When learning about the natural sciences, there comes a time when just reading and talking about your topics in the confines of a classroom just doesn’t cut it. This semester, we had reached that point in a class I’m teaching at Emory University (Barrier Islands), in which we all needed a serious reality check to boost our learning. So how about a week-long field trip, and to some of the most scientifically famous of all barrier islands, which are on the coast of Georgia?
Last Friday, March 8, our excursion officially began with a long drive from the Emory campus in Atlanta, Georgia to St. Marys, Georgia. Fortunately, Saturday morning was much easier, only requiring that we walk across the street, step onto a ferry, and ride for 45 minutes to Cumberland Island. Cumberland was our first island of the trip, and the southernmost of the Georgia barrier islands. I have written about other topics there, including the feral horses that leave their mark on island ecosystems, the tracks of wild turkeys, and those marvelous little bivalves, coquina clams.
So rather than my usual loquacious ramblings, punctuated by whimsical asides, this blog post and others later this week will be more photo-centered and accompanied by mercifully brief captions. This approach is not only a practical necessity for proper time management while teaching full-time through the week, but also is meant to give a sense of the daily discoveries that can happen through place-based learning on the Georgia coast. I hope you learn with us, however vicariously.
After a 45-minute ferry ride to Cumberland Island, the students received a different sort of lecture when naturalist extraordinaire Carol Ruckdeschel – who is writing a book about the natural history of Cumberland Island – met with them and gave them a brilliant overview of the island ecology. She mostly talked with the students about the effects of feral animals on the island, then spent another hour with us in the maritime forest and through the back-dune meadows. It was a real treat for the students and me, and a great way to start the field trip.
A leaf-cutter bee trace! Despite my writing about these and illustrating them in my book, these distinctive incisions were the first I can recall seeing on the Georgia barrier islands. These traces were abundantly represented in the leaves of a red bay tree we spotted along a trail through the maritime forest, making for a great impromptu natural history lesson for the students.
A freshly erupted ghost shrimp burrow on the beach at Cumberland, in which the students were lucky enough to witness the forceful ejection of muddy fecal pellets by the shrimp from the top of its burrow. I mean, really: explain to me how the life of an ichnologist-educator can get any better than that?
The fine tradition a field lunch, made even more fine by the addition of fine quart sand to our meals, freely delivered by a brisk sea breeze. Did the sand leave any microwear marks on our teeth? I certainly hope so.
A student is delighted to test my ichnologically based method for finding buried whelks underneath beach sands, and find out that it is indeed correct. (Was there any doubt?) Here she is proudly holding a live knobbed whelk, which I can assure you she promptly placed back into the water once its photo shoot was finished for the day.
Just to join in the fun, other students decided my “buried whelk prospecting” method required further testing. Let’s just say this student did not disprove the hypothesis, but rather seemed to confirm it, and doubly so. It’s almost as if ichnology is a real science! (Yes, these whelks went back into the water, too.)
OK, enough about marine predatory gastropods (for now). How about some of the largest horseshoe crabs (limulids) in the world? We found a large deposit of their carapaces above the high-tide mark, some of which were probably molts, but others recently dead. Sadly, though, we did not see any of their traces. Bodies only do so much for me.
Where do dunes come from? Well, a mother and father dune love each other very much… No wait, wrong story. What happens is that dead cordgrass from the salt marshes washes up onto the beach, where it starts slowing down wind-blown sand enough that it accumulates. Now it just needs some wind-blown seeds of sea oats and other plants to start colonizing it, and next thing you know, dune. Dude.
Ah, a geological tradition in action: comparing actual sand from a real outdoor environment to the sand categories on a handy grain-size chart, and using a hand lens. It’s enough to bring a tear to the eyes of this geo-educator. Or maybe that was just the wind-blown sand.
Finally, something that really matters, like ichnology! This is a three-for-one special, too: sanderling feces (left), tracks, and regurgitants (right), the last of these also known as cough pellets. Looks like it had coquina and dwarf surf clams for breakfast.
Wow, more shorebird traces! The tracks are from a loafing royal tern, and it clearly needed to get a load off its mind before moving on with the rest of its day.
Tired of shorebird traces? How about a modern terrestrial theropod? Wild turkey tracks in the back-dune meadows of Cumberland were a happy find, leading to my grilling the students with the seemingly simple question, “What bird made this?” They did not do well on this, but hey, it was the first day, and at least no one said “robin” or “ostrich.”
Did somebody say “doodlebug?” This long, meandering, and collapsed tunnel of an ant lion (a larval neuropteran, or lacwing) tells us that this insect was looking for prey in all the wrong places.
Behold, tracks that bespeak of great, thundering herds of sand-fiddler crabs that used to roam the sand flats above the salt marsh. Where have they gone, and will they ever come back? Who knows where the males might be waving their mighty claws? Do the female fiddler crabs suffer from big-claw envy, or are they enlightened enough to reject cheliped-based hierarchies imposed upon them by fiddler-crab society? All good questions, deserving answers, none of which make any sense.
Yes, that’s right, feral horses are really bad for salt marshes. Between overgrazing and trampling, they aren’t exactly what anyone could call “eco-friendly.” My students had heard me say this repeatedly throughout the semester, and Carol Ruckdeschel said the same thing earlier in the day. But then there’s seeing it for themselves, another type of learning altogether.
And the day ended with beautiful ripple marks, beckoning from the sandflat below the boardwalk on our trip back onto the ferry. Even this ichnologist can appreciate the aesthetic appeal of gorgeous physical sedimentary structures.
What’s the next island? Jekyll, which is just north of Cumberland along the Georgia coast, visited yesterday. Stay tuned, and look for those photos soon.
Authors of books are sometimes lucky enough to get people interested enough in both them and their books. Even better, these authors are sometimes invited to talk about their books to a receptive audience. Yet I’ll bet few authors get the opportunity to talk about their books with fellow book lovers while also standing on the front porch of a great American author. Even less probable is that the author of a natural history book – one related to paleontology, no less – would somehow have to relate his or her work to a deceased author best known for her Southern Gothic fiction.
It’s a sign! Upon my arrival at Andalusia Farm, the former home of Flannery O’Connor, this sign greeted me at the door, reminding me why I was there. It was fun to think that during Flannery O’Connor’s life, this is how she might have announced a lecture at her place, using a sheet of paper with words, posted on her door. (For the sake of imagination, just ignore that the notice was created and printed by person using a couple of 21st century devices.) Photograph by Anthony Martin.
