Life Traces of a Master: A Tribute to Dolf Seilacher (Part II)

Posted on May 13, 2014 by TMartin

(This is the second in a three-part series honoring the memory of ichnologist-paleontologist-educator-artist Dolf Seilacher (1925-2014). For Part I, please go here.)

Dolf Seilacher and I crossed trails again in the fall of 1997, but through my initiative and in my backyard, here in Georgia. After the Evolutionary Biology Study Group at Emory University hosted a series of prominent biologists on the Emory University campus – such as George C. Williams, Richard Lewontin, and the Grants (Rosemary and Peter) – its director asked me which paleontologist we might bring to campus. Having invited theoreticians and lab-based or field biologists as our main guests, he wanted to give the members of our group more of a “deep time” perspective on evolutionary processes. So I immediately said, “Dolf Seilacher.”

Dolf Seilacher in Melton’s App & Tap, a neighborhood pub near the Emory University campus that served both Coca-Cola (which has economic connections to Emory) and proper adult beverages, the latter necessary for fueling meaningful paleontological conversations. (Photograph by Anthony Martin, taken in Atlanta, Georgia 1997.)

I recall a few snobbish members of the group doubted that any paleontologist could be a real evolutionary scientist: after all, paleontologists don’t do “experimental work.” (Yes, I’ve actually heard this smug, self-important drivel emit from the mouths of proudly lab-bound neontologists, making Sheldon Cooper look downright open-minded by comparison.) I was also at a university that had jettisoned its Department of Geology only eight years previously, meaning I had little support in my on-campus academic community for hosting an earth scientist. However, Dolf had won the Royal Swedish Academy of Sciences Crafoord Prize just five years before, thus he qualified as prestigious enough for most of the doubters. (Needless to say – but it bears saying anyway – none of his prejudiced skeptics had similar honors.)

Fortunately, Dolf did not disappoint, and hosting him at Emory University was among the most intellectually exhilarating three days I’ve experienced in the past 24 years at my institution. I had him mostly to myself on his first day in Atlanta, but we were joined by fellow ichnologist and friend Andrew (Andy) Rindsberg for dinner, with both of us feeling as if we had the world’s best private tutor in ichnology for that brief time. The next day, Dolf did a lunchtime seminar for the Evolutionary Biology Study Group, then later that afternoon delivered a talk in a big room open to the entire university and the general public. For his last full day in Georgia, he insisted we take him out in the field to see some of the Ordovician-Silurian rocks in the northwest corner of the state. (Other than transferring planes in Atlanta’s airport, Dolf had never been to Georgia and wanted to see our trace fossils.)

His second day in Atlanta, he began his engagement with the Evolutionary Biology Study Group, which was composed mostly of biologists, anthropologists, and psychologists; Andy and I were the lone paleontologists there. The lunchtime seminar was held in a cramped room, and most people there were awkwardly holding flimsy paper plates weighed down by slices of cheap pizza. The overall mood was one of curiosity, as Dolf was a complete unknown to most people there. (Remember, this was 1997: “Googling” was still a year away from being anything, let alone a verb.)

His seminar topic was on fossil tracks, and he started with the classic historical example of how some Early Triassic tracks from Germany (named Chirotherium) had been badly misinterpreted by some of the greatest scientists of their time, such as Alexander von Humboldt, Richard Owen, and Charles Lyell. Later, with more scrutiny and the application of a few key ichnological principles, other scientists revealed what animals made them and how, which Dolf explained in his book Trace Fossil Analysis (2007, p. 6-7).

Dolf Seilacher’s visual explanation for how the anatomy and dimensions of a tracemaker, its behavior, and the original substrate (a firm mud) all contributed to making a fossil trackway from the Early Triassic Period (about 245 million years old). He also included explanations of previous interpretations for these tracks and when they were proposed (middle right), neatly summarizing the progression of the science done on these tracks. (Figure from: Seilacher, A., 2007, Trace Fossil Analysis, Springer, p. 7.)

A reproduction of the Early Triassic (about 245 million-year-old) rock slab with mudcracks and Chirotherium tracks, both preserved in convex relief as natural casts. I said “reproduction” because this is a epoxy resin cast made from a latex mold that was also colored to mimic the original rock. Does this sound like a work of art? Well, as a matter of fact, this was one piece in a show Seilacher conceived called Fossil Art. (Photograph by Anthony Martin, taken in Krakow, Poland in 2008.)

Once introduced, Dolf took off, and his audience went with him. In a lively, mesmerizing presentation, Dolf deftly interwove history of science with detective-like applications of ichnology, anatomy, sedimentology, and evolution, all delivered with his trademark enthusiasm, humor, and charisma.

In one memorable instant, he used his hands and arms to play-act the wrongly interpreted gait of the Chirotherium maker, in which this wretched imaginary animal had to cross its limbs as it walked. (Later, paleontologists figured out its so-called “thumb” was actually its outermost digit, thus erasing any need for the animal to cross-step.) He then pantomimed the more correct gait, again bringing across his points far more effectively than if he had used, say, a computer-animated reconstruction of the tracemaker. The audience was enthralled, enchanted, engaged, or whatever words science communicators use to describe what happens when a speaker is rhetorically kicking butt.

How did I know Dolf’s talk was a success? About five minutes into it, one of the most egotistical and pedantic curmudgeons in the Evolutionary Biology Study Group (who may or may not have been an anthropologist) turned to me and said with genuine delight, “This guy is terrific!” Yes, he was.

Later that afternoon, Dolf gave a lecture in a, well, lecture hall, with about a hundred people attending. For me, this was less exciting than his noontime talk because trace fossils and ichnology only figured briefly in its message. Instead, it was more about the “big picture” of evolution as reflected by the fossil record, with emphases on constructional morphology and biological structuralism, and connecting these to the evolution of animal behaviors. Some of these concepts – which I won’t even try to explain here – represented expansions on research by Dolf’s Ph.D. advisor, Otto Schindewolf. Nonetheless, he delivered a thought-provoking lecture, and enthusiastically answered a variety of questions when the time came.

Dinner at a Lebanese restaurant after the lecture was an opportunity to see yet another side of Dolf. For instance, soon after our party had been seated, he and the restaurant owner exchanged pleasantries (and jokes) in Arabic. I had forgotten that Dolf taught at the University of Baghdad early in his career and did much field work in Libya and other parts of the Middle East. The dinner – which included many field stories Dolf had experienced around the world – went well into the night, but did not hinder Dolf’s observation skills at the end of it.

As we exited the restaurant, he pointed to the cement on the doorstep and said, “Look, evidence of a former biomat, helping to preserve this footprint.” We looked down and saw where a shoe-clad human had stepped into the originally wet cement. But wrinkle marks around its edges – as Dolf explained – showed where plastic sheeting had been placed over the cement in a vain attempt to prevent people from stepping on it. It was a moment when we felt like Watson to his Sherlock.

Following his triumphant visit to the Emory campus in Atlanta, Dolf was then ready to experience something that really mattered, like trace fossils. The next day, we took him to northwestern Georgia to look at trace fossils in the Ordovician-Silurian rocks there, a mere 2.5 hour drive from Atlanta.

