Life can certainly imitate art, as can life traces. I was reminded of this last week while doing field work on St. Catherines Island (Georgia), and after encountering traces made by two very different animals, alligators and fiddler crabs. What was unexpected about these traces, though, was how they intersected one another in a way that, for me, evoked scenes from the recent blockbuster summer movie, Pacific Rim.
Could these be the tracks of a kaiju, making landfall on the shores of Georgia? Sorry to disappoint you, but they’re just the right-side and very large tracks of an American alligator (Alligator mississippiensis), accompanied by its tail drag-mark, left on a sandy area next to a salt marsh. Note the scale impressions in its rear-foot track, a symbol of the awesome reptilian awesomeness of its tracemaker. But wait: what nefarious nonsense is happening to the tail drag-mark, which is being covered by tiny balls of sand? Who made that hole next to the drag-mark? And what the heck was a raccoon (Procyon lotor) doing in the neighborhood, leaving its track on the tail drag-mark? With such a monster on the loose, shouldn’t that raccoon be hiding in the forest? (Photo by Anthony Martin, taken on St. Catherines Island; scale in centimeters.)
For anyone who has not seen Pacific Rim, you can read what I wrote about its distinctive fictional ichnology here. But what came to my mind while I was doing field work was one of the themes expressed early on in the film: how quickly humanity returned to normalcy following a lull in attacks by gigantic monsters (kaiju) that emerged from the ocean, destroyed major cities, and killed millions of people. It reminded me of how horrific hurricanes can strike a coast, such as the 1893 Sea Islands Hurricane that hit Georgia, but because no hurricane like it has happened there since, coastal developers think it’s hunky-dory to start building on salt marshes.
But enough about malevolent evil as exemplified by kaiju and coastal developers: let’s get back to traces. Last week, I was on St. Catherines Island for a few days with my wife (Ruth) and an undergraduate student (Meredith) to do some field reconnaissance of my student’s proposed study area. The area was covered by storm-washover fans; these are wide, flat, lobe-shaped sandy deposits made by storm waves, which span from the shoreline to more inland on barrier islands. We were trying to find out what traces had been left on these fans – tracks, burrows, scrapings, feces, and so on – which would tell us more about the distribution and behaviors of animals living in and around the washover fans.
Part of a storm washover fan on St. Catherines Island (Georgia), with the sea to the left and salt marsh (with a patch of forest) in the background. Say, I wonder what made those tracks coming out of the tidal creek and toward the viewer? (Photograph by Anthony Martin.)
It didn’t take long for us to get surprised. Within our first half hour of walking on a washover fan and looking at its traces, we found a trackway left by a huge alligator, split in half by a wavy tail-drag mark. I recognized this alligator from its tracks, as I had seen them in almost exactly the same place more than a year before. Besides their size, though, what was remarkable about these tracks was their closeness to a salt marsh behind the washover fan. When we looked closer, we could see long-established trails cutting through the salt-marsh vegetation, which were the width of a large adult alligator.
That ain’t no skink: the distinctive tracks and tail drag-mark of a large alligator, strolling through a storm-washover fan and next to a salt marsh. You think these animals are “freshwater only”? Traces disagree. Scale = 10 cm (4 in). (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)
Alligator trail cutting through a salt marsh. Trail width was about 45-50 cm (18-20 in), which is about twice as wide as a raccoon trail. And it wasn’t made by deer or feral hogs either, because, you know, alligators. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)
So although the conventional wisdom about alligators is that these are “freshwater-only” animals, their traces keep contradicting this assumption. Sure enough, in the next few days, we saw more alligator tracks of varying sizes going into and out of tidal creeks, salt marshes, and beaches.
Based on a few traits of these big tracks, such as their crisp outlines (including scale impressions), the alligator had probably walked through this place just after the tide had dropped, only a couple of hours before we got there. But when we looked closer at some of the tracks along the trackway, we were astonished to see that something other than the tides had started to erase them, causing these big footprints to get fuzzy and almost unrecognizable.
The culprits were sand fiddler crabs (Uca pugilator), which are exceedingly abundant at the edge of the storm-washover fans closest to the salt marshes. These crabs are industrious burrowers, making J-shaped burrows with circular outlines corresponding to their body widths. They also scrape the sandy surfaces outside of their burrows to eat algae in the sand, then roll up that sand into little balls, which they deposit on the surface.
In this instance, after this massive alligator had stomped through their neighborhood, they immediately got back to work: digging burrows, scraping the surface, and making sand balls. Within just a few hours, parts of the alligator trackway was obscured. If these parts had been seen in isolation, not connected to the clear tracks and tail drag mark, I doubt we would have identified these slight depressions as large archosaur tracks.
Hey, what’s going on here? Who would dare to erase and fill in giant alligator tracks? Don’t they know who they’re dealing with? (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)
Going, going, gone: alligator tracks nearly obliterated by burrowing, surface scraping, and sand balls caused by feeding of sand fiddler crabs (Uca pugilator). (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia; scale in centimeters.)
What was even neater, though, was how some of the fiddler crabs took advantage of homes newly created by this alligator. In at least a few tracks, we could see where fiddler crabs had taken over the holes caused by alligator claw marks. In other words, fiddler crabs saw these, said, “Hey, free hole!”, and moved in, not caring what made them.
Don’t believe me about fiddler crabs moving into alligator claw marks? OK, then what’s that I see poking out of that alligator claw mark (red square)? (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia; scale in centimeters.)
Why, it’s a small sand fiddler crab! Does it care that its new home is an alligator claw mark? Nope. Does ichnology rule? Yup. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)
Need a free burrow? Then why start digging a new one when alligator claw marks (arrow) gives you a nice “starter burrow”? Notice the sculpted, round outline, showing the claw mark was modified by a crab. Also check out the sand balls left outside of the other claw marks, meaning these have probably been occupied and mined for food by fiddler crabs, too. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia; scale in centimeters.)
As a paleontologist, the main lesson learned from this modern example that can be applied to fossil tracks, is this: any tracks made in the same places as small, burrowing invertebrates – especially in intertidal areas – might have been destroyed or otherwise modified immediately by the burrowing and feeding activities of those much smaller animals. The secondary lesson is on how large vertebrate tracks can influence the behaviors of smaller invertebrates, resulting in their traces interacting and blending with one another.
More symbolically, though, these alligator tracks and their erasure by fiddler crabs also conjured thoughts of fictional and real analogues: Pacific Rim and coastal development, respectively. With regard to the latter, it felt too much like how, as soon as a hurricane (a meteorological “monster”) passes through a coastal area, we begin to talk about rebuilding in a way that, on the surface, wipes out all evidence that a hurricane ever happened.
Yet unlike fiddler crabs, we have memories, we have records – including the plotted “tracks” of hurricanes – and thanks to science, we can predict the arrival of future “monsters.” So the preceding little ichnological story also felt like a cautionary tale: pay attention to the tracks while they are still fresh, and be wary of those that vanish too quickly.
Last week I surrendered to geekdom peer pressure and went to see the new summer blockbuster Pacific Rim. Living up to my namesake, St. Anthony, I normally don't have a problem resisting such temptations, and just wait to see a movie like this in some other format: DVD, Netflix, or the way movies were originally intended to be seen, on a tiny screen on the back of an airplane seat. But what really pushed me to go was the following image, only glimpsed for a few seconds in one of the trailers:
Ooo, look, a trace made in an intertidal sandflat! Perhaps it's from a ghost crab, moon snail, or shorebird. Hey, wait a minute, something doesn't quite look right. Are those people next to it? (Image from http://www.comicbook.com.)
Yes, that’s right: it's a gigantic footprint, and in what looks like an intertidal coastal environment, between the low tide mark and coastal dunes. That was all the incentive I needed, as I further wondered what other ichnological wonders would be included in the film. I was also encouraged to see where other scientifically inclined bloggers had fun with Pacific Rim by taking a look at its biology (here,here, and most recently, here) and physics (here, here, and most recently, here). So given a $5 afternoon matinee and a spouse (Ruth) willing to indulge my sci-fi inner nerd (OK, so it’s not so “inner”), I had every reason to document the various traces and tracemaking activities in the film. You know, for science and science education.
The verdict? Well, I have to admit some mild disappointment with how the director – Guillermo del Toro - chose to focus on the conflicts between massive amphibious creatures (kaiju) constructed by interdimensional aliens and human-guided fighting machines (jaegers), rather than on their traces. Nonetheless, I managed to find some ichnological gems scattered throughout. For example, the footprint shown in the trailer did indeed look glorious on a big screen, and the human figures associated with it reminded me of Jason Isley’s whimsical underwater photos. But let’s take a closer look at what this footprint tells us about its maker.
Although viewed from an oblique angle, the track seems longer than wide, and has four clearly defined digits, although a probable fifth digit is visible on the side farthest from the viewer. All of the digits are forward-pointing and taper abruptly at their ends. The tracks also has an indentation on the “heel” (proximal) part of the foot, and is more-or less-bilaterally symmetrical. Pits inside of the track may represent additional anatomical traits, such as scales or other bumps on its skin, or could be sediment that underwent liquefaction or other soft-sediment deformation.
Interpreted kaiju track, extrapolated from oblique view. Scale = 10 m (33 ft).
Using the people around the tracks as informal units of measurement, and assuming from the hiragana-katakana in the newscast image that this track - like many items - was made in Japan, we can estimate the dimensions of the track. Average heights for Japanese males and females are 1.71 m and 1.58 m, respectively, and the average of those is 1.64 m. Using one figure (boxed) as a unit that equals 1.64 m (5.4 ft), the footprint had about 18.4 Japanese-Person-Units (JPU) length and 10.1 JPU width, which converts to about 30 m (98 ft) long and 17 m (56 ft) wide. This results in a length:width ratio of about 1.8.
Length and width measurements for kaiju track, including figure used as 1.0 JPU = 1.64 m. Width measurement is assumed on basis of probable fifth digit impression on side of track furthest from the viewer.
Unlike in most articles published in high-impact journals, I'll actually admit potential sources of error in these measurements before I'm forced to retract this blog post under a cloud of scandal, followed by my accepting a high-paying position on Wall Street, where such inaccuracies are rewarded without penalty. For example, the width measurement, because it is being taken from an oblique angle (not so accurate) instead of from directly above (much more accurate) probably underestimates the actual width. So the actual width is probably closer to 20 m (67 ft), which reduces the length:width ratio to about 1.5. The length measurement would also benefit from more of an overhead view, and probably would best be studied using aerial high-resolution LiDAR scanning. So there.
To put this in ichnological perspective, when these dimensions are compared to typical sauropod dinosaur tracks from the Early Cretaceous of Texas - where everything is supposed to be bigger - the sauropod comes out looking pretty puny indeed. In this example, the rear track length is 87 cm (34 in) and width is 59 cm (23"), and although its length:width ratio comes out fairly close to my estimation for the kaiju track (1.47), it is only about 2% of its size. Some "thunder lizard."
