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Most Intriguing Traces of the Georgia Coast, 2012

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The end of another revolution of the earth around the sun brings with it many “best,” “most,” “worst,” “sexiest,” or other such lists associated with that 365-day cycle. Tragically, though, none of these lists have involved traces or trace fossils. So seeing that the end of 2012 also coincides with the release of my book (Life Traces of the Georgia Coast), I thought that now might be a good time to start the first of what I hope will be an annual series highlighting the most interesting traces I encountered on the Georgia barrier islands during the year.

In 2012, I visited three islands at three separate times: Cumberland Island in February, St. Catherines Island in March, and Jekyll Island in November. As usual, despite having done field work on these islands multiple times, each of these most recent visits in 2012 taught me something new and inspired posts that I shared through this blog.

For the Cumberland Island visit, it was seeing many coquina clams (Donax variabilis) in the beach sands there at low tide, and marveling at their remarkable ability to “listen” to and move with the waves. With St. Catherines Island, it was to start describing and mapping the alligator dens there, using these as models for similar large reptile burrows in the fossil record. Later in the year, I presented the preliminary results of this research at the Society of Vertebrate Paleontology meeting in Raleigh, North Carolina. For the Jekyll trip, which was primarily for a Thanksgiving-break vacation with my wife Ruth, two types of traces grabbed my attention, deer tracks on a beach and freshwater crayfish burrows in a forested wetland. So despite all of the field work I had done previously on the Georgia coast, these three trips in 2012 were still instrumental in teaching me just a little more I didn’t know about these islands, which deserve to be scrutinized with fresh eyes each time I step foot on them and leave my own marks.

For this review, I picked out three photos of traces from each island that I thought were provocatively educational, imparting what I hope are new lessons to everyone, from casual observers of nature to experienced ichnologists.

Cumberland Island

Coyote tracks – Coyotes (Canis latrans) used to be rare tracemakers on the Georgia barrier islands, but apparently have made it onto nearly all of the islands in just the past ten years or so. On Cumberland, despite its high numbers of visitors, people almost never see these wild canines. This means we have to rely on their tracks, scat, and other sign to discern their presence, where they’re going, and what they’re doing. I saw these coyote tracks while walking with my students along a trail between the coastal dunes, and they made for good in-the-field lessons on “What was this animal?” and “What was it doing?” Because Cumberland is designated as a National Seashore and thus is under the jurisdiction of the U.S. National Park Service, I’m  interested in watching how they’ll handle the apparent self-introduction of this “new” predator to island ecosystems, which may begin competing with the bobcats (Lynx rufus) there for the same food resources.

Ghost Shrimp Burrows, Pellets and Buried Whelk – Sometimes the traces on the beaches at low tide are subtle in what they tell us, and the traces in this photo qualify as ones that could be easily overlooked. The three little holes in the photo are the tops of ghost shrimp burrows. Scattered about on the beach surface are fecal pellets made by the same animals; ghost shrimp are responsible for most of the mud deposition on the sandy beaches of Georgia. The triangular “trap door” in the middle of the photo is from a knobbed whelk (Busycon carica), which has buried itself directly under the sand surface. The ghost shrimp are perhaps as deep as 1-2 meters (3.3-6.6 ft) below the surface, and are feeding on organics in their subterranean homes. These homes are complex, branching burrow systems, reinforced by pelleted walls. Hence these animals and their traces provide a study in contrasts of adaptations, tiering, and fossilization potential. The whelk trace is ephemeral, and could be wiped out with the next high tide, especially if the waiting whelk emerges and its shallow burrow collapses behind it. On the other hand, only the top parts of the ghost shrimp burrows are susceptible to erosion, meaning their lower parts are much more likely to win in the fossilization sweepstakes.

Feral Horse Grazing and Trampling Traces – Probably the most controversial subject related to any so-called “wild” Georgia barrier islands is the feral horses of Cumberland Island, and what to do about their impacts on island ecosystems there. A year ago, I wrote a post about these tracemakers as invasive species, and discussed this same topic with students before we visited in February. But nothing said “impact” better to these students than this view of a salt marsh, overgrazed and trampled along its edges by horses. This is a example of how the cumulative effects of traces made by a single invasive species can dramatically alter an ecosystem, rendering it a less complete version of its original self.

St. Catherines Island

Suspended Bird Nest – I don’t know what species of bird made this exquisitely woven and suspended little nest, but I imagine it is was a wren, and one related to the long-billed marsh wren (Telmatodytes palustris), which also makes suspended nests in the salt marshes. This nest was next to one of several artificial ponds with islands constructed on St. Catherines with the intent of helping larger birds, such as egrets, herons, and wood storks, so that they can use the islands as rookeries. These ponds are also inhabited by alligators, which had left plenty of tracks, tail dragmarks, and other sign along the banks. With virtually no chance of being preserved in the fossil record, this nest was a humbling reminder of what we still don’t know from ichnology, such as when this specialized type of nest building evolved, or whether this behavior happened first in arboreal non-avian dinosaurs or birds.

Ant Nest in Storm-Washover Deposit – As you can see, the aperture of this ant nest, as well as the small pile of sand outside of it, did not exactly scream out for attention and demand that its picture be taken. But its location was significant, in that it was on a freshly made storm-washover deposit next to the beach. This “starter nest” gives a glimpse of how ants and other terrestrial insects can quickly colonize sediments dumped by marine processes, such as storm waves. These sometimes-thick storm deposits can cause locally elevated areas above what used to be muddy salt marshes. This means insects and other animals that normally would never burrow into or traverse these marshes move into the neighborhood and set up shop, blissfully unaware that the sediments of a recently buried marginal-marine environment are below them. Ant nests also have the potential to reach deep down to those marine sediments, causing a disjunctive mixing of the traces of marine and terrestrial animals that would surely confuse most geologists looking at similar deposits in the geologic record.

Alligator Tracks in a Salt Marsh – These alligator tracks, which are of the left-side front and rear feet, along with a tail dragmark (right) surprised me for several reasons. One was their size: the rear foot (pes) was about 20 cm (8 in) long, one of the largest I’ve seen on any of the islands. (As my Australian friends might say, it was bloody huge, mate.) This trackway also was unusual because it was on a salt pan, a sandy part of a marsh that lacks vegetation because of its high concentration of salt in its sediments. (According to conventional wisdom, alligators prefer fresh-water environments, not salt marshes.) Yet another oddity was the preservation of scale impressions in the footprints, which I normally only see in firm mud. Finally, the trackway was crosscut by trails of grazing snails and burrows of sand-fiddler crabs (Uca pugilator). This helped me to age the tracks – probably less than 24 hours old, and not so fresh that I should have reason to get worried. (Although I did pay closer attention to my surroundings after finding them.) Overall, this also made for a neat assemblage of vertebrate and invertebrate traces, one I would be delighted to find in the fossil record from the Mesozoic Era.

Jekyll Island

Grackle Tracks and Obstacle Avoidance – These tracks from a boat-tailed grackle (Quiscalus major), spotted just after sunrise on a coastal dune of Jekyll Island, are beautifully expressed, but also tell a little story, and one we might not understand unless we put ourselves down on its level. Why did it jog slightly to the right and then meander to the left, before curving off to the right again? I suspect it was because the small strands of bitter panic grass (Panicum amarum), sticking up out of the dune sand, got in its way. Similar to how we might avoid small saplings while walking through an otherwise open area, this grackle chose the path of least resistance, which involved walking around these obstacles, rather than following a straight line. If we didn’t know about this from such modern examples, but we found a fossil bird trackway like this but didn’t look for nearby root traces, how else might we interpret it?

Acorn Worm Burrow, Funnels and Pile – When I came across the top of this acorn-worm burrow, which was probably from the golden acorn worm (Balanoglossus aurantiactus), and on a beach at the north end of Jekyll, I realized I was looking at a two-dimensional expression of a three-dimensional structure. Acorn worms make deep and wide U-shaped vertical burrows, in which they quite sensibly place their mouth at one end and their anus at the other. These burrows usually have a small funnel at the top of one arm of the “U,” which is the “mouth end.” The “anus end” is denoted by a pile of what looks like soft-serve ice cream, which it most assuredly is not, as this is its fecal casting, squirted out of the burrow. What was interesting about this burrow is the nearby presence of a second funnel. This signifies that the worm shifted its mouth end laterally by adding a new burrow shaft to the previous one, superimposing a little “Y” to that part of the U-shaped burrow.

Ghost Crab Dragging Its Claw – As ubiquitous and prolific tracemakers in coastal dunes of the Georgia barrier islands, and as many times as I have studied their traces, I can always depend on ghost crabs (Ocypode quadrata) to leave me signs telling of some nuanced variations in their behavior. In this instance, I saw the finely sculpted, parallel, wavy grooves toward the upper middle of its trackway, made while the crab walked sideways from left to right. A count of the leg impressions in the trackway yielded “eight,” which is the number of its walking legs. This means the fine grooves could only come from some appendage other than its walking legs: namely, one of its claws. Why was it dragging its claw? I like to think that it might have been doing something really cool, like acoustical signaling, but it also might have just been a little tired, having spent too much time outside of its burrow.

