Tag Archives: animal behavior

Enter The Evolution Underground

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It seemed all too fitting that author copies of my new book, The Evolution Underground: Burrows, Bunkers, and the Marvelous Subterranean World Beneath Our Feet (Pegasus Books, 2017) arrived on February 2. In the U.S., this is Groundhog Day, which is named after a burrowing animal and one in which its burrow plays a key role in its mythology. Did it cast a shadow or otherwise predict the weather for the next six weeks? No, but it may enlighten as you travel through geologic time, learning all about how animals and their burrows altered the world, and how animals used burrows to survive the worst the earth (or solar system) could toss at them.

It’s here! After about two years from start to end, The Evolution Underground is out of its literary bunker and into your hands. (Photo by Anthony Martin.)

Is a book about burrows and burrowing animals too far beneath you to read? Well, as the immortal Kenny Loggins might say: Do what you like, and do it naturally.

The Evolution Underground is my seventh book and the second written overtly for a popular-science audience, following Dinosaurs Without Bones: Revealing Dinosaur Lives through Their Trace Fossils (2014, also by Pegasus Books). Dinosaurs Without Bones was a successful debut for me as a popular writer, with not-bad sales and mostly positive reviews (such as this, this, and this). That book was also my first attempt to make the word “ichnology” (the study of traces) more mainstream, and by using those always-charismatic dinosaurs as a hook. It worked, and I now think the percentage of people confusing ichnology with ichthyology has gone down ever so slightly since that book came out.

It’s ichnology, not ichthyology. Make sure you get it right, because you do not want to be slapped by Batman.

For fans of Dinosaurs Without Bones, I’m happy to report my new book – which is officially published today, February 7, 2017 – includes dinosaurs and it’s about ichnology. But it also includes plenty of paleontology, geology, ecology, and good, old-fashioned natural history throughout. Moreover, this book gave me a chance to introduce readers to a panoply of animals representing the past 550 million years of earth history, while also exploring the big idea that burrowing impacted the evolution of many animals and their ecosystems.

What’s it like to be a gopher tortoise? Kind of like being a subterranean landlord, considering that you might be sharing your burrow with 300-400 other species of animals.(Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)

Along those lines, main themes of the book are expressed in subtitles I considered for it: How Burrows Changed the World and Better Surviving through Burrows. For the former, the mere collective action of burrowing animals – from the deep seafloor to mountaintops – is an essential part of how most ecosystems function. For the latter, burrows were all-natural bunkers enabling animals to escape the worst the Earth (or solar system) could throw at them and allowing their evolution to continue underground. Want to survive a mass extinction? Start digging.

Lungfishes since the Devonian Period (more than 350 million years ago) have burrowed to avoid droughts, and their lineage has survived four mass extinctions. Coincidence? Probably not. (Original illustration by Anthony Martin, in The Evolution Underground (2017).)

Must you buy this book, or at least persuade your local public library to get it? Well, yes, if you insist. Still, just in case you first need to know a bit more about the burrowing animals and geologic times represented in between its front and back covers, here’s a chapter list with brief descriptions of their contents. Thanks in advance, and I hope you and other readers enjoy reading it.

The Evolution Underground: Chapter Titles and Synopses

Chapter 1: The Wondrous World of Burrows – Did you know that alligators make burrows? They do indeed, and they’re awesome burrows. Learn how these body-armored saurians straight out of central casting from the Mesozoic Era provide superb living examples of how many animals use (or used) burrows to survive and thrive, thus symbolizing many of the main themes of the book.

Chapter 2: Beyond “Cavemen”: A Brief History of Humans Underground – Since the time of living in caves, humans have gone beneath the Earth’s surface during times of environmental or societal stress, and we still do. In this chapter, travel to Turkey, China, Russia, Australia, Canada, and the far-off exotic land of Pennsylvania (home of weather-predicting groundhogs) to marvel at how humans, time and time again, have looked below when seeking safety.

One of these is a map of a naked mole rat burrow system, and the other is of an underground city made by humans in central Turkey. Which is which? That might be one of many questions answered by reading my new book. (Original illustration by Anthony Martin, in The Evolution Underground.)

