Fossil Visions in the Two Medicine

(This post is the third in a series of three about my field work on the trace fossils of the Late Cretaceous (75 million-year-old) Two Medicine Formation, which I just completed a week ago. My previous two posts, which mostly explain the scientific importance of this field work, are Tracing the Two Medicine and Burrowing Wasps and Baby Dinosaurs.)

Looking back on three weeks of field work in the Late Cretaceous Two Medicine Formation, one of the realizations I had was how long it took before I could see more of what was there. The most frustrating part of this realization, though, is also knowing that I still missed plenty. This mix of satisfaction and unease is the duality that often accompanies the birthing and honing of search images, a visual training that enables paleontologists to find the fossils we want to find whenever we walk around a field site and look.

Tony-Martin-Searching-Fossils-Two-MedicineThis outcrop of the Late Cretaceous (75 mya) Two Medicine Formation in central Montana is chock-full of fossils, but you might not know that from just looking at this picture. That means you have to get out onto the rocks and look closely for them, but first make sure you have the right search images for finding them. (Photograph by Ruth Schowalter.)

The Two Medicine Formation in particular presents a major challenge for cultivating search images because of the variety of fossils in it. Moreover, most of these fossils require very different search images. For example, over my three weeks of prospecting, I looked for the following fossils:

  • Plant root traces
  • Invertebrate burrows and tracks
  • Insect cocoons and pupal chambers
  • Dinosaur tracks
  • Dinosaur nests
  • Dinosaur eggshells
  • Dinosaur coprolites
  • Dinosaur bones
  • Dinosaur toothmarks (on dinosaur bones)

I also found a few other fossils I didn’t expect to find, but there they were. This happenstance served as a good reminder that simply going out into the field with a bullet-point checklist of what you think you’ll find (like what you just read) isn’t good enough. In other words, you also need to see what’s there, rather than just what you expect to be there.

On top of looking for these fossils, I’m a geologist, too. This means I also paid close attention to the rock types in the Two Medicine Formation – sandstones, mudstones, conglomerates, limestones – and their physical sedimentary structures – such as cross-bedding or graded bedding. Moreover, Two Medicine strata in the field area are not necessarily in their original horizontal positions, but instead are bent, tilted, and faulted in places. This is where training I had in structural geology – the study of how rocks were deformed – came in handy.

Geologic-Anticline-Two-MedicineOriginally horizontal sedimentary strata were bent upward into a fold, which we geologists normally call an anticline. In such folds, the fossils in the center of the fold are geologically older, whereas the fossils on the outside of the fold are younger. That is, unless the strata were overturned, in which case we’d call it antiformal syncline, then the fossils would have the opposite age relations. Thank you for teaching this, structural geology professors! (Photograph by Anthony Martin.)

Geologic-Fault-Two-MedicineIt’s not my fault, so we’ll blame the Two Medicine Formation for this breakage of sedimentary rocks. Based on how it looks like the fault block on the right moved up relative to the one on the left, I think this is a reverse fault, which – like the anticline and almost everything else on earth – was caused by plate tectonics. (Photograph by Anthony Martin.)

Thus whenever I stepped into the field each day, I had to rapidly switch, combine, or otherwise tap into different types of vision. I’ve often jokingly referred to my ability to spot traces and trace fossils in the field as “ichnovision” (my most likely comic-book hero superpower), and my geological training means I’m using “geovision.” Yet in the Two Medicine Formation – a rock unit world-famous for its dinosaur bones and eggs – I also had to use “osteovision” (seeing fossil bones) and “oovision” (seeing fossil eggshells). These forms of fossil vision are tough for me, as I never see dinosaur bones or eggshells in the southeastern U.S., which is where I spend most of my time in the field.

So just to give you an appreciation of what it was like during my three weeks of looking for fossils in the Two Medicine Formation, here are a few photos and brief descriptions of some fossils I found. To be sure, there was much more than this, but at least I can share these for now so you can begin to see through my eyes.