We had a varied group, composed of a few paleontologists – Andy Rindsberg, Sally Walker, and me – along with the director of the Evolutionary Biology Study Group (Michael Zeiler), a couple of evolutionary biologists and biology graduate students, and a few undergraduate students from one of my geology classes. Our only goal for the day was to see the I-75 Ringgold roadcut, which through its height, breadth, and gently tilted strata afforded an opportunity to stroll along its length, find many trace fossils, and put them into the context of changing environments from more than 440-430 million years ago.

The start of the field trip with Dolf Seilacher to see Ordovician-Silurian rocks near Ringgold, Georgia. This photo was taken about 10 minutes before he took over the field trip, which immediately followed Andy Rindsberg and me getting “Dolfed.” (Photograph taken by Anthony Martin in November 1997.)

Andy and I were thrilled to have Dolf at this outcrop with us because we had done a lot of work there, and we wanted to show off what we had found. Andy studied the Ordovician and Silurian trace fossils there in an M.S. thesis done at the University of Georgia, and I completed a bed-by-bed analysis of its Upper Ordovician rocks as part of my Ph.D. dissertation, also at the University of Georgia. Because we worked for the same graduate advisor (Robert “Bob” Frey), Andy and I communicated well with one another, and we mostly agreed on what trace fossils were there and what they meant. Moreover, Frey had published a paper with Dolf in 1980 (well before he died in 1992). Thus Andy and I felt as if we were fulfilling an ichnological legacy by taking Dolf to see trace fossils that Frey had studied here in Georgia.

A first sign that Andy and I were not leading this field trip: within minutes of arriving at the site, the group gathered around Dolf to listen to what he had to say about the Late Ordovician rocks under our feet and around us. Did I mention this was his first time there? (Photograph by Anthony Martin, taken near Ringgold, Georgia in November, 1997.)

Probably my favorite photograph of Dolf, showing him in full lecture mode while surrounded by Late Ordovician rocks in northwest Georgia. His synapses also might have been firing double time because of the caffeinated beverage he picked up at a Golden Gallon convenience store just beforehand. (Photograph by Anthony Martin, taken near Ringgold, Georgia in November, 1997.)

When we got to our destination, we parked and walked a short ways to our first stop. Rather than going directly to the road cut, we first looked at big slabs of sandstone in a former quarry site. These sandstones were from the Late Ordovician Sequatchie Formation, and they made for wonderful teaching specimens, containing many fossil burrows, mudcracks, and reddish clay, all indicating formerly intertidal environments. However, Andy and I didn’t know what made the burrows. Little did we know (but we should have), we were about to find out.

After Andy and I gave a brief introduction to this site and a preview of what to expect at the outcrop, Dolf strolled over to a large slab of sandstone, and nonchalantly placed his hand over a bump on its surface. “This trilobite resting trace shows how they were well adapted to living in intertidal environments at this time…” he began.

Andy and I exchanged startled looks. “Trilobite resting traces?” we both said. In all of our years of field work at this site, we had found very little evidence of a trilobite presence. We also had never recognized a trace fossil showing where a trilobite dug into mud or sand in one place and left an outline of its body, a so-called “resting trace,” sometimes called Rusophycus.

That’s when we realized it. We’d been Dolfed. And on our own field trip.

Fortunately, we didn’t care. Dolf then went on to propose that the more common burrows in these rocks were also made by trilobites, but smaller ones. I’ve written previously about this trilobite-themed revelation and how Andy and I tried later to disprove it, only to find that Dolf was probably right. This served as yet another example of why experience matters in ichnology, and why we ichnologists should always listen to those who have it.

Dolf in action, as he started to put together the story of how trilobites were burrowing on and into tidal flats more than 400 million years ago in a place we now call Georgia. Notice how Dolf was using pencil and paper to assist in his explanations of what was in front of us, no doubt drawing out his conclusions. (Photograph by Anthony Martin, taken near Ringgold, Georgia in November, 1997.)

Dr. Sally Walker, getting a close look at the bedding-plane surface of the sandstone, which is loaded with natural casts of mudcracks. But wait: what’s that blurry, whitish bump in the lower left corner?

Why, that’s a trilobite resting trace, the first ever found in this formation and locality. Thanks for the Dolfing, Dolf. (Both photographs by Anthony Martin, taken near Ringgold, Georgia in November, 1997.)

Don’t quite see the trilobite resting trace fossil, and you think it’s a just a random bump on that rock surface? Here’s an illustration by Dolf that should help to enlighten. Take a look at the left-hand side of this figure with his depictions of trilobite resting traces, then look again at the photograph of the “random bump.” Yes, that’s right: you’re wrong. And you know what? It’s perfectly fine to be wrong in science. Just make sure you learn from your mistakes. (Figure from: Seilacher, A., 2007, Trace Fossil Analysis, Springer, p. 39.)

The rest of the field trip seemed almost anti-climatic after Dolf’s discovery, but it was still quite enjoyable. We left the quarry site and walked along the roadcut itself for the next few hours, stopping to look at whatever caught our attention. Its titled strata meant were were going forward in geologic time, from oldest to youngest (Middle Ordovician –> Early Silurian). This provided a nice lesson for the geological novices in our group in how to interpret changing environments through time. We found more trace fossils, and even a few body fossils, giving everyone plenty of paleontological stimulation to get them through that day and beyond.

Dolf Seilacher, master ichnologist and consumate teacher. We will greatly miss his pointing out the obvious to the oblivious. (Photograph by Anthony Martin, taken near Ringgold, Georgia in November, 1997.)

When it came time to leave, we walked out with Dolf, feeling exceedingly grateful for his requesting this trip. Later, we joked with him about the success of his “first visit to Georgia.” Alas, we did not know then that it would also his last. Nonetheless, what remains are the provocative thoughts and methods he imparted on so many of us during his brief time here, no doubt inspiring future generations of paleontologists, ichnologists, and all others interested in learning about the wondrous history of the earth.

A group picture following our field trip with Dolf Seilacher to northwest Georgia in November 1997 (and much gratitude to whoever suggested it and took it). For me (far right, big hat), the road behind us seems to symbolize a trail he blazed for us to follow. Thanks for all of the cognitive traces, Dolf: may they continue to reach into the fossil record.

Reference

Seilacher, A. 2007. Trace Fossil Analysis. Springer, Berlin: 226 p.

Life Traces of a Master: A Tribute to Dolf Seilacher (Part I)

Posted on May 8, 2014 by TMartin

Every paleontologist has a Dolf story. Or at least it seems that way, especially for the past couple of weeks. One-by-one, like feather-duster worms poking their heads out of burrows, these stories have all emerged since the paleontological community heard the sad news that Adolf (Dolf) Seilacher died on April 26, 2014.

This manifestation of Dolf connecting with so many paleontologists over multiple generations symbolizes his ultimate and most lasting trace as a scientist and teacher. During his 89 years with us, he observed, discovered, pondered, argued, and argued more over the evidence that life left in the rocks of the past 600 million years or so. Much of this evidence is preserved as trace fossils, the vestiges of animal behavior that imparted their former presence as burrows, trails, tracks, feces, or other signs of life that almost never connect to their undoubted makers. Although Dolf was no slouch when pontificating on the bodily remains of ancient animals, either, it was with trace fossils where he truly excelled.

