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

For today’s entry in the holiday-and-ichnology inspired countdown of Georgia-coast traces, we will move from the maritime forest to the shoreline, where a trace made through the behavior of one species of molluscan – the knobbed whelk (Busycon carica) – influenced the behavior (and hence traces) of another molluscan – the dwarf surf clam (Mulinia lateralis).

These traces then attracted shorebirds, which added their tracks and beak probe marks to the molluscan traces. This is a excellent modern example of how the interaction of one species of animal with a sediment can affect the interactions of other species with that same sediment, leading to their creation of composites traces.

Whelks-Dwarf-Surf-Clams-Burrowing-JekyllSee all of the knobbed whelks (Busycon carica) in this photo? I know, you don’t actually see their shells because they buried themselves, but you see their outlines on this sandy beach surface because of the many dwarf surf clams (Mulinia lateralis) that burrowed around them. Also look for all of the bird tracks and probe marks around the whelks. (Photograph by Anthony Martin, taken on Jekyll Island, Georgia.)

I’ve already written about these composite traces and the ecological story they tell, so for those details, go to this link and this link. But the summary version goes like this:

  • Low tide stranded the whelks and clams on the beach.
  • Whelks used their muscular feet to pull themselves into the still-wet sand to avoid desiccation and predation.
  • Clams took advantage of disturbed (liquified) sand around the whelks and buried themselves, also to avoid predation and desiccation.
  • Shorebirds saw whelk-shaped concentrations of clams, chowed down on them.

The story gets more complicated in places, especially when seagulls decided they also wanted to eat the whelks, but that’s most of it. So next time you’re on a beach and you see a triangular-shaped concentration of small clams, take a second look to see whether there’s a live whelk underneath it: traces begetting traces.

Further Reading

Busycon carica: Knobbed Whelk. Smithsonian Marine Station at Fort Pierce.

Mulinia lateralis: Dwarf Surf Clam. Smithsonian Marine Station at Fort Pierce.

Links to Previous Posts in This Theme

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

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

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

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

Continuing the theme this week of celebrating the traces of the Georgia barrier islands, we this time move inland to the maritime forests, where a myriad of traces await us, most of them made by the true rulers of our planet, insects. In this instance, let’s focus on those insects that leave many well-defined and easily visible traces in so-called “dead” trees in those forests.

Beetle-Borings-SapeloA fortuitous exposure of insect tunnels bored into the wood of a “dead” pine tree (probably a loblolly, Pinus taeda). Most of these traces are probably from beetles, although other borings in any given tree could also be from carpenter ants, carpenter bees,and termites. And what made the big, deep holes? Just some insect-eating dinosaurs that some people insist on calling “woodpeckers.” (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)

Although I’ll admit that I’m just an enthusiastic novice when it comes to insect traces, I can’t help but notice and stop to admire those left in wood. Although termites, carpenter bees, and carpenters ants are arguably more famous (or infamous) for their wood-drilling abilities, by far the most intriguing traces for me are those left by wood-boring beetles.

Often nicknamed “bark beetles,” they belonging to an evolutionarily related group represented by thousands of species, Scotylinae. Bark-beetle traces consist of shallow tunnels made just below the bark surface of a tree, sometimes back-filled with chewed woody material, called frass. Their pathways can be smooth, simple, meandering tunnels, but also commonly branch into complicated patterns. My favorites of these are the galleries made by beetle larvae that, upon hatching from their eggs, drill outward from a central tunnel, rendering a centipede-like form. Incidentally, this behavior has also been around for a very long time: I’ve seen trace fossils in Late Triassic petrified trees – from nearly 200 million years ago – nearly identical to those made by modern beetles.

On the Georgia coast and elsewhere in the southeastern U.S., the most likely makers of these tunnels are Southern pine beetles (Dendroctonus frontalis). However, invasive species of beetles are also leaving their marks on native trees, such as the red bay ambrosia beetle (Xyleborus glabratus), which is quite rightly blamed for the decline of an important plant species on the Georgia coast, red bay (Persea borbonia). The overall trace this beetle leaves is a dying red bay, its once green and aromatic leaves reduced to brown, odorless husks.

These insect traces serve as a dual reminder during our walks through the maritime forests of the Georgia barrier islands. One is that none of these trees we label as “dead” actually fulfill such a glib description: in fact, they are teeming with thousands of insect lives. A second note to make is that the larger, deeper holes preserved in the tree – alongside and intersecting the insect borings – tell of their ecological and co-evolutionary connection with living dinosaurs, the insectivorous birds that specialize in pounding wood. When did such dinosaur-on-insect-in-wood behavior first start? As far as I know, we don’t know. Nevertheless, I have every confidence that trace fossils will eventually guide us to a much more satisfying answer than our current collective shrug.

Further Reading

Scolytinae – Bark and Ambrosia Beetles: BugGuide

Bark Beetles: University of California (Davis) Integrated Pest Management

Bark and Wood-Boring Beetles of the World: Barkbeetles.org

Links to Previous Posts in This Theme

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

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

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

As mentioned in yesterday’s post, I will be celebrating the traces of the Georgia barrier islands over a 12-day period approaching the holidays (you know: Winter Solstice, Christmas, Kwanzaa, Boxing Day, and New Year’s). To keep it relatively simple, each post will be about traces from a Georgia barrier island depicted in a single photograph, followed by my pithy descriptions and trenchant analyses, which may be accompanied by witty asides (or not). Today’s topic is on the feeding traces made by those cute little shorebirds, semipalmated plovers (Charadrius semipalmatus).

Plover-Tracks-ProbesSeimpalmated plover (Charadrius semipalmatus) tracks and probe marks made by their beaks on a sandy mudflat of Sapelo Island, Georgia. See the differences between the fresher probe marks versus the older ones? And what made those really tiny holes? (Photograph by Anthony Martin.)

Plover tracks in general show just three toes registering (no rear toe impression), are asymmetrical with an acute angle between the inner two toes, and have some webbing between the outermost two toes. If the toes were completely webbed, like that of a duck or goose, the foot form would be called palmate, but because it’s only semi-webbed, it’s called, well, I think you get it.

