Along those lines, I had published a paper in 2009 about physical sedimentary structures—such as ripple marks, mudcracks, and so on—and traces—such as invertebrate burrows and vertebrate tracks—next to the Colville River on the North Slope of Alaska. Hence, the rocks in front of us, when combined with what I had learned from that Alaskan riverbank a few years beforehand, almost acted like a time machine. The Cretaceous rocks of Australia and the modern sediments of Alaska could be compared as polar ecosystems, despite being separated by more than 100 million years and thousands of kilometers.
Yet another justification for my growing elation was that these burrows closely resembled trace fossils I had seen in rocks at another place: Knowledge Creek, just a few kilometers east of us. Knowledge Creek is the place where the only well-documented dinosaur track from the Eumeralla Formation was discovered. In 1980, a little more than thirty years before Tom, Greg, and I stepped foot on Milanesia Beach together, Tom and Pat Vickers-Rich found this track. It was probably made by a small ornithopod dinosaur, which was not surprising to them, seeing that nearly all of the skeletal remains of dinosaurs in Victoria belonged to such dinosaurs.
I had visited Knowledge Creek three times in recent years—2006, 2007, and 2009—but did not find any other definite dinosaur tracks there, only a few vague outlines. Still, I was lucky enough to have discovered possible dinosaur burrows and invertebrate trace fossils there, the latter nearly identical to the ones we were seeing that morning at Milanesia Beach. Similar sedimentary rocks and trace fossils at Knowledge Creek and Milanesia Beach implied that similar environments had produced these rocks. So perhaps the conditions at both places were conducive to dinosaurs walking across floodplain surfaces, allowing their tracks to get preserved well enough that they would be identified some day.
After photographing and noting the locations of these trace fossils, Greg and I continued down the eastern extent of the beach. Tom, on the other hand, had already gone well ahead of us, looking for bones. I think he was glad that Greg was helping with my ichnological investigations, which allowed him to concentrate more on finding dinosaur bones or those of other vertebrates. In his previous scouting of Milanesia Beach with others of his body-fossil-hunting ilk more than twenty years before, they had not found any bones or teeth. As a result, they had since written it off as a place to look for such fossils. But he also knew that during that elapsed time, rock falls and weathered surfaces might have revealed previously hidden fossil bones, new to human eyes.
Happy about the invertebrate burrows and their host rocks, I turned to Greg as we sauntered down the beach and said, casually, “Now all we have to do is find some of those other things we’ve been looking for. But I won’t say what, because I don’t want to jinx it!” Greg grinned and said “Righto, say no more!” Somehow he knew I was talking about dinosaur tracks. In our previous forays, I had mentioned these trace fossils as something we should be looking for at every turn.
Tracing through Recent Time
What was the reason for such vigilance about dinosaur tracks? Well, up until that day, only four dinosaur tracks had been found in all of the Cretaceous rocks of Victoria, a part of Australia just a bit smaller than California. The first track—the one discovered by Tom and Pat at Knowledge Creek—was only about 10 cm (4 in) wide and long. They were doubly fortunate that day: once for finding the track, and twice for having the right tools to collect it. Using a hammer and chisel, they carved it out of the rock, put it in a backpack, and hiked out of the site. Upon their return to Melbourne, they immediately placed the specimen in the Museum Victoria fossil collection. This track later became the template for thousands of reproductions used for science education in Victoria, and photographs of it appeared in many popular articles and books. In other words, it became iconic: For many people, and for more than twenty-five years, this was the dinosaur track from the Cretaceous of Victoria.
In 1989, another isolated dinosaur track was found during a fossil hunt by a group led by Tom Rich. They discovered it at a place called Skenes Creek, which was more than 30 km (19 mi) east of Knowledge Creek, but with rocks the same age as those at Knowledge Creek, Dinosaur Cove, and Milanesia Beach. This specimen was also a small ornithopod track and nearly the same as the one from Knowledge Creek. Fortunately, the field crew had a rock saw with them, so they neatly cut the surrounding rock into an easily transportable square slab, and likewise took it to Museum Victoria. Once deposited, it received a catalog number and sat in the museum for the next 21 years. I saw it in its museum drawer in May 2010—only three weeks before our sojourn to Milanesia Beach—and verified it as the second dinosaur track reported from the Eumeralla Formation. However, it still has not been formally described in the scientific literature, so it remains known to only a few paleontologists and does not get any of the public notice showered on its almost-identical twin from Knowledge Creek.
The other two dinosaur tracks from Victoria were both made by large theropods and are east of Melbourne, at the Dinosaur Dreaming dig site in the geologically older rocks (115–120 million years old) of the Strzelecki Group. I found one in 2006 during my first visit to Dinosaur Dreaming. Sadly, Tom Rich—who was with me at the time—had not yet accepted my ichnological abilities and disregarded it as a dinosaur track. A year later, in 2007, a dig site volunteer, then-student Tyler Lamb, found a nicely defined track of about the same size only about 5 m (16 ft) from the main dig site. Yes, I felt vindicated, but also very happy for Tyler that he’d discovered such an important specimen. Later in 2007, I reported on both tracks in a poster presented at the Society of Vertebrate Paleontology meeting in Austin, Texas. This poster got a fair amount of media attention because it was touted as evidence of a “polar predator” from the Cretaceous, a mixing of theropods and polar dinosaurs that somehow inspired the public imagination.