Chapter 3: Kaleidoscopes of Dug-Out Diversity – Gopher tortoises of the southeastern U.S. dig burrows that are both deep and meaningful, as these burrows host underground menageries of many other species, boosting the biodiversity of their ecosystems. How did tortoises and other turtles evolve and survive mass extinctions of the past? If you answered “burrowing,” you’re catching on to what this book is about.

Chapter 4: Hadean Dinosaurs and Birds Underfoot – Although burrowing dinosaurs of the Mesozoic past were apparently rare, a few of their living descendants (birds) evolved to put their nests not in trees, but underground. In this chapter, penguins, puffins, shearwaters, owls, kiwis, bee-eaters, and other birds raising underground families are lauded for their digging family values.

Chapter 5: Bomb Shelters of the Phanerozoic – This chapter opens with a piece of fiction about a Lystrosaurus (or two) embarking on a post-apocalyptic journey. This allegory conveys how burrowing helped their kind and a few other animals to survive the worst mass extinction in the history of life at the end of the Permian Period (about 250 million years ago). This chapter also summarizes other mass extinctions and how burrowing provided an advantage for making it through the worst ecological crises of the geologic past.

Chapter 6: Terraforming a Planet, One Hole at a Time – When did animals move from the sea to freshwater and then onto land? Burrowing may have helped animals to make transitions from such environmental extremes, which ultimately resulted in their shaping landscapes as we know them today. Featured animals in this chapter include trilobites, horseshoe crabs, lungfish, amphibians (frogs, toads, salamanders), lizards, and snakes.

Chapter 7: Playing Hide and Seek for Keeps – For a long time, all animal life was superficial, living either on seafloor surfaces or just underneath. Then about 550-540 million years ago, animals starting plumbing deeper. What caused this downward shift, and how did animals’ churning of oceanic sands and muds forever change the oceans, atmosphere, and the evolution of life? Also, the evolution of predators gave animals yet another reason to burrow: That is, before the predators started burrowing, too, starting an underground “arms race” that continues through today.

Chapter 8: Rulers of the Underworld – What animals are the real ecosystem engineers for our planet? Mostly the small and spineless ones, invertebrates. This chapter starts with those marvelous earthworms that so beguiled Charles Darwin, then pays tribute to the amazing feats of burrowing and animal architectures created by ants, crayfish, crabs, lobsters, and more.

Chapter 9: Viva La Evolución: Change Comes from Within – This chapter starts with the second fictional story in the book, following the exploits of an ecological hero – a pocket gopher – following the 1980 volcanic eruption of Mount St. Helens. The rest of the concluding chapter of The Evolution Underground looks at burrowing mammals (especially rodents), but also considers the largest burrowing animals of all time. Also, what can we as mammals learn from our fellow furry underground relatives as we head into an uncertain future posed by rapid climate change?

Appendix: Genera and Species Mentioned in The Evolution Underground – A listing of the animals name-dropped in the book, some of which may surprise you.

What are you waiting for? Leave your underground hidey-hole and get my book! P.S. Thanks for reading it. (Photograph by Anthony Martin, taken in Decatur, Georgia.)

 

Teaching about Traces as Evidence

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With the start of a new academic year, many university professors might be deliberating on what they’ll be teaching, and many students similarly (and hopefully) might be wondering what they will be taught. For me this academic year, my plan is not to put so much emphasis on the “what,” but more on the “how,” and put it in the form of a basic question: How could I be wrong?

In my experience, this is a question we professors and other educators we often ask, regardless of whether we are in the natural sciences, social sciences, humanities, or some blend of those educational realms. Now, this is not to say that we should continuously live our lives in doubt of our hard-earned skills and knowledge, succumbing to imposter syndrome. So what I will suggest is that we use it in our teaching, leading by example for our students. For instance, when my students see me question an initial interpretation of mine, correct that wrong interpretation, and show delight when this happens, then they will feel more comfortable asking themselves the same question, too.