Although I didn’t see the birds making these tracks and probe marks, I’m fairly sure they were done by semipalmated plovers – rather than other species of plovers – based on tracks sizes and the commonness of this species on the Georgia coast. (What’s the scale? My finger is about 2 cm (0.8 in) wide, and don’t worry, it’s just my index finger.) These birds either walk fast, run, or stand still when they’re on the ground, and about the only reasons they have for standing still are to eat. The spacing between their tracks can act as an informal speedometer, with short spaces corresponding to walking and longer ones to running.

OK, so I identified the trackmaker, which means we’re done with all of that bothersome thinking stuff and we just end this post now, right? In a word, nope. It’s time to apply the awe-inspiring wisdom and power of ICHNOLOGY to this photo.

The combination of tracks and probe marks here, along with the teensy-weensy holes on the surface (did you just now see those?), give us insights on why the plovers were there in the first place. The tiny holes are probably made by the siphons of small clams: notice how some of them are paired, a typical pattern caused by incurrent (inhalant) and excurrent (exhalant) siphons for bringing in and pumping out water, respectively. The plovers were probably hunting these clams at low tide, along with any other yummy invertebrate treats they might have found once they stuck their beaks into someone’s business.

Notice also how the probe marks vary considerably in their diameters. This is a result of the plover finding its prey on the first try, or having to insert its beak several times to seek out their meals; the latter caused overlapping probe marks and a small depression. In some instances, these depressions collapse and form not-so-clear evidence of shorebird predation. Take another look at the photo: how many “old” feeding probes do you see now?

So if you’re a geologist looking at rocks of the right environments and ages for containing the traces of shorebirds – basically from the Early Cretaceous Period (~120 million years ago) onward – don’t just get all proud of yourself for just finding their tracks, slapping a name on those tracks, and dashing off a paper to your favorite journal. Look again for probe marks with those tracks, collapsed probe marks, and traces of those little invertebrate morsels that might have attracted those birds to that place, and then. There’s some little, once-breathing lives preserved in those rocks, wanting you to probe below the surface and learn about more about them.

Further Reading

Semipalmated plover. National Audubon Society.

Semipalmated plover. Cornell Lab of Ornithology.

Charadrius semipalmatus: semipalmated plover. Animal Diversity Web, University of Michigan.

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

In a celebration of the traces of the Georgia barrier islands and the holidays (in order of importance), over the next 12 days I will attempt to post photographs of Georgia-coast traces, along with brief explanations of them. As a special bonus, I may even point out why they’re interesting. But maybe the visual information provided by the photos of these traces (and sometimes their tracemakers) will do the talking for me.Periwinkles-Grazing-Sapelo-IslandMarsh periwinkles (Littoraria irrorata) on a muddy high-marsh surface of Sapelo Island, Georgia, leaving nicely defined trails through their grazing. (Photograph by Anthony Martin.)

By happy coincidence, this photograph depicts 12 marsh periwinkles (Littoraria irrorata) on a marsh surface, making meandering trails while grazing on delectable algae. Normally this snail does most of its grazing on fungi and algae growing on stems and leaves of smooth cordgrass (Spartina alterniflora). So it was a treat to see these little tykes on a sedimentary surface, leaving some traces comparable to what earth scientists might find as trace fossils in the geologic record.

The trails they make are shallow furrows with millimeter-high levees, which they form by extending, anchoring, and pulling with a muscular foot, which helps the perwinkle’s shell to catch up with the rest of its body. They also leave mucus on their trails, which helps smooth out the ride for them, but also aids in preserving the form of their trails, as the mucus weakly binds the mud underneath where they travel.

A cautionary note for all budding ichnologists out there: notice how some of the trails made by different periwinkles intersect one another. This creates a false “branching” structure that – if fossilized – could be mistaken for a branching burrow made by one animal, which would make you doubly wrong. So if you encounter a trace fossil that looks like this, look at the “burrow” junctions (branching points), and see whether one part of the “burrow” cross-cuts the other, which may be marked by a levee. In other words, be a good scientist and test your hypothesis using, like, you know, evidence-based reasoning.

What will be the subject of the next traces, on the 11th day of Ichnology? I have no idea yet, but suppose we’ll both know by tomorrow. In the meantime, happy trails to you!

Further Information

Littorina irrorata: Marsh Periwinkle. Animal Biodiversity Web.

Littorina irrorata: Marsh Periwinkle. Smithsonian Marine Station at Fort Pierce.

Littorina irrorata: Marsh Periwinkle. Encyclopedia of Life.

Life Traces of the Victoria Coast: Australia’s Oldest Bird Tracks

The track seemed familiar, like a face I had seen before but couldn’t quite identify. Then I realized who it belonged to, and where I had seen many others like it. It was a bird track, remarkably similar to those in the sands and muds of the Georgia coast, made daily by the herons, egrets, and shorebirds. The other two tracks near it were similar in size and shape, but not nearly as evocative as this one. This footprint conjured an image of a bird slowing its descent from flight, then abruptly halting, planting its feet on a moist, sandy surface.

Modern-Fossil-Bird-Flight-TracksFootprints of flying birds, separated by 10,000 miles and more than 100 million years. The track on the left is from a great egret (Ardea alba), which landed on a hard-packed fine-grained sand of a coastal beach on Jekyll Island, Georgia. The track on the right is from a similarly sized bird that landed on a moist, loose fine-grained sand of a polar river floodplain during the Early Cretaceous Period, in a place now called Dinosaur Cove, Victoria, Australia. Oh yeah, it’s also one of two of the oldest bird tracks in Australia. (Both photographs by Anthony Martin; each track is about 10 cm (4 in) wide.)

Except this track was from a vastly different time, place, environment, and climate from the modern-day Georgia coast. It was fossilized in an Early Cretaceous (105-million-year-old) sandstone and collected from the coast of Victoria, Australia, at an auspiciously named spot called Dinosaur Cove. Because Australia was close to the South Pole then, this track and the other two near it were made in a polar environment. The environment was not coastal, either, but the sandy floodplain of a river valley shaped by melt-waters that flowed with each spring thaw.

Even more incongruously, I first saw this track and its petrified companions in the basement of Museum Victoria in downtown Melbourne, Australia, a thriving, cosmopolitan city of more than 4 million just outside the quietude I was experiencing then. Mentally and physically, I was about as far away from the Georgia coast as I could be, rendering the track’s familiarity both jolting and eerie.