This past Sunday, I was just so fortunate and challenged, having been invited to speak about my new book, Life Traces of the Georgia Coast, at Andalusia Farm, the former home of famed American writer Flannery O’Connor. Andalusia is located just north of Milledgeville, Georgia, and despite many previous trips to Milledgeville, this was my first visit to Flannery O’Connor’s former haunts. The house and grounds are in a formerly rural setting, its clay-laden driveway just off a busy highway and directly across from a chain hotel. Yet her house is still surrounded by more than 500 acres of forest, streams, and a pond; the pond is visible from the front porch of the house. These natural areas are what attracted me to coming, and provided an avenue for connecting themes of my book with this place.
A view of the main house at Andalusia Farm, where Flannery O’Connor spent more than a third of her life. Her bedroom, where much of her writing also happened, is just to the left after passing through the front porch. Photograph by Anthony Martin.
A sign telling about the recent history of Andalusia. Sadly, it does not include any mention of the Alleghanian Orogeny that contributed to the Piedmont Province there, nor does it inform visitors about the maximum extent of the Cretaceous and Eocene seaways just to the south, nor does it acknowledge the former presence and effects of the Pleistocene megafauna that used to live there. But I suppose all of that would have required a much bigger sign. Photograph by Anthony Martin.
O’Connor is much revered in the Southern U.S. and elsewhere, a loyalty that stems partly from the fact that she was indeed a terrific writer of Southern-inspired literature – consisting of short stories, novels, and essays – and partly from a wistful longing of “If only”: namely, if only she had lived longer. Born in Savannah, Georgia in 1925, she traveled to what was then called State University of Iowa (now the University of Iowa), where she earned an MFA, and soon afterwards began her illustrious writing career. In 1951, she was diagnosed with the same disease (lupus) that killed her father while he was still relatively young. She lived with this debilitating condition for the next 14 years, the last 12 of which were at Andalusia. She was only 39 years old when she died in 1964.
So how did I become a character in a Flannery O’Connor story? I blame it all on a paleobotanist friend of mine at nearby Georgia College and State University, Dr. Melanie DeVore, who suggested to me several years ago that I come to speak at Andalusia about my upcoming book. “Why?” was my first response. After all, as a long-time resident of Georgia, I was embarrassed to admit that I had read very little of O’Connor’s works until just recently. I also could not figure out how the plant and animal traces of the Georgia barrier islands could be related to a Southern author whose home was just above the fall line, between the Piedmont and Coastal Plain provinces of Georgia. Even the Cretaceous seaway from 70 million years past had not washed onto the landscape of O’Connor’s home. Thus I felt hard-pressed to come up with a way for my book to be relevant to her literary contributions and a sense of place.
Still, Melanie continued to encourage me to think about it. Admirably enough, she was trying to find ways in which natural scientists might contribute their perspectives to the considerable scholarship behind O’Connor’s works and the popular appeal of her former home. So I delved into O’Connor’s biographies, and searched for an ichnological connection between what she did and my interests. This is when I found the key, the theme that united: birds.
It turns out that O’Connor was a great lover of birds, and the thought that perhaps she had too many birds never occurred to her during her last years at Andalusia. Peafowl were her favorites for many reasons, some of which she explained ever-so-eloquently in several essays, including one of her most well-known works of non-fiction, The King of Birds. Domesticated birds also abounded on her property, including chickens, ducks, geese, and swans, all part of her avian menagerie. At one time, she evidently owned more than a hundred peafowl, a daunting number when one considers the vociferous qualities of these birds.
A peacock in a spacious enclosure just outside of Flannery O’Connor’s home, graciously displaying his tail feathers for us. See those feet? We’ll take a closer look at those soon. Photograph by Anthony Martin.
One of two peahens in the same enclosure, not nearly as resplendent and gaudy as her male companion, but still a very attractive bird. Of course, I was looking at her feet too, thinking about the tracks she would make, and how these might differ from those of the peacock. Photograph by Anthony Martin.
O’Connor’s earliest few minutes of fame were also bird-related, and established her life-long association with oddities of the South. When she was only five years old, she somehow taught a chicken to walk backwards. This feat attracted a film-reel company (Pathé News), which sent a crew from New York to Georgia to record this atypical avian mode of locomotion. The film reel, shown in theaters in 1932, also parodied O’Connor’s childhood accomplishment by reversing the film for other walking domestic animals, making these animals also appear to also walk backwards.
DO YOU REVERSE?
It’s one thing to read about Flannery O’Connor and her backwards-walking chicken, but it is another to actually see an original film about it. In the reel, she is mistakenly identified as “Mary O’Connor,” but no matter, as it was a start to her enduring fame for inventing quirky actions, plots, and characters reflecting the off-kilter cultures of her Southern environs. Incidentally, just how would you tell the difference between tracks made by a chicken moving forward or backwards? Maybe that should be the topic of a future post…
O’Connor’s link to paleontology was an oblique one, in that (as far as I know) she did not express any interest in it as a subject. Nonetheless, she was a great admirer of paleontologist, Jesuit priest, and philosopher Tielhard de Chardin, and the title of one of her anthologies, Everything That Rises Must Converge (1965), came directly from one of his writings. Also, in an “if only” moment of my own during my talk on O’Connor’s porch, I wondered what sort of fiction or essays would have come out of O’Connor had she lived long enough to learn that birds are actually living dinosaurs, and hence she had unwittingly surrounded herself with the progeny of those Mesozoic monsters.
Oh yes, my talk on O’Connor’s porch. How did that go? Fantastically. Because of the gorgeous weather that day, Craig Amason, my host and executive director of the Flannery O’Connor-Andalusia Foundation, thought that we might hold the discussion on the screened front porch, rather than inside in one of the more spacious rooms of the house. I was all for this idea, partially for its atmosphere (I mean, how cool would it be to talk about Flannery O’Connor with some of her fans on her front porch?), but also because we planned to have everyone walk on the trails with us later, looking for tracks and other traces of the animals that live there. Melanie and I had already scouted the trails in the morning and found a few surprises, so we knew that part of the program would be great fun, too: might as well get them halfway outside already by being on the porch. Fortunately, all of the dozen or so people who showed up also approved of this plan, which was helped in no small part by a heaping helping of cookies and soft drinks, enticing them to stay right there on the porch for a spell, and perhaps even relax in a rocking chair.
Dr. Bruce Gentry of Georgia College and State University, having just bought a copy of my book, opens it to take a look inside. Dr. Gentry is a scholar of Flannery O’Connor works and heads the Flannery O’Connor Studies Program at Georgia College and State University, in nearby Milledgeville.Meanwhile, I’m in the background, gesturing grandly to the delicious cookies on the table next to mewhile also introducing everyone to the topic of bird tracks and sign. Photograph by Melanie DeVore.