So how do I apply this method to my research disciplines of paleontology and ichnology? If I am observing a natural phenomenon in the field, museum, or other settings, and I find myself jumping to a conclusion too rapidly, I take a moment to pause, back up, and try to disprove that hasty conclusion. Sometimes it turns out that, yes indeed, I was an idiot. But if this debunking process fails to find anything terribly wrong with my original explanation, or I modify it accordingly in the face of newly acquired evidence, then I’ll think this: So far, so good.

Eight-Legged-Otter-TracksWhoa, check out the tracks made by this eight-legged river otter! This eight-legged otter must have been the result of some freak mutation, or genetic engineering, or joined twin otters, or a robot spider with otter feet…What? Was it something I said? (Scale in centimeters; Photo by Anthony Martin.)

Moreover, because so much of paleontology and ichnology involves interpreting the products of non-witnessed lives, behaviors, and environments, such as bones, shells, leaves, tracks, and burrows, careful documentation of this evidence is key for making reasonable interpretations. Because we can’t prove ourselves wrong by watching a video of whatever happened in the pre-human past, we also have to ensure that the evidence can be shared and evaluated by other paleontologists and ichnologists.

In the following video, I explain these two basic scientific principles – how could I be wrong, and so far, so good – by using a few examples from a forested area next to the Emory University campus in Atlanta, Georgia. This is the place where I often teach first-year (freshman) students in a small-class seminar how to track the animals on and around our campus. Because most of these animals are nocturnal, most remain “invisible” to the students’ during their four years on campus. So my students really do learn how to use trace evidence to make reasonable hypotheses about animal presence and behaviors, and by the end of the semester, they get pretty good at it.

This sort of educational fruition is what made for the most fun part about doing this video, which was having a former student of mine who took the class four years ago play the role of my willing and eager “student.” In this, we demonstrated how the two basic principles – how could I be wrong, and so far, so good – are applied when in the field. It actually wasn’t much of a stretch for my former student, as Dorothy (Dottie) Stearns (Emory College ’16) was one of my best students in the class when she took it, and she really enjoys getting outside and tracking, so her enthusiasm is genuine.

The video is part of a series that Emory is producing on the theme of Evidence at Emory, with professors from a wide variety of disciplines explaining how they incorporate evidence-based reasoning in their courses. First-year students at Emory are the specific target of the videos so they are exposed to different disciplines and how scholars evaluate evidence in those disciplines. But there’s also hope that students will retain these discernment skills in life after college. Nonetheless, I think anyone who likes observing and thinking about what they observed can benefit from watching them. I could be wrong on that, but if not, I’m fine with that, too: for now.

Eight-Legged-Otter-TracksWait a minute, you’re saying these tracks could have been made by two otters, with one following closely behind the other? Huh, hadn’t thought of that. But that doesn’t mean eight-legged otters aren’t out there somewhere. Or freak mutated otters. Or genetically engineered otters. Or a robot spider with otter feet. What? Was it something I said?

Acknowledgements: Thanks to the Quality Enchancement Plan of Emory University for encouraging me to more overtly incorporate evidence as a main theme in my class, to Dottie Stearns for being such an awesome student/actor, and to the Center for Digital Scholarship, also of Emory University, for their fine work on the video production.

A Birds-Eye View of a Georgia Barrier Island

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All scientists use tools when investigating how the natural world works. Yet as a traditionally trained field scientist – and an ichnologist – I’ve always been wary of adopting anything more complicated than field notebooks, pencils, tape measures, hand lenses, and cameras. Granted, I did add GPS units to my equipment list starting about 12 years ago and now consider these location-finding devices as standard (and essential) field gear. Still, if you told me even a year ago that I would happily welcome the services of flying robots while tracking alligators on the Georgia barrier islands, I would have smiled and said, “Yes, and Bud Light is my favorite beer.” (Just to clarify: It is not, nor will it ever be.)