Cretaceous-Bird-Track-LRA closer look at this fossil track, made by the right foot of a descending bird about 105 million years ago. Try to match the following verbal description with what you see here. (Photograph by Anthony Martin; scale to the left in centimeters.)

It had four thin toe impressions, like a slightly askew “peace” sign, with three forwardly pointing and spread widely, and one pointing behind. A linear claw mark – nearly as long as the three-toed part of the footprint – corresponded with the rearward-pointing toe, which had also left a faint impression. Sand piles only millimeters high were in front of the other three digits; another small mound of sand in the center toe impression was neatly bisected by a claw mark from that digit. This central claw mark was a trace of its next step, in which it pushed against the sand with the bottom of its foot and cut through the resulting hillock as its foot retracted. The forward toes made for a foot length slightly greater than the fingers on my hands, so it was about the right size for a small heron- or egret-like bird.


A more analytical look at this track. (A) Photograph showing how it looks on the sandstone surface, along with some of the little hills and valleys associated with it. (B) Interpretative drawing, showing: each digit, labeled from I (hallux) to IV; an approximation of the foot’s overall form (gray outline), the structures around and in the track, the main direction of movement by the foot as the bird landed (big arrow), and the direction of movement taken by that foot in its next step (little arrow). (Both photo and drawing by Anthony Martin; scale bar in both figures = 5 cm (2 in).)

The long, linear claw mark behind most of the track was the primary clue to both its identity and behavior. This was from a hallux, which in humans is our “big toe,” (digit I). But in birds, it is the backward-pointing toe of those that perch, a trait that better allows them to grasp branches in trees. Earlier that year (2011), I had told Tom Rich – a vertebrate paleontologist at Museum Victoria – that the thin-toed theropod dinosaur tracks we discovered in rocks just east of Dinosaur Cove in 2010 were likely not made by birds because they all lacked this identifying feature. Although Cretaceous bird tracks identified elsewhere in the world (Canada, the U.S., Korea, and China) do not always have a hallux, its absence makes it much more challenging to separate these tracks from those of similar looking non-avian dinosaurs.

Yet it was not just the hallux impression that convinced me of its identity, but its lengthiness. This mark was not a mere anatomy lesson, but also a window into what that bird was doing one day 105 million years ago, which was flying. The then-soft, wet sand had been sliced by the sharp claw on the hallux, which contacted the sand first before the rest of the foot registered. As this toe slid forward and stopped, the other digits came down, and forward momentum caused their leading edges to push against the sand, mounding it in front of these toes.

For those of you who saw my previous post about modern bird landing tracks (here), you probably watched this slow-motion video of a sparrow landing and taking off, and you probably watched it twice, because it’s just so stunningly beautiful. Regardless of whether you’ve watched it or not, view it one more time, then look at my interpretative drawing below to see how the same landing movement can be applied to a larger, heron-sized bird, and in a moist sand.

Cretaceous-Bird-Landing-Track-LRIn this partly interpretive, partly speculative drawing, I’m trying to show how the right foot of a heron-like bird, combined with its behavior and a wet, sandy substrate, could have caused the primary features in the Early Cretaceous bird track from Dinosaur Cove. Because the left footprint is not preserved in the rock, I’m assuming that it landed ahead of the right foot. As a result, it is shown here not quite landing, just a fraction of a second behind the right foot, and only represented in my mind by an imagined shadow. So what’s with the feather? Hey, I’m an artist, too. Feel free to find your own meaning in that, preferably aided by bongos.

Based on my years of experience with Georgia-coast bird tracks, the qualities of this fossil track were consistent with those in tracks made by similar-sized birds – such as small herons or egrets – that landed after flight. Ichnologists call such traces volichnia (= “flight traces”), which are rare in the fossil record, but abundantly represented in soft substrates today wherever flying birds might live. Some of the most evocative of such traces are left in snow, such as those made by owls preying on small mammals, but look closely for them on beaches or river floodplains, and you will find them. Volichnia thus neatly answer the oft-asked question: why do birds’ tracks suddenly appear?

Egret-Landing-Tracks-2Close-up of great egret tracks made by landing on a hard-packed beach sand, Jekyll Island. Both feet left long hallux claw impressions, although in this instance the left foot preceded the right when landing. (Photograph by Anthony Martin, scale in centimeters.)

Tricolored-Heron-Landing-2Close-up of landing tracks of a tricolored heron (Egretta tricolor) on a looser, moister, fine-grained sand in the back-dune area of St. Catherines Island, Georgia. The substrate conditions for these tracks are much closer to original ones for the Victoria tracks than those of a hard-packed beach sand. Notice how the hallux claw impression in the left foot is longer than the one on the right foot, which only shows up as a dot. (Photograph by Anthony Martin, scale in centimeters.)

I described bird-flight tracks in my book Life Traces of the Georgia Coast (pages 386-391) in a section where I advised paleontologically inclined readers to apply and test these criteria with fossil bird tracks. But with these tracks from Victoria, I was unexpectedly following my own advice, a situation that encourages uncomfortable feelings in scientists who tend to be overly self-critical of their work (guilty as charged).

Moreover, at the time I was looking at these and the other two tracks (July 2011), my book had not been published yet, nor had I ever written or published any peer-reviewed paper on bird tracks. Sure, I’m an example of what Malcolm Gladwell wrote about in his book Blink, an expert who had a minimum of 10,000 hours of field experience backing up my intuition (a number that, quite frankly, he must have pulled out of his cloaca). Backing up this intuitive and experience-based conclusion, however, posed a huge challenge, like a fledgling trying to decide whether it was time to leave its nest and take a test flight. It’s not the ill effects of possible free-fall to fear, but the predators waiting to pounce on an avian-ichnological novice like myself.

Frustratingly, though, the rock holding these tracks lacked any other evidence of that next step, as well as the other foot. The track was of the bird’s right foot. As seen in the previous photos, volichnia made by landing birds have paired footprints, right and left together but slightly offset, and with either the right or left foot behind the other. But the slab of rock had no track behind this right-foot impression, and it was broken along the front edge of the middle digit. If this bird had landed with the right foot first – which I think it did – then the left foot would have been more than a track length ahead of the right. If so, it may be gone forever, taken by the same coastal erosion of the Victoria coast that gave its discoverers the surviving tracks, who arrived just in time to save them.