Fossil-Plant-Root-Traces-Two-MedicineThese odd-looking structures weathering out of an outcrop in the Two Medicine Formation had variable diameters, central cores filled with calcite, and branched in places. I’m fairly sure these are fossil plant root traces, but they were the only ones I saw like them during three weeks of field work. So I remain a little skeptical of my identification, and remain open to their being some geological features I’ve just never seen before then. (Photograph by Anthony Martin.)

Horizontal-Burrows-Two-MedicineThese are longitudinal sections of horizontal burrows in a sandstone, showing off their beautifully expressed internal structures called meniscae. Meniscae are formed by burrowing invertebrates – such as beetle larvae or cicada nymphs – that pack their burrow with sediment behind them as they move. This means the convex side of the meniscae points in the direction the animal was moving. Go ahead, apply that principal and see what you figure out for yourself. (Photograph by Anthony Martin.)

Vertical-Burrows-Two-MedicineThese are more invertebrate burrows, but they’re vertically oriented, meaning you only see their circular cross-sections when you look at the top bedding-plane surface of this sandstone. Notice how some of them are open but others are filled with sandstone. The open ones were filled with mud originally, but that softer sediment has since weathered out, leaving them hollow. (Photograph by Anthony Martin.)

Limulid-Tracks-Two-MedicineThese are invertebrate tracks, and they form a distinctive enough pattern that I recognized them as a trackway, where the trackmaker (probably a freshwater horseshoe crab) turned. But they’re also preserved in positive relief (“sticking out”) because the original traces were filled with sand, which made a natural cast of the tracks. Think about how you have to reverse your concept of tracks to recognize these. (Photograph by Anthony Martin.)

Fossil-Cocoons-Two-MedicineOne of my main research interests in the Two Medicine Formation is its insect trace fossils, which include some of the best-preserved fossil insect cocoons I’ve ever seen in the geologic record. See where the patterns of their original weaves? These cocoons were likely made by wasps – or something acting very much like wasps – 75 million years ago. I usually prospected for these cocoons by looking for their distinctive oval shapes on the ground, then looked more closely for the weave pattern. (Photograph by Anthony Martin.)

Fossil-Cocoon-in-situ-Two-MedicineThis is what a fossil insect cocoon looks like in an outcrop. Sometimes a burrow would be connected to the cocoon, showing where the original mother insect dug a brooding chamber for its intended offspring. (Photograph by Anthony Martin.)

Dinosaur-Bone-Two-MedicineA rare piece of dinosaur bone that actually looks like a bone, even to an untrained eye. Although this one is white, the dinosaur bones in the Two Medicine Formation varied wildly in their colors. So spotting these fossils was more a matter of looking for both a shape and texture that translate into “bone.” (Photograph by Anthony Martin.)

Fragmented-Dinosaur-Bone-Two-MedicineThis is more what most dinosaur bones looked like when I found them in the field area. You probably spotted the big chunk right away, but how about the smaller ones that tend to blend in with the non-dinosaur-bone rocks around them? (Photograph by Anthony Martin.)

Adult-Hadrosaur-Track-Two-MedicineHere’s another example of how fossil tracks are not like modern ones in size, shape, and how it’s preserved. This is a three-toed dinosaur track (probably made by a hadrosaur), but it was originally made in mud, then sand filled in the track-sized hole to make a natural cast, which 75 million years later weathered out so that it’s sitting by itself on the eroded surface of a mudstone. What’s the scale? My boot’s a size 8 1/2 (men’s). Yes, I felt a little inadequate.  (Photograph by Anthony Martin.)

Hadrosaur-Track-in-situ-Two-MedicineWhat does a natural sandstone cast of a dinosaur track look like when it’s still in outcrop? Look for a lump on the bottom of a sandstone bed. From a side view, you might then see a couple of “toes” pointing in one direction, like in this one: the central toe is to the left and one of the outer toes is on the side, clser to you. Note how the sandstone bed also has a few open invertebrate burrows in it, too. Ichnobonus! (Photograph by Anthony Martin.)

Hadrosaur-Coprolite-Two-MedicineCheck out this big piece of, well, dinosaur coprolite. These trace fossils contained blackened (carbonized) wood fragments that originally passed through the gut of a dinosaur (probably a hadrosaur), and were later cemented by calcite. But you had to look at them doubly, because some of these trace fossils included their own trace fossils made by insects, namely dung beetle burrows. (Photograph by Anthony Martin.)