Adolf (“Dolf”) Seilacher in his natural habitat, teaching students and professors alike when in the field. Notice how he was using paper and pencil as tools, which were instrinsic to his teaching methods. (Photo taken by Anthony Martin at Ringgold, Georgia in November 1997; Dr. Sally Walker (right) for scale.)

Dolf is often acknowledged as the founder of modern ichnology, the study of traces and trace fossils. Through this science, he could divine the original intents and purposes of trilobites, worms, clams, snails, shrimp, fish, pelycosaurs, dinosaurs, and many other former denizens of the earth. He accomplished this Sherlockian feat through the careful examination of ancient animals’ signatures, or the jots and tittles in those signatures: miniscule clues he reconstructed as entire manuscripts or symphonies that spill their secrets to those who pay heed. Dolf’s marvelous ability to spin fossil gold from carbonized straw is most of what inspired the many stories we paleontologists tell about him, although his personality was intrinsically linked to this, too (more on that later).

Nonetheless, what was truly remarkable about how Dolf worked his ichnological magic was his use of such old-fashioned methods. What were his primary tools for observing? His eyes, brain, pencil, paper, and drawing: no laser scanners (let alone “laser cowboys”), CT imaging, digital photogrammetry, rotating 3-D visualizations, or other modern technological tools were necessary for what he did. If someone had a time machine, they could have inserted Dolf into the late 19^th century among the naturalists of those days, and he would have blended. Paradoxically, though, we 21^st century paleontologists remember him as someone who surpassed all of us with his observational and intuitive skills. In this sense, he was a reminder of the readily available and valuable means we already possess that allow us to make sense of our planet and its vast history.

The Hand of Dolf, drawing onto a Middle Jurassic trace fossil (Zoophycos) to teach me and others how it was made by worm-like animal on a deep seafloor about 170 million years ago. (Photograph taken by Anthony Martin in Switzerland, 2003.)

A composite trace (drawings plus writings) made by Dolf and me. The central figure is a visual explanation he drew for me, showing how one could figure out whether the Zoophycos-making animal was moving down below the sediment surface (protrusive) or moving up (retrusive) as it burrowed. Under his watchful eye, I then parceled out the details below. Field notes and drawings done on July 16, 2003, at the outcrop indicated in Switzerland.

Still, Dolf vigorously disagreed whenever anyone praised him as an “artist,” insisting he was a mere illustrator. With all due respect to his memory, he was wrong on this, and most of the paleontological community likewise rejected such statements. He was a fine artist and scientist, inseparably partnered in one person.

One of many examples of how Dolf Seilacher was both a scientist and an artist, in which through drawing he interpreted a series of movements made by a trilobite along an Early Cambrian seafloor, more than 500 million years ago. (Figure from Seilacher, A., 2007, Trace Fossil Analysis, Springer: p. 27. If you support the unification of science and art, then you must get this book.)

Like all students of paleontology who took their first toddling steps in the 1970s-80s, I first learned of Seilacher through his papers. In those readings, I also soon realized the most effective way to discern the key points of his papers was to skip straight to his exquisite illustrations. Following a long tradition of German artist-scientists, such as Albrecht Dürer, he could accurately reproduce what might have been evident from a photograph of a trace fossil, or the specimen itself. Yet the salient qualities of a trace fossil were somehow more deeply understood – and thus better communicated – through his drawing of that specimen. His illustrations often impelled a viewer to take a second, third, or fourth look at a trace fossil, prompting more learning and often provoking marvel at what he perceived.

In some instances, he “cheated” in his drawing by using a camera lucida. This is a clever device that, through a prism, projects the image of a subject onto paper, where its proportions and details can be traced and thus captured accurately by the person drawing it. However, in Dolf’s drawings, his tracings were often fortified and embellished with dramatic black-and-white contrast rendered by pen and ink. Even better, these so-called “illustrations” were used as launching points for interpretive drawings that presented provocative explanations for how a trace fossil was made. Sometimes he even added a whimsical touch to these figures, such as placing a little windmill next to the cross-section of a marine-invertebrate burrow. Was this science, or was this art? Yes.

When did I first meet Dr. Adolf Seilacher, a person many other paleontologists and I would later casually call “Dolf”? It was on a Geological Society of America field trip in Cincinnati, Ohio, in the fall of 1992. In retrospect, I was extremely lucky with that first meeting to watch him perform his expertise – and it was always a performance – in the field, rather than the sterile confines of a convention hall or conference room.

On this field trip, we paleontologists were looking at outcrops in the Cincinnati area, which bear some of the best Late Ordovician fossils (about 445 million years old) in the world. Among these fossils are brachiopods, bryozoans, snails, clams, crinoids, and other animals – such as trilobites – that have no living relatives today. You can walk up to most of these outcrops, close your eyes, and scoop up a handful of these fossils. I had also done my M.S. thesis in this area, so it was a trip back to familiar territory, and some of the fossils felt like old friends: I mean, really old friends.

Yet thanks to Dolf, these body fossils were not the stars of the field trip that day. When we went to an outcrop with numerous U-shaped burrows preserved in its limestones – trace fossils the field-trip leaders called Rhizocorallium – I witnessed his scientific process at work. After we had all listened to the field-trip leaders give their interpretation of the burrows, he sat down next to one of these trace fossils, and for about 10 minutes, he quietly drew in his field notebook. Gradually, some of us gathered around to see what had attracted his attention and we watched him draw. Once he had a critical mass for what he considered an adequate audience, he began sharing his thoughts, a didactic lecture accompanied by more drawing as he explained his conception of how the burrows were made by small animals living in a shallow sea hundreds of millions of years before that moment.

A field-trip memory expressed through drawing: my recollection of what Dolf Seilacher illustrated in his field notebook in October 1992 while explaining a 445-million-year-old burrow and how it was made. The burrow is the main U-shaped structure, and the lines in between are spreite, showing where the former location of the animal’s burrow. In my illustration here, the animal – either a small arthropod or worm – adjusted its burrow downward into the sediment, then to the right. The behaviors recorded here may have been from the animal feeding, reacting to changes in the surrounding sediment, or a combination of ecological cues.

“You see, this so-called ‘Rhizocorallium’ is just the beginning of a Zoophycos,” he said with his patented Teutonic confidence mixed with professorial charm. He then drew more in his field notebook to show what he meant, a slow-motion visualization that delivered his lesson unambiguously. In his estimation, the U-shaped burrow, which had curved lines showing where the animal had moved it, was only the start of a more complex feeding probe. In Dolf’s assessment, one trace fossil (what ichnologists would call Rhizocorallium) could have thus easily merged into another form, one we would then assign another name (Zoophycos). This was a clarifying moment for me as a young scientist and educator about the communicative power of drawing. As a result, I have tried to use drawing in my research articles, books, and teaching ever since.

Based on this sample of one, I did not know then that Dolf’s “hijacking” of field trips was a time-honored tradition for him. Moreover, I did not know then that nearly every paleontologist who had ever disagreed with him, or presented a hypothesis he somehow found lacking, was running the risk of being subjected to an intense and aggressive interrogation that over the years was nicknamed “Dolfing.”