Drone+VultureNeed a better overhead view of barrier-island ecosystems with identified locations, and don’t feel like waiting for the latest satellite photos? I suggest strapping a camera and GPS unit onto a vulture and training it to take pictures while simultaneously recording waypoints. Or, have an aerial drone do the same for you, which will do a much better job, while also not annoying the vulture. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)

So here I am, ready to buy everyone a round of their favorite beverage (perhaps Kool-Aid) in celebration of my being wrong. Earlier this year, an Emory colleague of mine – Michael Page – convinced me that an aerial drone might be a good tool for getting overhead views of ecosystems on the Georgia barrier islands. So as soon as Emory purchased a new, state-of-the-art drone in early 2015, Michael and I plotted to take it to St. Catherines Island for its first real field test in March 2015.

Drone-1Yeah, I know, it’s not New Horizons, but this drone is still a pretty nifty piece of field equipment, and I’m glad to have added it to my ichnology utility belt. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)

The last time Michael and I were on St. Catherines Island together was two years ago, when we had a group of Emory students help us map gopher tortoise burrows and alligator dens there. (That was fun.) We’ve also been working with a few other colleagues at Georgia Southern University to describe the gopher tortoise burrows and alligator dens on St. Catherines Island over the past few years. So Michael and I figured we could use the drone to aid in this research, starting with the gopher-tortoise burrows.

Perhaps the most persuasive point Michael made about the drone’s potential value was its winning combination of built-in GPS and high-definition video camera. This meant we could instantly map (“georeference”) gopher-tortoise trails between their burrows, as well as the burrows themselves. The latter were easily visible from the wide, white, sandy aprons just outside burrows entrances, and sometimes even show up in satellite photos of the area. The big difference with using a drone versus satellite photos, though, would be in their ‘real-time” capture of these traces – rather than a randomly taken satellite image – while also having much better resolution.

Tortoise-Burrow-ApronSee that hole in the ground? That’s a gopher-tortoise burrow. See those breaks in the grass to the left and right in the foreground, and elsewhere? Those might be trails that connect this burrow to others in the area. How to map all of them? Call in the drone! (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)

GT-Aprons-Trails-SCICan you see gopher tortoise traces from space? Surprisingly, yes. Not only are burrow aprons visible in this GoogleEarth™ photo (denoted by the arrows), but also trails connecting some of the burrows. Although if you find yourself squinting and turning your head sideways to see these, you’ll understand why sending up a drone with a high-resolution camera might be a better way to map these traces. (Image taken from a presentation I gave at the 2011 annual meeting of the Geological Society of America in Minneapolis, Minnesota.)

Most of the gopher-tortoise burrows are in a broad, flat area on St. Catherines that used to be pasture land, but is now being restored to the tortoises’ long-leaf pine-wiregrass ecosystem. This re-located tortoise population has done quite well here, and because of its isolation on St. Catherines, it’s an example of one that does not face as many human-related problems as their compatriots on the Georgia mainland. Its remote location also helped us with trying out the drone, as we didn’t have to worry about it dodging buildings, power lines, or gawking locals, all of which might have complicated its flights.

Tortoise-Burrow-Drone-PilotsAlmost ready for take-off! Drone pilots/wranglers Alison Hight (left) and Michael Page (right) look for a flat place near a staked gopher-tortoise burrow for setting down our “eyes in the sky.” (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)

This was the drone’s maiden voyage on St. Catherines Island, taking off from the gopher-tortoise field. It did just fine. (Video footage by Anthony Martin, taken on St. Catherines Island, Georgia.)

Drone-Above-Tortoise-FieldThe drone pilots doing a great job, sending the drone around the gopher-tortoise field for a spin. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)

This flight was a big success, in that the drone went up, took lots of video and photos while in the air – all of which was georeferenced – and it came down without crashing. So we decided to try it elsewhere. That’s when we remembered the Atlantic Ocean was only about 500 meters away on the eastern edge of St. Catherines, with a lengthy beach, salt marshes, storm-washover fans, tidal creeks, and a bluff of Pleistocene sand with maritime forest on top of it. So off we went, and we did Flight #2 over the storm-washover fans, salt marshes, and tidal creeks near the north end of the island.

Drones (much like me) operate well in places with wide-open spaces that involve Georgia beaches. Check out how quickly it disappears from view once in the air. (Video footage by Anthony Martin, taken on St. Catherines Island, Georgia.)