So now you know a little more about who left their marks on the Georgia barrier islands in 2012. What will 2013 bring? Let’s find out, with open eyes and minds.

 

Tracking Wild Turkeys on the Georgia Coast

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Of the many traditions associated with the celebration of Thanksgiving in the U.S., the most commonly mentioned one is the ritual consumption of an avian theropod, Meleagris gallopavo, simply known by most people as “turkey.” The majority of turkeys that people will eat this Thursday, and for much of the week afterwards, are domestically raised. Yet these birds are all descended from wild turkeys native to North America. This is in contrast to chickens (Gallus gallus), which are descended from an Asian species, and various European mammals, such as cattle, pigs, sheep, and goats (Bos taurus, Sus scrofa, Ovis aries, and Capra aegagrus, respectively).

Trackway of a wild turkey (Meleagris gallopavo) crossing a coastal dune on Cumberland Island, Georgia. Notice how this one, which was likely a big male (“tom”), was meandering between clumps of vegetation and staying in slightly lower areas, its behavior influenced by the landscape. Scale = 20 cm (8 in). (Photograph by Anthony Martin.)

American schoolchildren are also sometimes taught that one of the founding fathers of the United States, Benjamin Franklin, even suggested that the wild turkey should be elevated to the status of the national bird, in favor of the bald eagle (Haliaeetus leucocephalus). With an admiring (although I suspect somewhat facetious) tone, he said:

“He [the turkey] is besides, though a little vain & silly, a Bird of Courage, and would not hesitate to attack a Grenadier of the British Guards who should presume to invade his Farm Yard with a red Coat on.”

There are eight of us, and only one of you. Do you really want to mess with us? (Photograph by Anthony Martin, taken on Cumberland Island, Georgia.)

Unfortunately, because I live in the metropolitan Atlanta area, I never see turkeys other than the dead packaged ones in grocery stores. Nonetheless, one of the ways I experience turkeys as wild, living animals is to visit the Georgia barrier islands, and the best way for me to learn about wild turkey behavior is to track them. This is also great fun for me as a paleontologist, as their tracks remind me of those made by small theropod dinosaurs from the Mesozoic Era. And of course, as most schoolchildren can tell you, birds are dinosaurs, which they will state much more confidently than anything they might know about Benjamin Franklin.

Compared to most birds, turkeys are relatively easy to track. Their footprints are about 9.5-13 cm (3.7-5 in) long and slightly wider than long, with three long but thick, padded toes in front and one shorter one in the back, pointing rearward. In between these digits is a roundish impression, imparted by a metatarsal. This is a trait of an incumbent foot, in which a metatarsal registers behind digit III because the rear part of that toe is raised off the ground. The short toe is digit I, equivalent to our big toe, but not so big in this bird. Despite the reduction of this toe, its presence shows that turkeys probably descended from tree-dwelling species, as this toe was used for grasping branches. Clawmarks normally show on the ends of each toe impression, and when a turkey is walking slowly, it drags the claw on its middle toe (digit III), thus making a nicely defined linear groove.

Wild turkey tracks made while it was walking slowly up a gentle dune slope, dragging the claw on the middle digit of its right foot, making a long groove. Also notice the bounding tracks of a southern toad (traveling lower right –> upper left), cross-cutting the turkey tracks. (Photograph by Anthony Martin, taken on Cumberland Island.)

A normal walking pace (right foot –> left foot, left foot –> right foot) for a turkey is anywhere from 15-40 cm (6-16 in), and its stride (right foot –> right foot, left foot –> left foot) is about twice that, or 30-80 cm (12-32 in), depending on the age and size of the turkey. Their trackways show surprisingly narrow straddles for such wide-bodied birds, only 1.5 times more than track widths. This is because they walk almost as if on a tightrope, with angles between each step approaching 180°; so they still make a diagonal pattern, but nearly define a straight line. However, turkeys meander, stop, or change direction often enough to make things interesting when tracking them. Their flocking behavior also means their tracks commonly overlap with one another or cluster, making it tough to pick out the trackways of individual turkeys. However, in such flocks, the dominant male’s tracks are noticeably larger than those of the females or younger turkeys, so these can be picked out and help with sorting who’s who.

Turkey trackway in which it walked across the wind-rippled surface of a coastal dune on Cumberland Island, meandering while moseying. Same photo scale as before. (Photograph by Anthony Martin.)

An abrupt right turn recorded by a turkey’s tracks. Check out that beautiful metatarsal  impression in the second track from the right, and how the claw dragmark in the thrid track from the right points in the direction of the next track. (Photograph by Anthony Martin.)

One of the more remarkable points about these Georgia barrier-island turkeys, though, is how their tracks belie their stereotyped image as forest-only birds. Although they do spend much of their time in the forest, I’ve tracked turkeys through broad swaths of coastal dunes, and sometimes they will stop just short of primary dunes at the beach. So however difficult it might be to think about these birds as marginal-marine vertebrates, their tracks overlap the same places with ghost-crab burrows and shorebird tracks. Geologists and paleontologists take note: this exemplifies the considerable overlap between terrestrial and marginal-marine tracemakers that can happen in coastal environments. This also happened with dinosaurs that strolled onto tidal flats or otherwise passed through marginal-marine ecosystems.

Turkey tracks heading toward the beach, with the open ocean visible just beyond. Is this close enough to consider turkeys as marginal-marine tracemakers? (Photograph by Anthony Martin.)

Do these turkeys also have an impact on the dunes themselves? Yes, although these effects vary, from trackways disrupting wind ripples to more overt changes to the landscape. For instance, one of the most interesting effects I’ve seen is where they’ve caused small avalanches of sand downslope on dune faces. Interestingly, this same sort of phenomenon was also documented for Early Jurassic dinosaurs that walked across dry sand dunes, which caused grainflows that cascaded downhill with each step onto the sand.

Grainflow structure (arrow), a small avalanche caused by a turkey walking down a dune face. (Photograph by Anthony Martin.)

Close-up of grainflow structure (right) connected to turkey tracks, which become better defined once the turkey reached a more level surface. (Photograph by Anthony Martin, taken on Cumberland Island.)

What other traces do turkeys make? A lot, although I’ve only seen their tracks. Other traces include dust baths, feces, and nests. Dust baths, in which turkeys douse themselves with dry sediment to suffocate skin parasites, must be awesome structures. These are described as 50 cm (20 in) wide, 5-15 (1-3 in) deep, semi-circular depressions, and feather impressions show up in those made in finer-grained sediments. Although such structures would have poor preservation potential in the fossil record, I hold out hope that if paleontologists start looking more at modern examples, they are more likely to find a fossil dust bath, whether in Mesozoic or Cenozoic rocks.

Turkey feces, like most droppings from birds, have white caps on one end, but are unusual in that these can tell you the gender of their depositor. Male turkeys tend to make curled cylinders that are about 1 cm wide and as much as 8 cm long (0.4 X 3 in), whereas females make more globular (not gobbular) droppings that are about 1 cm (0.4 in) wide. These distinctive shapes are a result of their having different digestive systems. Turkeys are herbivores, so their scat normally includes plant material, but don’t be surprised to see insects parts in them, too. Still think about how exciting it would be to find a grouping of same-diameter cylindrical and rounded coprolites in the same Mesozoic deposit, yet filled with the same digested material, hinting at gender differences (sexual dimorphism) in the same species of dinosaur maker.

Turkeys normally make nests on the ground by scratching out slight depressions with their feet, but evidently this is a flexible behavior. On at least one of the Georgia barrier islands (Ossabaw), these birds have been documented as building nests in trees. Although this practice seems very odd for a large, ground-dwelling bird, it is an effective strategy against feral hogs, which tend to eat turkey eggs, as well as eggs of nearly every other species of bird or reptile, for that matter. Just to extend this idea to the geologic past, ground nests are documented for several species of dinosaurs, but tree nests are unknown, let alone whether species of ground-nesting dinosaurs were also capable of nesting in trees.

As everyone should know from their favorite WKRP episode, domestic turkeys can’t fly. But wild turkeys can, and use this ability to get into the branches of live oaks (arrow), high above their predators, or even curious ichnologists. (Photograph by Anthony Martin, taken on Cumberland Island.)

So whether or not you have tryptophan-fueled dreams while dozing later this week, keep in mind not just the evolutionary heritage of your dinosaurian meal, but also what their traces tell us about this history. Moreover, it is an understanding aided by these magnificent and behaviorally complex birds on the Georgia barrier islands. For this alone, we should be thankful.

Paleontologist Barbie, tracking wild turkeys on the Georgia coast to learn more about how these tracemakers can be used as modern analogs for dinosaur behavior and traces, and once again demonstrating why she is the honey badger of paleontologists. (Yes, photograph by me, and taken on Cumberland Island. P.S. Happy Thanksgiving!)

Further Reading

Dickson,J.G. (editor). 1992. Wild Turkeys: Biology and Management. Stackpole Books, Mechanicsburg, Pennsylvania: 463 p.

Elbroch, M., and Marks, E. 2001. Bird Tracks and Sign of North America. Stackpole Books, Mechanicsburg, Pennsylvania: 456 p.