A sample of our front-porch chat about Flannery O’Connor and her birds, in which I point out the close resemblance between a rooster’s feet and those of a peacock. Although the peacock tracks would have been noticeable larger than those of her chickens, their overall forms would have been nearly the same, with three long thin toe-prints pointing forward, one shorter one pointing backward, and all four ending with clawmarks. Video footage by Craig Amason, exceutive director of the Andalusia-Flannery O’Connor Foundation.
A close-up of a rooster’s feet. Think about the tracks this would produce, whether walking forward or backwards. Rooster was known as “Tom” (R.I.P.), formerly owned by Carol Ruckdeschel on Cumberland Island, Georgia. Photograph by Anthony Martin.
Now compare the rooster’s feet to those of this peacock at Andalusia Farm, and you’ll see for yourself how close they are to one another in their overall form, despite the rear digits being hidden in this photo. I could not help but think that O’Connor, while seeking the pleasure of the company provided by her birds, also saw thousands of similar-looking peacock and chicken tracks every day she went outside. Photograph by Anthony Martin.
The talk itself was mercifully brief on such a fine day, with tracks and other sign awaiting us. So I simply expressed my gratitude for being there with all of us gathered in this special place, talked about Flannery O’Connor’s love of birds, and jumped into a speculative discussion of what tracks she might have seen every day on the farm. My presentation was decidedly low-tech, in which my only visual aids were paper print-outs of bird tracks and feet and a couple of my illustrations from the book, which were of bird-track categories and nests. These were supplemented by my acting out birds motions (walking, mostly), demonstrating how these behaviors would result in certain trackway patterns. One of these, much to the amusement of audience, was of a peacock doing its little circular and sideways-stepping dance, which was followed by my asking them to imagine the trackway patterns that would have resulted from such courting.
I also did a short reading from my book that introduces the topic of bird tracks, which fairly drips with admiration for the complexity of behaviors captured by such traces, thus hopefully echoing O’Connor enthusiasm for birds. Many questions were asked and observations of bird behavior offered, a give-and-take that I thoroughly enjoyed in the role of a “guide on the side” rather than a “sage on the stage” (or a “torch on the porch”). Once done, we had a short break for people to buy my book (thanks, y’all!), then walked onto a nearby trail to look at what the wild animals had left us the previous few days.
This outing was enjoyable, a bit of a treasure hunt and an eye-opening experience for many of how much animal activity is embodied by their traces in a typical Piedmont forest and its water bodies. Some of the traces I had seen earlier in the day while out scouting with Melanie, but we saw more, such as previously missed raccoon tracks and woodpecker sign. The highlights included the discovery of fresh (less than 12-hour-old) beaver tracks on one of the stream banks. This delighted several people, who told me that beavers had supposedly moved out of the area years ago, so they were pleased to know that at least one was back in the neighborhood. I was also excited to find coyote scat on the trail, which inspired earthy, amusing comparisons between the territorial markings of mammals in the wild versus those of corporate board members and academics (which, not surprisingly, are not so different in practice).
Coyotes just can’t help themselves: where we see a human footpath, they see an advertising opportunity. Here I excitedly point out an example of coyote scat, which had been strategically placed in the middle of the trail so that all other mammals would know this was her/his territory. You know, just like you might see happen in a professional meeting. Photograph by Melanie DeVore.
Fresh beaver tracks on a stream bank! This was a happy find, as it demonstrated that at least one beaver was in the area, following a nearly five-year absence of their species. These tracks show the beaver turned to its right and walked down the bank and into the water; look for the large rear-foot track to the left, and the tail dragmark in the middle. Swiss Army knife is about 6 cm (2.4 in) long. Photograph by Anthony Martin.
Once this short, ichnologically-infused hike was over, people thanked me and bid goodbye, but a few of stayed behind to take a gander at the peafowl, which were in a large enclosure just behind O’Connor’s house. One male and two females are kept there, and our timing was impeccable, as the male was in full display mode, feathers fully erect and dazzling as he strut about the grounds, while the peahens stayed in the background, mildly impressed or nonchalant. (“Oh yes, he does that all of the time,” I imagined them thinking, mildly bored.) Nevertheless, as far as we non-avian bipeds were concerned, he was indeed the king of birds.
But that’s when my ichnologist hat popped onto my head, askance from its sudden appearance. Craig had told me earlier about the peafowls making a dust bath in the confines of their enclosure, and sure enough, there it was. It matched the width, depth, and shape of dust baths I had written about in Life Traces of the Georgia Coast, only for wild turkeys. Birds make dust baths for alleviating skin parasites, in which they hunker down in them, using their wings to distribute enough fine-grained sediment on them to smother the offending lice or other arthropods. Could such traces preserve in the geologic record, whether they were made by feathered dinosaurs, birds, or mammals? How could we recognize or distinguish these from other shallow depressions? And most importantly, did Flannery O’Connor ever see such dips in the landscape, and if so, did she know their meaning?
A dust bath made by peafowls, about 50 cm (20 in) wide on its longest dimension, and looking a little less dusty after several days of intense rain the preceding week. Still, this was a cool trace to see, and conjured some imaginative thoughts about these as trace fossils. (Peafowl feces extra in the pit: no charge.) Photograph by Anthony Martin.
Another ichnologically inclined thought occurred to me while there at the enclosure, and is worthy of further experimentation. How might we tell the male (peacock) tracks from those of the female (peahen)? Take a look at the following photo, and you tell me. Anything there that might leave a distinctive mark identifying the gender of its tracemaker?
Here comes the groom! Any aspect of this tracemaker’s anatomy that might leave traces telling you he was a boy bird? Photograph by Anthony Martin.
So from this day trip to Andalusia Farm, I was awed, inspired, and ever slightly more enlightened by it all, and hoped that a small amount of the same feelings had been experienced by others who participated in this special day. Still, I was also humbled, realizing how little I still know about Flannery O’Connor, why she connected so well with birds, bird traces and behavior, or how these traces might manifest themselves to us and grace us with wisdom as recognizable trace fossils made in a distant past. Hence from my time there and into my future, I will endeavor to keep in mind the words spoken by Dr. Block, a character of O’Connor’s in The Enduring Chill from the anthology, Everything That Rises Must Converge:
“Most things are beyond me,” Block said. “I ain’t found anything yet that I thoroughly understood.”