How were these tracks found? Not by me, that’s for sure. They were discovered by the invaluable, indispensable, and intrepid allies of desk-bound, exam-grading, lab-teaching, and meeting-imprisoned paleontologists everywhere: volunteers. On November 29, 2010 – almost three years ago – Museum Victoria volunteers Sean Wright and Alan Tait were at Dinosaur Cove, scouting for bones along its rugged, rocky shore. The name for this place was not bestowed on it because it resembled a Stegosaurus or some other pareidolia, but because it was the same place where most of the dinosaur bones known in Australia were found and recovered.

Excavated during the 1980s-1990s, Dinosaur Cove – which is about a three-hour drive west of Melbourne – was among the most logistically difficult dinosaur dig-sites in the world, as described by Tom Rich and Patricia (Pat) Vickers-Rich in their book, Dinosaurs of Darkness (2000, Indiana University Press). It and another site about a two-hour drive east of Melbourne, Dinosaur Dreaming, have resulted in the most complete assemblage of polar-dinosaur bones in the Southern Hemisphere.

Thus Wright and Tait were not searching randomly along the coast, but were looking for rocks that might contain fossil bones that had eroded out of the coastal outcrop. Instead of bones, though, Wright spotted the three-toed patterns of fossil tracks in a slab of rock amongst the boulders and cobbles in the surf zone. With this discovery, Dinosaur Cove was suddenly and inadvertently added to a very short list of Cretaceous vertebrate tracksites in southern Australia.

Tait-Photo-Dinosaur-Cove-TracksThe slab of rock with the oldest known bird tracks in Australia. The two on the right we diagnosed as from birds, whereas the one on the left is probably a mere non-avian theropod track. (Photograph by Alan Tait.)

At the time, Wright and Tait figured these were probably fossil footprints of dinosaurs, such as theropods or ornithopods, both of which make three-toed tracks. When Tom e-mailed me photos of the tracks, I confirmed that they were tracks, and that they looked a lot like the theropod-dinosaur tracks I had described from rocks of the same age from Milanesia Beach, about 9 kilometers ( 5.5 miles) east of Dinosaur Cove.

About four months later, on March 31, 2011, Tait went back to Dinosaur Cove with some hand tools and a backpack, and broke the slab into four large pieces so they could be transported on foot: which he did, and with all 45 kg (100 lbs) on his back. For anyone who has hiked into and out of Dinosaur Cove – which I have several times – this was a remarkable one-person recovery effort, one that some people might term as “crazy.” But this craziness paid off big time.

The bird tracks had also come in for a landing a second time on the rocky shore of Dinosaur Cove, having fallen off the outcrop as a consequence of coastal erosion. Tom recognized the rock as coming from a sandstone bed just above the Slippery Rocks Tunnel site, where he, Pat, and many volunteers dug, broke, blasted, sifted, cursed, and otherwise labored in their quest to collect the dinosaurs there.

Tait-Photo-Dinosaur-CoveThe Slippery Rocks Tunnel (SRT) site, where what was originally the greatest number of polar dinosaur bones in the Southern Hemisphere were found in the 1980s-1990s. The arrow shows where the slab holding the tracks was located until Alan Tait took it out of there and to Museum Victoria. The probable source bed (SB) for the tracks is just above the tunnel. (Photograph by Alan Tait, taken on November 29, 2010, the day the tracks were discovered.)

Dinosaur-Cove-WrightAnother look at where the tracks were discovered, but from the other direction (looking west). I’m not sure if that’s Alan Tait in the photo and it was taken by Sean Wright, or whether it’s Sean Wright and the photo was taken by Alan Tait. Anyway, check out all of those Cretaceous rocks!

Great discovery, huh? Obviously, it was time for us to contact the press and breathlessly report that we had the oldest bird tracks in Australia. Except that, no, that would have been totally wrong, and would have served as a great example of how science is not done. This had to go through peer review, which meant that no matter how confident I might have been about their identity, they’re being described in a peer-reviewed publication and acceptance by the rest of the paleontological world was not guaranteed. So I asked Pat Vickers-Rich and Tom Rich to coauthor it, and was delighted when they accepted; sedimentologist Mike Hall of Monash University later joined us as a co-author, too.

Figure-2-DraftThe broken slab of rock found by Sean Wright and Alan Tait at Dinosaur Cove, then taken out of there by Alan Tait, but now in its final resting place, the basement of Museum Victoria in Melbourne, where it’s been given a specimen number. Tracks ! and 2 (T1 and T2) are interpreted as bird tracks, whereas the one on the far left (T3) is probably a non-avian theropod dinosaur track. The arrow shows where the rock was sampled for describing the nature of the original sediments. What do I really love about this discovery?  That the theropod-dinosaur track is the ho-hum and so-what part of it. Take that, non-avian theropods! Birds rule!

To make an already long story much brief, a year-and-a-half went by before the paper was finally accepted and published in the journal Palaeontology last Friday. Peer review on this paper was tough, and among the most challenging I’ve faced in my career. Different versions of the paper went through two rounds of review with four different reviewers, two of whom were anonymous, and two of whom were not (thank you, Matteo Belvedere and Jenni Scott!). I almost gave up on it several times, having been so discouraged by negative comments that I overlooked the most affirming part, which was this: all of the reviewers agreed we had bird tracks, and that they were the oldest known in Australia. That kept me going.

Notice I said “tracks,” as in plural. A great benefit of the sometimes-demoralizing scrutiny provided by these reviewers was that most pointed to the track just left of the “landing” track and said, there’s another one. Although I originally thought it was from a non-avian theropod, they were correct: this was from a bird’s left foot, and one with a foot close in size and form to the other one, although it had a much less obvious hallux impression. One of the more interesting traits of this track, too, was how one of its digits flexed as the foot moved against the sand, leaving a curved impression.


Close-up of the other large bird track on the same surface and close to the first one. Although I don’t think this one represents flight – just walking – it was the right anatomical traits for a bird, including that hallux impression on the lower right side. (Photography by Anthony Martin, scale in centimeters.)