Field-of-Feces-Two-MedicineYou’ve heard of ‘Field of Dreams’? This is a ‘Field of Feces.’ The ground here is adorned with dinosaur coprolites, which are weathering out of the mudstone and breaking apart on the surface. This serves as a good example of how once you know what the dinosaur coprolites look like in this area, you’re less likely to just walk by them, singing “Where Have All the Coprolites Gone?”. (Photograph by Anthony Martin.)

Eggshell-Fragments-Two-MedicineThe Two Medicine Formation is famous for its dinosaur eggs and babies, but even more common than those are bits and pieces of dinosaur eggshells. These show up as black flakes on ground surfaces and sometimes in a rock, which you then must distinguish from all other black flakes that are not dinosaur eggshells. (Photograph by Anthony Martin.)

Find-Dinosaur-Eggshell-Two-MedicineCan you find the dinosaur eggshell in this photo? I’ll bet the answer was “yes,” but I made it a little easier for you by cropping the photo, placing the eggshell near the center of the image, and oh yea, showing you what typical eggshells look like in the previous photo. Now think about detecting this bit of eggshell from a standing height and while walking. (Photograph by Anthony Martin.)

After viewing the photos and reading the descriptions, do you think you could recognize each of these fossils if you were somehow magically transported to the Two Medicine Formation in Montana?

The likely answer to that question is, maybe, maybe not. For instance, despite all of my previous paleontological and geological field experience, it took me about two weeks of being in the field before I started accurately identifying dinosaur bones and eggshells. This humbling situation gave me a renewed appreciation for the people who regularly work in the Two Medicine Formation, but also imparted a lesson about taking the time to learn from misidentified burrows, cocoons, coprolites, bones, and eggshells in it. Most things I saw in the Two Medicine were not these fossils, meaning my ways of seeing had to become more discriminating over time.

Thus given enough practice and “dirt time” seeking fossil in the field and correcting your mistakes – preferably with an expert peer-reviewing your finds beside you – the fossil visions will come to you. Then, next thing you know, you start noticing more of what you didn’t see before, expanding your consciousness of the lives that preceded your own.

* * *

Many thanks to Dr. David Varricchio for inviting me to be part of his NSF-sponsored research project in the Two Medicine Formation this summer, and by extension, my deep appreciation to Montana State University and Museum of the Rockies for their logistical support at Camp Makela. May it have many more successful field seasons.

Seven-Samurai-PaleontologyThe Seven Samurai of paleontology at Camp Makela, ready for action in the Two Medicine Formation of central Montana. These ruffians/malcontents/Guardians of the Cretaceous Galaxy are otherwise known as (left to right): Ulf, Jared, me, Ashley, Emmy, Paul, and Eric. (Photograph and choreography by Ruth Schowalter.)

For more about these people and other human connections between the paleontological research that took place in the Two Medicine Formation – and told from a non-paleontological perspective – go to Cretaceous Summer 2014, which had links to four blog posts done on site by my wife Ruth Schowalter. Also be sure to check out Brad Brown’s blog post from the Burpee Museum of Natural History about his experiences at the field site, Just What the Doctor Ordered: Two Medicine Delivers High Biodiversity in a Low Profile Area.

Tracing the Two Medicine

Field scientists have to get into the field. If they don’t, they get cranky, narrow-minded, and – worse of all – feel like frauds. What’s the cure for this malady? Getting into the field.

Tony-in-the-FieldSee that smile? That’s a field scientist, who is out standing in his field. (Photograph by Paul Germano.)

This is the first summer since 2008 in which I did not have to edit or write a book. From 2008 to 2012, I was writing and editing Life Traces of the Georgia Coast (2013, 692 pages), and from 2012-2013, my literary efforts were devoted to Dinosaurs Without Bones (2014, 460 pages) So with these two books behind me and none in the making now, along with three merciful months off from my “day job” of being a college professor, I had few excuses for not getting outside to see some rocks and fossils this summer.