“Dolfing” in action, in which Dolf Seilacher would ask a series of penetrating questions as a follow-up to a helpful statement informing the “Dolfee” that she/he is completely wrong about everything ever. And just to show how no one was excused from potential “Dolfing,” regardless of their accomplishments and seniority, here he is subjecting Dr. Roland Goldring (1928-2005) to this treatment, just like he would have done to a well-meaning but woefully misguided graduate student. (Photograph by Anthony Martin, taken in Basel, Switzerland in July 2003.)

This harrowing critique was equal opportunity, in that he applied it to graduate students, senior professors, and everyone in between. For Dolf, getting the science right was far more important than honoring silly academic hierarchies. Although “Dolfing” occasionally caused discomfort in those getting “Dolfed,” these lopsided personal lectures often resulted in more details emerging, clearer explanations, and deeper understanding about a paleontological problem, meaning both the “Dolfer” and “Dolfee” learned more in the process. “Dolfing” became such a badge of honor, graduate students even wished for it to happen (“I’ve been Dolfed!”, they would say excitedly after surviving such an encounter.) One paleontologist friend of mine – after a colleague and I described “Dolfing” to her – said wistfully, “Oh…I want to be Dolfed!”

It was with much pleasure, then, that I got to watch “Dolfing” happen again during a field trip to the Cretaceous-Paleogene stratigraphic boundary in Recife, Brazil in 1994. This was when the “end-Cretaceous meteorite” hypothesis was still debated fiercely at professional meetings, with both proponents and skeptics fighting over the evidence. Preceding the field trip was a morning symposium on this contentious topic, much of which dealt with the 65-million-year-old boundary exposed at a nearby outcrop we would see later that afternoon.

In this session, one of the geologist speakers referred to a “massive” deposit of limestone as a tsunamite (a deposit formed by a meteorite-induced tsunami), which we were all supposed to see on the field trip. As soon as this speaker finished and the question-answer period began, Dolf sprang to his feet and declared, “You realize, of course, that if we find one burrow, it will completely negate your hypothesis.” Very simply, an animal would not have continued burrowing blithely on and in the ocean sediments while a gigantic sea wave washed over it. The speaker, taken aback by Dolf’s confident pronouncement, simply repeated that the deposit was “massive,” meaning it lacked any defined layering (bedding), and had no burrows. Ichnologists know better, though, as we sometimes translate “massive” as “There’s no bedding because it’s been completely burrowed, you ichnologically ignorant geologist!”

Dolf’s statement turned out to be a prophetic one. Later that afternoon, we field trip participants walked along the outcrop, looking at the layer of limestone interpreted as a meteorite-induced “tsunamite.” Sure enough, within ten minutes of inspecting, I found a burrow. Acting as a field-trip troll, I called out, “Oh Dolf, look what I found!” He came over and confirmed that yes indeed, it was a burrow, he quickly spotted dozens more, and the rest of the field trip was his for the taking. Many of the participants on the trip sat back and watched the fireworks, enjoyed the show, and we very nearly applauded at the end. Although I felt a little sorry for the field-trip leaders, it served as a good reminder that all you need is one burrow (or its factual equivalent) to upset a hypothetical apple cart.

Dolf Seilacher (left) delivering the intellectual equivalent of a bolide impact while standing in front of an outcrop containing evidence from the Cretaceous-Paleogene boundary. (Photograph by Anthony Martin, taken in 1994 near Recife, Brazil.)

After such a memorable conference and field trip, when would Dolf and I cross trails again? Not until 1997, and through my initiative and in my backyard, here in Georgia. But that story is worth its own post, one I promise to tell next time.

(To Be Continued)

Reference (Which is Also Quite Likely the Best Book Ever Done on Trace Fossils That Also Includes Some Incredible Artwork):

Seilacher, A. 2007. Trace Fossil Analysis. Springer, Berlin: 226 p.

‘Dinosaurs Without Bones’ Leaves Its First Marks

Posted on March 6, 2014 by TMartin

Life Traces of the Georgia Coast was published just a little more than a year ago, which as far as authoring goes, seems like yesterday. (Well, unless you’re James Patterson.) Yet as of now, it’s now my second-most recent book.

Hey, look: it’s a book. How about that? (Photograph by the person whose name is on the cover.)

So I’m proud to announce today is the official launch date of my latest book, Dinosaurs Without Bones: Dinosaur Lives Revealed by Their Trace Fossils (Pegasus Books). What’s it about? Yeah, I know, the main title implies the existence of invertebrate or incorporeal dinosaurs. But the subtitle makes clear that it’s all about the fossil record of dinosaurs apart from just their bones: tracks, nests, burrows, toothmarks, gastroliths, feces, and much more. It’s not only the first comprehensive book written about dinosaur trace fossils, it’s my first overt attempt at popular-science writing in book form. How was it for me? Great fun, and I hope readers feel the same about it.

In a sure sign that authoring might be addictive, I started writing Dinosaurs Without Bones before the publication of Life Traces of the Georgia Coast. The latter book took nearly four years to complete, from proposal to holding that rather hefty volume in my hands. In contrast, I wrote and illustrated Dinosaurs Without Bones in just a little over a year, starting in the summer of 2012 and finishing in December 2013.

This marsupial-like gestation for Dinosaurs Without Bones can be attributed to several fortunate factors coming together, such as my having written two editions of a college textbook on dinosaurs (Introduction to the Study of Dinosaurs, 2001, 2006), writing about dinosaur trace fossils in a 2010-2011 blog (The Great Cretaceous Walk, now defunct), having the fresh experience of writing Life Traces of the Georgia Coast, and the freedom to write with a popular audience in mind. Write? Right.

Although today seems like a firm starting point for its availability to readers, it’s actually been in an incremental “soft launch” during the past few weeks. For example, my publisher made it available for sale by Charis Books in Atlanta, Georgia when I gave a talk to the Atlanta Science Tavern at their annual Darwin Day Dinner on February 9. Other people have told me via Facebook, Twitter, and in person that their pre-ordered copies had already arrived last week. Then just last week, I had a bit of a coming-out party for the book at the annual Science Online 2014 meeting, where it was among the featured new science books, which were all given away in a raffle to lucky meeting participants.

My colleague Paleontologist Barbie, happily posing next to Dinosaurs Without Bones during its first big public viewing at the Science Online 2014 meeting last week in Raleigh, North Carolina. (Photograph by the author again. Unfortunately, Paleontologist Barbie’s arms, much like those of a tyrannosaur, are too short for her to do a selfie.)

I know what you’re thinking: Where can I buy this book? (Your second most likely question is: Does it mention cats? The answer is yes, several times.) If you do get the book and read it, please let me know what you think of it, either via Twitter (@Ichnologist), its Facebook site, e-mail, or most retro of all, in person. Here’s a list of suggested means for acquisition:

Your local independent bookstore. Tell the owner I sent you.
Order it directly from Pegasus Books here.
Order it from Powell’s Books here.
Order it from Barnes and Noble here.
Order it from that online business that’s trying really hard to make all of those other just-mentioned businesses go extinct. (And I ain’t naming it, because that gives it more power.)