Fletcher, W.O., and Parker, W.A. 1994. Tree nesting by wild turkeys on Ossabaw Island, Georgia. The Wilson Bulletin, 106: 562.

Loope, D.B. 2006. Dry-season tracks in dinosaur-triggered grainflows. Palaios, 21: 132-142.

Different Coastlines, Same Traces, and Time

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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.

Tracking Bookzilla

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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!)

 

Mistaken Point and the Limits of Actualism

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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.

Traces of Toad Toiletry and Naming Trace Fossils

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Sometimes I envy those people on the Georgia barrier islands who, through sheer number of hours in the field, come upon animal traces that I’ve never seen there. But this was one of those instances where the find was so extraordinary that I will suppress my jealous urges, celebrate the person who found it, marvel at it, and share its specialness with others.

Gale Bishop, a fellow ichnologist who is currently on St. Catherines Island, found an intriguing sequence of traces during a morning foray on its dunes and beaches there last week. In his second life – his first was as a geology professor at Georgia Southern University – he has transformed into an indefatigable sea-turtle-nesting monitor on St. Catherines and coordinator of a teacher-training program. Part of his daily routine there, among many other duties, includes looking for mother-turtle traces – trackways and nests – during the nesting season, which in Georgia is from May through September.

Along the way, with his eyes well trained for spotting jots and tittles in the sand, Gale often notices oddities that likely would be missed by most people, including me. The following photograph, which he shared on the St. Catherines Island Sea Turtle Program page on Facebook, is from a find he made about 7:15 a.m. on Saturday, July 7. Take a look, and please, if you haven’t already, forget the title of this post as you ponder its clues.

A mystery in the dune sands of St. Catherines Island on the Georgia coast, begging to be interpreted. No, not the shovel: those are never mysterious. Look at the traces to the left and above the shovel. What made these, what was it doing, and who else was in the neighborhood afterwards? Oh, and again, stop staring at the shovel. (Photograph by Gale Bishop.)

Gale called me out specifically when he posted this and several other related photos on Facebook, and asked me to tell a story about it. I gave him my abbreviated take in the comments, kind of like an abstract for the research article:

Looks like southern toad (Bufo terrestris) to me. What’s cool is the changes of behavior: hopping, stopping, pooping, and alternate walking (which people don’t expect toads to do – but they do).

That was my knee-jerk analysis, which took a grand total of about a minute to discern and respond. (After all, this was Facebook, a forum in which prolonged and deep thinking is strongly discouraged.) But I also kept in mind that quick, intuitive interpretations later need introspection and self-skepticism, especially when I’m making them. (See my previous post for an example of how wrong I could be about some Georgia-coast traces.) So rather than fulfill some Malcolm Gladwell-inspired cliché through my intuition, I sat down to study the photo with this series of questions in mind:

  • Why did I say “Southern toad” as the tracemaker for the sequence of traces that start from the lower left and extend across the photo?
  • What indicates the behaviors listed and in that order: hopping, stopping, pooping, and alternate walking?
  • What signified the changes in behavior, and where did these decisions happen?
  • Why did I assume that most people don’t expect toads to walk (implying that they think they just hop)?

The first leap in logic – how did I know a Southern toad (Bufo (Anaxyrus) terrestris) was the tracemaker – was the easiest to make, as I’ve often seen their tracks in sandy patches of maritime forests and coastal dunes. These hardy amphibians leave a distinctive bounding pattern, with the front-foot impressions together and just preceding the rear-foot ones; the toes of their front feet also point inward. In the best-expressed tracks, you will see four toes on the front feet and five toes on the rear.

Close-up of bounding pattern (from lower left of previous photo), showing front-foot impressions just in front of and more central than the rear feet impressions. Direction of movement is from bottom to top of photo. (Photograph enhanced to bring out details, but originally taken by Gale Bishop.)

The only other possible animal that could make a trackway pattern confusable with a toad in this environment is a southeastern beach mouse (Peromyscus polionotus). Still, mice mostly gallop, in which their rear feet exceed their front feet as they move. Mouse feet are also very different from those of a toad, with toes on both feet all pointing forward (remember, toad toes point inward). So although dune mice live in the same environment as these tracks, these weren’t mouse tracks. The only alternative tracemakers would be spadefoot toads (Scaphiopus holbrookii) or a same-sized species of frog, such as the Southern leopard frog (Rana sphenocephala). But neither of these species is as common in coastal dunes as the Southern toad, so I’ll stick with my identification for now.

Mouse tracks – probably made by the Southeastern beach mouse (Peromyscus polionotus) – on costal dunes of Little St. Simons Island, Georgia. The two trackways on the left are moving away from you, whereas the one on the trackway on the right is heading toward you. All three show a gallop pattern, in which the larger rear feet exceeded the front feet. Scale = 10 cm (4 in). (Photograph by Anthony Martin)

The second conclusion – the types of behaviors and their order – came from first figuring out the direction of travel by the tracemaker, which from the lower left of the photo toward its middle. This shows straight-forward hopping up to the point where it stops.

From there, it gets really interesting. The wide groove extends to the left past the line of travel and had to be made by the posterior-ventral part of the toad’s body (colloquially speaking, its butt). This, along with the disturbed sand on either side of the groove, shows that the toad turned to its right (clockwise) and backed up with shuffling movement. That’s when it deposited its scat, which I’ve also seen in connection with toad tracks (and on St. Catherines, no less). This really helped me to nail down the identity of the tracemaker, almost being able to declare, “Hey, I know that turd!”

Southern toad bounding pattern that abruptly stops, followed by clockwise turning, backing up, and, well, making a deposit. (Photograph by Gale Bishop, taken on St. Catherines Island.)

How about the alternate walking? Turns out that toads don’t just hop, but also walk: right side, left side, right side, and so on. This pattern – also called diagonal walking by trackers – is in the remainder of the photo (with the direction of movement left to right). When toads do this, the details of their front and rear feet are better defined, and you can more clearly see the front foot registers in front of the rear and more toward the center line of the body.

This side-by-side movement is also what imparted a slight sinuosity to the central body dragmark, which was from the lower (ventral) part of its body, or what some people would call “belly.” In my experience, most people are very surprised to find out that toads can walk like this, which I can only attribute to sample bias. In other words, they’ve only seen frogs and toads hop away from them when startled by the approach of large, upright bipeds.

Close-up of alternate walking pattern and body dragmark made by Southern toad. Direction of movement is from upper left to lower right. (Photograph enhanced to bring out its details, but original taken by Gale Bishop on St. Catherines Island.)

But wait, what are those two dark-colored depressions in the center of the alternate-walking trackway? Well, it doesn’t take much imagination to figure those out, especially if you’ve already had a couple of cups of coffee. Yes, these are urination marks, and even more remarkable, there are two of them in the same trackway. So not only did this toad do #2, but also #1 twice.

Southern toad urination mark #1, not too long after doing #2. (Photograph by Gale Bishop.)

Urination mark #2 , which you might say was #2 of #1, but with both #1’s after #2, or, oh, never mind.

Notice that the second mark seems to have had less of a stream to it, which makes sense in a way that I hope doesn’t require any more explanation or demonstration.

So to answer to one of the questions above – what signified the changes in behavior – you have to look for the interruptions in the patterns, much like punctuation marks in a sentence. The commas, semi-colons, colons, dashes are all part of a story too, not just the words.

The summary interpretation of what happened. Let’s just say that this frog (or toad, whatever) didn’t come a courtin’.

Through the series of photos Gale shared in an album on Facebook, he also showed that he was following a protocol all good trackers do: he changed his perspective while observing the traces. Likewise, I teach my students to use this same technique when presented with tracks and other traces, that it’s a good idea to walk around them. While doing this, they see changes in contrast and realize how the direction and angle of light on the traces alters their perceptions of it. At some points, a track or other trace may even “disappear,” then “reappear” with maximum clarity with just a few more steps.

A different perspective of the same traces, viewed from another angle. Do you notice something new you didn’t see in the previous photo and its close-ups? (Photograph by Gale Bishop, taken on St. Catherines Island.)

Now, because I’m also a paleontologist, this interesting series of traces also prompts me to ask: what if you found this sequence of traces in the fossil record? Well, it’d be a fantastic find, worthy of a cover story in Nature. (That is, if the tracks somehow went across the body of a feathered dinosaur.) Right now, I can’t think of any trace fossils like this coming from vertebrates – let alone toads or frogs – so let’s go to invertebrate trace fossils for a few examples of similarly interconnected behaviors preserved in stone.

In 2001, a sequence of trace fossils was reported from Pennsylvanian Period rocks (>300 million years old), in which a clam stopped, fed, and burrowed along a definite path, with all of its behaviors clearly represented and connected. The ichnologists who studied this series of trace fossils – Tony Ekdale and Richard Bromley – reckoned these behaviors all happened in less than 24 hours; hence the title of their paper reflected this conclusion.