Sauropod tracks from the Early Cretaceous (about 120-million-years-old) Glen Rose Formation of central Texas.The larger track is from the left rear foot, and the smaller one in front of it is the left front foot; this sauropod was walking slowly with an "understep" gait, in which its rear foot stayed behind its front. Please read the preceding text for all of that measurement stuff, which ichnologists sometimes call "data." (Photograph taken by Anthony Martin in Dinosaur Valley State Park, near Glen Rose, Texas.)
To-scale comparison between sauropod track (arrow, lower left) and kaiju track (right) to same scale. Looks like some cute little saurischian would be feeling a little inadequate. As Cowboy Curtis once said on Pee Wee's Playhouse, "You know what they say: Big feet, big boots!" Scale = 10 m.
Speaking of high impact, how about track depth and other features of this individual track that might tell us about behavior of the kaiju tracemaker? Oddly enough, the kaiju track looks too shallow to me, measuring only about 1.6 JPU, or about 2.5 m (8 ft) deep. It also lacks pressure-release structures, which are sedimentary structures caused by the tracemaker applying and releasing pressure against the wall of the track. Considering that kaiju were supposed to weigh tens of thousands of tons, this track should have a greater depth, along with major ridges and plates outside of the track outline that would have been imparted by any forward or lateral movement of its foot.
Alternatively, this track may represent more of what I would call a “stamp,” which would have been made by placing a foot directly down onto a soft substrate and pulling it straight up, rather than from moving forward or laterally. Based on this evidence, the kaiju might have been attempting to squish pesky humans, rather thank performing its normal, forward-walking, city-destroying gait. Unfortunately, the preceding and next track are not shown in the photo, which would help to test this hypothesis.
Other than size, how does the form of this track compare to those of other known dinosaur tracks? The length: width ratio comes out close to that of a sauropod dinosaur, yet other qualitative traits of the track, such as thin digits that taper and end with sharp clawmarks, are more like that of a theropod. But I do want to point out a little coincidence. Have you ever seen the front-foot track of a typical raccoon? Hmmm...
I give you you raccoon tracks, and I give you kaiju track. That is all. (Photo of raccoon tracks taken by Anthony Martin on Cumberland Island, Georgia.)
What’s really fun, though, is if you compare the kaiju track to known theropod tracks. Theropod tracks bearing four or more forward-pointing toes are quite rare, and the few identified probably belong to a group of theropods called therizinosaurs, which - by a strictly enforced paleo-nerd law - cannot be mentioned in a sentence without also using the descriptor "bizarre." Late Cretaceous dinosaur tracks recently reported from Alaska with four long, forward-pointing digits have been attributed to therizinosaurs. Were the creators of the kaiju track trying to compare it to that of a really strange theropod dinosaur? Maybe, maybe not.
Artistic rendition of Nothronychus mckinleyi, a therizinosaur from the mid-Cretaceous of North America (left) and a four-toed rear-foot track credited to a therizinosaur from Late Cretaceous rocks of Alaska (right). Therizinosaur artwork by paleoartist Nobu Tamara and available in Wikipedia Commons here; photo of track by David Tomeo and reproduced from Everything Dinosaur.
Although the Pacific Rim kaiju designers used a mix of invertebrate and vertebrate elements for anatomical details appearances of their monsters (detailed splendidly by Darren Naish here), I do wonder how they came up with the track, and which real-life animals - modern or extinct - were supposed to be evoked by this track's brief appearance onscreen. Hopefully the DVD and its Special Features will reveal all once that comes out.
(Incidentally, this attempt to divine the evolutionary relatedness of a science-fictional animal from a single track reminds me of a scene from the classic science-fiction film Forbidden Planet. At some point, an invisible monster comes aboard a spaceship on the aforementioned planet and kills its chief engineer. The ship scientist, Dr. Ostrow, then gave a fine interpretation of the monster based on a plaster cast made from one of its footprints, including how it traits seemed to go against all known evolutionary principles. It's such a fun scene, I've shown it in some of my classes as an example of "extraterrestrial ichnology.")
Other tracemaking in the movie, of course, included wholesale destruction of major population centers by the kaiju, clawmarks left on various city substrates, as well as kaiju scat. Unlike other fans of the movie, I've only seen it once so far, and cannot recall whether the following picture of its droppings was flashed on the movie screen or not.
The banner for this news clip says it all: kaiju excrement, and you can bet this much did indeed contaminate a portion of Manila, Philippines (or the "Phillipines," which may be a gated community just outside of Philadelphia.) On the flip side, I'll bet a certain sick Triceratops in the movie Jurassic Park is now a little less self-conscious about having its wastes piled higher and deeper on the big screen.
One line about their excrement – uttered by kaiju-organ harvester, Hannibal Chau (played by a hilarious Ron Perlman) - alludes to its commercial value based on its phosphorus content. This would accord with the economic importance given to bat or bird guano, which has been mined and sold as fertilizer, and even inspired wars. (I am not making that up.) Still, it would have been beyond awesome to have just one scene showing a deposit of its scat enveloping a large, recognizable monument to a politician in one of those cities.
Hannibal Chau (Ron Perlman), selling kaiju products for whatever might ail you. Alas, their scat is not mentioned in this ad, but he could easily do another one directed at Whole Foods. After all, it would be 100% organic and free-range fertilizer!
What about the jaegers? Their traces are much tougher to discuss, semantically speaking. Ichnologists classify tools themselves as traces of behavior, but most do not count marks made by tools (or machines) as traces. Nonetheless, because the jaegers are being controlled by humans, the marks they leave on the landscape, seascapes, and upside some kaiju’s head, might count as traces, too.
However, in one scene of the movie, in which a kaiju picked up a jaeger and threw it – inflicting much destruction of private and public property – these traces would be those of the kaiju, not the jaeger. I pointed out a similar situation with Jurassic Park. Toward the end of the movie, the poor, misunderstood protagonist of the film - the Tyrannosaurus rex - in an action tinged with self-loathing, hurled a Velociraptor at a mounted T. rex skeleton, no doubt expressing doubt about her place in a post-Mesozoic world. Existentialist angst aside, the destruction of the skeleton was a trace of the tyrannosaur's behavior, not that of the Velociraptor.
So next time you go to a movie featuring multi-ton monsters emerging from the deep sea and massive fighting machines, look for them to make traces, note the traces they make, how these traces may reflect some sort of evolutionary history for the tracemakers, and ask yourself what constitutes a trace. Then no matter how bad the movie, you'll still be guaranteed to enjoy it. Happy movie viewing and tracking!
After a week of traveling and “touristing” in Turkey with my wife Ruth, which included a 16+ hour overnight bus ride from Goreme to Çanakkale (thus proving that “bus lag” is a real thing), it is now time to learn some ichnology. Every two years, ichnologists from around the world – normally 30-40 people hailing from 10-15 countries – gather for the 2013 International Ichnofabric Workshop which consists of six days of talks, field trips, and congenially conducted arguments about trace fossils, traces, and ichnology in general. The workshop, which I mentioned in the next-to-last chapter of my book (Life Traces of the Georgia Coast) is typically held in some beautiful place with lots of trace fossils and beer nearby (and not necessarily in that order of priority). This time is taking place in Çannakale – located on the western side of Turkey, across from Gallipoli.[Darth Vader voice] The ichnologists are here: I can sense them. Ichnologists, such as this one (who, incidentally, owes me money) are emerging from their burrows everywhere – much like periodical cicadas – to discuss ichnology here in Çanakkale, Turkey. (Photograph by Ruth Schowalter.)
Based on the program, most of the talks will be about marine invertebrate trace fossils and their uses in interpreting ancient animal behavior and their environments, although a few will also talk about how ichnofabrics – the sum effect of tracemakers on a given substrate, such as sediment or rock – can be applied to learning more about environmental change and evolution. You know, that weighty stuff we natural scientists crave doing.
So what the heck is an “ichnofabric”? Here’s an example provided by a paving stone in Goreme, Turkey, in which the people who placed it there thought, “Gee, this rock has some cool looking fabrics in it,” (although they likely thought that in Turkish.). But they probably did not know these fabrics were the result of trace fossils made on a sea bottom by marine invertebrate animals millions of years ago. (Photograph by Anthony Martin.)
So for those people who are not able to attend – most of the world, in other words – I will do my best to provide a regular report on what we are doing and learning here. For this, you can come back to this blog every few days, or for more instant gratification, you can follow me on Twitter (@Ichnologist), which I will use for quick assessments of the events as they’re happening. For those of you familiar with how the Twitterverse works, I and other ichnologists should be using the hashtag #Ichnofab2013 to denote the workshop. Teşekkür eridim!
Given the truth that the Atlantic horseshoe crab (Limulus polyphemus)is more awesome than any mythical animal on the Georgia coast (with the possible exception of Altmaha-ha, or “Altie”), it’s no wonder that other animals try to steal its power by eating it, its eggs, or its offspring. For instance, horseshoe-crab (limulid) eggs and hatchlings provide so much sustenance for some species of shorebirds – such as red knots (Calidris canutus) and ruddy turnstones (Arenaria interpres) – that they have timed their migration routes to coincide with spawning season.
Something hunted down, flipped over, and ate this female horseshoe crab while it was still alive. Who did this, what clues did the killer leave, and how would we interpret a similar scenario from the fossil record? Gee, if only we knew some really cool science that involved the study of traces, such as, like, I don’t know, ichnology. (Photograph by Gale Bishop, taken on St. Catherines Island, Georgia, on May 4, 2013.)
Do land-dwelling birds mammals eat adult horseshoe crabs? Yes, and I’ve seen lots of evidence for this on Georgia beaches, but from only three species: feral hogs (Sus crofa) and vultures (Coragyps atratus and Cathartes aura: black vultures and turkey vultures, respectively). In all of these interactions, no horseshoe-crab tracks were next to their bodies, implying they were already dead when consumed; their bodies were probably moved by tides and waves after death, and later deposited on the beach. This supposition is backed up by vulture tracks. I’ve often seen their landing patterns near the horseshoe-crab bodies, which means they probably sniffed the stench of death while flying overhead, and came down to have an al fresco lunch on the beach.
Nonetheless, what I just described is ichnological evidence of scavenging, not predation. So I was shocked last month when Gale Bishop, while he was monitoring for sea-turtle nests on St. Catherines Island (Georgia), witnessed and thoroughly documented an incident in which a raccoon (Procyon lotor) successfully preyed on a live horseshoe crab. Yes, that’s right: that cute little bandit of the maritime forest, going down to a beach, and totally buying into some Paleozoic diet plan, a passing fad that requires eating animals with lineages extending into the Paleozoic Era.
So what’s the big deal here? Horseshoe crab comes up on beach, gets lost, spirals around while looking for the ocean, and dies in vain, a victim of its own ocean-finding ineptitude: the end. Nope, wrong ending. For one thing, those horseshoe crab tracks are really fresh, meaning their maker was still very much alive, then next thing it knows, its on its back. Seeing that horseshoe crabs are not well equipped to do back-flips or break dance, I wonder how that happened? (Photograph by Gale Bishop, taken on St. Catherines Island, Georgia, and you can see the date and time for yourself.)
Here is part of the field description Gale recorded, which he graciously shared with me (and now you):
“Female Horseshoe Crab at 31.63324; 81.13244 [latitude-longitude] observed Raccoon feeding on upside-down HSC [horseshoe crab] on south margin of McQueen Inlet NO pig tracks. Relatively fresh HSC track. Did this raccoon flip this HSC?”