Thanks, hope you like it, and happy tracks, trails, nests, and burrows to you.

Pertinent Bibliography

Martin, Anthony J. 2014. Dinosaurs Without Bones: Dinosaur Lives Revealed by Their Trace Fossils. Pegasus Books, New York: 460 p.

Recent Signs of Life

Posted on March 4, 2014 by TMartin

Following a flurry of dozen posts in December 2013 loosely inspired by The 12 Days of Christmas, this site has been morbidly silent, a veritable vacuum of verbosity. This was probably a good thing, as my life has been occupied by a few other tasks and events, and will be in the near future. So in the proud tradition of Buzzfeed and other Web sites that rely on enumerated click bait for their traffic, here are the top five reasons why I haven’t been blogging lately.

5. I finished writing a book. Titled Dinosaurs Without Bones: Dinosaur Lives Revealed by Their Trace Fossils (Pegasus Books), I’ve been working on it since the summer of 2012, and I’m now holding it in my hands, which is a sure sign that it’s done. Overall, I’m very pleased with how it came out, and even more pleased that it’s out and available for others to enjoy reading. What’s it about? Just re-read the title, but if you’re still not quite sure, I guess you’ll have to get the book and read the whole thing.

Here’s a trace of what I’ve been thinking and writing since 2012. Hope you like it. (Photograph by Anthony Martin, taken at home.)

4. I taught a field course in the Bahamas. Once every two years, I organize and teach a field course for Environmental Sciences students at my university. This course, which lasts about 10 days, is held during winter break at the Gerace Research Centre on San Salvador Island, Bahamas. Yes, I know, you’re thinking the following: “Can I go?” “Do you need a field assistant?” “That must be nice!” “Poor baby!” [the last of these said sarcastically]. No offense, but I don’t think you would last a day in this course. (Yes, you. And especially you.) It’s a physically demanding course, with land- and water-based field work every day, along with nighttime lectures and discussions, and that happens all before everyone walks 3 km to the nearest bar. Nonetheless, it’s a wildly successful course, in which my initially scared-of-the-outdoors-and-anything-alive-or-dead students are transformed into something approaching field-hardy scientists by the end of their time on the island. I’ll write separately about our latest experiences in an upcoming post, so be looking for that.

Once every two years, this is my classroom. Notice how I even got a student to teach everyone else that day. Not seen in this photo? Fruity drinks with paper umbrellas. (Photograph by Anthony Martin, taken on San Salvador Island, Bahamas.)

3. I gave my first public talk about the new book. First, let me heap some praise on one of the most awesome organizations in the Atlanta area, the Atlanta Science Tavern. With nearly 4,000 members, the Atlanta Science Tavern organizes several science-related talks and events held each month, they’re involved in the upcoming Atlanta Science Festival, and in charge of the Science Track at the Decatur Book Festival, all of which I reckon makes them a force to be, well, reckoned with. Anyway, they invited me to speak about my book as part of their annual Darwin Day Dinner event last month, and I happily complied. It was also great fun being the warm-up act for paleobotantist (and friend) Dr. Melanie DeVore, who spoke later that evening taught us about Darwin’s connection to the “abominable mystery” surrounding the evolution of flowering plants.

2. I co-wrote and submitted a research paper. Sometimes when I’m on San Salvador Island and teaching my students in the field, we make discoveries. So when someone tells you matter-of-factly that teaching and research rarely converge, this pronouncement can be, like, totally falsified when you’re teaching outside of a classroom. Which is to say, outside.

For example, on December 30, while with my students at an coastal limestone outcrop on San Salvador, my student teaching assistant (let’s call her “Meredith”) pointed to some features and said, “Hey Dr. Martin, are these ___________?” To which I replied, “Why yes, I think those are ______________!” (I’d be glad to tell you what they are, but first they have to go through peer review.) So in the past few months, I wrote a draft of a short research paper reporting the find, “Meredith” added her editing suggestions, and we submitted it to an open-access journal for possible publication. But what was really neat about this discovery was that we shared it with the other students in the field, right then, right there, and used it as a teaching lesson on what you should do when making a potential fossil discovery in the field. Take that, false dilemma!

What is life, but a coastal limestone outcrop with a paleosol that is daily immersed by tides and inundated by waves, awaiting discovery of its hidden trace fossils, which are revealed by those same tides and waves? And by the way, watch out for those waves. (Photograph by “Meredith” – which may or may not be her real name – and taken on San Salvador Island, Bahamas.)

1. I’ve been teaching (more so). No matter how much it might pain pundits who love to bash those unproductive academics for their non-existent class loads, cushy tenure, exorbitant pay, and – most galling of all – academic freedom, I’ve been teaching 40+ students this semester in two classes, advising a senior honors-thesis student, and helping other students pick out courses for study-abroad programs. Incidentally, I’m also not tenured, my pay is far lower than that of the aforementioned pundits make, and I have no academic freedom (see previous statement about lack of tenure).

For a good summary list of what professors actually do in their jobs, read this. But if you’re one of those people who won’t have your mind changed by evidence-based reasoning, then by all means go back to watching your favorite cable-news show and watch people shout at one another about how climate change is a hoax, whether or not mermaids and Megalodon (or, better yet, a mermaid-eating Megalodon) really do exist, and other fascinating fare. Regardless, I’ve had fun teaching these two classes, although I’m guilty of putting off grading the Bahamas field-course reports. Que sera, sera.

0.5. (Bet you thought you were done, didn’t you?) I attended two conferences in the past few weeks. The first conference is one that meets only once every five years, the North American Paleontological Convention. It’s normally a wonderful conference, and this one – held in Gainesville, Florida and hosted by attended by about 500 paleontologists of all types – was no exception. Indeed, it’s one of the few times we can get micropaleontologists, paleobotantists, invertebrate paleontologists, vertebrate paleontologists, taphonomists, and even ichnologists under the same roof. Other than learning heaps from my paleontological ilk, I presented a talk summarizing Cretaceous trace fossil research I’ve done with colleagues in Victoria, Australia since 2006, and other colleagues of mine at the North Carolina Museum of Natural Sciences and I co-authored a poster about Ediacaran fossils in North Carolina.Here’s that poster on Ediacaran fossils from North Carolina, coauthored with Patricia Weaver and Chris Tacker from the North Carolina Museum of Natural Sciences. Notice it’s also undergoing peer-review by our hero, Paleontologist Barbie. Is there nothing she can’t do? (Photograph by Anthony Martin, taken in Gainesville, Florida.)

The other conference, still fresh on my mind, was Science Online 2014, which was held in Raleigh, North Carolina last week. It was my first time to this conference, and my main reason for going was to promote my book, which was on display there and being given away to lucky attendees in a raffle. But I also had the nice fringe benefits of meeting many very nice (and very smart) folks from the science-communication community who I had only known previously through digital media, while also learning much about online-science communication during sessions on a variety of topics. From what I gathered, a good time was had by most.

What’s coming up in the next future? Plenty! For one, Dinosaurs Without Bones is officially released this Thursday, May 6, 2014. So I’ll probably have something to say about that. Ta-ta for now, and thanks for reading about my latest signs of life, which may or may not preserve in the fossil record.