Ichnologists have a sometimes-annoying and always-confusing practice of naming distinctive trace fossils, giving them ichnogenus and ichnospecies names. (For a detailed discussion of this naming method, I talked about it in another blog from the dim, dark, distant past of 2011 here.) For instance, Ekdale and Bromley stated in their study that three names could be applied to the distinctive trace fossils made by a single clam, with each a different form made by a different behavior: Protovirgularia (burrowing), Lockeia (stopping), and Lophoctenium (feeding).

Along those lines, another ichnologist (Andy Rindsberg) and I also suggested that an assemblage of trace fossils in Early Silurian rocks (>400 million years old) of Alabama, with many different ichnogenera, were all made by the same species of trilobite. The take-home message of that study, as well as Ekdale and Bromley’s, is that a single species or individual animal can make a large number of traces. This also means that ichnodiversity (variety of traces) almost never equals biodiversity (variety of tracemakers).

So let’s go back to the toad traces, put on our paleontologist hats, and think about a “what if.” What if you found this series of traces disconnected from one another: the hopping trackway pattern, the diagonal walking pattern, the urination marks, the groove, and the turd, all found in disparate pieces of rock? Taken separately, such trace fossils likely would be assigned different names, such as “Bufoichnus parallelis,” “B. alternata,” “Groovyichnus,” “Tinklichnus,” and “Poopichnus.” (Please do not use these names beyond an informal, jovial, and understandably alcohol-fueled setting.)

Color, present-day version of the variety of traces made by a Southern toad (above), and a grayscale imagining of it fossilizing perfectly (below). Key for whimsically named ichnogenera in fossilized version: Bp = “Bufoichnus parallelis,” Ba = “Buofichnus alternata,” G = “Groovyichnus,” P = “Poopichnus,” and T = “Tinklichnus.” Please don’t cite this.

Granted, the environment in which Gale noted these traces – coastal dune sands – are not all that good for preserving what is pictured here, but other environments might be conducive to fossilization. To quote comedian Judy Tenuta, “It could happen!”

So if someone does find a fossil analogue to Gale’s evocative find on St. Catherines Island, I will understand their giving a name to each separate part, even if I won’t like it. The most important matter, though, is not what you call it, but what it is. And in this case, the intriguing story of toiletry habits left in the sand one July morning by a Southern toad is worth much more than any number of names.

Further Reading

Ekdale, A.A., and Bromley, R.G. 2001. A day and a night in the life of a cleft-foot clam: Protovirgularia-Lockeia-Lophoctenium. Lethaia, 34: 119–124.

Halfpenny, J.C., and Bruchac, J. 2002. Scats and Tracks of the Southeast. Globe Pequot Press, Guilford, Connecticut: 149 p.

Jensen, J.B. 2008. Southern toad. In Jensen, J.B., Camp, C.D., Gibbons, W., and Elliott, M.J. (editors), Amphibians and Reptiles of Georgia. University of Georgia Press, Athens, Georgia: 44-46.

Rindsberg, A.K., and Martin, A.J. 2003. Arthrophycus and the problem of compound trace fossils. Palaeogeography, Palaeoclimatology, Palaeoecology, 192: 187-219.

Marine Moles and Mistakes in Science

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A first day of field work in the natural sciences can be expected to hold surprises, no matter what type of science is being attempted. Sometimes these are unpleasant ones, such as finding out the fuel gauge in your field vehicle – which you are driving for the first time, and in a remote place – doesn’t work. Other times, you make a fantastic discovery, like a new species of spider, a previously undocumented invasive plant, or a fossil footprint. But sometimes you see something that just makes you scratch your head and say, “What the heck is that?”, or more profane variations on that sentiment.

What is this long, meandering ridge making its way through a beach to the high tide mark on Sapelo Island, Georgia, and what made it? If you’re curious, please read on. But if you already know what it is, then you know a lot more than I did the first time I saw something like this. (Photograph by Anthony Martin.)

The last of those three scenarios happened to me on Sapelo Island, Georgia, in June 2004. My wife Ruth was with me, and we had just arrived on the island the previous afternoon, having stayed overnight at the University of Georgia (Athens) Marine Institute, or UGAMI. We decided that our first full morning in the field would be at Nannygoat Beach on the south end of Sapelo, which is a 5-minute drive or a 20-minute walk from the UGAMI.

We drove a field vehicle there (the gas gauge and everything else worked), parked, and took the boardwalk over the coastal dunes. Our elevated view from the boardwalk afforded a good look at many insect, ghost crab, bird, and mammal tracks made in the early morning. Circular holes punctured the dunes, made by ghost crabs (Ocypode quadrata). Sand aprons composed of still-moist sand were next to these burrow entrances, bearing crisply defined ghost-crab tracks, although early-morning sea breezes had already started to blur these.

At some point after walking onto the beach, though, we saw traces that we had not noticed in previous visits to Sapelo, and ones I have rarely seen there or on other Georgia barrier islands since. These oddities were meters-long, slightly sinuous to meandering ridges, about 15-20 cm (6-8 in) wide, extending in the sandy areas from the dunes through the berm and down to the high-tide mark, where they ended abruptly.

Same meandering ridge shown in the first photo, but viewed from the high-tide mark, showing how it connects with the primary dunes. Note how a few holes are punched in the part near me: more about those soon. (Photograph by Anthony Martin, taken on Sapelo Island, Georgia. P.S.: My wife Ruth is the scale in both photos, fulfilling one of the top 10 signs that I might be a geologist.)

Although a few ridges crossed one another, they rarely branched, and if they did, the branches were quite short, only about 10-15 cm (4-6 in). When we followed them to the dunes, they seemed to originate from some unseen place below the sandy surfaces. We investigated further by cutting through some of the ridges to see what they looked like inside. They turned out to be mostly open tunnels with circular cross sections about 5 cm (2 in) wide, slightly wider than a U.S. dollar coin. They were mostly hollow, and only occasionally did we encounter a plug of sand interrupting tunnel interiors. This supposition was backed up by ridges that had collapsed into underlying voids. A few of the ridges stopped with a rounded end the same diameter as the ridge, or as a larger, raised, elliptically shaped “hill.”

Ridge with quite a bit of meander in it. Check out the short branch toward the top right, where the tracemaker must have changed its mind and backed up, then continued digging toward the viewer. Scale = 15 cm (6 in). (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)

Two separate ridges intersecting, caused by one crossing the other, resulting in “false branching.” Also notice the partial collapse of sand into underlying hollow tunnels and how one of the ridges ends in a rounded mound. Scale = 15 cm (6 in). (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)

A short ridge ending in a raised, elliptical “hill,” connected to a partially collapsed tunnel that is not otherwise evident as an elevated surface. Same scale as before. (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)

Ruth and I agreed that these tunnels were burrows, instead of some random features made by the winds, tides, or waves. But by what? Clearly their makers were impressive burrowers, capable of digging through meters of sand. Their bodies also were probably just a little narrower than the burrow interiors, which helped us to think about body sizes. Then we considered where we were – dunes and beach – and what animals were the most likely ones to burrow in these environments.

A process of elimination – determining what they were not – was a good way to start figuring out their potential makers. For example, no way these burrows were from insects, such as beetle larvae, ant lion larvae, or mole crickets, because they were just too big. Insects also have a tough time handling salinity, so once they got to the surf zone with its saturated, saline sand, they would have had problems, or (more likely) an aversive reaction and turned around immediately instead of plowing ahead.

Insect burrow in coastal dune sand, made by a small beetle. Look at both the form and scale, and you’ll see this is not a match for what we were seeing. Scale in centimeters. (Photograph by Anthony Martin, taken on Cumberland Island, Georgia.)

Small mammals, like beach mice (Peromyscus polionotus), didn’t seem like good candidates either. Beach-mouse burrows are totally different from what we were seeing, and their burrows do not run all of the way down to the intertidal zone. Mice, like insects, also don’t like marine-flavored water; even if they might be able to temporarily tolerate it, they wouldn’t continue to burrow through moist, salty sand.

A beach-mouse burrow, with their tracks coming and going. Either the mice dug this burrow, or they occupied an abandoned ghost-crab burrow. Regardless, this also doesn’t match our mystery traces. Scale in millimeters. (Photograph by Anthony Martin, taken on Little St. Simons Island, Georgia.)

This led to an initial hypothesis that these burrows were from one of the most common larger burrowing animals in the area, and one comfortable in dune, berm, and beach environments with saturated, salty sand. These could only be from ghost crabs, I thought, an explanation supported by undoubted ghost crab burrows that perfectly intersected these tunnels, accompanied by undoubted ghost-crab tracks.

Ghost-crab burrows intersecting tunnels, accompanied by lots of ghost-crab tracks. Wow, that’s really convincing circumstantial evidence, wouldn’t you say? (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)

End of story, right? Well, no. I and a lot of other scientists have said this before, but it bears repeating: part of how science works is that in its practice we do not prove, we disprove. I somehow knew the “ghost crab burrowing horizontally through meters of sand from the dunes to the beach” hypothesis was a shaky one, and it bothered me that it just didn’t seem right. So I started reading as much as possible about ghost-crab burrowing behaviors. I thought I already knew a lot about this subject, but nonetheless was willing to acknowledge that there might be some holes in my learning (get it – holes?) that needed filling (get it – filling? Oh, never mind).