The third track presented a dilemma, as it had qualities of a thin-toed non-avian theropod track – think something like an oviraptorid or ornithomimid – but easily could have been that of a bird, in which its hallux didn’t register on the sand at the time. So we concluded that it was probably from a non-avian theropod, but are open to the possibility that it was from a bird, too.


The third track on the slab, which we interpreted as the right footprint of a non-avian theropod dinosaur. It also probably represents a double print, where the foot registered twice and distorted its features a bit. This track is also very similar to theropod tracks identified from rocks of the same age at Milanesia Beach, which is about 9 km (5.5 mi) east from Dinosaur Cove on the Victoria coast. (Photograph by Anthony Martin, scale in centimeters.)

Could we all be wrong, and none of these tracks are from birds, but from some theropod dinosaurs that were very close to birds in their foot anatomy? Sure, that’s possible, but not likely at this point. Could I be wrong about taking one track and interpreting it as evidence of flight? Again, that’s possible. Alternate explanations include that the bird just hopped – perhaps with a flap or two – before landing. Or its foot just slipped on the wet sand as it was walking forward. However, in my experience with modern birds, such tracks are even more rare than volichnia. Could Cretaceous birds in polar Australia have been more clumsy than those today, hence their slipping tracks would have been more common? OK, now that’s just silly. Let’s just celebrate this find for what it is:

  • The oldest known bird tracks in Australia.
  • The only Early Cretaceous bird tracks in the Southern Hemisphere.
  • The presence of fair-sized birds (herons or egrets) during the Early Cretaceous in a polar environment.
  • Evidence for flight in an Early Cretaceous bird track, one of the few examples known in the world.
  • The first vertebrate tracks known from Dinosaur Cove, a place previously famed for its dinosaur bones.
  • The first dinosaur track from Dinosaur Cove.
  • More evidence for Early Cretaceous birds in Australia to supplement the few bones that have been found thus far, including only a single furcula (wishbone) from Victoria.

All in all, it might just be three fossil tracks, but those three tracks just made the fossil record for the birds on an entire continent and the rest of the Southern Hemisphere just a little bit better. So now that they’ve landed, let’s allow our imaginations to take off, and go find some more.

Acknowledgments: My coauthors, Tom Rich, Pat Vickers-Rich, and Mike Hall; Sean Wright and Alan Tait; David Pickering and Rod Start at Museum Victoria; the Center for International Programs Abroad for transportation to and from Australia; my wife Ruth Schowalter for encouraging me during the 1.5 years of agonizing over the research; and of course, the tracemakers, avian and non-avian, who truly made the research possible by leaving tracks on that floodplain 105 million years ago.

Pertinent Links:

Martin, A.J., Vickers-Rich, P., Rich, T.H., and Hall, M. 2013. Oldest known avian footprints from Australia: Eumeralla Formation (Albian), Dinosaur Cove, Victoria. Palaeontology (published online October 25, 2013): DOI: 10.1111/pala.12082

ABC Science Show, October 26, 2013: “Fossilised Dino Bird Tracks 105 Million Years Old,” reported by Sharon Carleton.

Emory University Press Release (Eukekalert): “Tell-tale toes point to oldest-known fossil bird tracks from Australia.” (By Carol Clark, Emory University)



Why Do Birds’ (Tracks) Suddenly Appear?

Among my favorite tracemakers of the Georgia barrier islands are birds, a fondness inspired by their great variety (more than 200 species), numbers, and diverse behaviors. But if pressed to name my absolute favorite types of bird traces, I would not hesitate to say “flying tracks.”

Egret-Landing-TracksTracks from a great egret (Ardea alba) on a hard-packed beach sand that say, “I just flew in, and boy are my arms tired.” Notice the offset right-left tracks, long scratch marks left by claws on the rear toes, and cohesive bits of sand pushed forward by the egret’s feet when they contacted the sand. (Photograph by Anthony Martin, taken on Jekyll Island, Georgia.)

Now, “flying tracks” may sound contradictory, as a bird in flight leaves no tracks. But for those birds for which flight is an everyday habit, they take off and land, and many of these birds do so on the ground. This fact of avian life is recorded faithfully in the sands and muds of the Georgia barrier islands, and I have often delighted in encountering such tracks made by birds from sparrows to grackles to seagulls to pelicans to great blue herons. When covering this topic in my book (Life Traces of the Georgia Coast, just in case you needed reminding), I had to restrain myself from writing too much about it. Fortunately for readers, though, I described flight traces in enough detail there that I’m confident most people will be able to spot and recognize them. The following pictorial guide, most of which I showed during a recent talk to the Atlanta Audubon Society, should also help.

Sparrow-Flying-TracksFlight tracks of a small songbird (probably a species of sparrow) on coastal-dune sands, showing that it didn’t stick around very long: landing, a hop, then take-off. (Photograph by Anthony Martin, taken on Little St. Simons Island, Georgia.)

How to tell whether a bird was landing or taking off? Your first clue should be a blank area in mud or sand, which will be devoid of tracks just behind a bird trackway, or the opposite, a trackless place just beyond the last footprints. In both instances, tracks are normally paired (side-by-side). For example, here’s an entire sequence made by a common ground dove (Columbina passerina), from landing to walking to take-off.

Ground-Dove-Flying-TracksEntire landing, walking, and take-off sequence for a common ground dove (Columbina passerina) in back-dune area. Notice how it avoided the ghost-crab burrow by walking around it just before deciding to exit the scene. (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)

Ground-Dove-Landing-TracksClose-up of landing tracks, in which this ground dove came in from the right, then shuffled its feet to shift direction to its right. (Photograph by Anthony Martin.)

Ground-Dove-Takeoff-TracksClose-up of take-off tracks, where this ground dove was walking normally, then put its feet together and did one of its typically instant take-offs. (Pro-ichnologist tip: the scratch marks to the right are ghost crab tracks, not wing impressions.) (Photograph by Anthony Martin.)

Look closer at potential flight tracks and you will see other details that tell you whether a bird was coming down to earth or bidding the ground goodbye. Landing tracks often have long impressions behind them, “skid marks” that show how the bird decelerated and controlled its fall through a combination of body positioning and calculated flapping.