Following this flight, we decided to send the drone father north to survey the bluff from just offshore. This was probably the most exciting flight, as we watched it go out to sea, then fly parallel to the shore, with its camera trained on the coastline.

Drone-Yellow-Banks-Bluff-1Michael setting down the drone on a almost-flat surface as Alison prepares it for take-off. The yellow yardstick serves as an easily visible scale that can be used to estimate ground-level distances. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)

Off we go, into the wild blue yonder. (Video footage by Anthony Martin, taken on St. Catherines Island, Georgia.)

Drone-Yellow-Banks-Bluff-3Bringing it back home. Look for the spot near the top-center of the photo for our “hand lens in the sky.” (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)

Coming in for a soft landing, which is much preferred over the other type of landing. (Video footage by Anthony Martin, taken on St. Catherines Island, Georgia.)

So following these inland and coastal successes, which clearly were applicable to studying gopher tortoises and coastal geology, it was time to try using the drone to look at the apex predators of the island – alligators – and their traces. The next day,while scouting areas further to the south for alligator dens and tracks, we paused on a causeway cutting through a salt marsh. Because the marsh was at low tide, its mudflats were exposed, which allowed a few big animals to walk across it and leave their tracks, and for us to see these tracks.

At least two of the trackways were from alligators, made distinctive by their sinuous tail drags, arcing footprints, and belly drags. I suspect the other trackways were from feral hogs, but I couldn’t tell for sure because they were in squishy mud beyond my carrying capacity. Which is to say, I would have quickly immersed myself in this environment had I gone any further out. Gee, if only we had some way to photograph those trackways from above, better helping us to see their lengths, patterns, and directions.

Alligator-Trackways-MarshA salt-marsh mudflat at low tide, with low marsh and a patch of forest (hammock) in the background. See the alligator trackway to the left, where the alligator turned? Look in the middle and you’ll see two more trackways that are probably from feral hogs, and another curving trackway to the right that is from another alligator. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)

Drone-Landing-Salt-MarshWhy wade into waist-deep salt-marsh mud to track an alligator when you can stay safely (and cleanly) on dry land, telling a drone what to do? (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)

So it was time for another flight, and the drone’s first alligator-track-mapping mission, which I’m pleased to say was a success. One example of that success is conveyed by the following photo, which made me gasp when I first saw it. There were the two alligator trackways and the two hog trackways, but also two not-so-clear trackways I had missed and a clear view of where the hogs had dug along the marsh edge. This photo similarly evoked a collective “Ooooo!” when I showed it to an audience the next week at the Southeastern Section meeting of the Geological Society of America meeting in Chattanooga, Tennessee. My talk was a progress report on the alligator dens of St. Catherines Island, but I threw in this photo toward the end of it to show how drones might help with some of our tracking alligator movements through difficult-to-access environments on the island.

DCIM100MEDIADJI_0100.JPGOK, you’re probably wondering by now how good those photos and videos taken by the drone might be, and whether or not any useful science can come from them. See that guy in the lower center of the photo? That’s me, pointing to each of the two alligator trackways, with the yellow yardstick providing an additional scale to the left. Notice also the probable feral hog trackways in the middle and fainter ones to the right, as well as the “hogturbation” (rooting disturbance caused by hogs) in the upper left of the photo. As an ichnologist, I was pretty darned pleased by this picture, and I want more like it. (Photograph by The Aerial Drone, taken on St. Catherines Island, Georgia.)

Lastly, I was also happy to see that drones have their own ichnology, in that they make flight traces. I’ve been long fascinated by flight traces – called volichnia by ichnologists – and have done my best to describe these in modern birds of the Georgia coast, as well as bird flight traces in the fossil record. Given the right substrate, anatomy, and behavior, the take-off and landing traces of birds and other flighted animals can preserve well enough for us to interpret them for their true nature.

Now, to do the same for a drone requires knowing how they have vertical take-offs and landings, using rapidly moving rotors. This means air will be pushed down onto the substrate directly underneath the drone, then dissipated abruptly outside that zone. The result would be a sem-circular depression slightly more that the maximum width of the drone, and one that would look very much the same whether made by a take-off or landing. The difference would be in the timing of the landing-pad traces: if obscured by the depression, then it was taking off, but if they are impressed on the depression, then it was landing.