Acknowledgements: Many thanks to: my good and long-time friend Melanie DeVore for encouraging me to visit Andalusia to share my science and sense of wonder; Craig Amason for being such a gracious host; Bruce Gentry for his continuing contributions to teaching his students about the complex and varied dimensions of Flannery O’Connor, a great American writer; the people who showed up and made for lively company; and of course the birds and their traces, which will outlive all of us, no matter the lengths of our lives.
Further Reading
Elbroch, M. and Marks, E. 2001. Bird Tracks and Sign of North America. Stackpole Books: 456 p.
Martin, A.J. 2013. Life Traces of the Georgia Coast: Revealing the Unseen Lives of Plants and Animals. Indiana University Press: 692 p.
O’Connor, F. 1955. A Good Man is Hard to Find, and Other Stories. Harcourt, Brace and Company: 265 p.
O’Connor, F. 1965. Everything That Rises Must Converge. Farrar, Straus and Giroux: 320 p.
Simpson, M. 2005. Flannery O’Connor: A Biography. Greenwood Books: 152 p.
This past Friday, I very happily received the first complimentary copy of my new book, Life Traces of the Georgia Coast from Indiana University Press. After years of field observations, photographing, writing, editing, drawing, teaching, and speaking about the plant and animal traces described in this book, it was immensely satisfying to hold a physical copy in my hands, feeling its heft and admiring its textures and smells in a way that e-books will never replace. So for any doubters out there (and I don’t blame you for that), here is a photograph of the book:
A photograph, purportedly documenting the publication of at least one copy of my new book Life Traces of the Georgia Coast. Photo scale (bottom) in centimeters.
Still, given that a photograph of the book only constitutes one line of evidence supporting its existence, I knew that more data were needed. So of course, I turned to ichnology for help. After all, a 692-page hard-cover book should also make an easily definable resting trace. Here is that trace, formed by the book in the same spot shown previously.
Ichnological evidence supporting the existence of my new book, Life Traces of the Georgia Coast. Using the “holy trinity” of ichnology – substrate, anatomy, and behavior – as guides for understanding it better: the substrate is a bedspread; the “anatomy” is the 6 X 9″ outline of the book, with depth of the trace reflecting its thickness (and mass); and the behavior was mine, consisting of placing the book on the bedspread and removing it. E-book versions of the book should make similarly shaped rectangular traces, although these will vary in dimensions according to the reading device hosting the book.
However, I also admit that hard-core skeptics may claim that such photos could have been faked, whether through the manipulative use of image-processing software, or slipping the cover jacket onto a copy of Danielle Steel’s latest oeuvre. As a result, the best and perhaps only way to test such a hypothesis is for you and everyone you know to buy the book (which you can do here, here, or here). Or, better yet, ask your your local bookstore to carry copies of it, which will also help to ensure the continuing existence of those bookstores for future book-purchasing and ichnological experiments, including books of other science-book authors.
Lastly, just to make this experiment statistically significant, I suggest a sample size of at least n = 10,000, which should account for inadvertent mishaps that may prevent deliveries of the book, such as lightning strikes, volcanic eruptions, or meteorite impacts. Only then will you be able to assess, with any degree of certainty, whether the book is real or not.
Thank you in advance for your “citizen science,” and I look forward to discussing these research results with you soon.
Suggested Further Reading
Martin, A.J. 2012. Life Traces of the Georgia Coast: Revealing the Unseen Lives of Plants and Animals. Indiana University Press, Bloomington, Indiana: 692 p.
After returning from a two-week vacation in California with my wife Ruth, we noticed a cardboard tube awaiting us at home. Intriguingly, the mystery package, which was only about 60 cm (24 in) long and 8 cm (3 in) wide, had been sent by Indiana University Press, the publisher of my new book, Life Traces of the Georgia Coast. We were a little puzzled by it, considering that it couldn’t possibly contain complimentary copies of the book. (As of this writing, I still have not held a corporeal representation of the book, hence my continuing skepticism that it is really published.) What was in this mystery tube?
Front cover and spine of my new book, Life Traces of the Georgia Coast: Revealing the Unseen Lives of Plants and Animals (Indiana University Press). The book, newly released this month, is not yet in stores, but supposedly on its way to those places and to people who were kind enough to pre-order it. But if you didn’t pre-order it, that’s OK: you can get it right here, right now.
Upon opening it, we were delighted to find that it held ten life-sized prints of the book jacket: front cover, spine, back cover, and front-back inside flaps. The cover art, done by Georgia artist Alan Campbell, looked gorgeous, and had reduced well to the 16 X 25 cm (6 X 9″) format, retaining details of traces and tracemakers, but also conveying a nice aesthetic sense. I was also amused to see the spine had the title (of course) but also said “Martin” and “Indiana.” Although I’ve lived in Georgia for more than 27 years, I was born and raised in Indiana, so it somehow seemed fitting in a circle-of-life sort of way to see this put so simply on the book.
Back cover of Life Traces of the Georgia Coast, highlighting a few of the tracemakers mentioned in the book – sea oats, sandhill crane, sand fiddler crab, and sea star – while also providing a pretty sunset view of primary dunes, beach, and subtidal environments on Sapelo Island. (P.S. I love that it says “Science” and “Nature” at the top, too.)
I had no idea what the back cover might be like until seeing these prints, but I thought it was well designed, bearing a fair representative sample of tracemakers of the Georgia barrier islands: sea oats (Uniola paniculata), a sandhill crane (Grus canadensis), sand fiddler crab (Uca pugilator), and lined sea star (Luidia clathrata), as well as a scenic view of some coastal environments. I had taken all of these photos, so it was exciting to see these arranged in such a pleasing way. My only scientifically based objection is that I would have like to see it include photos of insects, worms, amphibians, reptiles, or mammals (these and much more are covered in the book), as well as a few more tracks, trails, or burrows. Granted, I suppose they only had so much room for that 6 X 9″ space, and thus I understood how they couldn’t use this space to better represent the biodiversity of Georgia-coast tracemakers and their traces. (Oh well: guess you’ll have to read the book to learn about all that.)
Inside front and back flap material for Life Traces of the Georgia Coast, which also includes a summary of the book (written by me) and a rare photo of me (taken by Ruth Schowalter) in my natural habitat, which in this instance was on St. Catherines Island, Georgia.
I had written the summary of the book on the inside flap nearly a year ago, so it was fun to look at it with fresh eyes, almost as if someone else had written it for me. Fortunately, I banished my inner critic while reading it, and just enjoyed the sense that it likely achieved its goal, which was to tell people about the book and provoke their interest in it.