So there you go: four definite dinosaur tracks from all of the Cretaceous of Victoria after more than a hundred years of paleontological research in those rocks. The two tracks from 105-millionyear-old rocks west of Melbourne—Knowledge Creek and Skenes Creek—were attributable to small ornithopod dinosaurs, like Leaellynasaura. Large-sized theropods, about the size of a smaller version of Allosaurus, likely made the two 115-million-year-old tracks in rocks east of Melbourne. None of these tracks were preceded or succeeded by another track made by the same dinosaur, which meant, unlike many other places in the world, including in Australia, Victoria had no known dinosaur trackways like ones at Lark Quarry in Queensland or Western Australia.
This is where someone in the know about such things might ask, “What about other dinosaur trace fossils?” As covered before, there were supposed dinosaur burrows from Knowledge Creek, and that was it. No dinosaur nests, gastroliths, stomach contents, or coprolites have been interpreted from the Cretaceous rocks of southern Australia. I had heard from a few paleontologists that some of the dinosaur bones from this area had theropod toothmarks on them, but these were apparently rare too. No one had even done a study on tooth microwear. Although there seemed to be a good number of invertebrate trace fossils, I was traveling in uncharted territory for dinosaur trace fossils, an ichnological analog to “The Ghastly Blank,” an endearing term applied to the desert interior of Australia.
In contrast, dinosaur bones—most of which had been found by many people working with Tom and Pat during the past thirty years in this part of Australia—indicated a more diverse fauna was there than this apparent lack of trace fossils might suggest. Moreover, these dinosaurs should have at least been leaving tracks on soft sands and muds during the springs and summers in between harsh polar winters. Yet these tracks seemed to be hiding from paleontologists. We deal with gaps in the fossil record all of the time, but this was a big one for the fossil record of polar dinosaurs in Australia.
Back to the Cretaceous Again
All of this paleontological history was running through my mind and was why I tried to temper any anticipation during our excursion along Milanesia Beach. Yet seei
ng the physical sedimentary structures and small burrows in that outcrop told me we were looking at the former deposits of river floodplains. These environments would have been perfect for preserving dinosaur tracks made during a polar spring or summer. Regardless, I reminded myself to stop entertaining such thoughts and just be a cold, clear-headed, objective scientist: you know, a dismal pessimist.
Just to dissipate these inward distractions, I decided to look intently at more of the little burrows in the outcrop. At this point Greg abandoned me, and I didn’t blame him. He walked ahead to join Tom, who was already several hundred meters east of us. Meanwhile, I took more photographs and measurements of the trace fossils we had found twenty minutes before. Once that was done, I moseyed along, scanning both the outcrop and large boulders strewn across the beach. While walking, I still carefully picked where my feet landed, avoiding those nearly invisible slippery algal surfaces on the rocks. I had already fallen a few times during more than a hundred kilometers of walking along the Victoria coast and did not want to add another bruise, bump, or scrape to my three-week-old collection.
To this day I don’t know why, but one large rectangular block of rock among dozens along the shoreline compelled me to stop and take a moment to have a second look at it. All I can imagine now is that this sensation stemmed from more than ten years of tracking animals in the sands and muds of the Georgia barrier islands and other places in the world, a collective experience that led to an intuitive recognition of something worth noticing on the periphery of my vision.
I looked to my left, then down at the top surface of the boulder. There was a small three-fold impression, looking vaguely like the middle three fingers of a human hand. It was close enough to touch, so I did. My own three middle digits molded to the indentations, confirming what my eyes had seen but not quite believed.
It was a small dinosaur track.
After a quick inhalation, almost trembling, I dared to look at the rest of the rock, scanning from left to right. More patterns of three came into focus, one after another, each identified faster than the previous one. Within about ten seconds, I realized the bumpy surface was loaded with dinosaur tracks.
One of these footprints—a chicken-sized one only about 7 cm (2.8 in) long—was close to the edge of the slab. With my heart beating faster, I then did something I almost never do with modern tracks, which was backtracking. I shifted my focus behind the track nearest me to see if any similar ones preceded it. Sure enough, there was another of the same size, aligned with the previous one. Hesitating in disbelief, I backtracked one more time. Another track was exactly where it should be, at a distance nearly identical to the space between the other two, although slightly off the line of travel. One, two, three steps in sequence, with a slight rightward turn; it was a preserved motion from more than 100 million years ago, made by a small theropod dinosaur on a river floodplain during a polar summer. It was the first known dinosaur trackway in all of southern Australia, and the first polar-dinosaur trackway from the Southern Hemisphere.
There was no time to celebrate; I needed to get to work. I looked more closely, feeling the rock surface. Then I began sketching what was there and marking locations of the tracks, using graph paper in my geological field notebook to make a scaled drawing that served as a sort of “track map.” Unlike taking photographs, drawing forced me to look at the rock and its fossil tracks repeatedly, carefully, and critically, a time-honored observational technique I teach to my students.