The gentle reader probably surmised what happened next. That’s right: not a single peer-reviewed reference mentioned ghost crabs digging meters-long shallow tunnels from the dunes to the beach. So either I was wrong, or I had documented a previously unknown and spectacular tracemaking behavior in this very well-studied species. A single cut by Occam’s Razor simply said, “You’re wrong.”

You thought I made long horizontal burrows that go all of the way from the dunes to the surf zone? Wow, you primates are dumber than I thought. (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)

If not a ghost crab then, what else could make meters-long horizontal burrows of the diameter we had seen? This is when I began to reconsider my original rejection of moles as possible tracemakers.

So what am I: chopped liver? (Photograph from Kenneth Catania, Vanderbilt University, and taken from Wikipedia.org here.)

Here’s what was the most interesting about this mistaken interpretation: it was made because of where we were. In other words, our initial mystification about these traces stemmed from their environmental context. Had we seen these burrows winding down a sandy road in the middle of a maritime forest on Sapelo Island, we would not have hesitated to say the word “mole.” Yet because we saw exactly the same types of burrows in coastal dunes and beaches, we said, “something else.”

A long, meandering mole burrow in the sandy road going through a maritime forest on the north end of Sapelo Island. So if you see a burrow like this in the forest, you instantly say “mole.” But if you see it on the beach, you say, “Um, uh, duh…must be something else!” My tracks (size 8 1/2, mens) and 15 cm (6 in) photo scale for, well, scale. (Photograph by Anthony Martin.)

Another long, meandering ridge ended in a rounded “hill,” a trace that no one would hesitate to call a mole burrow, especially because it’s in the middle of a maritime forest. (Photo by Anthony Martin, taken on Sapelo Island, Georgia.)

A trip back to the literature further confirmed the mole hypothesis while also serving up a big slice of humble pie. I was embarrassed to find that these same burrows were described and interpreted as mole burrows in an article published in 1986. Even more mortifying: my dissertation advisor (Robert “Bob” Frey) was the first author on the article; it had been published while I was doing my dissertation work with him; and I had read the article years ago, but didn’t remember the part about mole traces. It was like these burrows were saying to me, “Go back to school, young man.”

OK, so these are mole burrows. Case closed. Now that we’ve identified them, we can stop thinking about them, and go on to name something else. But that ain’t science either, is it? This one answer – mole burrows – actually inspires a lot of other questions about them, which could lead to heaps more science:

• Which moles made these burrows? The Georgia barrier islands have two documented species of moles, the eastern mole (Scalopus aquaticus) and star-nosed mole (Condylura cristata). Of these two, eastern moles are relatively common on island interiors, whereas star-nosed moles are either rare or locally extinct from some of the islands. But star-nosed moles are also more comfortable next to water bodies and seek underwater prey. So could these traces actually signal the presence of star-nosed moles in dune and beach environments? Frey and his co-author, George Pemberton, originally interpreted these as eastern mole burrows, but they also didn’t eliminate the possibility of star-nosed moles as the tracemakers, either.

• What is the evolutionary history of moles on the Georgia barrier islands? Are these moles descended from populations isolated from mainland ones 10,000 years ago by the post-Pleistocene sea-level rise, or do they represent more modern stock that somehow made its way to the islands? A genetic study would probably resolve this issue, but who the heck is going to compare the genetic relatedness of moles from the Georgia barrier islands to those on the mainland?

• What were they eating? Moles don’t just burrow for the exercise, but for the food. While burrowing, they are also voraciously chowing down on any invertebrate they encounter in the subsurface. But what would they eat in beach sands? As many shorebirds know, Georgia beaches are full of yummy amphipods, which would likely more than substitute for a mole’s typical earthworm– and insect-filled diet in terrestrial environments. Yet as far as I can find in the scientific literature, no one has documented mole stomach contents or scat from coastal environments to test whether these small crustaceans are their main prey or not.

• What happened to these moles once their burrows got to the surf zone? Did they turn around and burrow back, or did they go for a swim in the open ocean? The latter is actually not so far fetched, as moles are excellent swimmers, especially star-nosed moles. But how often would they do this?

• Just how common (or rare) are these burrows in beaches? Just because I just perceive these burrows as rare could be an example of sample bias. Yes, I wrote an entire book about Georgia-coast traces and tracemakers and have done field work on the islands since 1998. But I don’t live on the Georgia barrier islands, nor have I spent more than a week continuously on any of them. Keenly observant naturalists who live on the islands or otherwise spend much time there could better answer this question than me. I suspect they’re actually much more common than I originally supposed, and now look for them to photograph or otherwise document whenever I go back to any of the islands.

• Would such burrows preserve in the geologic record? Probably so, especially if they were made in dunes and filled with a differently colored or textured sand. But I’ll bet that nearly every paleontologist or geologist would make the same mistake I did, and reach for a burrowing marginal-marine crab or some other invertebrate as the tracemaker.

Geologists would be further fooled if fossil mole tunnels were intersected by genuine ghost-crab burrows, which would constitute a great example of a composite trace made by more than one species of animal. But why did the crabs burrow into the mole tunnels? Because it was easier. After all, the moles left hollow spaces and loosened sand over wide areas, practically begging ghost crabs to exploit these disturbed areas.

Anyway, I doubt many geologists would think of a small terrestrial mammal as a tracemaker for such burrows in sedimentary rocks formed in marginal-marine environments, although I’d love to be proved wrong on this. I’m hoping my writing about it here will help to prevent such confusion, and that whoever benefits from it will buy me an adult beverage as thanks.

In summary, this example of making a crab burrow out of a mole tunnel thus serves as a cautionary tale of how where we are when making observations in the field can influence our perceptions. But it also goes to show us how our wonderment with what we observe in natural environments can be renewed and encouraged by daring to be wrong once in a while, and learning from those mistakes.

Further Reading

Frey, R.W., and Pemberton, S.G. 1986. Vertebrate lebensspuren in intertidal and supratidal environments, Holocene barrier island, Georgia. Senckenbergiana Maritima, 18: 97-121.

Gorman, M.L., and Stone, R.D. 1990. The Natural History of Moles. University of Chicago Press, Chicago, Illinois: 138 p.

Harvey, M.J. 1976. Home range, movement, and diel activity of the eastern mole, Scalopus aquaticus. American Midland Naturalist, 95: 436-445.

Henderson, R.F. 1994. Moles. Prevention and Control of Wildlife Damage, Paper 49, University of Nebraska, Lincoln: D51-58. (Entire text here.)

Hickman, G.C. 1983. Influence of the semiaquatic habit in determining burrow structure of the star-nosed mole (Condylura cristata). Canadian Journal of Zoology, 61: 1688-1692.

Darwin, Worm Grunters, and Menacing Moles

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In my most recent previous post, I teased readers with the promise of revealing how Charles Darwin used a piano as a scientific tool for studying the behavior of earthworms. Regardless of whether or not you already looked up the answer through The Google, by reading Darwin’s last book (The Formation of Vegetable Mould through the Action of Worms with Observations on Their Habits), or other means, I will now gladly make connections between the seemingly disparate subjects of Darwin’s musically inclined experimentation, earthworm behavior, and fishermen of the southeastern U.S. catching earthworms as bait.

What makes this earthworm (Diplocardia) run away as fast as its little chetae, mucus, and peristalic movement can carry it through the soil? Let’s just say it’s not picking up good vibrations. Photograph by Bruce A. Snyder, from here, from www.discoverlife.org.

In writing about earthworms and their traces in my upcoming book, I devoted several pages to Mr. Darwin’s fascination with earthworms. In this exploration, I tell how Darwin was on to something when he tried applying sound – which included those made by playing musical instruments – to earthworms he had gathered from the English countryside. These musical performances were not an instance of Darwin trying to entertain these worms, boost their self esteem, or otherwise help them get in touch with their emotions. Rather, he was simply testing whether worms reacted to sound. What happened? Well, instead of me describing his results, I’ll let Darwin’s words inform you directly:

Worms do not possess any sense of hearing. They took not the least notice of the shrill notes from a metal whistle, which was repeatedly sounded near them; nor did they of the deepest and loudest tones of a bassoon. They were indifferent to shouts, if care was taken that the breath did not strike them. When placed on a table close to the keys of a piano, which was played as loudly as possible, they remained perfectly quiet.

– Charles Darwin, The Formation of Vegetable Mould through the Action of Worms with Observations on Their Habits (1881), p. 27.

Hence it was with deep appreciation last month when I gazed at the piano in the drawing room of Down House, the former Darwin family home, and thought about these experiments. Smiling, I imagined Darwin carefully watching a container of worms while he or someone else in his family forcefully banged on the keys of this piano. Of course, you also can’t help but wonder what was played “as loudly as possible.” Were these single, random notes, chords, or actual musical compositions? If the last of these, what pieces were played? Ideally, I like to think Mr. Darwin or one of his family members played a sea shanty learned during his days on The Beagle (or perhaps even songs learned from pirates), rather than just pounded random notes up or down a scale.