In short, this cover jacket symbolizes a next-to-last step toward the book being real in my mind. Now, like any good scientist, all I need is some independently verifiable evidence in the form of tactile data, such as a physical book in my hands. Stay tuned for that update, which I’ll be sure to share once it happens. In the meantime, many thanks to all of the staff at Indiana University Press – who I’ll mention by name next time – for their essential role in making the book happen and promoting it in this new year.
Information about the Book, from Indiana University Press
Life Traces of the Georgia Coast: Revealing the Unseen Lives of Plants and Animals, Anthony J. Martin
Have you ever wondered what left behind those prints and tracks on the seashore, or what made those marks or dug those holes in the dunes? Life Traces of the Georgia Coast is an up-close look at these traces of life and the animals and plants that made them. It tells about the how the tracemakers lived and how they interacted with their environments. This is a book about ichnology (the study of such traces), a wonderful way to learn about the behavior of organisms, living and long extinct. Life Traces presents an overview of the traces left by modern animals and plants in this biologically rich region; shows how life traces relate to the environments, natural history, and behaviors of their tracemakers; and applies that knowledge toward a better understanding of the fossilized traces that ancient life left in the geologic record. Augmented by numerous illustrations of traces made by both ancient and modern organisms, the book shows how ancient trace fossils directly relate to modern traces and tracemakers, among them, insects, grasses, crabs, shorebirds, alligators, and sea turtles. The result is an aesthetically appealing and scientifically accurate book that will serve as both a source book for scientists and for anyone interested in the natural history of the Georgia coast.
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.
Two weeks ago, during an all-too-brief visit to Jekyll Island (Georgia) over the Thanksgiving holiday weekend, I decided to check in on some old friends. When I was first introduced to them about four years ago (2008), their presence on Jekyll was a big surprise for me. But thanks to their distinctive traces and a little bit of detective work, I now know they’re on other Georgia barrier islands, too.
Why look, miniature volcanoes in the middle of a maritime forest on Jekyll Island! Or, could they be something else? (In science, that’s what we like to call an “alternative hypothesis.”) Photo scale (left) in centimeters. (Photograph by Anthony Martin.)
These “friends” were conical towers, which look like small lumpy volcanoes (stratovolcanoes, that is, not shield volcanoes), were the traces of freshwater crayfish. A few of the structures, composed of piled balls of sandy mud, also had circular holes in their centers, and they had all seemingly popped out of the forest floor along the edge of a pool of fresh water. All I needed to do to find them was look in the same place where I was first introduced to them, which was by a Jekyll Island resident who knew about their whereabouts.
The towers were 10-25 cm (4-6 in) wide at their bases, 7-10 cm (3-4 in) tall, and each of the rounded, oval balls of sediment was about 1-1.5 cm (0.4-0.6 in) wide. The overall appearance of the towers said “still fresh,” having not been appreciably weathered, and all that I saw in the area looked about the same age. Knowing a little bit about crayfish behavior, I figure they were made just after the last rainfall on Jekyll, maybe a week or so before I spotted them.
Close-up of a crayfish tower, with a circular hole in the center (that’s the burrow). Scale in centimeters. (Photograph by Anthony Martin, taken on Jekyll Island, Georgia.)
Crayfish that dig burrows adjust their depth according to the water table, which they must do to stay alive because they have gills. If the water table drops, they burrow deeper, but if the water table rises, they move their burrows up. For example, where I live here in the metro Atlanta area, crayfish towers often pop up in people’s backyards the day after a hard rain. (This also means that these people need to get flood insurance, because their backyards are on a floodplain. Thus also demonstrating yet another practical reason to know a little basic ichnology.)
Burrowing was (and still is) accomplished by crayfish using their prominent claws (chelipeds) as spades, rolling up the balls of sediment and placing them outside of the burrow entrance, and thus building up towers. But they also smooth out burrow interiors with their bodies through up-and-down and back-and-forth movement, resulting in their burrows having near-perfect circular cross sections. Crayfish burrow systems can be complicated, with vertical shafts connecting the surface with the below-ground parts, which can consist of branching horizontal tunnels and chambers; the last of these can even be occupied by multiple crayfish.
When I first saw these these towers and burrow cross-sections on Jekyll Island in 2008, I immediately knew they were from crayfish. My certainty was because such traces had been described in loving detail by crayfish researchers and ichnologists, linking these directly to their crustacean makers. In fact, just a few months ago, I saw an example of this connection between traces and tracemakers in my home of Decatur, Georgia, where the drying of a human-made pond there caused the crayfish to burrow into the former pond bottom and move about on its sediments in a desperate attempt to stay wet.
A high density of crayfish burrows in a recently drained human-made pond in Decatur, Georgia. Note the similarity of the towers, circular burrow cross-sections, and rounded balls of sediment to those of the Jekyll Island crayfish burrows. Scale with centimeters. (Photograph by Anthony Martin.)
“Are you looking at me?” Crayfish, about 5 cm (2 in) across, and probably a species of Procambarus, copping an attitude while guarding its burrow entrance. (Photograph by Anthony Martin, taken in Decatur, Georgia.)
With about 70 species documented in the state, Georgia is quite rich in crayfish diversity, qualifying it and bordering states in the southeastern U.S as a “biodiversity hotspot” for these animals. Freshwater crayfish are also geographically widespread – occurring in North and South America, Europe, Madagascar, Australia, New Zealand, New Guinea – a direct result of plate tectonics, which spread and isolated populations from one another during their evolutionary history.
In terms of that history, these crustaceans (decapods, more specifically) split from a common ancestor with marine lobsters about 240 million years ago, an age based on molecular clocks, which have been integrated with fossil evidence. I’ve also seen trace fossils that look very much like crayfish burrows in Late Triassic rocks, from about 210 million years ago, which suggests that burrowing began in this lineage early in the Mesozoic Era.
In a 2008 article I co-authored and published with six other scientists – three paleontologists and three zoologists – we described fossil burrows in rocks from the Early Cretaceous Period (about 115-105 million years ago) of Australia, and named what is still the oldest fossil crayfish in the Southern Hemisphere, Palaeoechinastacus australanus. In this article, we pointed out how burrowing was an adaptation that likely helped these crayfish survive polar winters in Australia during the Cretaceous, but also how burrowing abilities in general have given crayfish an upper claw, er, hand in making it past environmental crises in the geologic past.
Here’s the oldest known fossil freshwater crayfish in Australia and the rest of the Southern Hemisphere, Palaeoechinastacus australanus (= “ancient spiny crayfish of Australia”), found in 105-million-year-old rocks (Early Cretaceous) of southern Victoria. Not everything is there, but you can see most of its tail to the left and the right-side legs. Specimen is Museum Victoria, Melbourne, Australia. (Photograph by Anthony Martin.)