Well, well. Looks like we had a little commotion here. Lots of marks made from this horseshoe crab getting pushed against the beach sand, and by something other than itself. And that “something else” left two calling cards: a urination mark (left, middle) and just above that, two tracks. I can tell you the tracks are from a raccoon, and Gale swears the urination mark is not his. (Photograph by Gale Bishop, taken on St. Catherines Island, Georgia, and on May 4, 2013.)
I first saw these photos posted on a Facebook page maintained by Gale Bishop, the St. Catherines Island Sea Turtle Program (you can join it here). This was one of this comments Gale wrote to go with a photo:
GB: “This HSC must have been flipped by the Raccoon; that was NOT observed but the fresh crawlway indicates the HSC was crawling across the beach and then was flipped – only tracks are Rocky’s!”
[Editor’s note: “Rocky” is the nickname Gale gives to all raccoons, usually applied affectionately just before he prevents them from raiding a sea-turtle nest. And by prevent, I mean permanently.]
My reply to this:
AM: “VERY fresh tracks by the HSC, meaning this was predation by the raccoon, not scavenging.”
In our subsequent discussions on Facebook, Gale agreed with this assessment, said this was the first time he had ever seen a raccoon prey on a horseshoe crab, and I told him that it was the same for me. This was a big deal for us. He’s done more “sand time” on St. Catherines Island beaches than anyone I know (every summer for more than 20 years), and in all my wanderings of the Georgia barrier island beaches, I’ve never come across traces showing any such behavior.
(Yes, that’s right, I know you’re all in shock now, and it’s not that this was our first observance of this phenomenon. Instead, it is that we used Facebook for exchanging scientific information, hypotheses, and testing of those hypotheses. In other words it is not just used for political rants, pictures of cats and food, or political rants about photos of cat food. Which are very likely posted by cats.)
Now, here’s where ichnology is a pretty damned cool science. Gale was on the scene and actually saw the raccoon eating the horseshoe crab. He said it then ran away once it spotted him. (“Uh oh, there’s that upright biped with his boom stick who’s been taking out all of my cousins. Later, dudes!”) And even though I trust him completely as a keen observer, excellent scientist, and a very good ichnologist, I didn’t have to take his word for it. His photos of the traces on that Georgia beach laid out all of the evidence for what he saw, and even what happened before he got there and so rudely interrupted “Rocky” from noshing on horseshoe-crab eggs and innards.
Another view of the “death spiral” by the horseshoe crab, which we now know was actually a “life spiral” until a raccoon showed up and updated that status. Where’s the evidence of the raccoon? Look in the middle of the photos for whitish marks, grouped in fours, separated by gaps, and each forming a backwards “C” pattern. Those are raccoon tracks, and it was galloping away from the scene of the crime (toward the viewer).
So you don’t believe me, and need a close-up of that raccoon gallop pattern? Here you go. Both rear feet are left, both front feet are right, and the direction of movement was to the left; when both rear feet exceed the front, that’s a gallop, folks. Notice the straddle (width of the trackway) is a lot narrower than a typical raccoon trackway, which is what happens when it picks up speed. When it’s waddling more like a little bear, its trackway is a lot wider than this. Conclusion: this raccoon was running for its life.
Although this is the only time Gale has documented a raccoon preying on a horseshoe crab – and it is the first time I’ve ever heard of it – we of course now wonder whether this was an exception, or if it is more common that we previously supposed. The horseshoe crab was a gravid female, and was likely on the beach to lay its eggs. Did the raccoon somehow know this, and sought out this limulid so that – like many shorebirds – it could feast on the eggs, too, along with some of the horseshoe crab itself? Or was it opportunistic, in that it was out looking for sea-turtle eggs, saw the horseshoe crab, and thought it’d try something a little different? In other words, had it learned this from experience, or was it a one-time experiment?
All good questions, but when our data set is actually a datum set (n = 1), there’s not much more we can say about this now. But given this new knowledge, set of search patterns, and altered expectations, we’re more likely to see it again. Oh, and now that you know about this, so can you, gentle reader. Let us know if you see any similar story told on the sands of a Georgia beach.
You want one more reason why this was a very cool discovery? It shows how evolutionary lineages and habitats can collide. Horseshoe crabs are marine arthropods descended from a 450-million-year-old lineage, and likely have been coming up on beaches to spawn all through that time. In contrast, raccoons are relative newcomers, coming from a lineage of land-dwelling mammals (Procyonidae) that, at best, only goes back to Oligocene Epoch, about 25 million years ago. When did a horseshoe crab first go onto land and encounter a land-dwelling raccoon ancestor? Trace fossils might tell us someday, especially now that we know what to look for.
So once again, these life traces provided us with a little more novelty, adding another piece to the natural history of the Georgia coast. Moreover, a raccoon preying on a horseshoe crab was another reminder that even experienced people – like Gale, me, and others who have spent much time on the Georgia barrier islands – still have a lot more to learn. Be humble, keep eyes open, and let the traces teach you something new.
(Acknowledgement: Special thanks to Dr. Gale Bishop for again spotting something ichnologically weird on St. Catherines Island, documenting it, and sharing what he has seen during his many forays there.)
Given all of the controversy over a recent cable-TV program, in which its broadcasting channel decided mythical marine animals deserved more air-time than real ones, I thought it was important to highlight one extant animal that never fails to surprise me. This animal’s lineage is more ancient than dinosaurs, reptiles, or even amphibians, with its oldest fossils dating from about 450 million years ago. It is also the largest living marine invertebrate animal you are likely to see on beaches of the eastern U.S. and Gulf Coast. And at this time of year, if you see it crawling around on a beach, it’s because of sex. For the past month or so, this animal has been participating in massive orgies. Pictures of this gamete-laden frenzy somehow made it past prudish censors of Facebook and other social-media sites, titillating prurient invertebrate enthusiasts everywhere and filling them with cockle-warming glee.
Behold, a fine juvenile specimen of the Atlantic horseshoe crab (Limulus polyphemus)! Although it lives in the ocean, it can walk on land for hours, like some sort of reverse Aquaman, but totally cooler than him. And some day, if this one lives long enough, it will use those legs to walk on land again, but in pursuit of sex. Sounds to me like this animal deserves its own planet. (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)
As you already know from reading the title of this post, I’m talking about horseshoe crabs. More properly known as limulids by real marine biologists and paleontologists, these ultra-cool, über-hip, but totally retro critters are more closely related to spiders than they are to true crabs, but their common name is so, well, common, that scientists just sigh and begrudgingly go along with it for the sake of public communication.
Modern limulids are represented by four species, three of which are in Asia, but the grandest of them all is the Atlantic horseshoe crab, Limulus polyphemus. This species is at its largest here in Georgia, which may be a function of the Georgia Bight, an extensive offshore shelf that affords more food and habitat than other areas. How big? I’ve seen some as long as 70 cm (27 in) – tail included – and 40 cm (16 in) wide, big enough to scare both of our cats at home. They grow to these sizes after hatching as little limulids not much bigger than the period on this sentence, an astonishing increase in mass if they make it to adulthood (which most don’t).
The circuitous trail of a baby limulid, made on a sandflat at low tide. Its body width can be estimated by the width of the interior of the trail, and its body length was slightly more than that, meaning it was smaller than my fingernail. See that central groove? That’s from its tail, but if you want to impress your friends, call it a telson. (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)
Horseshoe crabs are so astounding that I could go on endlessly about all sorts of facts about them. Fortunately for you, gentle reader, other folks have written entire books about them and heaps of popular and scientific articles. (For starters, try going here.) So I don’t want to needlessly duplicate what others have done, and done well. Instead, I’ll focus on my main interest in these animals – their traces – and will regale you with tales of the traces they can make with their tails.
Horseshoe crab tails are spiky projections called telsons. Based on lots of the traces I’ve seen on the Georgia coast and a few direct observations, the main function of a telson is to help a horseshoe crab to get back on its feet after being knocked onto its back. That is, whenever a limulid is upside-down, it immediately start using its telson as a sort of sideways pole vault to lever itself into a less vulnerable position.
Without a telson, an upside-down horseshoe crab is stuck; its legs run furiously, but to no avail. However, with a telson, it can put the pointy end into the sand or mud underneath its body, and push itself up from a surface. This gives a limulid a fighting chance to get back to where it once belonged and start walking. This strategy works best if it turns to its right or left side, as limulids are longer than wide. They may be wonders of nature, but they’re not doing back flips or somersaults.
A large adult horseshoe crab that was right-side-up when trying to get back to the sea, got tired, and tried to use its telson to move itself along. In this instance, it didn’t work, but the traces made by the telson show its range of motion, working like a windshield wiper. (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)
OK, all of the preceding information I already knew. After all, I have: coauthored an edited book chapter about juvenile limulid traces and their close resemblance to trace fossils made by trilobites; coauthored another article on the history of limulid-trace studies (which go back to the 1930s!) that’s now in review; and devoted a lengthy section of a chapter in my book to limulids as tracemakers. So you could say I’ve been feeling pretty cocky about what I knew about these animals as tracemakers. That is, until one horseshoe crab showed me how much I still need to learn about them and what they can make.
The humility-inspiring traces showed up in a photo on a Facebook page I follow (and so should you), the St. Catherines Island Sea Turtle Conservation Program. The program organizers – Gale Bishop and Robert (Kelly) Vance – regularly add photo albums showing sea turtle traces (trackways, body pits, nests), and otherwise report on other facets of natural history they observe on St. Catherines Island beaches. As a result, I live vicariously through these pictures while marooned in the metro-Atlanta area. But they also like to throw me ichnological stunners once in a while, such as the following photo that Kelly posted last week.
Who needs made-up animals on TV when traces like these, made by awesome invertebrates like horseshoe crabs, turn up on a Georgia beach? (Photograph by Robert Kelly Vance, taken on St. Catherines Island, Georgia; scale is about 15 cm (6 in) long.)
Kelly found these traces while patrolling the beaches of St. Catherines Island for other traces, namely those of expectant mother sea turtles. Although these distracted briefly from his mission, I was very happy he stopped to document these, as I had never seen anything like them, despite much looking at traces on Georgia beaches.
The holes in the sand, defining a nearly perfect circle, were made by the telson of an adult horseshoe crab that kept on trying to right itself after landing on its back. Each puncture mark shows where it inserted the telson into the sand and then pushed itself up and to its side. Based on the number of holes, direction of sand flung out of each hole, and little “commas” made by extraction of the telson, it tried to flip itself a minimum of 16 times, and all to the right. These separate actions culminated in a 360° clockwise rotation of its body. Also check out the central depression with smaller drag marks; this is where its head shield was in contact with the sand. To imagine the movement represented by these traces, think of a horseshoe crab doing a slow-motion, step-by-step, break-dance backspin.
Seeing the evidence for such persistence was wow-inducing in itself, but in my ichnologically influenced euphoria, I figured the limulid finally succeeded in righting itself. After all, the trackway just to the left of the trace, indicates where it walked away from the scene of its gravitationally challenged situation.