As conclusive as Darwin’s paragraph might seem about the lack of earthworm reactions to sound, he, like any good storyteller, then injected a dramatic twist when reporting his results. He followed up the preceding paragraph with one describing how earthworms, although deaf, are extremely sensitive to vibrations transmitted through solid media. Here he revealed exactly which notes were played (C on the bass clef, G in the treble clef, C in the treble clef) while two worms were in pots placed on top of the piano.

The vibrations transmitted through solid media – not air – caused the worms to withdraw from the soil surface, presumably hiding from the source of the vibrations. As an extension of this experiment, Darwin also used a fork to agitate the soil underneath other worms, which then provoked them to move up to the surface. Darwin correctly surmised that this stirring activity, like sound, also sent vibrations through the soil, which likewise produced aversive reactions in the earthworms.

These responses made sense in an evolutionary way, and show how Mr. Darwin was applying his principle of natural selection to the predator-prey relationships that had evolved between earthworms and moles. The behaviors he observed would have favored the survival of earthworms that associated vibrations with their most feared predators, and reacting accordingly, which is to say, fleeing in terror. And just what were their aversion-inducing predators? They were not robins or other species of birds – early, punctual, or otherwise timed – but the earthworm version of graboids: burrowing moles.

Eastern mole (Scalopus aquaticus) emerging from its burrow, seeking earthworms and other fresh food. Photograph by Kenneth Catania, from Fairfax County Schools.

Graboid emerging from its burrow, seeking humans and other prey. Note the eerie resemblance of its behavior to that of an eastern mole, albeit orders of magnitude larger and accompanied by a keen interest in large, surface-dwelling, bipedal prey. Photo from Wikipedia, but originally taken from the greatest ichnologically inspired horror film of all time, Tremors.

So you didn’t know about graboids, those burrowing predators of the underworld? Fortunately, this educational video provides all of the details you need to know. But if you’re interested in studying their neoichnology, be careful, and stay on the pavement.

As yet another example of ‘backyard science,” Darwin observed many traces of the European mole (Talpa europaea) in the fields just outside Down House, most of which were their mounds, or “molehills.” Indeed, last month as I admired one of Darwin’s original wormstones in the pasture behind Down House, I also noticed a good number of molehills on the grounds. Rather stupidly, I neglected to take a photo of one of these. (I mean, how cool would it have been to share images of the traces of moles that descended from those whose traces Darwin noticed?) Nonetheless, some of my photos of the grassy area near the wormstone show 20-30 cm wide bare patches in this otherwise meticulously maintained lawn. These spots, I suspect, are traces of the Down House groundskeepers, who probably level molehills as quickly as they appear, an ichnological version of “whack a mole.”

The pasture just behind Down House (Charles Darwin’s former home), with a “wormstone” in the lower right, and a few bare patches of ground just to the left. Could the latter mark recent sites of mole tunnels and molehills leveled by Down House groundskeepers, or are these just places where grass did not grow, and hence the products of an ichnologist’s overactive imagination? Anyway, I did see molehills out there, but don’t blame y’all for being a bunch of skeptical scientists and wanting more evidence than my just saying so.

OK, now how does all of this wonderfully elucidated Victorian-era science relate to the ecosystems and biota of the southeastern United States? Enter the “worm grunters.” Worm grunters are people who, independently of Darwin, figured out the same adaptive responses of earthworms to underground vibrations. Through their own experiments, worm grunters, who were interested in efficiently gathering many worms in a short time for putting on fishhooks (or making money selling earthworms to people who put them on hooks), rubbed steel slabs across the top of wooden posts stuck in the ground. Much later, researchers interested in finding out how this technique worked calculated frequencies of the seismic vibrations that caused earthworms to flee upward away from perceived predators.

The southeastern U.S., including the Georgia barrier islands, not only has its own species of earthworms (Diplocardia mississippiensis), but also has its own species of moles: the eastern mole (Scalopus aquaticus) and the less common star-nosed mole (Condylura cristata). Both types of moles no doubt strike fear in the multiple hearts of earthworms, and natural selection being how it is, the fastest burrowing moles (who are most likely to catch worms) also cause considerable vibrations from their digging. This accordingly means the earthworms that detect and escape these vibrations live long enough to reproduce and pass on whatever genes that aided in such perceptions.

In getting caught by this mole, this earthworm may have just won the worm equivalent of a Darwin Award, depending on whether it had reproduced or not. (Which it probably did, considering earthworm hermaphroditism means they are at least twice as likely to get lucky.) Photo from University of Illinois Extension; Home, Yard, and Garden Pests Newsletter, here.

Thus a visit to Down House in southern England and consideration of Darwin’s contributions to ichnology and behavioral ecology are not so far removed conceptually from the practical knowledge gained by some people in parts of the southeastern U.S. Moreover, many of these same people are of English, Irish, or Scottish descent, and effectively applied the same knowledge surmised by Darwin about worms and moles, which is kind of neat in a heritage sort of way.

Would all of these findings count as applied science, despite its historical lack of Ph.D.-bearing investigators, grant funding, publications, and press conferences announcing the results? Yup. After all, science is about its methods.

So next week, we’ll take a closer look at the traces moles make on the Georgia barrier islands. Do these moles just go after earthworms in the forests and meadows of those islands? Nope. After all, science is not just about its methods, but also surprises.

Further Reading

Darwin, C. 1881. The Formation of Vegetable Mould through the Action of Worms, with Observations on their Habits. John Murray, London, U.K.: 326 p.

Edwards, C.A., and Bohlen, P.J. 1996. Biology and Ecology of Earthworms (3rd Edition). Springer, Berlin: 426 p.

Gorman, M.L., and Stone, R.D. 1990. The Natural History of Moles. University of Chicago Press, Chicago, Illinois: 138 p.

Hendrix, P.F. 1995. Earthworm Ecology and Biogeography in North America. CRC Press, Boca Raton, Florida: 244 p.

Mitra, O., Callaham, M.A., Jr., and Yack, J.E. 2009. Grunting for worms: seismic vibrations cause Diplocardia earthworms to emerge from the soil. Biology Letters, 2009: 16-19.

Of Darwin, Earthworms, and Backyard Science

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On the other hand, I sometimes think that general & popular Treatises are almost as important for the progress of science as original work.

– Charles Darwin, in a letter to Thomas Huxley, written in his home (Down House) on January 4, 1865

A combined blessing and burden that comes with travel, especially to new places, is the memory we carry of other places. The blessing part comes from the opportunity to connect previously disparate bodies of knowledge and experiences. This is always exciting for anyone who likes that sort of thing, while also satisfying purported promoters of “interdisciplinarity” (which was probably not a word until academia invented it, then pretended to reward those who practice it). On the other hand, the burden is that these thoughts of previous places can act as a veil, obscuring or overlaying our perception of novel sensations. In extreme cases, these remembrances can smother original ideas, especially if the places of our past are idealized and held as some worldly standard to which all other things must be compared.

What does this roundish stone, lying in the ground of the English countryside south of London, have to do with life traces of the Georgia coast? Good question, and if you’d like the start of an answer, please read on.

This Janus-like duality of travel occurred to me after my wife (Ruth) and I left Georgia for a few weeks of vacation in the United Kingdom, yet once there, I thought about my original home of Indiana and the barrier islands of Georgia. Ruth had never been to the U.K., and I hadn’t visited since attending an ichnology conference and field trip in Yorkshire, held in 1999. Fortunately, Ruth has a friend on the northeastern side of London who generously offered us a place to stay before we headed elsewhere. This refuge gave us a few days to learn what London had to offer us while we otherwise adjusted to cultural and temporal differences.

Among the myriad of educational opportunities in the London area is one that had been on my mind for quite a while, thanks to my writing about the Georgia coast. This was an intended visit to Down House, the former home of Charles Darwin and his family. Down House is located in a rural setting of the greater London area – Downe Village in the former parish of Kent – well southeast of Big Ben and all of the other typical touristy trappings of downtown London. Still, it can be visited via public transportation, which became doable for us Yanks once we figured out the needed connections in the intricate rail and bus system weaving throughout the London area.

From where we were staying, it took us nearly two hours to reach Down House. It was a mildly aggravating sojourn by train and bus, but made much better once we realized that driving there in London traffic with a hired car would have been far worse for both us and other people sharing the road (or sidewalk, as it may be). After our bus dropped us off in Downe Village, we saw a small sign pointing the way to Down House, and walked for  15 minutes on a quiet, country road before reaching our goal, a stroll only occasionally interrupted by brief terror induced when cars approached from the direction opposite of our expectations.

 When you step off the bus in Downe Village, this is one of the few clues that you’re near Darwin’s home, a place where scientific thought and human history changed in a big way.

A signpost in Downe Village provides a clue that Darwin has something to do with this area, although some horse named “Invicta” gets equal billing, and “St Mary the Virgin” gets bigger typeface. Still, it was nice to see Darwin’s visage there, too.

Blink and you’ll miss it: after walking about 10 minutes down the road, here’s the sign pointing the way to Down House. Personally, I thought it could use a neon fringe, or at least some DayGlo™ colors, but subdued is probably the way Darwin would have liked it.