Drone-Making-Landing-TraceDrone coming in for a landing, already pushing aside pine needles on the forest floor and making its landing trace. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)

Drone-Landing-Trace-2Drone landing trace, minus the drone. Do you see the square pattern in the middle of the oval depression? That’s the outline of the drone, defined by its landing gear. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)

So now we know that a drone can be used for conservation biology, coastal geology, behavioral ecology, and – most importantly – ichnology. How about art? Yes indeed. Once we got back to the Emory campus, Michael handed over the footage to Steve Bransford, a skilled videographer employed by Emory and founder of Terminus Films. Given all of the drone footage, he snipped out the boring parts (always a good thing to do), added a few maps at the start to orient the viewers, put in a soothing soundtrack, and basically created an aesthetically pleasing and extraordinarily educational video. So we submitted it for consideration as an video in the peer-reviewed online journal Southern Spaces, which was founded at Emory University. Much like an aerial drone on an unobstructed coastline, it sailed through peer review and is now available for viewing by all who have an Internet connection.

St. Catherines Island Flyover from Southern Spaces on Vimeo. Never mind the stern message: just click on the link or the video and it will play. Once it does start playing, please watch it on a big screen, sit back, and enjoy the ride. Also be sure to read the accompanying article linked to the peer-reviewed online journal Southern Spaces.

What’s aerial adventures await us next? We’ll see, as we have plenty of visual information and data to process from our previous visit. But for now we can be pleased to have shown the value of an aerial drone as both a scientific instrument and a means for engaging our senses with soaring imaginations.

Acknowledgements: Many thanks to the St. Catherines Island Foundation for its support of our research on St. Catherines, and to Royce Hayes and Michael Halstead for their assistance on field logistics. We also appreciate the expert piloting of the drone by Alison Hight while on St. Catherines. Steve Bransford did a fantastic job with creating the video for the Southern Spaces article, which should win the Georgia equivalent of an Oscar. Input from the editor of Southern Spaces, Allen Tullos, improved our article accompanying the video, and we are grateful to the staff of Southern Spaces for their quality service in putting this video and article online. And as always, many thanks to Ruth Schowalter for her help and support, in and out of the field.

Emory News (July 15, 2015): Drone Offers Stunning Aerial Views of Georgia’s St. Catherines Island.

Tales of Trails by Seahorse Tails

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I’ve always been a big fan of aquariums. Having grown up in the landlocked Midwest and not seeing an ocean with its bountiful life until I was 20 years old, I am still drawn to the old-school charm of big tanks filled with salt water and populated by exotic fish and other sea critters. These environments, however artificial, never fail to inspire awe and wonder. Even better, they often teach me something new and relevant each time I pay closer attention to what they hold.

Seahorse-Making-Resting-TraceA seahorse, of course, is not a horse. But that’s not the only way seahorses differ from horses, in that they leave trails instead of tracks. Intrigued? Yeah, me too. (Photograph by Anthony Martin, taken at the UGA Aquarium, Skidaway Island, Georgia.)

Nonetheless, I also have a “problem,” which manifests itself whenever I’m at an aquarium, walking along a beach, sitting on a park bench, driving down a  road, or, well, conscious. As an ichnologist, I’m constantly looking for animal traces. Then once found, I study these traces carefully so that they may inform me whenever I see similar traces in the fossil record. But because I’m a land-dweller and rarely have the opportunity to snorkel or scuba-dive, aquariums come in handy for observing traces of aquatic animals I might not often see. Particularly helpful are aquariums in which the people caring for them were kind enough to include sand on their bottoms (the aquariums, that is).

So last weekend, while leading a class field trip to the Georgia coast and after a wonderful boat ride to Wassaw Island and back, I eagerly joined my students in viewing a salt-water aquarium. This particular venue was the UGA Aquarium (UGA = University of Georgia, Athens) is maintained by the UGA Marine Extension Service (MAREX) on Skidaway Island, Georgia. Our visit was especially satisfying because we were there on a Sunday afternoon, when the aquarium is closed to the public. This luxury afforded us plenty of room and quietude, qualities that are rumored to enhance learning.