But then I realized there was no “impact mark.” This large horseshoe crab flipping itself onto the sandy surface should have registered an outline of its body before it started walking. Instead, the place where it started walking showed no such impression, meaning it must have made a soft landing, with only its legs and telson digging into the sand. What happened? Did it use mind over matter and levitate itself through telekinesis? Or was it gently picked up and placed on its feet by a merciful mermaid? (Or merman: let’s make sure we’re being inclusive when talking about made-up stuff.)
It turned out that Kelly was the dues ex machina that entered this limulid’s drama, providing divine intervention just when it was needed. When I expressed my puzzlement to Kelly about how this large arthropod finally turned itself over, he confessed to saving it, in which he lifted it and put it back on its feet, where it promptly walked away in a series of tight spirals. The spiraling is something I’ve seen before in their tracks, a method used to find the downslope direction, which normally leads horseshoe crabs to the low-tide mark and the comfort of a watery environment.
Another perspective of the “escape” traces made by the limulid’s telson (background), but this time with its tracks, showing how it started spiraling clockwise in an attempt to make its way back to the sea. Check out those telson drag marks in the trackway, doing a little bit of back-and-forth movement as its owner walked. (Photograph by Robert Kelly Vance, taken on St. Catherines Island, Georgia.)
OK everyone, start singing “Born Free!” The spiraling helped this limulid (arrow) to find a downslope direction, which took it in the right direction to the sea. But it’s not all sunshine and lollipops for other limulids, some of which are visible in the background, and look like they’re still stuck. Given the tidal range on the Georgia coast – 2.5-3 m (8.2-9.8 ft) – strong wave energy, and wide beaches, lots of big limulids that come in with the flood tide get knocked onto their backs by waves and left behind. It’s almost as if some sort of natural selection is taking place, and something similar might have happened in the geologic past, affecting the evolution of its lineage. (Photograph by Robert Kelly Vance, taken on St. Catherines Island, Georgia.)
In the last photograph, I was glad to see how the story told by these traces promised a happy ending for this limulid that had so stubbornly tried to put itself back on its feet. Yet when you also notice how many of its compatriots did not make it back into the life-nourishing sea, it also serves as a sobering reminder that storybook endings don’t always happen in nature, and what we wish to be true sometimes isn’t.
In this instance, I don’t know whether this horseshoe crab made it back into the sea to live another day or not. Still, the lesson it left for us in the sand lives on, and I am now slightly more confident that if any limulids were stuck on their backs at any point in their 450-million-year history, made similar traces with their tails, and these marks were preserved as trace fossils, we just might recognize them for what they are. For that alone, I am grateful. Thank you, horseshoe crabs, for being real, making traces, and continuing to share this planet with us today.
(Acknowledgement: Special thanks to Drs. Robert Kelly Vance and Gale Bishop for being my ichno-scouts on St. Catherines Island, and feeding my mind with such tasty treats while I am landlocked.)
Martin, A.J., and Rindsberg, A.K. 2007. Arthropod tracemakers of Nereites? Neoichnological observations of juvenile limulids and their paleoichnological applications. In Miller, W.M., III (editor), Trace Fossils: Concepts, Problems, Prospects, Elsevier, Amsterdam: 478-491.
Shuster, C.N., Jr., Barlow, P.B., and Brockmann, H.J. (editors). 2003. The American Horseshoe Crab. Harvard University Press, Cambridge, Massachusetts: 427 p.
When you hear the word “shrimp,” you probably picture those that show up in grocery stores and restaurants throughout the world, which are then consumed voraciously by their terrestrial admirers. Also, some recent attention has been given to mantis shrimp, and deservedly so, because they are among the most gorgeous and terrifying of marine invertebrates today. But there are other marine crustaceans bearing the name “shrimp” that are neither gracing seafood buffets nor awesome predators, yet are worthy of our adoration, documentary films, and epic songs, the latter of which will be no doubt performed on Eurovision 2014. Yes, you guessed it: I’m talking about ghost shrimp.
What’s this? We’re looking down on the surface of a Georgia beach at low tide. The collapsed top of a ghost shrimp burrow is in the lower left, but it’s connected to a trackway, which ends in a shallow horizontal burrow, which holds the maker of all three types of traces. Lots of other ghost-shrimp burrow tops are in the upper part of the photo, too. Life doesn’t get much better than this for an ichnologist. You may now envy me. (Photo by Anthony Martin, taken on Jekyll Island, Georgia; scale in centimeters. )
Why ghost shrimp? Because they can burrow like nobody’s business. Take a typical ghost shrimp in the Bahamas or the Caribbean, such as Glypterus acanthochirus. This crustacean is only about 10-cm (4-in) long, but if it lives for eight years and burrows continuously through that time, it will have processed a cubic meter of sediment. Individual ghost-shrimp burrows can go as deep as 5 m (16 ft). These would be like a human shoveling more than a cubic kilometer of dirt, or a vertical shaft about 100 m (330 ft) deep, but without a shovel, backhoes, augers, drilling rigs, or other tools. These vertical shafts then connect with extensive branching tunnels, making complicated networks in the sand and mud below the level of the low tide. Now multiply that industriousness by millions, and we’re talking about enormous volumes of sediment processed by ghost shrimp in their respective shallow-water environments. Ghost shrimp are like the ants of the ocean, only not as organized: no queens, workers, soldiers, or other divisions of labor, just lots of individual shrimp burrowing, eating, mating, and defecating.
Every one of these holes is the top of an occupied ghost-shrimp burrow. Now imagine meters-long vertical shafts from each of these going down into the beach sand, then turning into branching horizontal networks of such grandeur, they would further embarrass naked moles rats, which are already apologizing for how they look. (Photo by Anthony Martin, taken on Sapelo Island, Georgia. Human foot (upper right), still attached to human, for scale.)
Ghost shrimp share a common ancestor with crabs, lobsters, crayfish, and shrimp, all of these having four pairs of walking legs and one pair of claws. (Mantis shrimp are actually not true shrimp – or even decapods – but stomatopods.) Ghost shrimp are also known by marine biologists and ichnologists as callianassid shrimp, belonging to an evolutionarily linked group (clade), Callianassidae.They burrow through sand and mud using their front two claws, but also carry sediment on their other legs. Ghost shrimp are also well-known for depositing much of the mud on Georgia beaches as elegantly packaged little cylindrical fecal pellets. These bear enough of a resemblance to “chocolate sprinkles” on cupcakes that they become tempting to sample, until you remember that they’re, like, you know, fecal.
Ghost-shrimp fecal pellets, each about 5 mm long, and recently ejected by a ghost shrimp through the top of the burrow, which is the little hole just to the right. If you use them with any cupcake recipes, let me know how that worked for you. (Photo taken by Anthony Martin on St. Catherines Island, Georgia.)
Geologists love ghost shrimp, too, because of how their burrows are so numerous, fossilize easily, and are sensitive shoreline indicators. I wrote about this before with regard to how geologists in the 1960s were able to map ancient barrier islands of the Georgia coastal plain by looking for trace fossils of these burrows. Since then, geologists and paleontologists have identified and applied these sorts of trace fossils worldwide, and in rocks from the Permian Period to the Pleistocene Epoch.
I could prattle on about ghost shrimp and their ichnological incredibleness for the rest of the year, but will spare you of that, gentle reader, and instead will get to the point of this post. Just when I thought I’d learned nearly everything I needed to know about ghost-shrimp ichnology, one shrimp decided I needed to have my eyes opened to some traces I had never seen them make before just a few months ago. I mentioned these traces briefly in a previous blog post, when I was teaching undergraduate students from my barrier-islands class on Jekyll Island (Georgia) in mid-March. They were tracks and a shallow horizontal burrow made on the surface on the northernmost beach of Jekyll Island, and they were made by a ghost shrimp. How do I know they were made by a ghost shrimp? Well, maybe because they had a ghost shrimp attached to them, but that’s beside the point.
A close-up of the left side of the trackway shows more clearly how it definitely is connected to the funneled top of a burrow. The trackway shows small pointed impressions and a central groove in places, showing that this is an animal with legs and a tail, respectively. The irregular path of the trackway is a record of pauses, where the trackmaker stopped briefly before moving on. The body length of the tracemaker is subtly revealed along the way too, but explaining that would require a more advanced lesson in ichnology. So maybe another time. (Photo by Anthony Martin, taken on Jekyll Island, Georgia.)
The right side of the trackway, ending in a short and shallow horizontal tunnel, just under the sandy beach surface. (Photo by Anthony Martin, taken on Jekyll Island, Georgia.)
The trackway and tail-trail ends in a tunnel with a thin roof of sand. The bilobed pattern was made by the claws and other legs on either side moving sand up and around the body of the tracemaker. Notice the roof collapsed a little on the right, and that its tail is sticking out on the left: kind of like hiding under a too-short blanket. (Photo by Anthony Martin, taken on Jekyll Island, Georgia.)
Ta-da – the tracemaker revealed! I’m fairly sure this is a Georgia ghost shrimp (Biffarius biformis), but would appreciate all of those marine biologists out there to correct me if I’m wrong. (And not those fake marine biologists, either.) Rest assured, after showing it to my students and allowing them to photograph it, I put it back in the ocean, where it burrowed happily ever after. Unless it died, that is. (Photo by Anthony Martin, taken on Jekyll Island, Georgia.)
What truly amazed me about these traces, though, was their rarity. As I shared with my students, in more than 15 years of field work on the Georgia coast, I had never seen anything like this sequence of traces. Even better, the tracemaker was right there, and like the period at the end of a sentence in the story.
Furthermore, the story told by these traces was that something must have threatened the life of this shrimp to cause it to behave in such an unusual way. These shrimp almost never see the light of day, and prefer to stay deep in their burrows, away from the prying eyes and beaks of shorebirds, fish, and other predators. Consequently, they remain largely invisible to humans; hence the “ghost” part of their nickname. This means something very bad must have happened to this one in its burrow, prompting it to abandon its refuge and expose itself so vulnerably. It would be like a fire forcing people out of their fortified underground bunkers, but when they know tyrannosaurs are lurking just outside. Damned if you do, damned if you don’t, but something in this ghost shrimp’s evolutionary program made it take the path of the lesser damned.
What happened? Did a predator find its way into the burrow and chase it out? Was it a chemical cue of some sort, like oxygen-poor water flooding into the bottom of its burrow? Was it competition from another ghost shrimp, evicting it from its home? Was it a mate that decided it had enough of sharing this burrow and needed some “alone time,” or took up with another more comely shrimp? I don’t know, but it made for a good little mystery, yet another posed by life traces on a Georgia beach, and one I was delighted to discover and share with my students on Jekyll Island.
All paleontologists remember their first time. Mine was in 1993, during a hot, steamy summer in Atlanta, Georgia. I had just spent the previous month camping in wilderness areas of Wyoming, so coming back to a big city with all of its urban temptations meant I was weak and susceptible to seeking out unusual sources of pleasure. Although I was not quite ready to be taken for such an exhilarating ride, it was an experience I’d never forget. Afterwards, once I had recovered enough to be able think about it, I wanted to do it again.