So it was with much joy when my long-time friend and fellow paleontologist David (Dave) Varricchio asked me earlier this year if I’d be interested in coming out to Montana to do some field work with him this summer. Even better, I’d get to do paleontological field work with him in the Late Cretaceous Two Medicine Formation (~75 million years old) at “Egg Mountain,” a paleontologically classic area near Choteau, Montana. I said yes, have been here for a week now, and it’s been glorious.

Egg-Mountain-Digging-2 To look for traces, sometimes you have make your own traces. Here’s this summer’s Montana State University field crew excavating at Egg Mountain, where they’re looking for dinosaur bones and eggs, while also cataloging trace fossils like insect cocoons and burrows. If you’re looking for Dr. Varricchio, he’s the one in the middle with the jackhammer. (Photograph by Anthony Martin.)

The main reason why the field site is called “Egg Mountain” is because it and other places in the area are where the first known dinosaur nests in North America were discovered by Jack Horner and Bob Makela in the late 1970s and early 1980s. They further uncovered evidence that at least one dinosaur here – the large hadrosaur Maiasaura peeblesorum – had extended parental care, taking care of its young in their nests well after hatching.

Later in the 1990s, Dave and his colleagues showed that the small theropod Troodon formosus made rimmed ground nests and arranged it eggs carefully in these nests. This combination of body fossils (bones and eggs) and trace fossils (nests and egg arranging) changed many of our views of dinosaurs, rendering their behaviors much less like reptiles and more like birds.

Maiasaura-Nesting-Site Sometimes I hear paleontology referred to as a “historical science,” but it also has its own human history. This marker and several others in the field area mark where some of that history was made, with the discovery of the first known dinosaur nests in North America. (Photograph by Anthony Martin.)

Two-Medicine-Formation-OutcropI love waking up to the Two Medicine Formation in the morning. And there’s no shortage of trace fossils to discover in it with each waking day. (Photograph by Anthony Martin.)

Hadrosaur-Track-Two-MedicineA natural sandstone cast of an adult hadrosaur, weathered out of the surrounding softer mudstone that – in the absence of bones – serves as a visual reminder of who lived in this area. (Photograph by Anthony Martin.)

I had been to this site three times before – 2000, 2008, 2009 – but each of those were short visits, the longest lasting only a week. This time, I would get to stay for as long as three weeks, which allows for plenty of time to better document the invertebrate and vertebrate trace fossils here. So far, I’ve only published one paper with Dave based on previous work in the Two Medicine Formation, which was on some of the insect trace fossils near the nest sites. These trace fossils gave valuable clues about how these insects lived, and in the same ecosystems as the nesting dinosaurs, which I’ll happily cover in detail in my next blog post.

Fossil-Cocoons-MontanaInsect burrow with pupal chamber (left) and two insect cocoons, one of which has a “hatching window” where the adult insect left the cocoon. Look closely and you’ll see the original silk-weave pattern still on the cocoons, which are preserved as finely crystallized calcite. (Photograph by Anthony Martin.)

So with one week of field work done, I’m happy to report that plenty of trace fossils have revealed themselves to us, and I have every expectation that more will be found in the next two weeks. And this, boys and girls, is why I am a field scientist and paleontologist: to experience that joy of discovery that happens in the same places where the plants and animals of their ecosystems breathed and died 75 million years ago. Field work never fails to take me back in time, to when those animals behaved in ways that left their traces for us recent arrivals on this earth to appreciate with wonder.

Fun-With-Field-Work-MontanaThis is my office for the next two weeks. Not bad, huh? I could get used to this, and plan to. (Photograph taken by my camera, which was set on an automatic timer.)

(For another introduction to this field work, here’s a blog post done cooperatively with my wife Ruth, who will be joining me here at the field site in just a few days.)

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)



Deep in the Dinosaur Tracks of Texas

Given the continuing public mania over dinosaurs, and recent important discoveries of yet more exquisite specimens of feathered theropod dinosaurs discovered in countries far away from the U.S. (here and here), it is sometimes easy to forget what has long been known about these animals, and right here in my own “backyard” (globally speaking).