We were also a little surprised at the subdued signage pointing us in the right direction to our goal, and I mused briefly about the homes of people who had far less impact on the advancement of human knowledge and world perspectives whose homes are accorded far more attention and adulation. (Yes, I’m looking at you, Graceland.)

The front of Down House, the home of Charles Darwin and his family from 1842 and after his death in 1882.

Down House is both modest and grand, not palatial at all, but impressive inside. Rooms on the second floor (or first floor, if you live in the U.K.) hold displays with a neatly presented synopsis of Darwin’s life and scientific findings, starting with his little boat journey in 1831-1836 through his grand synthesis of evolutionary principles. The ground floor of the house is more or less restored to the time when the Darwin family lived there, with particular attention paid to Mr. Darwin’s study, which was his main writing and experimentation room, or what modern-day scientists might call his “research space.” This is where On the Origin of Species and most other books of his were born. Infused with a purely fan-boy sort of joy, I was thrilled to be in the same place where many of his revolutionary ideas about evolution became expressed through words.

However, one item in the family living room (drawing room) intrigued me in a special way. It was a piano. This object was certainly used for the enjoyment of Darwin family members and guests, with the degree of delight of course depending on the proficiencies and musical choices of whoever played it. But then I was reminded – by the disembodied voice of Sir David Attenborough, no less – that this was not just a musical instrument, but also a scientific tool. (Disappointingly, Sir Attenborough volunteered this information in a recorded audio tour provided with admission to Down House, not through clairvoyance in a Sir Arthur Conan Doyle sense.) On this piano in the room and in the nearby Down House backyard are the places where Darwin conducted some of the earliest quantitative experiments in the behavioral ecology and neoichnology of terrestrial infauna. Or, in plain English, Darwin used this piano and a few other tools to measure and test the behavior of earthworms as tracemakers in soil.

The rear of Down House, with the two windows to the left looking into the drawing room, where the Darwin family piano is located. Unfortunately, photographs are not allowed in the interior of Down House, hence the external, voyeuristic perspective.

Darwin enthusiasts know well that the last book Darwin wrote was about a personal passion of his, the biology and behavior of earthworms. This book, titled The Formation of Vegetable Mould through the Action of Worms with Observations on Their Habits (1881), encapsulates many observations and conclusions he made from his long-term study of the oligochaete annelids that lived abundantly in the backyard and gardens of Downe House. As some biographers have noted, Darwin became quite a homebody after his years of voyaging on The Beagle, and he stayed close to Down House for much of his life after moving there in 1842. Nonetheless, this geographically restricted lifestyle did not mean he stopped inquiring about the natural world around him. On the contrary, he carried out intensive studies in and just outside of Down House, some of which dealt with earthworms, a subject that interested him for more than half of his life.

Darwin’s wonderment at worms was jump-started by something he noticed nearly thirty years after he innocuously tried to improve the soil in the pasture behind Down House. Told that he could get rid of mossy areas by laying down cinders and chalk, he obediently did so, and checked those same areas 29 years afterwards. It turned out the anomalous sediments had been buried about 18 cm (7 in) below the surface.

Darwin soon suspected this surface was newly made, formed by generations of earthworms bringing up soil over the preceding three decades. Through the technical support of his son Horace, an engineer, Darwin began to measure just how much earth an earthworm could worm. He already knew that earthworms burrowed through, consumed, and defecated sediment, which resulted in thoroughly mixed and chemically altered soils. So using his geologically inspired sense of time and rates of processes, he also rightly imagined that the daily activities of earthworms, multiplied by millions of worms and enough years, changed the very ground underneath his feet in a way so that it, well, evolved.

Ever the good scientist, though, Darwin tested this basic idea through experimentation. His assessment was accomplished through a precise measuring device invented by his son and flat, circular rocks, nicknamed wormstones, which were set out in the backyard of Down House. Based on my visual and tactile examination of the one wormstone that still lies outside of Down House, it looked like a quartz sandstone. However, out of respect for it and its ichnological and historical heritage, I did no other tests of its composition.

One of Darwin’s original “wormstones” (foreground center) placed in a pastoral setting behind Down House. Paleontologist Barbie (just behind the wormstone), who has accompanied me for much field work on the Georgia coast, helpfully provides scale.

Close-up view of wormstone, showing three metal slots set into a central ring and two rods, which provided the datum for measuring change in the wormstone’s depth over time. £10 note (with Darwin’s portrait on the right) for scale.

The experiment was elegantly simple. Using a device invented by Horace in 1870 (illustrated below, and photo here), the surface of the wormstone was measured relative to the height of the surrounding soil surface. This change in relative horizon was discerned by fitting the device on three metal slots that had been added to the edge of a central hole in the wormstone. Metal rods inserted through this same hole were connected to underlying bedrock, ensuring that these would stay stationary as worms churned the surrounding soil. Thus these rods acted as a horizontal datum through which any changes in the ground surface could be compared.

Illustration of Horace Darwin’s “wormstone measuring instrument,” with “K” pointing to where the instrument was placed to contact with the metal rods; the change with each measurement over time between this and “A” (a metal ring) would then show how much the stone had sunk downward. My source of this figure is from an online PDF by the Bromley Partnerships, Discover Darwin: An Education Resource for Key Stage Two, but its primary source is not cited there, and I could not otherwise find an attribution.

Darwin figured that the burrowing activity of earthworms underneath the stone, as well as sediment deposition at the surface as fecal castings, would result in the stone “sinking” over time, becoming buried from below. He was right. Using the wormstone and Horace’s measuring device, he calculated the approximate rate of sinking (2.2 mm/year). This was also a measure of soil deposition, which he attributed to earthworms depositing the sediment through fecal castings. Extrapolating these results further, he estimated that 7.5 to 18 tons (6.8-16.4 tonnes) of soil were moved by worms in a typical acre (0.4 hectares) of land.

Something very important to remember in Darwin’s approach to this study was that he was not just a biologist, but also an excellent geologist, taught early in his career – and later befriended – by one of the founders of modern geology, Charles Lyell. Consequently, he had a long-term view of how small, incremental changes every year added up to big changes over time. Or, to put it in Darwin’s own words (The Formation of Vegetable Mould, p. 6), when he responded to a critic claiming that earthworms were too small and weak to have any large-scale effect on their surroundings:

Here we have an instance of that inability to sum up the effects of a continually recurrent cause, which has often retarded the progress of science, as formerly in the case of geology, and more recently in that of the principle of evolution.

Darwin wasn’t just a quantitative ichnologist, but he also described and illustrated some of the traces made by earthworms, such as their burrows, aestivation chmabers, fecal pellets, and turrets made by their fecal casts. (Much later, in 2007, South American paleontologists described fossil examples of fecal pellets and aestivation chambers from Pleistocene rocks of Uruguay.) Darwin even noted the orientations and species of leaves earthworms pulled into burrows to plug these (p. 64-82), then he independently tested these results with pine needles and triangles of paper (p. 82-90)!

Illustrations of turrets made by fecal pellets of earthworms, in The Formation of Vegetable Mould through the Action of Worms with Observations on Their Habits (1881): from left to right, Figure 2 (p. 107), Figure 3 (p. 124), and Figure 4 (p. 127).

In short, Darwin, through combining his vast knowledge of biology with geological principles, had all the right stuff to make for a formidable ichnologist. Even better, he was keenly interested in the ichnological processes happening just outside his house, and didn’t feel the need to take a long boat trip to watch these processes in some far-off, exotic land. Unknowingly, he was also providing an example of how to do “backyard science” long before this term became associated with cost-effective means for introducing children to nature observation.

All of this marvelous research done by Darwin, culminating in his writing a book at Down House that ended up being one of his most popular, leads me to a bit of a mini-rant, followed by my connecting this science to my homes of Indiana and Georgia, and ending with a message of hope, if I may.

Darwin’s earthworm research epitomized the sort of long-term, DIY experimentation that seemingly only Darwin could have done, and in his day. In contrast, to show how far science has changed since his time, the current profit-oriented business model afflicting modern research universities might have demanded Darwin write a multi-million dollar (or pound) grant to conduct this study. (I suppose the piano would have been the most expensive item on the equipment list, and the wormstones the least.)

Moreover, in this hypothetical scenario, Darwin only could have written such a grant after “pre-confirming” most of his results by publishing a series of research papers. And not just by publishing these papers, but also by making sure they were in prestigious journals, most of which would require expensive subscriptions to read, ensuring that only a small handful of people would read about his work. (A book written for a popular audience? Please.) Had Darwin been a young man, the completion of a 30-year-long study also would have depended on whether he was granted tenure early on. This likely would have been decided by people with little or no expertise in geological processes, earthworms, and bioturbation, but who could certainly count grant revenue and compare journal impact factors.

Fortunately, though, Darwin was independently wealthy, well established as a senior scientist, and never had to worry about tenure or other such trivial matters. Instead, he could just focus on studying his much beloved worms, then think of how to share his vast knowledge of them with a broader audience. Darwin never used the word “ichnology” in his writings, let alone “neoichnology,” and he wrote a book on this topic for natural-history enthusiasts, rather than through a series of research papers published in inaccessible journals. Nonetheless, in his own way, he surely advanced the popularization of ichnology through his slow, deliberate, careful, and imaginative methods, which he combined with a desire to communicate these results to all who were interested.

