy River near Glen Rose, Texas. More about this tracksite and its role in the history of dinosaur paleontology is ably conveyed by Brian Switek here.

Photos at the visitor’s center at Dinosaur Valley State Park, showing the sequence of clearing (left) and extraction (right) of the limestone bed containing the theropod and sauropod dinosaur tracks. (Photographs taken of the photographs, then enhanced, cropped, and placed side-by-side by Anthony Martin.)

A lasting trace today of Roland Bird and his field helpers from the 1940s, in which they took out a sauropod and theropod trackway from this place and transported it to New York City. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

Other than some of the best-preserved Early Cretaceous dinosaur tracks in the world, one other claim to fame for the Glen Rose area, and not such a proud one, is its attraction to evolution deniers, a few charlatans who used the tracks to promote what might be mildly termed as cockamamie ideas. You see, Glen Rose is also the site of the infamous “man tracks.” These tracks are preservational variants of theropod tracks that – through a combination of the theropods sinking into mud more than 100 million years ago and present-day erosion of the tracks in the Paluxy River – prompted some people to claim these were the tracks of biblical giants who were also contemporaries of the dinosaurs. (Perhaps this is as good of a time as any to start humming the theme music for The Flintstones.)

Rare documentary footage of humans and dinosaurs interacting with one another during the Early Cretaceous Period, or the Late Jurassic Period. Whatever. Note the inclusion of other seemingly anachronistic mammals, too, such as the saber-toothed felid Smilodon. Perhaps this footage could be included in the curriculum of some U.S. public schools, providing a formidable counter to the views of 75 Nobel laureate scientists. Then we’ll let the kids decide which is right.

I will not waste any further electrons or other forms of energy by continuing to flog this already thoroughly discredited notion, but instead will direct anyone interested to a thorough accounting of this debacle to some actual scholarship here, summarizing original research by Glen Kuban and others in the 1980s through now that have laid to rest such spurious notions. Speaking of Mr. Kuban, I was delighted to meet him for the first time during while in Glen Rose (we had corresponded a few times years ago). I was even more gratified to spend a few hours in the field with him, discussing the genuinely spectacular trace fossils there in Dinosaur Valley State Park with these directly in front of us. Again, I’m a lucky guy.

The expedition was scheduled in Glen Rose for three weeks during late July through early August, but with so many commitments for this summer, I could only carve out a week for myself there, from July 22-29. Fortunately, this was enough time for me to accomplish what was needed to do, while also having fun getting to know the rest of the expedition crew – teachers, artists, videographers, laborers – and enjoying wonderful discussions (and debates) with colleagues in the field. The people of Glen Rose were also exceedingly welcoming and accommodating to us: we felt like rock stars (get it – “rock”?), and were feted by local folks three nights in a row during the week I was there. Many thanks to these Glen Rose for the the exceptional hospitality they extended to our merry band of paleontologists, geologists, river sweepers, or what have you.

You can’t see it, but I’m standing in a sauropod dinosaur track, which is a little deeper than the rest of the river bed. You also can’t see the invertebrate burrows that are in the limestone bedrock, which is fine, because I can’t show them to you yet anyway. But be patient: you’ll learn about them some day. (Photograph by Martha Goings, taken in Dinosaur Valley State Park, Texas.)

I can’t yet say much more about what I did during that week, as all participants signed an agreement that National Geographic has exclusive rights to research-related information, photos, and video unless approved by them. But if you’re a little curious about the daily happenings of the expedition (which just ended last week), Ray Gildner maintained a blog that succinctly touched on all of the highlights, Glen Rose Dinosaur Track Expedition 2012.

Still, I can say, with great satisfaction, that I did successfully describe and interpret invertebrate trace fossils that were in the same rocks as the dinosaur tracks. Hopefully my colleagues and I will have figured out how these burrows related to environments inhabited by the dinosaurs that walked through what we now call Texas.

All in all, my lone week in the Lone Star State was a marvelously edifying and educational experience, one I’ll be happy to share with many future generations of students and all those interested in learning about the not-so-distant geologic past of the southeastern U.S.

Group photo from the Glen Rose Dinosaur Track Expedition 2012. Names of all participants can be found here, but in the meantime, just sit back and admire those Dinosaur World t-shirts everyone is wearing. (Photograph by James Whitcraft or Ray Gildner: they can fight over who actually took it. Although, the automatic timer on his camera took the photo, so maybe it should get credit instead.)

Further Reading

Bird, R.T. 1985. Bones for Barnum Brown: Adventures of a Dinosaur Hunter. Texas Christian University Ft. Worth, Texas: 225 p.

Farlow, J.O. 1993. The Dinosaurs of Dinosaur Valley State Park. Texas Parks and Wildlife Department, Austin, Texas: 30 p.

Jasinski, L.E. 2008. Dinosaur Highway: A History of Dinosaur Valley State Park. Texas Christian University, Ft. Worth, Texas: 212 p.

Kuban, G.J. 1989. Elongate Dinosaur Tracks. In Gillette, David D., and Martin G. Lockley (editors), Dinosaur Tracks and Traces, Cambridge University Press, Cambridge, U.K.: 57-72.

Pemberton, S.G., Gingras, M.K., and MacEachern, J.A. 2007. Edward Hitchcock and Roland Bird: Titans of Vertebrate Ichnology in North America. In Miller, William, III (editor), Trace Fossils: Concepts, Problems, Prospects. Elsevier, Amsterdam: 32-51.

Life Traces of the Georgia Coast

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Author Archives: TMartin

How to Track a Vampire (Bat)

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Deconstructing an Ichnology Abstract, with Alligators

Martin, A.J., Page, M., Vance, R.K., and Skaggs, S. 2012. Dens of the American alligator (Alligator mississippiensis) as traces and their predictive value for finding large archosaur burrows in the geologic record. Journal of Vertebrate Paleontology, 32 [Suppl. to No. 3]: 136.

Descent with Modification

The Traces We Leave Behind: A Tribute to Jordi Maria de Gibert

A Mirror Less Distant in Time

Tracking Bookzilla

Out of One’s Depth in the Ediacaran

Mistaken Point and the Limits of Actualism

Deep in the Dinosaur Tracks of Texas

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Martin, A.J., Page, M., Vance, R.K., and Skaggs, S. 2012. Dens of the American alligator (Alligator mississippiensis) as traces and their predictive value for finding large archosaur burrows in the geologic record. Journal of Vertebrate Paleontology, 32 [Suppl. to No. 3]: 136.

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