On the 1st Day of Ichnology, My Island Gave to Me: 1 Sea Star Gliding

Posted on December 26, 2013 by TMartin

The last of my holiday-inspired series of photos depicting traces from the Georgia barrier islands is of one most people will see only rarely, but is a glorious one to spot. It is the trail left by a lined sea star (Luidia clathrata), best observed on the lower parts of sandy beaches.

A beautifully expressed trail left by a lined sea star (Luidia clathrata). The sea star itself is only about 10 cm (4 in) across, but its trail shows how far it traveled, from its initial “resting” spot to where you see the tracemaker itself. (Photograph by Anthony Martin, taken on Sapelo Island.)

Sea stars make such trails when stranded on the lower part of a beach by a high tide. Once exposed, especially under a summertime sun, they can either dry out quickly or become easy prey for a wandering seagull. If they’re fortunate enough to be on or otherwise near a saturated sand, they’ll bury themselves by moving their hundreds of tube feet underneath them. This makes a sort of localized quicksand around them, and they will sink into the sand, which normally solves their dual problem of dehydration and predation. However, the resulting trace this makes is a star-shaped bump on the sand surface, which to many seagulls still translates as “food.” Many times I have seen and photographed spots on beaches where a gull was practicing its own form of ichnology, where it walked straight to a buried sea star, plucked it from its temporary resting spot, and took it somewhere else to eat.

In this photo, though, the sea star had an even greater challenge when it was left on a sandflat. It was dumped by a high tide onto a part of the beach with a thin layer of wet sand overlying a more firmly packed sand. This meant that the sea star’s tube feet could only get it so far down into the sand, having been stopped by the hard, packed layer underneath. So its only other choice was to move laterally along the wet sand, which it accomplished through a combination of tube feet and arms, causing it to glide through and on top of the sand.

My interpretation of this behavior is that the sea star was desperately seeking moisture – whether a softer, wetter sand or a submerged area – and that this journey was more likely to ensure its survival than to simply sit and wait for the next tidal cycle. Considering that sea stars have been around for more than 450 million years, I can only assume this behavior worked quite well for at least of few of this species’ ancestors. Thus I would not be surprised at all by the discovery of trace fossils matching the form and intent of the modern traces shown here.

Meanwhile, let’s give thanks for how lucky we are to see them and understand the meaning of these and other traces being made by Georgia-coast animals every day. Each vestige is a lesson in natural history, beckoning us to learn more about the evolutionary processes that led to what we observe now.

Further Information

Luidia clathrata: Lined Sea Star. Encyclopedia of Life.

Links to Previous Posts in This Theme

On the 12th Day of Ichnology, My Island Gave to Me: 12 Snails Grazing

On the 11th Day of Ichnology, My Island Gave to Me: 11 Plovers Probing

On the 10th Day of Ichnology, My Island Gave to Me: 10 Beetles Boring

On the 9th Day of Ichnology, My Island Gave to Me: 9 Molluscans Hiding

On the 8th Day of Ichnology, My Island Gave to Me: 8 Crab Legs Walking

On the 7th Day of Ichnology, My Island Gave to Me: 7 Lizards Looping

On the 6th Day of Ichnology, My Island Gave to Me: 6 Hatchlings Crawling

On the 5th Day of Ichnology, My Island Gave to Me: 5 Bivalves Drilling

On the 4th Day of Ichnology, My Island Gave to Me: 4 ‘Gators Denning

On the 3rd Day of Ichnology, My Island Gave to Me: 3 Ghost Shrimp Pooping

On the 2nd Day of Ichnology, My Island Gave to Me: 2 Otters Running

On the 2nd Day of Ichnology, My Island Gave to Me: 2 Otters Running

Posted on December 25, 2013 by TMartin

On this Christmas of 2013, I thought that the second-to-last post of my “On the __th Day of Ichnology” series would be a gift, one speaking of the beautiful harmony we sometimes are so fortunate to see recorded in the sands of the Georgia barrier islands. The traces composing this gift are the tracks of a male-female pair of river otters (Lutra canadensis).

Synchronicity expressed in traces: a pair of river otters, running and turning together along a Georgia beach. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia; scale is about 10 cm (4 in) long.)

A normal gait for river otters is a lope, which registers as a 1-2-1 pattern, in which one rear foot is in front, a rear and front foot are next to one another, and a front foot is behind. However, in this instance, I think both otters were galloping, as it looks like both rear feet exceeded their front feet, and a well-defined space is in between each set of four tracks.

What really struck me about these tracks, and made me gasp with joy when I saw them, was their near-perfect symmetry and how they hint of one otter reacting to the other otter’s movement. I can’t say for sure right now what evidence lends to my discerning the following interpretation (sorry, fellow scientists). But my hunch is that the otter on the left was running just in front of the other, maybe separated by a body length at this point, and then turned just slightly to her/his left. The otter on the right was galloping to catch up, saw its partner turn to the left, and decided to turn her/his body in response to this change in direction. Notice how the gap between their trackways is narrowed just a bit, and how the tail of the second otter left an arc-like impression on the sand that points directly to the next set of tracks.

Such a gorgeous set of traces, left by a species we humans often revere (or envy) for its love of play! But I also found these tracks even more gratifying for how they told of two otters linked to one another, perhaps through play, but certainly through their mirrored behaviors, and how this in turn held up a mirror to ourselves. What interactive traces do we similarly leave in our lives? In which instances are we the otter on the left, leading the way and making decisions to change course? In which instances do we follow just behind and to the side of others, and run to catch up? Why do we sometimes lead, why do we sometimes follow, and what makes us come together? Thoughts for Christmas, thoughts for the end of this year, and thoughts for the start of a new year, bestowed by the symbolism of these traces.

Links to Previous Posts in This Theme

On the 12th Day of Ichnology, My Island Gave to Me: 12 Snails Grazing

On the 11th Day of Ichnology, My Island Gave to Me: 11 Plovers Probing

On the 10th Day of Ichnology, My Island Gave to Me: 10 Beetles Boring

On the 9th Day of Ichnology, My Island Gave to Me: 9 Molluscans Hiding

On the 8th Day of Ichnology, My Island Gave to Me: 8 Crab Legs Walking

On the 7th Day of Ichnology, My Island Gave to Me: 7 Lizards Looping

On the 6th Day of Ichnology, My Island Gave to Me: 6 Hatchlings Crawling

On the 5th Day of Ichnology, My Island Gave to Me: 5 Bivalves Drilling

On the 4th Day of Ichnology, My Island Gave to Me: 4 ‘Gators Denning

On the 3rd Day of Ichnology, My Island Gave to Me: 3 Ghost Shrimp Pooping

On the 3rd Day of Ichnology, My Island Gave to Me: 3 Ghost Shrimp Pooping

Posted on December 24, 2013 by TMartin

Everyone poops. More specifically, every animal has to eat, converting this food into energy and otherwise applying it to bodily functions. As we also know through daily experience, this conversion is never 100% efficient. Thus waste is produced and excreted from all animal bodies, sometimes liquid, sometimes solid, or a mixture of the two.