For larger birds with a backwards-pointing toe (hallux) – such as herons or egrets – these tracks usually leave a lengthy scratch mark from the claw on that foot. While landing, one foot plants in front of the other – either as an offset right-left or left-right pair – and the first track normally has the longer scratch mark. Either footprint also may have some mounding of mud or sand in front of it, as the forward momentum of the bird exerted pressure against whatever medium it encountered.

Egret-Landing-Tracks-2Another look at those great egret landing tracks shown previously, but now probably understood a little better through the power of words combined with images. ¡Viva Comunicación de la Ciencia! (Photograph by Anthony Martin.)

Flight-Trace-EgretClose-up of that great egret’s right track, with features showing how its foot slid across the beach surface as it slowed its descent, then stopped. (Photograph by Anthony Martin.)

In the following video of a sparrow both landing and taking off, watch how it points its rear claws toward the surface as it approaches, then make first contact, followed by the forward-pointing toes. Also notice how one foot barely precedes the other, which in its tracks would should up as a very slight offset between the two. (Warning: This video is exquisitely beautiful, and is best watched with mouth agape in wonder.)

Depending on how fast a bird came down, and taking into account lots of other factors (for example, wind direction and speed), this landing pattern could be followed by a hop, or it could just segue into a normal diagonal walking pattern. Also keep in mind that birds with small or absent halluces (plural of hallux) and full webbing between their toes – such as gulls – may just show their forward three digits skidded, leaving no claw marks in the rear part of the tracks.

Gull-Landing-Hop-SapeloLanding tracks of a laughing gull (Leucophaeus atricilla), in which it first skidded, but must have had enough forward momentum to keep it going forward with a big hop. (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)


Close-up of a different set of landing tracks from a laughing gull with nicely defined skid marks on both feet. (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)

Take-off patterns involve opposite movements, in which the feet come together, but the digits dig in and push off, leaving scratch marks from the claws and well-defined mounds of sand or mud behind the digits, instead of in front of them. They can also be quite ungainly: I’ve seen pelican and vulture trackways in which they either run or skip for five-six steps before they were aloft, with increasing distances between each successive set of tracks. But sometimes a large bird like a pelican can impress me with its tracks, showing where it successfully accomplished a sudden take-off from a standing start.


Take-off tracks of a brown pelican (Pelecanus occidentalis) in which it must have flown from a standing start. Also note the water-drop impressions in front of the tracks, indicating that the pelican had just been in the water and still had wet feathers when it took off. (Photograph by Anthony Martin, taken on Sapelo Island, Georgia.)

So given these search images, lots of birds, and blank canvases of coastal sand or mud, you should now be able to find and diagnose your own “flying tracks.” But you also don’t need to restrict your searches to beaches: these traces can be found wherever flying birds live and visit the ground.

Using such clues, could we ever apply them to recognize flying tracks from the fossil record? Why, yes indeed. And for those of you who read this fair, here’s your Easter egg. The contents of this post relate to a major scientific discovery that will be announced in a few days: you heard it here first. So look for that news to come in for a landing soon.


When You Write about Traces, Does It Make a Sound?

Nearly anyone who enjoys writing or reading good science writing knows there are a few tricks of the trade used to interest readers and motivate them to go from one sentence to the next. One technique I’ve heard about – and have used in Life Traces of the Georgia Coast, as well as my upcoming book Dinosaurs Without Bones – is the “sensory” one.

In this method, the writer refers to stimuli that connect with one, several, or all of the human senses in the narrative. Sometimes the inclusion of more than one sense is tough to do in science writing, especially if the science is being conducted in a lab. Yet it works very well with reporting natural history in the field, in which the writer experiences sights, sounds, smells, touch, and sometimes even taste while outside, and in less controlled circumstances.

Alligator-Tracks-Fiddler-Crab-Burrows-1Never mind the appearance of these alligator tracks and tail dragmark, and fiddler-crab burrows and feeding pellets. How do they sound?

I see writing as a continual exercise in which I will keep learning by doing it and honing it (with a recent instance of that here). My wife Ruth also recognizes this quality in me, and was thoughtful enough to give me a book related to this goal: Steering the Craft (1998) by famed author and poet Ursula Le Guin. What I love about this book is that Le Guin does not just dole out writing advice, but does it succinctly (thus leading by example), with good humor, and most importantly, puts theory into practice with writing exercises at the end of each chapter.

The first writing exercise dealt with sounds, and how language – even when written – should pay attention to it sounds. Here were her instructions:

BEING GORGEOUS: Write a paragraph to a page (150-300 words) or narrative that’s meant to be read aloud. Use onomatopoeia, alliteration, repetition, rhythmic effects, made-up words or names, dialect – any kind of sound-effect you like – but NOT rhyme or meter.

So just to make it easy on myself with this first writing assignment, I picked an ichnologically based example, and one I had blogged about just last month, Erasing the Tracks of a Monster. I originally wrote about this topic from the perspective as a field scientist reporting some very cool (to me) observations in the field, and didn’t really enrich the writing beyond that.

Thus for Le Guin’s exercise, the following came out of me, and it sure was was different from how i wrote about the same phenomena a few weeks before. In writing this, I asked myself: How do traces sound? So I hope you enjoy it, and if you did, read it aloud with gusto for maximum effect.

The Daily Terror

An alligator ambling along with ankles all akimbo
Plopping scaley feet on sloppy mud, then pulling them up
Moist resistance, a sucking sound that pops with each step.

Tail, big and keeled, flopping from one side to another
Dragging on its side, scraping along, swathing its way
Then hup-two, back up again, a ship righting itself on land.

Fiddler crabs scramble and scurry, getting out of his wake
A monster invader, Godzilla incarnate, legendary vengeance
Claws are waved, then tucked against carapaces, recoiling in fear.

Hiding in burrows, the thunder rumbles overhead on a ground
Trembling with the motion of the oblivious and massive reptilian
Locomotive with an unheeding mind, while mindless of their plights.

Homes are squashed, a few fiddlers too, destruction and chaos
However, quickly passes, and then slow, like molasses, they return
Burrowing, gathering, mating, breathing, exoskeletons dancing.