Within just a few minutes of entering the main room, one tank to the right caught my eye, and not just because of its pretty colors, but for its denizens and traces on the sandy bottom of that tank. It contained seahorses, fishes that are so odd compared to other fishes, we humans had to compare them to hoofed domesticated mammals. The best part of all, though, was that this tank had lots of intersecting grooves and circular imprints on its sandy surface, which no doubt had been made by the seahorses.

Seahorse-Making-TrailA seahorse (Hippocampus sp.) showing off its lack of swimming skills by moving along the sandy bottom of a tank. Gee, what are all of those meandering and intersecting grooves in the sand and circular imprints? I wonder what made those? Sorry, first guess doesn’t count. (Photograph by Anthony Martin, taken at the UGA Aquarium, Skidaway Island, Georgia.)

All seahorses are under the genus Hippocampus, which consists of more than fifty species. Evolutionarily speaking, they are ray-finned fish (actinopterygians) and share a common ancestor with pipefish and sea dragons (Sygnathidae). The oldest known fossil seahorses are in Miocene Epoch rocks, from about 13 million years ago. Besides their equine-like profiles, they are well known for their prehensile tails, which can either grasp onto algae, sponges, or corals, or curl up underneath them as they swim.

However, seahorses are never going to inspire bets at underwater race tracks, as they are among the slowest-swimming of fish, propelled mostly by tiny pectoral fins while moving upright. Still, they don’t need to be fast, as they are very successful predators, with about 90% accuracy in nabbing fast-swimming small crustaceans that get too close to their mouths. Seahorses also don’t need to swim away from larger predatory fishes that might wish to pick them from a seafood menu. Whenever seahorses attach to algae and corals, they sway in harmony with their temporary hosts, effectively blending in with their surroundings.

One point I keep in mind whenever visiting an aquarium, zoo, or other such enclosures is how these can alter so-called “normal” behaviors of their animals. In this instance, the smaller space of this tank, combined with little material for attachment, meant these seahorses were more likely to swim along its bottom then they might in an open ocean. Accordingly, they had made lots of traces in the sand: mostly undulating grooves, but a few circular impressions from their curled tails plopping onto one side or the other.

Seahorse-Making-Trail-2A seahorse making tail trails while swimming along the bottom of an aquarium. Notice how the trail would become less linear, wider, and more circular if the tail flops over to one side or another, involving a greater area of the curled end. (Photograph by Anthony Martin, taken at the UGA Aquarium, Skidaway Island, Georgia.)

Seahorse-TrailsA close-up of those trails left by swimming seahorses dragging their tails along a sandy surface. Also, check out the overlapping circular “plop” traces on the right, made by the curled part of the tail? (Photograph by Anthony Martin, taken at the UGA Aquarium, Skidaway Island, Georgia.)

What’s the take-home message of these observations for ichnologists, geologists, and paleontologists? That experience matters, as does questioning preconceived notions about what we might observe from the geologic record. Take a look at the preceding photo, and tell me – quite honestly – that your very first interpretation of the tracemakers would have been “fish,” let alone “seahorse.” Instead, I think nearly everyone (yes, me too) would have reached for the easiest answer, which would have been “worm trails,” similar to how geologists reflexively apply “worm burrows to anything small, tubular trace fossil they encounter at an outcrop. Wrong, wrong, wrong.

So next time when looking at rocks formed in marine environments – whether from the last 13 million years or much older – and these rocks host lots of “worm trails” on their surfaces, ask yourself who else could have made such trails, and how. Reach beyond easy and ordinary explanations, and imagine. Oh, and when you go to aquariums, don’t just look at their sea-life, but also the traces of the sea-life in them.

Deconstructing an Ichnology Abstract, with Alligators

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Dude. Those are big burrows. Dude.

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

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

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

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

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

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

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

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

Source of Abstract (Reference):

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