Need to see some of the best dinosaur tracks in the world, and you live in the southeastern U.S.? Guess what: you can seen them in Glen Rose, Texas. Not China, Mongolia, Canada, Utah, or some other far-off land inhabited by strange people with unusual customs, but Texas. Saddle up! (Photograph by Michael Blair, taken in Dinosaur Valley State Park, Texas.)

So on July 22, just to jog my memory a bit, I flew from Atlanta, Georgia to the Dallas-Ft. Worth (Texas) airport, and only a few hours later was gazing upon dinosaur tracks accompanied by the burrows of invertebrate animals, both trace fossils having been made more than 100 million years ago. It was a fitting welcome to Glen Rose, Texas, a place famous for its dinosaur trace fossils since the 1930s, and where dinosaurs were an integral part of its culture long before it was cool, hip, and contemporary elsewhere.

In Glen Rose, Texas, the dinosaur tracks are so abundant, you can choose whether to see these just outside of your hotel room, or go to the hotel jacuzzi and pool. Naturally, I chose both. (Photograph by Anthony Martin, taken in Glen Rose, Texas.)

So just how did I end up in Glen Rose, Texas, looking at Cretaceous dinosaur tracks and invertebrate burrows? I was lucky enough to be there as an invited participant in an expedition sponsored by the National Geographic Society. I say “lucky” because luck was certainly a part of it, a fortuitous connection made through my writing a book about the modern traces of the Georgia coast. James (Jim) Farlow, a paleontologist at Indiana-Purdue University Fort Wayne (IPFW) and an associate editor with Indiana University Press, reviewed the first draft of my book, but he was also in charge of this dinosaur-track expedition to Glen Rose. Evidently he was impressed enough about what I knew about invertebrate burrows (or at least what I wrote about them) that he considered me as a possible member for his team of scientists, field assistants, and teachers on this expedition.

Dr. Jim Farlow, the world expert on the Glen Rose dinosaur tracks, having a reflective moment at Dinosaur Valley State Park near Glen Rose, Texas. What’s with the broom? He and other people in the expedition used these to sweep river sediment out of dinosaur tracks submerged in the river. In 100° F (38° C) temperatures. On the other hand, I just described invertebrate trace fossils, which was more of a job, not work. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

Thus when Jim asked me last fall if I would be interested in joining them to describe and interpret the Cretaceous invertebrate burrows that occur with the dinosaur tracks there, I jumped at the opportunity. The Glen Rose dinosaur tracksites, most of which crop out in the Paluxy River bed in Dinosaur Valley State Park, are world famous for their quantity and quality, and they connect with an important part of the history of dinosaur studies. Going there, experiencing these tracks for myself, and better understanding their paleoecological and geological context would be of great benefit to me, my students, and of course, you, gentle readers.

Just to back up a bit, and clarify for anyone who doesn’t know why these tracks are so darned important, here’s a brief background. In November 1938, Roland T. Bird, an employee of the American Museum of Natural History and a field assistant to flamboyant paleontologist Barnum Brown (the guy who named Tyrannosaurus rex), saw large, isolated limestone slabs with theropod dinosaur tracks in a Native American trading post in Gallup, New Mexico. Upon inquiring about the origin of these tracks, Bird was told they came from Glen Rose, Texas. So he set out in his Buick for Glen Rose to see for himself whether these tracks were real or not, and whether there were any more to see in the rocks around Glen Rose. The theropod track set in the town bandstand – pictured below – was one of the first sites that greeted him, and Glen Rose locals told him about the tracks in the Paluxy River.

Glen Rose, Texas, the only place in the world where the town bandstand has an Early Cretaceous theropod dinosaur track on display. Wish I could also tell you about all of those little holes in the rock with that track, but I can’t right now. Nonetheless, rumor has it they are burrows made by small, marine invertebrates that lived at the same time as the dinosaurs. (Photograph by Anthony Martin, taken in Glen Rose, Texas.)

Bird had hit the jackpot, the motherlode, the bonanza, the surfeit, the, well, you get the point. Not only did the Paluxy River outcrops contain hundreds of theropod dinosaur tracks – many as continuous trackways – but also the first known evidence of sauropod dinosaur tracks.