I am, of course, talking about seeing the film Jurassic Park on a movie screen. Sure, this movie has been around long enough (20 years) that nearly every paleontologist has also watched it on a TV, computer, or mobile device. But there is something about seeing dinosaurs – which, let’s face it, are most famous for their size – shown big. The initial glimpse of a Brachiosaurus munching on the tops of tall trees, a herd of Paralophosaurus ringing a glistening lake, an ill Triceratops dwarfing its human caretakers, the grand entrance of the Tyrannosaurus: all of these “actors” were meant to be seen large, and fill us with awe. It worked. Plot, acting, and science aside, Jurassic Park was, and probably still is, the best movie made for conveying what it would feel like for us humans, separated by a minimum of 65 million years, to see real, living dinosaurs.
“It’s, it’s a dinosaur.” That pretty much said it all in 1993, and still does. But what traces were being made by this Brachiosaurus as it strolled through its all-you-can-eat salad bar, known to you and me as a “landscape”? Please read on.
In 1993, though, I did not have an appreciation for some of the smaller details included in this film, and how my research specialty of ichnology – the study of traces, like tracks, burrows, and nests – was reflected throughout it. What dinosaur traces were included in the movie, and how were these traces used to serve or advance the plot? I also wondered how 20 years of field experience and scholarly research in ichnology might have changed my perceptions of it since that first viewing.
So with the re-release of Jurassic Park in 3-D last week, I decided it was time to view it from an ichnological perspective and share these thoughts with others. After all, my next book, Dinosaurs Without Bones (Pegasus Press), is about dinosaur trace fossils, and written for a popular audience. Also, in between the movie’s first release and now, I wrote two editions of a college textbook on dinosaurs (Introduction to the Study of Dinosaurs). Thus I went to the theater well justified in watching Jurassic Park once more, to see for myself how dinosaur traces were portrayed in the most well-loved of all dinosaur movies. And oh yes, for the fun.
For the sake of simplicity, I’ve divided these traces into two categories: those viewers could directly observe in the film, and others that could be inferred from the dinosaurs’ behaviors. Wherever possible, I also connect traces shown in the movie to research done on dinosaur trace fossils during the last 20 years, giving a broad sense of how far dinosaur ichnology has progressed since 1993.
(Ichnologist’s note: Even though all of the live dinosaurs in the movie were set in the 1990s, the study of their modern traces still qualifies as neoichnology. In contrast, any reference I make to actual dinosaur trace fossils is paleoichnology. Just so you know.)
Dinosaur Traces in Jurassic Park
• Velociraptor hatchling traces.Jurassic Park shows two different but complementary examples of hatchling traces for “Velociraptor.” (I will call this dinosaur Velociraptor throughout this post, but as most dino-philes know, the director, Steven Spielberg, scaled up the Late Cretaceous Velociraptor to maximize its frightfulness. Hence it is actually more like the Early Cretaceous Deinonychus or Utahraptor.)
One is an egg-emergence trace, which is the hole left in an eggshell where a dinosaur broke out of its egg. In this scene, a cooing Velociraptor hatchling pokes its cute little nose out of its egg. (This nose, if everything worked out for it, would some day would be warmed by fresh human viscera.) We first witness this tracemaking in the Jurassic Park laboratory toward the start of the film, the same day most of the protagonists arrive on the island (Isla Nublar). As far as I know, such trace fossils have not been interpreted from the fossil record, or if they have, they have not been referred to as trace fossils: which they should be.
The next day, after dinosaur paleontologist Alan Grant and his two companions – Lex and Tim Murphy – were sufficiently terrified (and enthralled) by various dinosaur encounters out in the park, they come across a Velociraptor nest. The nest has about 15-20 broken eggs, and the fracture patterns of the eggshells provide clear evidence of hatching. But these traces also had tiny, two-toed tracks leading away from them. The tracks, with two toes studded by digital pads, were typical for deinonychosaurs. However, unlike nearly every theropod track I’ve seen, these tracks lacked claw marks at their ends. (Tsk, tsk, says this nitpicking ichnologist.)
Aw, look at the cute little Velociraptor tracks and hatched eggs. Don’t these traces just make you want to say, “Who’s the cutest little predator in the world?” Still from Jurassic Park (1993), taken from www.anyclip.com.
Even though these tracks were flashed on the screen for only a few seconds, what’s really cool is how they convey three important pieces of information. One is that the Velociraptor chicks hatched after the torrential rainstorm of the previous night, and thus only mere hours before our wandering heroes saw their traces. Second, the tracks demonstrate that the hatchlings were not altricial, but ready to move and leave the nest immediately, presumably without parental care. Third, Dr. Grant realizes that these successfully fertilized and hatched eggs mean the “female-only” genetic fail-safe plan for the dinosaurs just got disproved. In other words, these traces mattered.
One point about that nest: as far as I could tell from, this Velociraptor mother did not make a rimmed structure to protect the eggs, such as those made by another Late Cretaceous theropod, Troodon, or LateCretaceous sauropods in Argentina. Instead, the eggs were laid out in the open, like some ground-nesting shorebirds might do. In contrast, the Jurassic Park sequels featured Velociraptor nests that were much more overt as traces, such as a rimmed nest seen in Jurassic Park III.
Partially preserved rimmed nest structure of Troodon, a Late Cretaceous theropod that lived in what we now call Montana. The rim has eroded quite a bit since its discovery in the mid-1990s; the Troodon egg clutch was in the area of the foreground before its extraction. (Photograph by Anthony Martin; scale in centimeters.)
• Triceratops feces. “That is one big pile of sh*t,” observes Dr. Ian Malcolm, the “chaotician” (mathematician) who supplies both pessimism and comic relief throughout the movie. In this scene, where the main protagonists attend to an under-the-weather Triceratops, two impressive piles of fecal material inspire Dr. Ellie Satler, a paleobotanist, to figure out whether or not the ceratopsian had eaten any toxic plants.
Somehow I suspect this scene was meant as a metaphor for what most paleontologists have to do in their day jobs in order to do any paleontology at all.
Still, when added together, this amount of still-moist waste was far too voluminous to have been from one or two depositional events: I mean, this dinosaur was sick, but not that much. As a result, park personnel must have been responsible for making these dung heaps from several days worthy of Triceratops contributions. (Strictly speaking, then, these heaps were composite traces.) If so, this would have been a rather unenviable job, but maybe they were better paid than Dennis Nedry, the disgruntled computer programmer who later provided ample fodder for Dilophosaurus.
Unfortunately, fossil Triceratops feces (coprolites) are thus far unknown from the geologic record. What is exciting, though, is that several excellent studies have been done by Dr. Karen Chin on Late Cretaceous hadrosaur coprolites. These coprolites, like the fictionalized Triceratops feces, contain lots of plant material, telling us much about what these hadrosaurs ate 75 million years ago. They also tell us what ate the feces or grazed on them, which were dung beetles and snails, respectively. (Indeed, I now wonder if Isla Nubar had a severe shortage of dung beetles, which might explain how those Triceratops feces got piled higher and deeper.)
Dinosaur coprolite – probably from a large hadrosaur, such as Maisaura – and filled with wood fragments, accompanied by special bonus trace fossils: dung beetle burrows! Specimen from the Two Medicine Formation (Late Cretaceous, Montana) as part of a Museum of the Rockies traveling exhibit at Fernbank Museum of Natural History. (Photograph by Anthony Martin, taken in 2001 and scanned from a 35-mm slide; scale in centimeters.)
• Tyrannosaurus tracks. Probably the most memorable scene in Jurassic Park is the grand entrance of the Tyrannosaurus, whose approach is first detected by “impact tremors” transmitted in cups of water on the dashboard of a jeep. Following this first bout of terror and the arrival of Ellie Sattler and big-game hunter Robert Muldoon, Malcolm, convalescing in the back of a jeep, looks down at a three-toed Tyrannosaurus track. The track, filled with water from the rain, communicates a warning as it vibrates from the footfalls of the approaching giant theropod. This repeats the previous image of the trembling water in the cup, but is made doubly dreadful by happening in a freshly made footprint of the same animal causing the tremors.
So what was by far the most exciting moment in the movie for me, ichnologically speaking? The Tyrannosaurus making a track, in which mud pushes up and out to the sides of its right foot, observed at 2:38 in the following video clip. Just watch:
This was already a great scene for all of its action, suspense, and lawyer eating. But check out that track-making!
Only a few fossil tracks have been attributed to Tyrannosaurus or other tyrannosaurids, mostly for being the right size (really big) and geologic age (Late Cretaceous). One was discovered in New Mexico in 1983, but wasn’t reported in a scientific journal until the year after Jurassic Park came out. More than a decade passed before another was found in Montana in 2007 and reported in 2008. Tragically, both were isolated tracks, and a Tyrannosaurus trackway, with two or more consecutive steps, has not yet been found. If so, it would make for a pretty darned nice find. So please do let the world know if you find one.
A large and well-preserved three-toed theropod track from the Early Cretaceous Glen Rose Formation of Texas, made about 95 million years ago. Although this track was more likely made by Acrocanthosaurus, rather than Tyrannosaurus rex, you can be assured that this theropod, like all living things, was a distant relative of T. rex. (Photograph taken by Anthony Martin; scale in centimeters.)
• Velociraptor tracks (adults). These tracks, shown only for a few seconds, are outside of the Velociraptor enclosure after the power was shut down. Muldoon, accompanied by Sattler, spots the footprints, and he wordlessly identifies them. (His expression also tells the audience that Sattler and he are going to be in deeper doo-doo than the Triceratops piles.) The twisted and broken bars of the enclosure provide additional traces affirming the conclusion that these ‘raptors are on the loose. All of these traces are shown only minutes before Muldoon utters his meme-inspiring last words, “Clever girl.”
Uh oh: Velociraptor tracks, and these don’t look like they’re from hatchlings. Good thing Muldoon is a big-game hunter, who’s skilled at tracking and predicting Velociraptor behavior based on their tracks. But too bad his hypothesis was falsified in such an unpleasant way, but I suppose he could have picked kinder reviewers. Still from Jurassic Park (1993), taken from www.anyclip.com.
Here’s what a real deinonychosaur track looks like. This one, from the Early Cretaceous of Utah, is a right foot impression, and is just slightly smaller than the adult tracks depicted in Jurassic Park. Notice the digits are thinner and end with sharp clawmarks, too. (Photograph by Anthony Martin; scale in centimeters.)
• Bioerosion of fossil dinosaur bones by modern dinosaurs. Toward the end of the film, the main human heroes – Grant, Sattler, Murphy, and Murphy (which sounds like a law firm, but we know how T. rex feels about those) – are confronted by a Velociraptor pack in the Jurassic Park visitor center. During their attempts to flee the ‘raptors, both species end up disarticulating and breaking some of the mounted dinosaur skeletons in the atrium of the visitor center. Their actions were thus a form of bioerosion, in which the fractured dinosaur bones are traces of their activities. Alternatively, the bones may have been artificial casts, in which case their breakage would have constituted bioerosion of modern substrates.