The TICKTACKULAR returns to their village each time the tide subsides
Its prowling rejecting their presence and bringing them no presents
Good thing for them that instinctual cowering is so ephemeral.

[Appreciative clicking of fingers from the audience, a clacking of jaws from the alligators present, and the quick staccato tapping of pointed feet from the fiddler crabs on the wooden floor.]

Casting (or Molding) Your Characters

Writing is a process, and if you do it long enough, you produce. But knowing that the “process” part of that simple equation requires constant tuning – whether through expert feedback, writing exercises, editing, or other standard tools of the trade – it also means having to climb out of ruts and onto the high ground above the ruts, looking down, and saying, “Wow, those sure are deep ruts.” Then sometimes you jump back in, because it may be a rut, but it’s the rut you know and love. However, in other instances, you gain a new perspective and become aware of some new dimension that could be added to your writing that takes it in a slightly different direction: a side trail off the main one where you left your mark, so to speak.

Raccoon-Trail-Scat-Writing-MetaphorHere’s an ichnological metaphor, depicting what can happen with your writing. This is a raccoon trail cutting through a high marsh on Wassaw Island, Georgia. See those other trails branching away from the main one in the background? Do you also notice how the main trail has a pile of raccoon crap lying on it (lower right)? I know: it writes itself, doesn’t it?

This happened to me a little over two weeks ago when I signed up for and attended a science-writing workshop held just before the start of the AJC-Decatur Book Festival in Decatur, Georgia (which I wrote about here). Titled Science Storytelling: Writing for a Chemical Reaction, and taught by local science writer and reporter Sonya Collins, it was a real writing workshop, one in which its participants actually wrote. (I’ve heard anecdotes from other writers about “workshops” that mostly consist of the authors/workshop organizers talking authoritatively about their own writing and generally promoting themselves to a captive audience, where the only work is enduring excessive self-aggrandizing. No thanks.) It was a fine, concise, and imminently practical two-hour workshop on science writing, and if offered again, I urge anyone in the Atlanta area who is interested to take it.

Why did I feel the need to attend  a science-writing workshop when I’m already writing about science, and doing a lot of it? For example, earlier that week I had just finished and sent the first draft of a book manuscript, Dinosaurs Without Bones, and was feeling pretty darned good about having completed that major writing goal. Moreover, I was also being recognized as an author at the book festival, and in my own home town of Decatur. In one instance, I was given the honor of introducing fellow paleontologist-author Brian Switek (who gave a expertly delivered and enthused talk about his most recent book, My Beloved Brontosaurus, to an appreciative crowd co-sponsored by the Atlanta Science Tavern) and in another I talked with an audience about my most recent book, Life Traces of the Georgia Coast. I was on a science-author role, and instead of attending a workshop, I should have just been sitting back with my favorite adult beverage and toasting my greatness, entertaining thoughts of creating my own science-writing workshops in which I would talk to aspiring science authors about my favorite subject: you know, me.

Yet I still sometimes suffer from “imposter syndrome,” feeling like a fraud. Much of this insecurity stems from how much of what I know about science writing is intuitive, garnered largely through having written much of my life, but also through seeking out and reading good science writing. Otherwise, although I’ve had plenty of training in and practice with technical writing, I’ve had very little formal instruction and guidance in writing about science for a popular audience. Hence it was time for a reality check, and to see whether what I was doing was OK (jump back into that rut!) or whether I needed to tweak my writing in some way (make a new path out of the rut!). In other words, I still have a helluva lot to learn about science writing.

So how did it go? In short, I learned lots, but here was the one key insight I took away from the workshop: character development. I had not fully appreciated how science storytelling, like all other storytelling, requires an interesting cast of characters. But this presents a challenge; after all, one of my most frequent answers I give to people who ask if I ever write about human traces and behavior is the Ace Ventura line, “I don’t do humans!”

After all, I mostly write about non-human characters – animals and plants – and their tracks, burrows, nests, droppings, and other traces. How could those be characters, infused with their own personalities and figure into plots filled with conflict, drama, love, hilarity, tension, and resolution?

That’s when it hit me that the Georgia barrier islands host a proverbial cast of thousands worthy of an epic tragicomedy straight out of a Flannery O’Connor tale or a Coen brothers’ film. For example, look at the following common names of these plants and imagine them as characters – heroes, villains, lovers, siblings, and innocent (or not-so-innocent) bystanders – in a Southern Gothic story. Go ahead, anthropomorphize to your heart’s content, and read them aloud if so inclined:

  • Loblolly Pine
  • Yaupon Holly
  • Resurrection Fern
  • Smooth Cordgrass
  • Sea-oxeye Daisy
  • Bitter Panic Grass
  • Red Cedar
  • Black Needle Rush
  • Glasswort
  • Fiddle-leaf Morning Glory

And now for some of the inveterate, I mean, invertebrate characters:

  • Live-oak Stump Borer
  • Acrobat Ant
  • Bald-faced Hornet
  • Periodical Cicada
  • Cicada killer
  • Florida Harvester Ant
  • Mole crayfish
  • Southern Devil Scorpion
  • Southern Carpenter Bee
  • Fallen Angelwing
  • Silky Ribbon Worm
  • Thick-lipped Oyster Drill
  • Blood Brittle Star
  • Wood Gribble
  • Moon Snail
  • Ghost Crab
  • Hairy Hermit Crab
  • Sea Onion Anemone
  • Trumpet Worm
  • Baby’s Ear
  • Stout Razor Clam
  • Lightning whelk

Need some backbone to your story? How about these:

  • Congo Eel
  • Southern Short-tailed Shrew
  • Great Horned Owl
  • Spadefoot Toad
  • Belted Kingfisher
  • Tarpon Snook
  • Six-lined Racer
  • Nine-banded Armadillo
  • Chicken Turtle
  • Mottled Mojarra
  • Warmouth
  • Red-bellied Woodpecker
  • Wild Turkey
  • Bank Swallow
  • Northern Fence Lizard
  • Peninsular Ribbon Snake
  • Ruddy Turnstone
  • Sandbar Shark
  • Star-nosed Mole
  • Southern Stingray
  • Laughing Gull
  • Short-billed Dowitcher
  • Yellow-crowned Night Heron
  • Double-crested Cormorant
  • Boat-tailed Grackle
  • Marbled godwit

When you read such names, don’t you wonder a little bit about them, their secret lives, how they relate to one another, and how their pasts will collide in an uncertain future? And even if you’re a cool-headed, mechanistic materialist who only views animals and plants as vehicles for propagating genes, you might at least inquire about the varied behaviors of these living beings and what marks they leave on the world as a result. Either way, if you are curious, then I guess you’ll have to read my book. (Incidentally, an excerpt from the first chapter is free here, and introduces one of the previously mentioned characters, who becomes the prime suspect in a murder-mystery.)