And on the Georgia barrier islands, few animals are more visibly productive with their poop than ghost shrimp. So today’s photo and explanation celebrates those wondrous poopers of the Georgia coast.

We three burrows of Georgia coast are adorned with feces, showing that each of us is actively occupied by a ghost shrimp. In each burrow, the shrimp is probably just below the narrow aperture, doing a little housecleaning. (Photograph by Anthony Martin, taken on Jekyll Island, Georgia.)

I’ve written previously about ghost shrimp – otherwise known as callianassid shrimp – and the significance of their burrows to ecologists, geologists, and paleontologists (linked under “Further Reading”). But I haven’t focused on one of their most important roles as ecosystem engineers, which is their prolific pooping of pellets.

These pellets are small, dark, perfectly shaped cylinders that, because of their resemblance to “chocolate sprinkles,” never fail to capture the attention of cupcake lovers as they stroll along Georgia beaches. (Now that you know what they are, please don’t eat them. Unless you like them, in which case, I’m never buying a cupcake from you.) However, aside from inspiring confectionery allusions, these pellets are extremely important in Georgia beach environments as sources of mud.

Only two species of ghost shrimp are responsible for all of this mud dumping, the Georgia ghost shrimp (Biffarius biformis) and Carolina ghost shrimp (Callichirus major). Nonetheless, they make up for their lack of diversity through sheer numbers; look closely at most Georgia beaches at low tide and you will see thousands of little “sand volcanoes,” most with pellets. Nearly all of these represent a live ghost shrimp, down below your feet, burrowing, feeding, mating, and pooping.

After feeding on mud-rich organics in their burrows, these shrimp make and emit mud-rich fecal pellets, neatly shrink-wrapped by mucus. The shrimp can then collect these packets of poop and pump them out the tops of their burrows, an efficient form of waste disposal that keeps their homes clean. These pellets become the hydrodynamic equivalent of sand grains, rolling with the tides and waves and are commonly deposited in ripple troughs and other low spots on a sandy beach.

Eventually their mucus coverings break down and release the mud particles (silt and clay), but at least these sediments were deposited. This would almost never happen on its own because of tides and waves keeping it suspended in the water, and means that the mud would be much less likely to get recycled into coastal sediments, and Georgia coastal waters would be even muddier than normal.

So take note, geologists: those thin layers of mudstone you see in the troughs of a rippled sandstone that you might just label “flaser bedding” in your field notebook, then promptly forget? Those beds probably got there by something pooping in the ancient past. And for everyone else, give thanks for these gift-wrapped feces, and for what they do for Georgia coastal environments.

Further Reading

The Lost Barrier Islands of Georgia. Written by me, posted October 3, 2011.

Ghost Shrimp Whisperer. Written by me, posted May 20, 2013.

Links to Previous Posts in This Theme

On the 12th Day of Ichnology, My Island Gave to Me: 12 Snails Grazing

On the 11th Day of Ichnology, My Island Gave to Me: 11 Plovers Probing

On the 10th Day of Ichnology, My Island Gave to Me: 10 Beetles Boring

On the 9th Day of Ichnology, My Island Gave to Me: 9 Molluscans Hiding

On the 8th Day of Ichnology, My Island Gave to Me: 8 Crab Legs Walking

On the 7th Day of Ichnology, My Island Gave to Me: 7 Lizards Looping

On the 6th Day of Ichnology, My Island Gave to Me: 6 Hatchlings Crawling

On the 5th Day of Ichnology, My Island Gave to Me: 5 Bivalves Drilling

On the 4th Day of Ichnology, My Island Gave to Me: 4 ‘Gators Denning

On the 4th Day of Ichnology, My Island Gave to Me: 4 ‘Gators Denning

Posted on December 23, 2013 by TMartin

For today’s photo and explanation of traces of the Georgia barrier islands that beguile, I’ll turn to one of the more charismatic and well-known of tracemakers, and what are among the largest traces of any animals on the Georgia coast. These would be alligators (Alligator mississippiensis) and alligator dens, respectively.

See those two big holes just above the shoreline of this freshwater pond? Those are alligator dens, large burrows that benefit them in many ways. And just to prove this point, these two dens have a pair of alligators hanging out at their entrances. Both alligators are only about 1 meter (3.3 feet) long, though, which means they’re way too small to have been the alligators that made these dens. So what’s going on here? (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)

I’ve written several times before about alligator dens on the Georgia barrier islands, and these are a subject of on-going research for me and several colleagues. So I won’t go on about them here, and instead will just focus on what this specific photo of these dens and alligators tells us.

The picture was taken in March, 2011, at the start of spring on the Georgia coast. Hence the alligators might have been just then coming out of dens after overwintering in them. However, notice the mismatch in sizes of the alligators compared to the den entrances. The dens are much too large for their denizens, implying that these are not their original makers, but instead are secondary occupiers, reusing these dens. I was also surprised to see five alligators – all about the same size – sharing dens. Yeah, I know, the title of this post says “four ‘gators denning,’ but you’re only seeing four of them in the photo; the one on the right had at least three I saw that day.

A little bit of background might help with understanding what was happening there and then. I’ve been revisiting this freshwater pond on Sapelo Island for nearly 15 years, and can confirm that these are the same dens. Sometimes I’ll see evidence of alligators actively using them, as in, I see alligators lying at their entrances, and alligators that retreat into these dens if they get too shy from all of the enthusiastic ichnologically inspired love I’m sending their way.

Sometimes those alligators have been large, full-sized adults with body widths only slightly smaller than den widths. Other times the alligators will be most modestly sized, like these. Regardless, this shows that once a den is made, it can be used by many alligators of varying sizes, over more than a decade, and possibly over generations.

Something else interesting about this photo? All four of the visible alligators – and the one you don’t see that’s in the den to the right – were about the same length. Along with their congregating in the same location, this is a hint that they might have been siblings, having hatched from the same egg clutch and grown up together in this pond. Even better, their mother might have raised and protected them there by using one or both of these dens. This means that alligator dens might be passed down in families and occasionally shared out of necessity by family members. You know, just like us. Amazed? If so, thank ichnology for inducing that sense of wonder.

Further Reading

Into the Dragon’s Lair: Alligator Burrows as Traces. Written by me, published on this blog March 15, 2012.

Deconstructing an Ichnology Abstract, with Alligators. Written by me, published on this blog October 19, 2012.

What a Big Momma Alligator in Her Burrow Tells Us about Dinosaurs. Written by me, published on the BBC’s Walking With Dinosaurs site November 20, 2013.

Links to Previous Posts in This Theme

On the 12th Day of Ichnology, My Island Gave to Me: 12 Snails Grazing

On the 11th Day of Ichnology, My Island Gave to Me: 11 Plovers Probing

On the 10th Day of Ichnology, My Island Gave to Me: 10 Beetles Boring

On the 9th Day of Ichnology, My Island Gave to Me: 9 Molluscans Hiding

On the 8th Day of Ichnology, My Island Gave to Me: 8 Crab Legs Walking

On the 7th Day of Ichnology, My Island Gave to Me: 7 Lizards Looping

On the 6th Day of Ichnology, My Island Gave to Me: 6 Hatchlings Crawling

On the 5th Day of Ichnology, My Island Gave to Me: 5 Bivalves Drilling

On the 5th Day of Ichnology, My Island Gave to Me: 5 Bivalves Drilling

Posted on December 22, 2013 by TMartin

Today’s photo of Georgia-coast traces – similar to yesterday’s about sea turtles connecting to the land through their traces – shows how other marine animals depend on landward environments of the Georgia barrier islands for their livelihoods. In this instance, marine clams require trees to give them homes, and these clams leave marks of their dependency for us to see on formerly forest flotsam that made its way back to land.