A couple of beautifully preserved theropod tracks under shallow water in the Paluxy River. Note that the track at the bottom also has a partial metatarsal (“heel”) impression, and look closely for the digit I (“thumb”) imprint on the right. Scale is about 20 cm (8 in) long. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

Funny how those “potholes” in the limestone bedrock of the Paluxy River have oblong outlines and form regular alternating patterns, isn’t it? Well, them ain’t no potholes, y’all. They’re sauropod tracks, and were among the hundreds recognized as the first know =n such tracks from the geologic record. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

The discovery of sauropod tracks was as huge as the tracks. Up until then, sauropods were assumed to have been so large that they could not support their weights on land and spent most of their time in water bodies. These tracks said otherwise, that these sauropods were walking along mudflats along with the theropods. In short, the trace fossil evidence contradicted the assumed story about how these massive animals moved. After all, trace fossils are direct records of animal behavior, and if interpreted correctly, can tell paleontologists more about what an animal was doing on a given day than any amount of shells, bones, and yes, even feathers.

Sauropod tracks from the main tracksite in Dinosaur Valley State Park, Texas. The sauropod was moving away in this view, and the trackway pattern is a typical diagonal-walking one, right-left-right. In parts of this trackway, both the manus (front foot) and pes) rear foot registered, something Bird noticed in 1938, his observation accompanied by more than a little bit of excitement. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

The details preserved in these sauropod tracks are also astounding. Most sauropod tracks I have seen elsewhere, in Jurassic and Cretaceous rocks of the American West, Europe, and Western Australia, are only evident as large, rounded depressions that you would only know are tracks because they form diagonal-walking patterns. In contrast, the Glen Rose tracks include all five toe and claw impressions on the rear feet (pes) and full outlines of the front feet (manus). The original calcium-carbonate mud in the shoreline environments where the sauropods walked, similar to mudflats I’ve seen in the modern-day Bahamas, is what made this exquisite preservation possible. The mud had to be firm enough to preserve these specific details of the sauropods’ feet, but not so soft that the mud would collapse into the tracks after the sauropods extracted their feet.

Beautifully preserved tracks, manus (top) and pes (bottom). Note the five toe impressions in the pes, which along with its size confirms that these were made by a large sauropod. Meter stick for scale. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

One sauropod trackway, preserved with a theropod trackway paralleling and intersecting it, was actually quarried out of the river and taken to the American Museum. Once there, its pieces stay disassembled for years, before Bird helped with putting the puzzle pieces back together so that it could be used as part of a display there.

Archival video footage of Roland Bird and his field crew working on the dinosaur tracks in the Paluxy River near Glen Rose, Texas. More about this tracksite and its role in the history of dinosaur paleontology is ably conveyed by Brian Switek here.

Photos at the visitor’s center at Dinosaur Valley State Park, showing the sequence of clearing (left) and extraction (right) of the limestone bed containing the theropod and sauropod dinosaur tracks. (Photographs taken of the photographs, then enhanced, cropped, and placed side-by-side by Anthony Martin.)

A lasting trace today of Roland Bird and his field helpers from the 1940s, in which they took out a sauropod and theropod trackway from this place and transported it to New York City. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

Other than some of the best-preserved Early Cretaceous dinosaur tracks in the world, one other claim to fame for the Glen Rose area, and not such a proud one, is its attraction to evolution deniers, a few charlatans who used the tracks to promote what might be mildly termed as cockamamie ideas. You see, Glen Rose is also the site of the infamous “man tracks.” These tracks are preservational variants of theropod tracks that – through a combination of the theropods sinking into mud more than 100 million years ago and present-day erosion of the tracks in the Paluxy River – prompted some people to claim these were the tracks of biblical giants who were also contemporaries of the dinosaurs. (Perhaps this is as good of a time as any to start humming the theme music for The Flintstones.)