This bioerosion is made more complicated when the Tyrannosaurus rex (who everyone agrees is the ultimate protangonist of the movie) enters the atrium and, among other antics, smashes a skeleton of itself with a recently crunched Velociraptor. As a result, the jumbled assemblage of bones at the end is attributable to three separate, interacting tracemakers: four humans (two adult, two juvenile), two Velociraptors (both adults), and one Tyrannosaurus (adult). What should be noted, though, is that if the Velociraptor was already dead when flung by the Tyrannosaurus, then the broken skeleton is a trace of the Tyrannosaurus, not the Velociraptor. In other words, the Velociraptor body was just being used as a tool.
Bioerosion in action, as a result of Velociraptor and human interactions. Also, at 2:45: T. rex smash!
Dinosaur Trace-Making Behaviors in Jurassic Park
• Brachiosaurus tracks, browsing traces.When Drs. Grant and Sattler experience their first jaw-dropping glimpse of a Brachiosaurus, they watch it rear up on its hind feet, and come down hard on front feet. Considering that a Brachiosaurus this size might have weighed at least 30 tonnes, it surely would have left deep tracks in both the front and rear from the increased stresses imparted by these actions. Also, its cropping the tops of trees would have caused some easily visible gaps in the canopies of forests on Isla Nubar.
• Theropod toothmarks. Part of the fun of Jurassic Park was indulging in our worst nightmares about these non-avian theropods frequently sampling human flesh. Assuming that the theropod teeth in each instance penetrated skin and muscle and contacted bone, toothmarks would have included the following: (1) Tyrannosaurus toothmarks on goat, human, and Velociraptor bones; and (2) Velociraptor and Dilophosaurus toothmarks on human bones.
• Triceratops resting trace. When the paleontologists and others visit the ailing Triceratops, it was lying on its right side. I couldn’t help but think that if Triceratops or any other large ceratopsian dinosaur ever reclined like that, and in the right type of sediment, it would have left a gorgeous body impression. This scene also reminded me of bison traces I’ve seen in Yellowstone National Park, in which bisons roll onto their sides for a dust bath, leaving outlines of their bodies. Did dinosaurs – especially the feathered ones – ever take dust baths, and leave similar body impressions? We don’t know yet, but such trace fossils are something to look for.
• Dinosaur stampede. One of the most astonishing computer-generated effects of Jurassic Park, and one that was especially effective in 3-D, was of a dinosaur stampede. In this scene, a flock of Gallimus run toward and around Grant, Murphy, and Murphy, just before the ambush-hunting Tyrannosaurus rex slaughters one of them (the Gallimus, that is). I’ve written about this scene before, connecting it to a dinosaur tracksite in Queensland, Australia that has more than 3,000 tracks preserved. Although the site was originally interpreted as the only evidence of a dinosaur stampede, the tracks were recently reinterpreted as swim tracks. I’ll write about this topic at length in my upcoming book, so for now, I ain’t saying nothing more.
Run away, run away!
• Tyrannosaurus drag mark. After the Tyrannosaurus rex decides that a measly goat was just an appetizer and begins seeking out the nearest available mammals for nomming purposes, at some point it overturns and begins pushing an SUV, which still has Lex and Tim Murphy trapped underneath it. Its flipping the SUV with its head certainly would have left a substantial mark on the muddy ground, a trace that then would have been connected to a semi-circular dragmark (clockwise oriented), and with tracks directly adjacent to these traces. Her tracks also may have been deeper in their fronts because of her head being down as she pushed, reflecting a shift in her weight distribution. However, I should again remind everyone that just like with the dead Velociraptor used for bioerosion by this same T. rex later in the film, the SUV is not making the trace. It is only a tool being used by the tyrannosaur, which is the real tracemaker.
• Tyrannosaurus running trackway – This pulse-quickening chase scene, in which the T. rex pursues a jeep driven by Muldoon and with Malcolm and Sattler as passengers, very likely would have caused a wonderful sequence of tracks. These tracks would have shown increasing stride lengths from a standing start to full-speed run, and each successive track would have registered external and internal structures consistent with this acceleration. Even better, the tracks would have cross-cut the jeep tire-tracks at some points, demonstrating to a later observer that the tyrannosaur was very likely following the jeep. (The demolition of a low-hanging tree branch by the T. rex during the chase also counts as some bioerosion along the way.) Some convincing studies have been done since showing that an adult Tyrannosaurus could not have moved as fast as the one in Jurassic Park, but it still could have caught most running humans. And just to repeat what I said earlier, it’d be really nice for someone to find a T. rex trackway, which would give us more direct evidence of how these massive theropods moved.
• Velociraptor scratch marks and other traces. This time, while watching the harrowing and claustrophobic scene in which a pair of Velociraptors hunt the Murphy siblings in a kitchen, I started thinking about the traces they might have left. Did their claws leave scratch marks on the door handles and kitchen counters? Did they indent the steel counters when they jumped up on these surfaces? A broken window is also shown as a trace of their smashing through glass once they became frustrated with a locked door.
OK, enough of the fanciful ichnology. What about other dinosaurs and their traces? Well, it turns out that Jurassic Park saved the real, living dinosaurs for the very end of the movie. These were five brown pelicans (Pelecanus occidentalis), flying in formation as Grant, Sattler, and their companions leave Isla Nubar in a helicopter. For Grant, this is a poignant moment, as he is likely reflecting on how dinosaurs were still with us today as birds. With that thought, I will say “amen,” and add that dinosaur traces – tracks, nests, feces, bite marks, and all – are still here with us, too, and don’t require special glasses to see them in three dimensions. Thanks for that reminder, Jurassic Park.
Want to see some modern dinosaur traces? Here are tracks of a brown pelican, made in wet sand while it was loafing on a beach at low tide on Sapelo Island, Georgia. To see more modern dinosaur traces, just go outside, and you’ll find them wherever birds are found. (Photograph by Anthony Martin; scale in centimeters.)
Further Reading
Chiappe, L.M., Schmitt, J.G., Jackson, F., Dingus, L., and Grellet-Tinner, G. 2004. Nest structure for sauropods: sedimentary criteria for recognition of dinosaur nesting traces. Palaios, 19: 89–95.
Chin, K. 2007. The paleobiological implications of herbivorous dinosaur coprolites from the Upper Cretaceous Two Medicine Formation of Montana: why eat wood? Palaios, 22: 554-566.
Chin, K., and Gill, B.D. 1996. Dinosaurs, dung beetles, and conifers: participants in a Cretaceous food web. Palaios, 11: 280-285.
Elbroch, M., and Marks, E. 2001. Bird Tracks and Sign of North America. Stackpole Books, Mechanicsburg, Pennsylvania.
Erickson, G. M., Van Kirk, S. D., Su, J., Levenston, M. E., Caler, W. E., & Carter, D. R. 1996. Bite force estimation for Tyrannosaurus rex from tooth-marked bones. Nature, 382: 706–708.
Gignac, P.M., Makovicky, P.J., Erickson, G.M., and Walsh, R.P. 2010. A description of Deinonychus antirrhopus bite marks and estimates of bite force using tooth indentation simulations. Journal of Vertebrate Paleontology, 30: 1169-1177.
Hutchinson, J.R., and Garcia, M. 2002. Tyrannosaurus was not a fast runner. Nature,415: 1018-1021.
Jacobsen, A.R. 1998. Feeding behaviour of carnivorous dinosaurs as determined by tooth marks on dinosaur bones. Historical Biology, 13: 17-26.
Lockley, M.G., and Hunt, A.P. 1994. A track of the giant theropod dinosaur Tyrannosaurus from close to the Cretaceous/Tertiary Boundary, northern New Mexico. Ichnos, 3: 213-218.
Manning, P.L., Ott, C., and Falkingham, P.L. 2008. A probable tyrannosaurid track from the Hell Creek Formation (Upper Cretaceous), Montana, United States. Palaios, 23: 645-647.
Romilio, A., and Salisbury, S.W. 2011. A reassessment of large theropod dinosaur tracks from the mid-Cretaceous (late Albian–Cenomanian) Winton Formation of Lark Quarry, central-western Queensland, Australia: a case for mistaken identity. Cretaceous Research, 32: 135-142.
Romilio, A., Tucker, R., Salisbury, S. 2013. Reevaluation of the Lake Quarry dinosaur tracksite (late Albian-Cenomanian Winton Formation, central-western Queensland, Australia): no longer a stampede? Journal of Vertebrate Paleontology. 33: 1, 102-120.
Sellers, W.I., and Manning, P.L. (July 2007). Estimating dinosaur maximum running speeds using evolutionary robotics. Proceedings of the Royal Society of London, B, 274: 2711-2716.
Thulborn, R.A., and Wade, M., 1979. Dinosaur stampede in the Cretaceous of Queensland. Lethaia, 12: 275-279.
Varricchio, D.J., Jackson, F. and Trueman, C.N. 1999. A nesting trace with eggs for the Cretaceous theropod dinosaur Troodon formosus. Journal of Vertebrate Paleontology, 19: 91-100.
(This post is the fourth in a series about a spring-break field trip taken last week with my Barrier Islands class, which I teach in the Department of Environmental Studies at Emory University. The first three posts, in chronological order, tell about our visits to Cumberland Island, Jekyll Island, and Little St. Simons and St. Simons Islands. For the sake of conveying a sense of being in the field with the students, these posts mostly follow the format of a little bit of prose – mostly captions – and a lot of photos.)
When planning a week-long trip to the Georgia barrier islands with my students, I knew that one island – Sapelo – had to be included in our itinerary. Part of my determination for us to visit it was emotionally motivated, as Sapelo was my first barrier island, and you always remember your first. But Sapelo has much else to offer, and because of these many opportunities, it is my favorite as an destination for teaching students about the Georgia coast and its place in the history of science.
Getting to Sapelo Island requires a 15-minute ferry ride, all for the low-low price of $2.50. (It used to cost $1.00 and took 30 minutes. My, how times have changed.) For my students, their enthusiasm about visiting their fourth Georgia barrier island was clearly evident (with perhaps a few visible exceptions), although photobombing may count as a form of enthusiasm, too.
I first left my own traces on Sapelo in 1988 on a class field trip, when I was a graduate student in geology at the University of Georgia. My strongest memory from that trip was witnessing alligator predation of a cocker spaniel in one of the freshwater ponds there. (I suppose that’s another story for another day.) Yet I also recall Sapelo as a fine place to see geology and ecology intertwining, blending, and otherwise becoming indistinguishable from one another. This impression will likely last for the rest of my life, reinforced by subsequent visits to the island. This learning has always been enhanced whenever I’ve brought my own students there, which I have done nearly every year since 1997.
As a result of both teaching and research forays, I’ve spent more time on Sapelo than all of the other Georgia barrier islands combined. Moreover, it is not just my personal history that is pertinent, but also how Sapelo is the unofficial “birthplace” of modern ecology and neoichnology in North America. Lastly, Sapelo inspired most of the field stories I tell at the start of each chapter in my book, Life Traces of the Georgia Coast. In short, Sapelo Island has been very, very good to me, and continues to give back something new every time I return to it.
So with all of that said, here’s to another learning experience on Sapelo with a new batch of students, even though it was only for a day, before moving on to the next island, St. Catherines.