This method soon paid off, for within about ten minutes I found a few more tracks, subtle ones that either consisted of very faint toe impressions or were missing parts. This partial preservation of fossil tracks is typical. Most fossil tracks are registered on surfaces below where the animal actually walked as undertracks, like those made by a pen or pencil on an underlying sheet of paper. What then happens, erosion wipes away the “true tracks” made on the uppermost surface, taking away those footprints that may have shown skin impressions, toe pads, claw marks, and minute movements of individual toes. This seemingly unfair erasure of information means that the underlying impressions of a track have a better chance of making it into the fossil record than ones that resulted from direct contact with a foot. The penalty paid by such preservation, though, was a loss of details. For instance, two of the tracks before me were only apparent as paired marks made by sharp claws from two toes, when they should have had three fully formed digits.
A quick initial count of the rock surface yielded about fourteen tracks, all showing three or fewer toes. The surface itself only had an area of about 0.7 m2 (7.5 ft2), or the size of a typical dining room table for a family of four, so it held a lot of information in a small space. This was a busy little piece of real estate during the Early Cretaceous.
I used a handheld GPS unit to document the location of the rock, and it quickly determined the latitude–longitude coordinates of where I was standing. These were saved as a waypoint in the unit, but I also wrote them in my field notebook just in case the unit somehow ended up in seawater, was smashed by a falling rock, or both. Strong waves crashed behind me, acting as a reminder for me to back up this record of my position using old-fashioned analog methods.
This was about when Greg noticed I had become rooted to the same spot for nearly 45 minutes and writing intently in a notebook. Curious, he left Tom and came back down the beach to see what had been holding my attention. He was all smiles as he walked up to where I sat on another boulder in front of the track-bearing slab.
“What’d you find?” he asked cheerfully.
I grinned back, gestured toward the slab surface, and said, with a mixture of pride and awe, “Dinosaur tracks.”
Greg’s jaw dropped, and he briefly looked like a stunned mullet as his eyes took in what was there. In silence, I enjoyed watching him re-discover each dinosaur footprint, a wonderful moment to share with a field compatriot. Once he regained his voice, he exclaimed “Wow, this is fantastic!” Yes, it was.
I was curious to learn what Greg—a non-paleontologist but skilled observer—would see. I asked him to point to everything he thought was a dinosaur track. Within a few minutes of studying the surface, he quickly identified nearly every one I had detected, with only a few misses. “Nice job!” I told him, and we then went over his test results, just like I would with any eager and talented student of mine. We were getting very happy indeed.
Tom soon joined us. Like Greg, he also wondered what had held our interest so raptly, and he asked the same question as Greg: “What’d you find?”
My reply to him was slightly different, though, as I got a little professorial and answered his question with a question: “What do you think is there?”
Tom looked coolly at the rock surface, bringing to bear more than 40 years of paleontological experience, with more than 30 of those years spent studying the Cretaceous rocks and fossils of Victoria. A moment passed, then he pointed to the best-preserved dinosaur track and said, matter-of-factly, “Looks like a dinosaur track.”
I nodded. “Yes, it is. See any others?”
One by one, he pointed to each track, and like Greg he found nearly every one I had identified. This was another great example of a little scientific principle called repeatability. That is, a scientist should be able to have her or his results repeated independently by other scientists.
I wasn’t through with Tom, though, and asked him to take a close look at the little chicken-sized track nearest me. “Anything special about this one?”
That stumped Tom. “Help me out. What am I supposed to see?”
“Look behind it. See anything like it?”
He quickly put his finger on the small track preceding the one nearest me.
“Good. Anything behind that one?” I said.
“That one,” he said, putting his finger on another identical small-sized track.
I beamed again. “It’s a trackway.”
When that little bit of information sank in, Tom allowed himself the indulgence
of a very small Mona Lisa-like smile. Of all people in the entire continent of Australia, there were maybe five who would appreciate the significance of what was in front of us now, and Tom was one of them.
So with this affirmation from my field partners spurring me on, I resumed measuring track dimensions and writing notes, then took photographs. Greg helped with the data collection, acting as a scribe with my field notebook as I measured lengths, widths, and depths of the footprints with digital calipers.
As we did this, I could tell Tom’s mind had gone somewhere other than gathering data about the dinosaur tracks. At some point he asked to borrow my tape measure, and he immediately went about measuring the length, width, and thickness of the slab. He sat down, wrote in his notebook, and then revealed what he was thinking.
“Greg, do you think we could get a front-end loader down here to take this up?”
I was surprised by Tom’s question but shouldn’t have been. As an ichnologist, I’ve never been much of a collector. My work normally consists of describing, sketching, measuring, and photographing trace fossils, recording their locality information, then saying goodbye, sometimes never seeing them again. After all, I did not have either a museum with storage space or research labs at my disposal, let alone collection managers and the means for picking up large heavy rocks. On the other hand, Tom has all of these amenities available to him, along with a collecting permit. In Great Otway National Park—which is where we were—no fossils could be taken without the written permission of the Australian government, but Tom and Pat had that.
Dinosaurs Without Bones Page 31