And here’s a bedding plane (horizontal) view of trace fossils attributed to freshwater crayfish burrows, preserved in 115-million-year-old rocks (also Early Cretaceous) near Inverloch, Victoria (Australia). The burrows were filled with sand originally, which cemented differently from the surrounding sediment, making them stand out in positive relief as they weather on the outcrop. Scale = 10 cm (4 in). (Photograph by Anthony Martin.)
So how did these crayfish get onto the Georgia barrier islands? Before answering that, I can tell you how they did not get there, which was from people. Because these are burrowing (infaunal) crayfish, and not ones that hang out on lake or stream bottoms (also known as epibenthic), it’s not very likely that humans purposefully introduced them on the islands for aquaculture. Let’s just say that digging up each crayfish burrow, which may or may not contain a crayfish, would require too much work to make crayfish etoufee worth the effort, no matter how good your recipe might be.
Mmmmm, flavorful freshwater decapod concoction [drooling sounds]. But first imagine having to dig up every single crayfish for this dish. Just to prevent this from happening, your recipe should have some qualifying statement, such as, “Make sure to use epibenthic crayfish, not infaunal ones!” (Original image, modified slightly by me, from Wikipedia Commons here.)
Another point to remember about crayfish is that they are freshwater-only animals, incapable of tolerating salt-water immersion, let alone swimming kilometers through marine-flavored waters to reach offshore islands. Yet I’ve seen their traces on Jekyll and two other Georgia barrier islands, and crayfish species have been reported from two additional islands. (For now I won’t say which other islands or identify the probable species of these crayfish until they’ve been properly studied. Sorry.)
What might seem strange to most people, though, is that I still haven’t seen a single living crayfish on any of the Georgia barrier islands. Nonetheless, seeing and documenting their traces is good enough for me to know where they’re living and how they’re behaving. This again demonstrates one of the many advantages of ichnology: you don’t actually have to see an animal to know it’s there, just as long as it leaves lots of identifiable traces.
Oh yeah: almost forgot about the title of this post. What’s my explanation for how the crayfish got to the islands, including Jekyll? I think they lived on the islands before they were islands. In other words, present-day crayfish on the islands descended from ones that originally lived on the mainland part of Georgia, but these were cut off from their original homeland by the last major sea-level rise (well before the current one, that is). This rise started as long as 11,000 years ago, when the last great ice age of the Pleistocene ended, shedding water from continental glaciers and expanding the seas.
So think of a salty moat filling in the low areas between what are now the Georgia barrier islands and the rest of Georgia, with crayfish on either side of it, metaphorically waving goodbye to one another with their claws. In this scenario, the crayfish of the Georgia barrier islands may represent relics left behind and isolated from their ancestral populations. They may have even undergone genetic drift and became new species, or are well on their way to reproductive isolation from their mainland relatives. But that’s just speculation on my part right now. Like I said, these critters need to be studied before anything can be said about them.
All of this neatly illustrates how our knowledge of the geological past ties in with the present, as well as how ichnology can be applied to conservation biology. With regard to the latter, these little muddy crayfish towers exemplify one of the dangers associated with any rapid, careless development of the Georgia barrier islands. What if most people aren’t aware of the unique plants and animals on the islands because at least some of this biodiversity lies below their feet? Without such knowledge, unheeded development may very well wipe out rare or previously unknown species that have been part of the ecological legacy of the Georgia coast for the past 10,000 years.
This is one of many reasons why environmental protection of the islands is still needed, even on semi-developed one like Jekyll. Fortunately, motivated people are working toward such protection on Jekyll, and most other Georgia barrier islands are under some sort of state or federal protection, or privately owned as preserves.
Nice maritime forest you got there. It’d be a shame if something happened to it. (Photograph by Anthony Martin, taken on Jekyll Island.)
What’s also happened on Jekyll Island is increased ecotourism, highlighted by the success of the Georgia Sea Turtle Center. The center, which opened in 2007, has a rehabilitation center for injured turtles, educates the public about sea turtles nesting on the Georgia coast, and helps to monitor turtle nests on Jekyll during the nesting season. And just how is this monitoring done? By looking for tracks of the nesting mothers on the beaches of Jekyll during nesting season, of course. (Say, didn’t I say something previously about using ichnology in conservation biology?)
So can a Jekyll Island Crayfish Center be far behind? Um, no. Still, it’s time to start thinking of species on the Georgia barrier islands and their traces as assets, bragging points that can be used to bolster ecotourism on the coast. Barrier-island biodiversity is an economic resource that will continue to pay off as long as the species survive and their habitats are protected, while simultaneously feeding our sense of wonder at how these species, including burrowing freshwater crayfish, got to the islands in the first place.
Further Reading
Breinholt, J., Ada, M. P.-L., and Crandall, K.A. 2009. The timing of the diversification of the freshwater crayfish. In Martin, J.W., Crandall, K.A., and Felder, D.L. (editors), Decapod Crustacean Phylogenetics, CRC Press, Boca Raton, Florida: 343-355.
Hobbs, H.H., Jr. 1981. The Crayfishes of Georgia. Smithsonian Institute Press, Washington, D.C.: 549 p.
Hobbs, H.H., Jr. 1988. Crayfish distribution, adaptive radiation and evolution. In: Holdich, D.M., Lowery, R.S. (editors), Freshwater Crayfish: Biology, Management and Exploitation. Croom Helm, London: 52-82.
Martin, A.J. 2011. Ichnology in a time of climate change: predicted effects of rising sea level and temperatures on organismal traces of the Georgia coast. Geological Society of America, Abstracts with Programs, 43(2): 86. Link here.
Martin, A.J., Rich, T.H., Poore, G.C.B., Schultz, M.B., Austin, C.M., Kool, L., and Vickers-Rich, P. 2008. Fossil evidence from Australia for oldest known freshwater crayfish in Gondwana. Gondwana Research, 14: 287-296.
P.S. So you’d like to hear more details on the crayfish of the Georgia barrier islands? Well, then you’re going to have to read my book, which starts out Chapter 5 (on terrestrial invertebrate traces) with a section titled The Crayfish of Jekyll Island. Yes, that’s a sales pitch, but you can also request your public library to get it, or borrow a copy from a friend. Which makes this more of a “knowledge pitch.”
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.
The arrival of Halloween reminds us to celebrate mythical creatures that frighten yet also intrigue us, although recent popular crazes have made this less of an annual event and more year-round. Along those lines, probably the top three of such imaginary beings are zombies, werewolves, and vampires. All of these can be classified as changelings of a sort, with two of them dead, but not really. Here in Georgia, public fascination with zombies has even provided employment opportunities, as many people compete for coveted slots as shuffling extras on the TV series The Walking Dead.