How does all of this link with Indiana and Georgia? Well, Darwin’s “backyard science” reminded me of how I, like many naturalists of a certain generation, grew up learning about nature through what was in my own backyard. Today I have no doubt that my fascination with the behavior and ecology of insects, plants, and yes, earthworms in my Indiana backyard all contributed to a subsequent desire to do science outside as an adult. To satisfy this urge, I later picked geology as my main subject of study, but also took advantage of my biological leanings by concentrating on ichnology in graduate school. My living in Georgia since 1985 and other serendipitous events then eventually led to my writing a book about traces of the Georgia barrier islands (being published through Indiana University Press). In one chapter of this book, when I introduce earthworms as tracemakers, I made sure to write at least a few pages about Mr. Darwin and his experiments with earthworms. So although Darwin never traveled to Indiana or the Georgia coast, I carried my boyhood and adult experiences of both places in my mind to his former home.

Now here’s the hopeful message (not to be confused with a “hopeful monster“). Lots of field-oriented scientists spend much of their time outside for their research, and many require only modest amounts of money for their studies. So what they have begun to do is side-step the reigning corporate mentality influencing so-called “big science” at universities, while also making active attempts to better connect their research with more people than their academic peers. Through organized efforts like The SciFund Challenge and other crowd-sourcing methods, scientists are seeking small personal donations from the public, allowing them to better focus on their research, rather than spending much time, energy, and angst in writing massive research grants that have little chance of being funded. Thus much like earthworm castings, these  donations add up over time and provide rich, fertile ground for conducting basic science. (OK, maybe not the best metaphor, but you get the point.)

Another facet of this research is the stated commitment of scientists to report their research progress through blogs, then publish their peer-reviewed results in open access journals, which provide articles free for anyone with an Internet connection and curiosity in a scientific subject. All of this means that small investigations with big implications – like Darwin’s study on earthworms – are more likely to happen, and are better assured of reaching a public eager to learn about these sciences, while giving the opportunity for people to witness the direct benefits of their investments.

So how does the Darwin family piano relate to his study of earthworms? Do the southeastern U.S., earthworms, and Darwin’s study of their behavior somehow intersect? In answer to the first question, it’s interesting, and in answer to the second, yes. But an explanation of both will have to wait until next time.

In the meantime, if you go out for a walk later today, pay attention to the ground beneath you, and think of how it reflects an ichnological landscape, a result of collective traces made by those “lowly” earthworms, and how Charles Darwin clearly explained this fact in 1881. For me, it was an honor to stand in the same area where Darwin made his measurements, used his humble instruments, and applied his fine mind; this despite my later realization that I was standing on a new ground surface relative to where Darwin stood. After all, 130 years has passed since his death, meaning the ground had been recycled by descendants of the same earthworms he watched with his appreciative and discerning eyes. All of which makes for a different kind of descent with modification, one that instead reflects an ichnological perspective well articulated and appreciated by Darwin.

Darwin’s “sandwalk,” a walking route behind Down House he often took to help with his thinking, and a visible trace today of Darwin’s legacy as one of the first popularizers of ichnology.

Further Reading

Darwin, C. 1881. The Formation of Vegetable Mould through the Action of Worms with Observations on Their Habits. John Murray, London: 326 p. (A scan of the original book, converted to a PDF document, is here.]

Pemberton, S. George and Robert W. Frey. 1990. Darwin on worms: the advent of experimental neoichnology. Ichnos, 1: 65-71. (Text for article here.)

Quammen, D. 2006. The Reluctant Mr. Darwin: An Intimate Portrait of Charles Darwin and the Making of His Theory of Evolution. W.W. Norton, New York: 304 p.

Verde, M., Ubilla, M., Jiménez, J.J., and Genise, J.F. 2006. A new earthworm trace fossil from paleosols: aestivation chambers from the Late Pleistocene Sopas Formation of Uruguay. Palaeogeography, Palaeoclimatology, Palaeoecology, 243: 339-347.

 

 

The Ichnology of Peeps

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Once a year, around Easter time, an attentive beachcomber might notice the unusual traces of a migratory animal on the sands of the Georgia barrier islands. Based on a few clues, its traces point toward five identically sized and conjoined tracemakers, indicating some sort of obligatory group behavior.

Eyewitnesses swear these tracemakers – nicknamed “peeps” – possess a few superficial avian qualities, yet they lack many of the anatomical traits we normally associate with birds, such as, well, wings and legs. Indeed, they apparently have flat ventral surfaces, which with their forward movement along beach sands cause trails, rather than trackways.

Peep trail, observed on berm of Nannygoat Beach, Sapelo Island, Georgia. Oddly enough, this trail shows both a sudden start and end, almost as if the peeps were placed and removed from the surface, respectively.

As a result, peep trails – which are sometimes sinuous, but always harmonious – consist of five parallel grooves, each spaced equally and separated by six ridges, four on the interior of the trail and one on each side. Lateral movements along the length of a peep trail can vary the height of these ridges, depending on whether the peeps are banking to the right or left as they turn.

Although flying ability in peeps has only been inferred on the basis of their possible avian affinity, peep traces show only very brief periods of airborne activity. These traces indicate a somewhat clumsy strategy when approaching ground surfaces, culminating in abrupt vertical descents best described to laypeople as “crashing.” Ideally, all five peeps leave impressions of their cranial anatomy, which includes rudimentary beaks and foreshortened premaxillas. I have no idea if this facial configuration reflects acquired characteristics – caused by frequent crashes – or are more attributable to their original genotype.

Peep landing trace, in which impressions of the anterior anatomy are preserved. Note the short beak marks and rounded dorsal portion of the torso, but with a thin shelf close to the ventral surface. Sand ridges around the impressions suggest the tracemaker bounced after landing.

Peep resting traces are sometimes subtle, owing to their light weight, which according to some sources is about 85 grams (3.0 ounces) in total, or 17 grams per peep. In such instances where their resting traces are recognized, though, peep ventral anatomy is more clearly discernible. Interestingly, the anterior portion of their bodies is rounded and broad, but tapers into a blunt, narrow posterior with a possible upturned tail, the latter suggested by a thin groove bisecting the dorsal part of this posterior mark.

But perhaps the puzzling aspect of these traces is their lack of feather impressions. This evidence shows that peeps, despite their inferred avian affinity, must have become secondarily featherless, despite a long history of descent from non-avian dinosaurs.

Peep resting trace, barely noticeable owing to the light weight of its tracemakers, yet still apparent through its typical overall five-part form.

As is typical with resting traces, these are often connected directly to traces of other behaviors, such as locomotion or burrowing. Indeed, peep resting traces sometimes segue into or out of shallow burrows, which again have five impressions on their bases. Burrowing is presumably an adaptive strategy to avoid predation, implying delectable qualities.

A peep resting trace that is also a burrow, and connecting to an exit mark (right) in which the peep tails left impressions with movement up and out of the excavation.

Peeps are rarely sighted outside of small, cellophane-wrapped boxes in urban shopping centers. Nevertheless, one spring I was lucky enough to see a gaggle of them (five, of course), exuberantly unbound. on a beach of Sapelo Island, Georgia. Thus I was able to observe them making trails, landing traces, resting traces, and actively burrow just above the intertidal zone, which may very well be their natural habitat.

Five peeps making a trail as conjoined unit on a Sapelo Island beach, a behavior predicted by their traces. Who says ichnology isn’t a real science?

Peep landing marks from a short aerial excursion, with the peep presence a short distance away also supporting the interpretation of their bouncing forward after landing.

Peeps exiting a shallow burrow that was also a resting trace, a blend of behaviors often implied by traces.

Peeps initiating a deeper burrowing strategy, perhaps as a form of predation avoidance. Note how the trail becomes shortened, straight, and produces a large pile of sand in front of the direction of movement.

Never-before-seen evidence of how these legless peeps burrow! They use a combination of minute lateral undulations and forward movement directed downward at a shallow angle. As a result, the trail entering the burrow becomes covered by sand ridges produced by the subsequent behavior.

Success! These peeps have managed to bury themselves, leaving only a small portion of their heads exposed, with all five watching warily for predators,

Peeps have been the subject of intensive research, but much of this work, however valuable, has been laboratory based and highly experimental. Thus the data I’ve presented here on their traces should greatly expand our understanding of their behavior in the context of natural settings. Further insights on the biology of peeps are currently murky, but their traces hold promise of fitting them into a taxonomic category more precise than “looks like little chicks.”

Although trace fossils of peep trails, landing traces, resting traces, and burrows have not yet been discovered, I propose these should have the following ichnogenus and ichnospecies names: Peepichnus quinquecalles (= “Peep trace of five trails”). However, I anticipate some of my ichnological colleagues will want to split the ichnotaxonomy of peep traces on the basis of whether they were moving horizontally versus vertically (the peeps, not my colleagues) and other such nuances. Personally, I think they just need to relax, stop coming up with so many silly, unpronounceable names, and just enjoy the sweetness of these little tracemakers of the Georgia coast.