Like any good scientist, I had to experiment with this possible creative breakthrough. As a result, I read an abbreviated list of these characters in my presentation about Life Traces of the Georgia Coast at the AJC-Decatur Book Fesitval, and as far as I could tell, the audience reaction varied from mildly amused to confused. Still, it was well worth getting off an established trail and trying something new, and gave me a new question to ask when doing any future science writing: who are the subjects of my stories, and why should other people find them interesting? So be looking for some of them in upcoming stories about the life traces of the Georgia coast and the characters who make them.

Acknowledgements: Many thanks to Sonya Collins for putting together such a fulfilling and affirming science-writing workshop; to the AJC-Decatur Book Festival for arranging and encouraging such workshops; to the Atlanta Science Tavern for their continued support of science authors and writing; Brian Switek for lucidly and honestly discussing science writing with me during his too-short visit to my home town; and to my wife Ruth Schowalter, who puts up with the character who is me, writing about science.)

Life Traces at the AJC-Decatur Book Festival

This Sunday (September 1), from 3:00-3:30 p.m., I’ll be speaking about my book, Life Traces of the Georgia Coast, at the AJC-Decatur Book Festival in Decatur, Georgia. The festival is one of the largest of its kind in the U.S., with more than 75,000 people estimated to have attended last year. I am extremely lucky to have this festival in my neighborhood, and must restrain myself from self-pinching (more so) given that all of the venues are only 15-20 minute walks from where I live.

So with just a short stroll here and there, I can listen to world-class authors and poets speak about their works, meet a few of them, gaze at thousands of books on display by hundreds of different vendors, and talk about books with fellow book lovers. And just when you thought it couldn’t get any better, Decatur is also recognized as the informal “craft beer capital of Georgia,” meaning there are plenty of fine libations to be had while enjoying all of the literary and cerebral stimulation.

Ichnologist-on-Board-AJC-DBFMe (minus the big floppy field hat) participating in a panel discussion sponsored by the Atlanta Science Tavern at the AJC-Decatur Book Fesitval in 2011; the discussion was with Maryn McKenna and Holly Tucker on the topic of science writers working with online media. Note my Twitter handle  (@Ichnologist), which I still have. If you follow me there, I promise to never give updates on what I had for breakfast, lunch dinner, snacks, or any other food items. (Photograph by Ruth Schowalter.)

In fact, one of my dreams when writing Life Traces of the Georgia Coast was that I would be able to speak about it in the book festival, giving back to my local community at a nationally prominent literary event. After all, with so many friends, acquaintances, fans, and possible stalkers in the Atlanta area, there might be plenty of people interested in hearing from a “local boy done good.” The book also describes plant and animal traces of all types from the world-famous Georgia barrier islands, which many people in the Atlanta area have visited for their natural wonders. So several months ago, I applied for a speaking slot in the Atlanta Writers’ Showcase Stage, and was lucky enough to be one of the few (of only about 15-20 authors) selected.

What will I talk about during my 30-minutes of fame there? I’ll have to be disciplined and focused, as a 700-page book certainly can’t be (nor should it be) expressed in any comprehensive way during such a short amount of time. So for those of you who will be there, this is not a spoiler alert, but more like a teaser:

  • What is the book about?
  • Where does its action take place?
  • Who makes up the cast of characters (tracemakers)?
  • What is the connection between these modern traces of the Georgia barrier islands and trace fossils in the rest of the world?
  • A brief (3-5-minute) reading from the first third of the book.
  • A brief reading from the middle of the book.
  • A brief reading from toward the end of the book.
  • A take-home message, about why reading this book will change your perspective, causing you to see life traces wherever you go, and not just on the Georgia coast.

So I hope to see some of you there, but if you’re not in the Atlanta area or otherwise can’t make it, I’ll be sure to tell you about it and other experiences with the festival here.

Anthony (Tony) J. Martin will be making two appearances at the AJC-Decatur Book Festival this weekend. The first will be to introduce Brian Switek, author of My Beloved Brontosaurus and Written in Stone, at 12:00 noon on Sunday, September 1, at the Marriott Conference Center Ballroom B in downtown Decatur. The second will be to talk about his book, Life Traces of the Georgia Coast, at 3:00 p.m. on the same day, and at the Atlanta Writer’s Showcase, which is all located in the Marriott Hotel in downtown Decatur. Full information can be found at this link, with more links to other authors, genres, and events there.

Bookzilla-AJC-DBFWill there be interesting tracemakers at the AJC-Decatur Book Festival? Yes, indeed. For example, here’s Bookzilla. As is traditional for photographs taken of cryptids, it is blurry, but as is also typical of cryptids, all you need are Bookzilla’s footprints to prove it exists.

Godzilla-Downtown-DecaturPresiding over book-related activities at the AJC-Decatur Book Festival will be this tracemaker, which is very likely a close relative of T. rex, but with possible shared ancestry with Bookzilla. What’s with the wires? Don’t ask.

Erasing the Tracks of a Monster

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.

Alligator-Trackway-St-Catherines-2Part 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.

Alligator-Trackway-St-Catherines-1That 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-Salt-Marsh-SCIAlligator 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.

Alligator-Tracks-Burrowed-Fiddler-CrabsHey, 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.)

Alligator-Tracks-Destroyed-Fiddler-Crab-Burrows-1Going, 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.

Alligator-Tracks-Destroyed-Fiddler-Crab-BurrowsDon’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.)

Fiddler-Crab-Burrow-Alligator-Claw-MarkWhy, 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.)

Fiddler-Crab-Burrow-Alligator-Claw-2Need 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.