A piece of driftwood rendered holey by abundant and active wood-drilling marine bivalves, some of which also left their bodies in their former homes. These borings are probably all the work of wedge piddocks (Martesia cuneiformis), which settled onto the wood as wee little clams (larvae, actually), then started drilling.(Photograph by Anthony Martin, taken on Jekyll Island, Georgia.)

After the larvae of these clams latched onto these woody substrates – whether these were floating on ocean currents or sunken on sea bottoms – they then lived out their lives drilling into the wood. They drill into wood by rotating or otherwise moving their ridged shells against the hard substrate, like a self-propelled screw.

A few species of wood-drilling clams – sometimes nicknamed “shipworms,” despite their molluscan heritage – actually eat the wood for food. But others, including wedge piddocks, are just making tight, secure homes, similar to how some animals make snug burrows for themselves. Once in a while we get to see the handiwork of these clams in pieces of wood that wash up on Georgia shorelines, a special delivery brought to us by tides and waves.

Wood-boring clams probably evolved about 150-200 million years ago during the Mesozoic Era, and their trace fossils are common in fossil driftwood from the Jurassic Period to just recently. For marine clams to start drilling into wood – whether for food, homes, or both – is pretty remarkable as a behavior, when you think about it evolving in response to the growth of forests on land. After all, bivalves lived in the world’s oceanscapes long before forests spread across landscapes, with the former starting in the Cambrian Period (more than 500 million years ago) and the latter starting in the Devonian Period (about 350 million years ago).

But it’s also interesting to think about how marine clams apparently did not take advantage of these terrestrial tissues for several hundred million years after wood first started floated out to sea. In contrast, mites, insects, and other land-dwelling invertebrates began chewing wood right away, and consequently left their own distinctive traces (mentioned last week with beetle borings). But thanks to trace fossils, we can better tell when terrestrial animals commenced wood-eating behaviors, and when certain marine clams began mixing their traces with those of their land-lubbing compatriots.

Further Reading

Martesia cuneiformis (Say, 1822) Wedge Piddock. Jaxshells.org, by Bill Frank, images by Joel Wooster.

The Second World That Forms on Sunken Trees. Ed Yong, Not Exactly Rocket Science, National Geographic Phenomena.

Wood: It’s What’s For Dinner. Craig McClain, Deep Sea News.

Links to Previous Posts in This Theme

On the 12th Day of Ichnology, My Island Gave to Me: 12 Snails Grazing

On the 11th Day of Ichnology, My Island Gave to Me: 11 Plovers Probing

On the 10th Day of Ichnology, My Island Gave to Me: 10 Beetles Boring

On the 9th Day of Ichnology, My Island Gave to Me: 9 Molluscans Hiding

On the 8th Day of Ichnology, My Island Gave to Me: 8 Crab Legs Walking

On the 7th Day of Ichnology, My Island Gave to Me: 7 Lizards Looping

On the 6th Day of Ichnology, My Island Gave to Me: 6 Hatchlings Crawling

On the 6th Day of Ichnology, My Island Gave to Me: 6 Hatchlings Crawling

Posted on December 21, 2013 by TMartin

For today’s photo of Georgia-coast traces and explanation of their meaning, we’ll look at some that are made only very briefly in the first moments of active life for their tracemakers, and in an environment very few of them will ever revisit. Moreover, those exceptional individuals who do make it back to the same environment – sometimes the same place where they took their baby steps – may take as long as three decades to do so. The traces are the trackways made by hatchling sea turtles, in this instance loggerhead turtles (Caretta caretta).

Yeah, I know, there are a lot more than just six sea-turtle hatchling trackways here, but it’s at least six. Regardless, they’re still in the spirit of the holiday season. These tracks were made only moments after the hatchlings emerged from a buried hole nest, which was behind coastal dunes on St. Catherines Island, Georgia. They hatched early in the morning of July 31, 2011 and promptly began making tracks. (Photograph by Anthony Martin; scale in centimeters.)

The trackways are relatively simple, consisting of alternating front-back flipper impressions and central body drag marks that are vaguely defined in dry sand (like in the photo) but become gorgeously expressed in wet sand. Overall trackway patterns tend to loop and intersect one another close to the nest as they tried to get oriented toward the sea, then become more linear and cross one another less often once they find the beach and waddle down slope. Trackways may be tens of meters long, depending on how far hatchlings must travel from their nests to the surf zone.

As an ichnologist, what I find remarkable conceptually about hatchling traces is knowing that their makers only leave traces on land for a few minutes after they’re born. All successfully hatched sea-turtle eggs are located in nests above the high-tide mark, and on the Georgia coast these are normally behind the first line of coastal dunes along a sandy shoreline. Then, assuming the hatchlings don’t die during their brief and vulnerable time on land (raccoons and herons and ghost crabs – oh my!) and that they do make it into the sea, almost all of their remaining tracemaking behaviors will be done in the Atlantic Ocean.

In other words, you’ll have to be very patient and relatively young to see traces made by those same individual turtles on Georgia beaches and dunes again, and these will only be from adult females. About 15-30 years pass before sea turtles reach sexual maturity, meaning it will take at least that long for pregnant mother turtles to come ashore. Even then, they do this seasonally, from about May through August, so you will only see adult female and hatchling tracks in the middle of any given year. Thus loggerheads and other sea turtles collectively are important tracemakers on the Georgia coast, but individually are rare.

For paleontologists, the huge trackways, covering pits, hole nests, and other marks of sea turtles comprise a trace assemblage with a great potential for preservation in the fossil record. Sure enough, sea turtle trace fossils have been reported from Cretaceous Period rocks in the western U.S. More are likely out there, and I have little doubt that these will be found by applying the right search images. Who will recognize the first trace fossils of sea-turtle hatchlings? My bet is that it will be someone who saw a lot of modern ones, perhaps even some from the Georgia coast. Good luck!

Further Information

St. Catherines Island Sea Turtle Conservation Program. (Mostly done by Gale Bishop.)

Georgia Sea Turtle Center. Jekyll Island, Georgia.

Links to Previous Posts in This Theme

On the 12th Day of Ichnology, My Island Gave to Me: 12 Snails Grazing

On the 11th Day of Ichnology, My Island Gave to Me: 11 Plovers Probing

On the 10th Day of Ichnology, My Island Gave to Me: 10 Beetles Boring

On the 9th Day of Ichnology, My Island Gave to Me: 9 Molluscans Hiding

On the 8th Day of Ichnology, My Island Gave to Me: 8 Crab Legs Walking

On the 7th Day of Ichnology, My Island Gave to Me: 7 Lizards Looping