(All photographs by Anthony Martin and taken on Sapelo Island.)
Next to the University of Georgia Marine Institute is a freshwater wetland, a remnant of an artificial pond created by original landowner R.J. Reynolds, Jr. More importantly, this habitat has been used and modified by alligators for at least as long as the pond has been around. For example, this trail winding through the wetland is almost assuredly made through habitual use by alligators, and not mammals like raccoons and deer, because, you know, alligators.
Photographic evidence that alligators, much like humans prone to wearing clown shoes, will use dens that are far too big for them. This den was along the edge of the ponded area of the wetland, and has been used by generations of alligators, which I have been seeing use it on-and-off since 1988.
An idealized diagram of ecological zones on Sapelo Island, from maritime forest to the subtidal. This sign provided a good field test for my students, as they had already (supposedly) learned about these zones in class, but now could experience the real things for themselves. And yes, this will be on the exam.
When it’s high tide in the salt marsh, marsh periwinkles (Littoraria irrorata) seek higher ground, er, leaves, to avoid predation by crabs, fish, and diamondback terrapins lurking in the water. Here they are on smooth cordgrass (Spartina alterniflora), and while there are getting in a meal by grazing on algae on the leaves.
Erosion of a tidal creek bank caused salt cedars (which are actually junipers, Juniperus virginiana) to go for their first and last swim. I have watched this tidal creek migrate through the years, another reminder that even the interiors of barrier islands are always undergoing dynamic change.
OK, I know what you’re thinking: where’s the ichnology? OK, how about these wide, shallow holes exposed in the sandflat at low tide? However tempted you might be to say “sauropod tracks,” these are more likely fish feeding traces, specifically of southern stingrays. Stingrays make these holes by shooting jets of water into the sand, which loosens it and reveals all of the yummy invertebrates that were hiding there, followed by the stingray chowing down. Notice that some wave ripples formed in the bottom of this structure, showing how this stingray fed here at high tide, before waves started affecting the bottom in a significant way.
Here’s more ichnology for you, and even better, traces of shorebirds! I am fairly sure these are the double-probe beak marks of a least sandpiper, which may be backed up by the tracks associated with these (traveling from bottom to top of the photo). But I could be wrong, which has happened once or twice before. If so, an alternative tracemaker would be a sanderling, which also makes tracks similar in size and shape to a sandpiper, although they tend to probe a lot more in one place.
Just in case you can’t get enough ichnology, here’s the lower, eroded shaft of a ghost-shrimp burrow. Check out that burrow wall, reinforced by pellets. Nice fossilization potential, eh? This was a great example to show my students how trace fossils of these can be used as tools for showing where a shoreline was located in the geologic past. And sure enough, these trace fossils were used to identify ancient barrier islands on the Georgia coastal plain.
Understandably, my students got tired of living vicariously through various invertebrate and vertebrate tracemakers of Sapelo, and instead became their own tracemakers. Here they decided to more directly experience the intertidal sands and muds of Cabretta Beach at low tide by ambulating through them. Will their tracks make it into the fossil record? Hard to say, but I’ll bet the memories of their making them will last longer than any given class we’ve had indoors and on the Emory campus. (No offense to those other classes, but I mean, you’re competing with a beach.)
The north end of Cabretta Beach on Sapelo is eroding while other parts of the shoreline are building, and nothing screams “erosion!” as loudly as dead trees from a former maritime forest with their roots exposed on a beach. Also, from an ichnological perspective, the complex horizontal and vertical components of the roots on this dead pine tree could be compared to trace fossils from 40,000 year-old (Pleistocene) deposits on the island. Also note that at this point in the trip, my students had not yet tired of being “scale” in my photographs, which was a good thing for all.
Another student eager about being scale in this view of a live-oak tree root system. See how this tree is dominated by horizontal roots? Now think about how trace fossils made by its roots will differ from those of a pine tree. But don’t think about it too long, because there are a few more photos for you to check out.
Told you so! Here’s a beautifully exposed, 500-year-old relict marsh, formerly buried but now eroding out of the beach. I’ve written about this marsh deposit and its educational value before, so will refrain from covering that ground again. Just go to this link to learn about that.
OK geologists, here’s a puzzler for you. The surface of this 500-year-old relict marsh, with its stubs of long-dead smooth cordgrass and in-place ribbed mussels (Guekensia demissa), also has very-much-live smooth cordgrass living in it and sending its roots down into that old mud. So if you found a mudstone with mussel shells and root traces in it, would you be able to tell the plants were from two generations and separated by 500 years? Yes, I know, arriving at an answer may require more beer.
Although a little tough to see in this photo, my students and I, for the first time since I have gone to this relict marsh, were able to discern the division between the low marsh (right) and high marsh (left). Look for the white dots, which are old ribbed mussels, which live mostly in the high marsh, and not in the low marsh. Grain sizes and burrows were different on each part, too: the high marsh was sandier and had what looked like sand-fiddler crab burrows, whereas the low marsh was muddier and had mud-fiddler burrows.SCIENCE!
At the end of a great day in the field on Sapelo, it was time to do whatever was necessary to get back to our field vehicle, including (gasp!) getting wet. The back-dune meadows, which had been inundated by unusually high tides, presented a high risk that we might experience a temporary non-dry state for our phalanges, tarsals, and metatarsals. Fortunately, my students bravely waded through the water anyway, and sure enough, their feet eventually dried. I was so proud.
So what was our next-to-last stop on this grand ichnologically tainted tour of the Georgia barrier islands? St. Catherines Island, which is just to the north of Sapelo. Would it reveal some secrets to students and educators alike? Would it have some previously unknown traces, awaiting our discovery and description? Would any of our time there also involve close encounters with large reptilian tracemakers? Signs point to yes. Thanks for reading, and look for that next post soon.
After visiting Cumberland Island and Jekyll Island, our Barrier Islands class had entered its third day (Monday, March 11), and was now about to embark onto our third and fourth barrier islands of the Georgia coast. These islands were a Pleistocene-Holocene pair – St. Simons and Little St. Simons, respectively – and the latter was our primary goal. After all, Little St. Simons is a privately owned and undeveloped island, one of the few that has not been logged or otherwise majorly altered by those ever-nefarious and industrious post-Enlightenment humans. St Simons, though, had its own lessons to teach us, including a realization I had that ichnological factors (bivalve feces, specifically) had played a role in deciding the fate of European power struggles on the Georgia coast during the 18th century.
Just like the previous two posts, this one will be told through photos and captions, which I hope captures much of what my students and I learned during our times on these two islands. Just watch out for those tails.
Little St. Simons is a privately owned island, but is available for day tours of groups like ours that are led by their knowledgeable and friendly naturalists. Soon after arriving by small boats on the island and being greeted by the naturalists assigned to us, Laura (pictured) and Ben (you’ll see him soon enough). While there, Laura provided a brief introduction to the geological history of Little St. Simons: Holocene (probably only a few thousands years old), and rapidly gaining weight (sediment, that is) each year, supplied by the nearby Altamaha River.
Check out our air-conditioned field vehicles! Seeing that this is a field course, traveling this way was ideal for experiencing the island a bit more directly, yet without descending in a Heart-of-Darkeness or Lord-of-the-Flies sort of mode. Because that would be bad.
Little St. Simons has a healthy number of freshwater wetlands for such a small island (like this one), more closely resembling what used to be on the Georgia barrier islands before a few people decided that plantations and paper mills were great ideas.
Say, isn’t that an all-American bird? Yes, it is, but more importantly, it has a rather prominent trace next to it – a bald eagle nest – that is also occupied by a couple of young eagles. (Here, one is sticking its head out of the nest while being overseen by a protective parent.) Bald eagle nests are among the largest tree nests made by any modern bird, leading me to wonder what tree-dwelling dinosaur nests from the Cretaceous Period must have looked like.
Sorry folks, can’t get enough of bird traces on this island. Many of the tree trunks on Little St. Simons bear the horizontally aligned holes of yellow-bellied sapsuckers. These woodpeckers pierce tree trunks to cause the tree to bleed sap, which attracts insects, which get stuck, which get eaten by the sapsuckers. Sap + insects = tasty treat!
Armadillo tracks on a coastal dune at the north end of the island show just how far-ranging these mammals can get. Having only recently arrived to the Georgia coast since the 1970s, these prolific tracemakers are now on every island.
Near the armadillo tracks, also in the coastal dunes, were these mystery burrows. I had no idea what made these, as they were too small to be mole burrows, too big to be insect burrows, and too horizontal to be mouse burrows. Just a reminder that even the author of a 700-page book about Georgia-coast traces still has a lot more to learn.
Aw, look at this cute little baby alligator, which was near its momma in one of the freshwater ponds on Little St. Simons. I wonder where it came from originally?
Why, there’s where it came from: it’s momma’s nest! The arrow is pointing toward a now mostly collapsed alligator nest, which hatched the little tykes that are now in the nearby wetland. Alligator nests are composed mostly of loose vegetation that the mother collects and piles, enough that it will give off heat to incubate her eggs. Such nests have very poor preservation potential in the fossil record, but it is still very interesting to study how they disintegrate so rapidly.
Alligators (left) and birds (right, with one on her nest) last shared a common ancestor early in the Mesozoic Era, but here they are, working together to their mutual benefit. Great egrets and woodstorks nest on islands, which are guarded by large alligators, who are good deterrents to egg predators. (In a grudge match between an alligator and raccoon, who do you think would win?) As payment for this protection, alligators get an occasional chick falling out of the nest, a small evolutionary price for the birds to pay when compared to an entire clutch of eggs getting munched.
My, what a noisy tail you have! We were delighted to encounter this diamondback rattlesnake on one of the sandy roads of Little St. Simons, which urged us to approach it carefully, using a clearly audible warning and threat postures. (P.S. It worked.)
Our other guide, Ben, had an obviously deep affection for venomous reptiles, expressed first through some impromptu snake-handling. (No, he did not use his hands, nor did he speak in tongues. See that snake-handling device in his right hand?) Following our not-too-close encounter, he expounded on the ecological importance of rattlesnakes to the island, and related some interesting facts about rattlesnake behavior. Gee, you think the students might remember some of this lesson? (Personal note: Bring rattlesnakes into the classroom more often.)
At the south end of Little St. Simons is a very nice beach, and on that beach were – you guessed it – shorebird tracks. Here are some plover tracks, which could be from Wilson’s plovers, semi-palmated plovers, or some other species.
Sadly enough, our tour of Little St. Simons lasted only until 3:00 p.m., so we had some time on St. Simons to do a bit more learning. So I decided we would stop at Fort Frederica National Monument, on the north end of St. Simons Island. It turned out this was a educationally sound decision, especially when one of the rangers on duty – Mr. Ted Johnson (right) – volunteered to give our group a spirited and informative lecture about the former military importance of Fort Frederica. However, judging from the downcast looks on several of the students, I imagine they were already missing alligators, snakes, and shorebirds of Little St. Simons Island, and (of course) their traces.
The most obvious human traces at Fort Frederica are these “footprints” (foundations) of some of the buildings there in the 18th century. Established as a British outpost in Georgia to compete with the Spanish presence to the south, Fort Frederica was a thriving town as long as the military was there.