Among these inspirations for Halloween costumes, short stories, novels, musicals, TV shows, and movies, which would be the toughest for an aspiring Van Hesling to track down using ichnological methods? Zombies would be far too easy, considering their slow-moving, foot dragging, bipedal locomotion; their trackways would also commonly intersect as they bump into one another in their search for cranial sustenance. In other words, zombie trackway patterns would closely match those of people texting.
As a result, we have many modern analogs for zombie traces, which would also make their recognition in the fossil record that much easier. Traces made by the zombie-like characters portrayed in 28 Days Later, however, would be far different, showing greater distances between tracks and reflecting more rapid movement. (And all kidding aside, we actually do have trace fossil evidence of zombie ants from about 50 million years ago, an example of reality trumping fiction.)
Similarly, tracking werewolves would be straightforward, in that trackway patterns should show normal human bipedal locomotion followed by abrupt changes to quadrupedal patterns that would range from a trot to full gallop, gaits that are comparatively rare in humans. Anatomical details of tracks would also include a transition from five-toed plantigrade tracks to four-toed digitigrade ones, and metatarsal impressions would be replaced by heel-pad impressions. Additional traces to expect from a werewolf would be the direct effects of successful predation, such as blood spatters, scattering of prey body parts, toothmarks, and so on. (Don’t ask me about werewolf scat, though. I don’t even want to think about some of the things that would show up in that, especially if they started consuming suburbanites.)
Mixed assemblage of wolf and human tracks, which no doubt proves the existence of werewolves. Or not. Your choice. (Photograph by Anthony Martin, taken in Yellowstone National Park, Wyoming: scale = 10 cm (4 in).)
A closer look at those supposed “wolf” tracks. Yes, I know, they’re in the same area of Yellowstone National Park where a successful wolf-release program took place. But my doubt means you have to consider the impossible as equally valid.
A gorgeous “wolf” track with evidence of skidding to a halt and turning to the right. Could this have been made immediately after a human transformed into a wolf? My Magic 8-ball says, “Ask again later.”
Scene from some movie I’ll never see, in which one of the characters undergoes a mid-air transformation from a human to a werewolf (Canis lupus hormonensis), abruptly changing his tracks from a more plantigrade bipedal running to digitigrade quadrupedal movement. Sorry, I don’t know if any evidence of teen angst would preserve in such a trackway, nor do I care.
In contrast to zombies and werewolves, vampires would be the most challenging to track, considering their occasional aerial phases of movement, as depicted in Bram Stoker’s novel Dracula (1897) and various popular adaptations. Traces made during a pre-transformation phase – while still in human form – would be indistinguishable from those of a non-undead human, texting or not, and once in the air, no evidence of its movement would be recorded.
A large bat (megachiropteran) in flight, leaving no traces of its passing when traveling in a substrate of air.
So just to leave vampires for a moment, let’s talk about bats, which are real and do leave traces of their activities. Knowing that bats are among the most diverse and abundant of mammals (more than 1,200 species), I made sure to discuss their traces in my upcoming book, Life Traces of the Georgia Coast. Although I personally have not yet seen any of their traces on the Georgia barrier islands, these are predictable and identifiable, so I hold out hope that I or someone else will find them some day.
Probably the most likely traces made by bats that one could encounter on the Georgia barrier islands are their feces, which in other places, through the right geology (think caves) and collective action, can form economic resources (more on that later). About 75% of bat species are insectivores, and because they catch their meals on the fly, their scat will mostly contain winged insect parts. However, the geology of the Georgia barrier islands lacks limestone, and thus precludes the formation of caves or other environments serving as roosting spots for bat colonies. Thus bat feces, such as those dropped by the common brown bat (Myotis lucifugus), will be hard to find unless you look in the right place, such as below a favorite roosting spot. If you are lucky enough to notice these, though, these traces are dark 2-3 mm (0.1 in) wide and 5-15 mm (0.2-0.6 in) long cylinders and filled with parts of flying insects.
Most other bats are fruit-eaters; this means these bats, like many birds, are also important seed dispersers through their excreting indigestible seeds covered in fertilizer. Speaking of fertilizers, massive deposits of bat feces (guano) also accumulate in caves and other places where millions of bats have roosted. These nitrogen- and phosphorous-rich deposits have been mined for fertilizers used in agriculture, an example of feeding traces helping to feed people.
Do bats come to the ground and leave tracks? Yes, once in a while they do, where they might forage and walk on all fours. When they do this, they make diagonal walking patterns, contacting with the thumbs on the tips of their wings – which are skin membranes connected to their other, elongated fingers – and their rear feet.
OK, now back to vampires, or rather, vampire bats. There are only three species of parasitic bats, all of which subsist on the blood of other mammals. For feeding, they slice skin with their sharp teeth, which leaves a small (several centimeters long, millimeters thin) incision. They then lap up whatever blood comes out, and the victim often isn’t aware of its blood loss. These wounds also heal, but leave visible scars.
What about other traces left by vampire bats? Surprisingly, scientists have actually asked themselves, “Hey, I wonder how vampire bats get around on the ground?”, and conducted experiments on terrestrial movement of the common vampire-bat (Desmodus rotundus), as well as the short-tailed bat of New Zealand (Mystacina tuberculata).
Just in case you needed another reason why science is cool, these scientists constructed bat-sized treadmills and placed these bats on them. This experiment confirmed that bats, including the common vampire bat, perform an alternating-walking movement in which the rear foot (pes) registers just behind the thumb, which also bears a claw. (This claw comes in handy as a sort of grappling hook at they climb onto their blood sources.)
Based on this video, here is what I would hypothesize as the trackway pattern of a walking vampire bat. Note that the rear foot has five digits, nearly equal in length, and that the feet point away from the midline of the trackway.
But then they found out something most people didn’t expect. When they increased treadmill speeds, the bats bound and almost gallop, in which their rear feet nearly move past their wings. While bounding, these bats land on one of the digits on their wings, then push off with their rear feet, causing a suspension phase, reaching maximum speeds of 1.2 m/s. (Which, incidentally, is about the same speed as most people walking while texting, or slow zombies.) The resulting trackway patterns would be in sets of four – rear feet paired behind thumb impressions – separated from one another by about a body length. Based on my viewing of the videos, the trackways would show both half-bound and full-bound patterns, in which the rear feet are either offset or parallel, respectively.
And here is the hypothesized trackway pattern for a running vampire bat, which is almost like a gallop pattern, but more like a half-bound or full-bound. The feet actually should point a little more inward than during walking, and depending on the substrate, deformation structures might be associated with track exteriors.