Rare documentary footage of humans and dinosaurs interacting with one another during the Early Cretaceous Period, or the Late Jurassic Period. Whatever. Note the inclusion of other seemingly anachronistic mammals, too, such as the saber-toothed felid Smilodon. Perhaps this footage could be included in the curriculum of some U.S. public schools, providing a formidable counter to the views of 75 Nobel laureate scientists. Then we’ll let the kids decide which is right.

I will not waste any further electrons or other forms of energy by continuing to flog this already thoroughly discredited notion, but instead will direct anyone interested to a thorough accounting of this debacle to some actual scholarship here, summarizing original research by Glen Kuban and others in the 1980s through now that have laid to rest such spurious notions. Speaking of Mr. Kuban, I was delighted to meet him for the first time during while in Glen Rose (we had corresponded a few times years ago). I was even more gratified to spend a few hours in the field with him, discussing the genuinely spectacular trace fossils there in Dinosaur Valley State Park with these directly in front of us. Again, I’m a lucky guy.

The expedition was scheduled in Glen Rose for three weeks during late July through early August, but with so many commitments for this summer, I could only carve out a week for myself there, from July 22-29. Fortunately, this was enough time for me to accomplish what was needed to do, while also having fun getting to know the rest of the expedition crew – teachers, artists, videographers, laborers – and enjoying wonderful discussions (and debates) with colleagues in the field. The people of Glen Rose were also exceedingly welcoming and accommodating to us: we felt like rock stars (get it – “rock”?), and were feted by local folks three nights in a row during the week I was there. Many thanks to these Glen Rose for the the exceptional hospitality they extended to our merry band of paleontologists, geologists, river sweepers, or what have you.

You can’t see it, but I’m standing in a sauropod dinosaur track, which is a little deeper than the rest of the river bed. You also can’t see the invertebrate burrows that are in the limestone bedrock, which is fine, because I can’t show them to you yet anyway. But be patient: you’ll learn about them some day. (Photograph by Martha Goings, taken in Dinosaur Valley State Park, Texas.)

I can’t yet say much more about what I did during that week, as all participants signed an agreement that National Geographic has exclusive rights to research-related information, photos, and video unless approved by them. But if you’re a little curious about the daily happenings of the expedition (which just ended last week), Ray Gildner maintained a blog that succinctly touched on all of the highlights, Glen Rose Dinosaur Track Expedition 2012.

Still, I can say, with great satisfaction, that I did successfully describe and interpret invertebrate trace fossils that were in the same rocks as the dinosaur tracks. Hopefully my colleagues and I will have figured out how these burrows related to environments inhabited by the dinosaurs that walked through what we now call Texas.

All in all, my lone week in the Lone Star State was a marvelously edifying and educational experience, one I’ll be happy to share with many future generations of students and all those interested in learning about the not-so-distant geologic past of the southeastern U.S.

Group photo from the Glen Rose Dinosaur Track Expedition 2012. Names of all participants can be found here, but in the meantime, just sit back and admire those Dinosaur World t-shirts everyone is wearing. (Photograph by James Whitcraft or Ray Gildner: they can fight over who actually took it. Although, the automatic timer on his camera took the photo, so maybe it should get credit instead.)

Further Reading

Bird, R.T. 1985. Bones for Barnum Brown: Adventures of a Dinosaur Hunter. Texas Christian University Ft. Worth, Texas: 225 p.

Farlow, J.O. 1993. The Dinosaurs of Dinosaur Valley State Park. Texas Parks and Wildlife Department, Austin, Texas: 30 p.

Jasinski, L.E. 2008. Dinosaur Highway: A History of Dinosaur Valley State Park. Texas Christian University, Ft. Worth, Texas: 212 p.

Kuban, G.J. 1989. Elongate Dinosaur Tracks. In Gillette, David D., and Martin G. Lockley (editors), Dinosaur Tracks and Traces, Cambridge University Press, Cambridge, U.K.: 57-72.

Pemberton, S.G., Gingras, M.K., and MacEachern, J.A. 2007. Edward Hitchcock and Roland Bird: Titans of Vertebrate Ichnology in North America. In Miller, William, III (editor), Trace Fossils: Concepts, Problems, Prospects. Elsevier, Amsterdam: 32-51.