OK, you’ve no doubt read this far to find out how bivalve feces helped the English to defeat the Spanish in the mid-18th century and consequently gain a permanent foothold in Georgia (until those pesky colonials defeated them later that century, that is). See where the fort is located? Right on a point, facing a tidal channel, and with salt marsh on either side of it. Because the salt marshes are largely composed of feces and similar muddy ejecta of ribbed mussels and other invertebrates, these make for wonderfully gooey substrates. Such substrates tend to discourage rapid movement of ordinance-laden ground troops, which forced the Spanish to try other means for attacking the fort, which failed. Bivalve feces for the win! Traces rule! ¡En la cara, los conquistadores!
As our day neared an end, my students decided that an appropriate way to signal their pleasure with all they had learned was for them to give me the now-official fiddler crab salute, waving their mock claws in unison. We all plan to still use this when greeting on the Emory campus, which should thoroughly mystify other students, faculty, and especially administrators, the latter of whom will wonder if it is some sort of secret-society sign. (Which, in a sense, it will be. Be afraid. Be very afraid)
What island was next on our journey? My old favorite, Sapelo Island, just to the north of Little St. Simons and St. Simons, and as different from these as the preceding islands were from one another. Stay tuned for those photos and comments in just a few days, and get ready to learn.
The second day of our Barrier Islands class field trip (Sunday, March 10), which is taking place along the Georgia coast all through this week, involved moving one island north of Cumberland (mentioned in this previous post), to Jekyll Island. I’ve been to Jekyll many times, but none of my students had, so they didn’t quite know what to expect other than what I had told them.
For one, I warned the students that Jekyll was not at all like Cumberland, which is under the authority of the U.S. National Park Service as a National Seashore. Consequently, it has a few residents, but is limited to less than 300 visitors a day. In contrast, many more people visit or live on Jekyll, and people have modified it considerably more. For example, Jekyll has a new convention center, regularly sized and miniature golf courses, a water park, restaurants, bars, and other such items absent during most of its Pleistocene-Holocene history. Another difference is that a ferry was need to get onto Cumberland, whereas we could drive onto Jekyll and stay overnight there in a hotel.
So why go there at all with a class that is supposed to emphasize the geology, ecology, and natural history of the Georgia barrier islands? The main reason for why I chose Jekyll as a destination for these students was so they could see for themselves the balance (or imbalance) between preserving natural areas and human development of barrier islands. Jekyll is one of those islands that is “in between,” where much of its land and coastal areas have been modified by people, but patches of it retain potentially valuable natural-history lessons for my students.
So what you’ll see in the following photos will focus on those more natural parts of Jekyll island, with some of the wonders they hold. However, this series of photos will end with one that will shock and horrify all. Actually, you’ll probably just shake your head and sigh with rueful resignation at the occasional folly of mankind, especially when it comes to managing developed barrier islands.
We started our morning like every day should start, with ichnology. Here, tracks of a gray fox, showing direct register (rear foot stepping almost exactly into the front-foot impression) cut between coastal dunes on the south end of Jekyll Island. The presence of gray foxes on Jekyll has caused some curiosity and concern among residents, with the latter emotion evoked because these canids are potential predators of ground-nesting birds, like the Wilson’s plover. Also, people have no idea how many foxes are on the island. If only we had some cost-effective method for detecting their presence, estimating their numbers, and interpreting their behavior. You know, like tracking.
My students show keen interest in the gray fox tracks, especially after I tell them to show keen interest as I take a photo of them. Funny how that works sometimes.
A Wilson’s plover! At least, I think it is.( Birders of the world, please correct me if this is wrong. And I know you will.) We spotted a pair of these birds traveling together on the south end of the island, causing much excitement among the photographers in our group blessed with adequate zoom capabilities on their cameras. Wilson’s plovers are ground-nesting birds, and with both gray foxes and feral cats on the island, their chicks are at risk from these predators. Again, if only we had some cost-effective method for discerning plover-cat-fox interactions. Tracking, maybe?
Here’s a little secret for shorebird lovers visiting Jekyll Island. Walk around the southwest corner of the island, and you are almost assured of seeing some cool-looking shorebirds along the, well, shore, such as these American oystercatchers, looking coy while synchronizing their head turns. These three were part of a flock of about twenty oystercatchers all traveling together, which I had never seen before on any of the islands. If you go walking on Jekyll, and know where to walk, you’ll see some amazing sights like this.
You were probably all wondering what American oystercatcher tracks look like, especially those made by ones that are just standing still. Guess this is your lucky day. Also notice the right foot was draped over the left one, causing an incomplete toe impression on the right-foot one. Wouldn’t it be nice to find a trace fossil just like this?
Black skimmers! We didn’t get to see them skim, but we still marveled at this flock of gorgeous shorebirds. These were in front of the oystercatchers, with an occasional royal tern slipping into the party, uninvited but seemingly tolerated.
Yeah, I know, you also wanted to know what black skimmer tracks look like. So here they are. Now you don’t need to use a bird book to identify this species: just look at their tracks instead!
You think you’re bored? Try being driftwood, with marine clams out there adapted for drilling into your dead, woody tissue. This beach example prompted a nice little lesson in how this ecological niche for clams has been around since at least the Jurassic Period, which we know thanks to ichnology. You’re welcome (again).
Beach erosion at the southernmost end of Jekyll gave us an opportunity to see the root systems of the main tree species there, such as this salt cedar (actually, it’s a juniper, not a cedar, but that’s why scientists use those fancy Latinized names, such as Juniperus virginiana). My students are also happily learning to become the scale in my photos, although I suspect they will soon tire of this.
Look at this beautiful maritime forest! This is what I’m talking about when I say “…patches of it [Jekyll Island] retain potentially valuable lessons in natural history.” This is on the south end of the island, and this view is made possible by walking just a few minutes on a trail into the interior.
Few modern predators, invertebrate or vertebrate, provoke as much pure unadulterated giddiness in me as mantis shrimp. So imagine how I felt when, through sheer coincidence, a couple walked into the 4-H Tidelands Nature Center on Jekyll, while I was there with my class, and asked if I identify this animal they found on a local beach. The following are direct quotations from me: “Wow – that’s a mantis shrimp!! Squilla empusa!! It’s incredible!!” I had never seen a live one on the Georgia coast, and it was a pleasure to share my enthusiasm for this badass little critter with my students (P.S. It makes great burrows, too.)
A stop at the Georgia Sea Turtle Center on Jekyll was important for my students to learn about the role of the Georgia barrier islands as places for sea turtles to nest. But I had been there enough times that I had to find a way to get excited about being there yet again. Which is why I took a photo of their cast of the Late Cretaceous Archelon, the largest known sea turtle. I never get tired thinking about the size of the nests and crawlways this turtle must have made during the Cretaceous Period, perhaps while watched by nareby dinosaurs.
At the north end of Jekyll, shoreline erosion has caused the beach and maritime forest to meet, and the forest is losing to the beach. This has caused the forest to become what is often nicknamed a “tree boneyard,” in which trees die and either stay upright or fall in the same spot where they once practiced their photosynthetic ways.
Quantify it! Whenever we encountered dead trees with root systems exposed, I asked the students to measure the vertical distance from beach surface to the topmost horizontal roots. This gave an estimate of the minimum amount of erosion that took place along the beach.
Perhaps a more personal way to convey the amount of beach erosion that happened here was to see how it related to the students’ heights. It was a great teaching method, well worth the risk of being photobombed.
Are you ready? Here it is, in three parts, what was without a doubt the traces of the day. Start from the lower left with that collapsed burrow, follow the tracks from left to right, and look at that raised area on the right.
A close-up of the raised area shows a chevron-like pattern, implying that this was an animal that had legs, and knew how to use them. Wait, is that a small part of its tail sticking out of the left side?
Violá! It was a ghost shrimp! I almost never see these magnificent burrowers alive and outside of their burrows, and just the day before on Cumberland Island, the students had just learned about their prodigious burrowing abilities (the ghost shrimp, that is, not the students). I had also never before seen a ghost shrimp trackway, let alone one connected to a shallow tunnel on a beach. An epic win for ichnology!
This may look like soft-serve ice cream, but I suspect that it’s not nearly as tasty. It’s the fecal casting of an acorn worm (Balanoglossus sp.), and is composed mostly of quartz sand, but still. These piles were common on the same beach at the north end of Jekyll, but apparently absent from the south-end beach. Why? I’m guessing there was more food (organics) provided by a nearby tidal creek at the north end. But I’d appreciate all of those experts on acorn worms out there to augment or modify that hypothesis.
This is how dunes normally form on Georgia barrier-island beaches: start with a rackline of dead smooth cordgrass (Spartina alterniflora), then windblown sand begins to accumulate in, on, and around these. Throw in a few windblown seeds of sea oats and a few other dune-loving species of plants, and next thing you know, you got dunes. Dude.
In contrast, here is how not to form dunes on Georgia barrier-islands beaches. Build a concrete seawall on the middle part of the island, truck in thousands of tons of metamorphic rock from the Piedmont province of Georgia, place the rocks in front of the seawall, and watch the beach shrink. So sad to see all of that dune-building smooth cordgrass going to waste. Anyway, the contrast and comparison you just saw is also what my students experienced by standing in both places the same day.
Jekyll Island gave us many lessons, but we only had a day there. Which islands were next? St. Simons and Little St. Simons, with emphasis on the latter. So look for those photos in a couple of days, in between new exploits and learning opportunities.
Part of a storm washover fan on St. Catherines Island (Georgia), with the sea to the left and salt marsh (with a patch of forest) in the background. Say, I wonder what made those tracks coming out of the tidal creek and toward the viewer? (Photograph by Anthony Martin.)
That ain’t no skink: the distinctive tracks and tail drag-mark of a large alligator, strolling through a storm-washover fan and next to a salt marsh. You think these animals are “freshwater only”? Traces disagree. Scale = 10 cm (4 in). (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)
Alligator trail cutting through a salt marsh. Trail width was about 45-50 cm (18-20 in), which is about twice as wide as a raccoon trail. And it wasn’t made by deer or feral hogs either, because, you know, alligators. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)
Hey, what’s going on here? Who would dare to erase and fill in giant alligator tracks? Don’t they know who they’re dealing with? (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)
Going, going, gone: alligator tracks nearly obliterated by burrowing, surface scraping, and sand balls caused by feeding of sand fiddler crabs (Uca pugilator). (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia; scale in centimeters.)
Don’t believe me about fiddler crabs moving into alligator claw marks? OK, then what’s that I see poking out of that alligator claw mark (red square)? (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia; scale in centimeters.)
Why, it’s a small sand fiddler crab! Does it care that its new home is an alligator claw mark? Nope. Does ichnology rule? Yup. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia.)
Need a free burrow? Then why start digging a new one when alligator claw marks (arrow) gives you a nice “starter burrow”? Notice the sculpted, round outline, showing the claw mark was modified by a crab. Also check out the sand balls left outside of the other claw marks, meaning these have probably been occupied and mined for food by fiddler crabs, too. (Photograph by Anthony Martin, taken on St. Catherines Island, Georgia; scale in centimeters.)