Just to insert a little paleontology into this consideration of bat traces: has anyone found a trackway, feces, or other traces made by bast in the fossil record? No, unless you count old guano deposits as trace fossils (which I would if they exceed 10,000 years old). The body fossil record for bats extends back to the Eocene Epoch, about 50 million years ago, but such fossils are rare, too. Far more impressive than a bat body fossil, though, would be a fossil bat trackway would be the discovery of a lifetime, almost as noteworthy as finding an actual vampire. And if you found a fossil bat trackway where it was running? Time to start playing the lottery.
More readily available in ancient strata, though, are pterosaur tracks, whose makers likely walked in a manner similar to bats when on land. Hence bats, although not directly related to these flying reptiles, may provide analogues for how some small pterosaurs moved about when on the ground. Despite their long study and many pterosaur fossils, though, a few people are still arguing about how pterosaurs moved on the ground. So hopefully more studies of bat locomotion will help us to better understand the earthbound behaviors of pterosaurs.
The take-home message of the preceding is that even though zombies, werewolves, and vampires still garner plenty of attention from the public, the truth is that real animals of the past and present – like bats and pterosaurs – are actually more fantastic than we sometimes know. Sure, let’s continue to have fun with our mythical creatures, but in the meantime, also keep an eye out for traces left by the marvelous animals of today and yesteryear.
Further Reading
Elbroch, M. 2003. Mammal Tracks and Sign: A Guide to North American Species. Stackpole Books, Mechanicsburg, Pennsylvania: 778 p.
Mazin, J.-M., Billon-Bruyat, J.-P., and Padian, K. 2009. First record of a pterosaur landing trackway. Proceedings of the Royal Society of London, B, 276: 3881-3886.
Padian, K., and Fallon, B. 2012. Meta-analysis of reported pterosaur trackways: testing the corrspondence between skeletal and footprint records. Journal of Vertebrate Paleontology, 32 [Supplement to 3]: 153.
Riskin, D.K. et al. 2006. Terrestrial locomotion of the New Zealand short-tailed bat Mystacina tuberculata and the common vampire bat Desmodus rotundus. Journal of Experimental Biology, 209: 1725-1736.
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.
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 Schowalterfor 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.
After a 45-minute ferry ride to Cumberland Island, the students received a different sort of lecture when naturalist extraordinaire Carol Ruckdeschel – who is writing a book about the natural history of Cumberland Island – met with them and gave them a brilliant overview of the island ecology. She mostly talked with the students about the effects of feral animals on the island, then spent another hour with us in the maritime forest and through the back-dune meadows. It was a real treat for the students and me, and a great way to start the field trip.
A leaf-cutter bee trace! Despite my writing about these and illustrating them in my book, these distinctive incisions were the first I can recall seeing on the Georgia barrier islands. These traces were abundantly represented in the leaves of a red bay tree we spotted along a trail through the maritime forest, making for a great impromptu natural history lesson for the students.
A freshly erupted ghost shrimp burrow on the beach at Cumberland, in which the students were lucky enough to witness the forceful ejection of muddy fecal pellets by the shrimp from the top of its burrow. I mean, really: explain to me how the life of an ichnologist-educator can get any better than that?
The fine tradition a field lunch, made even more fine by the addition of fine quart sand to our meals, freely delivered by a brisk sea breeze. Did the sand leave any microwear marks on our teeth? I certainly hope so.
A student is delighted to test my ichnologically based method for finding buried whelks underneath beach sands, and find out that it is indeed correct. (Was there any doubt?) Here she is proudly holding a live knobbed whelk, which I can assure you she promptly placed back into the water once its photo shoot was finished for the day.
Just to join in the fun, other students decided my “buried whelk prospecting” method required further testing. Let’s just say this student did not disprove the hypothesis, but rather seemed to confirm it, and doubly so. It’s almost as if ichnology is a real science! (Yes, these whelks went back into the water, too.)
OK, enough about marine predatory gastropods (for now). How about some of the largest horseshoe crabs (limulids) in the world? We found a large deposit of their carapaces above the high-tide mark, some of which were probably molts, but others recently dead. Sadly, though, we did not see any of their traces. Bodies only do so much for me.
Where do dunes come from? Well, a mother and father dune love each other very much… No wait, wrong story. What happens is that dead cordgrass from the salt marshes washes up onto the beach, where it starts slowing down wind-blown sand enough that it accumulates. Now it just needs some wind-blown seeds of sea oats and other plants to start colonizing it, and next thing you know, dune. Dude.
Ah, a geological tradition in action: comparing actual sand from a real outdoor environment to the sand categories on a handy grain-size chart, and using a hand lens. It’s enough to bring a tear to the eyes of this geo-educator. Or maybe that was just the wind-blown sand.
Finally, something that really matters, like ichnology! This is a three-for-one special, too: sanderling feces (left), tracks, and regurgitants (right), the last of these also known as cough pellets. Looks like it had coquina and dwarf surf clams for breakfast.
Wow, more shorebird traces! The tracks are from a loafing royal tern, and it clearly needed to get a load off its mind before moving on with the rest of its day.
Tired of shorebird traces? How about a modern terrestrial theropod? Wild turkey tracks in the back-dune meadows of Cumberland were a happy find, leading to my grilling the students with the seemingly simple question, “What bird made this?” They did not do well on this, but hey, it was the first day, and at least no one said “robin” or “ostrich.”
Did somebody say “doodlebug?” This long, meandering, and collapsed tunnel of an ant lion (a larval neuropteran, or lacwing) tells us that this insect was looking for prey in all the wrong places.
Behold, tracks that bespeak of great, thundering herds of sand-fiddler crabs that used to roam the sand flats above the salt marsh. Where have they gone, and will they ever come back? Who knows where the males might be waving their mighty claws? Do the female fiddler crabs suffer from big-claw envy, or are they enlightened enough to reject cheliped-based hierarchies imposed upon them by fiddler-crab society? All good questions, deserving answers, none of which make any sense.
Yes, that’s right, feral horses are really bad for salt marshes. Between overgrazing and trampling, they aren’t exactly what anyone could call “eco-friendly.” My students had heard me say this repeatedly throughout the semester, and Carol Ruckdeschel said the same thing earlier in the day. But then there’s seeing it for themselves, another type of learning altogether.
And the day ended with beautiful ripple marks, beckoning from the sandflat below the boardwalk on our trip back onto the ferry. Even this ichnologist can appreciate the aesthetic appeal of gorgeous physical sedimentary structures.
