Dinosaurs Without Bones (41 page)

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 seeing 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 m
²
(7.5 ft
²
), 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.

So Tom wasn’t planning to let this big hunk of rock stay here on Milanesia Beach, but instead was already plotting how to put it in Museum Victoria. His scribblings consisted of back-of-the-envelope calculations of the approximate length, width, and height measurements of the rock. This then yielded its approximate volume, which he then multiplied by the probable density of the rock. Because it had alternating layers of sandstone and siltstone, which consisted mostly of quartz and other silica-bearing minerals, it was about 2.7 grams/cubic centimeter, or more than 2.5 times the density of water. This yielded an estimated weight of about 700 kg (1,500 lbs) for the slab in front of us.

Nearly a year later, in early June 2011, Tom—with the help of Pat Vickers-Rich, their daughter Leaellyn (yes, the namesake for the dinosaur
Leaellynasaura
), Greg Denney, David Pickering from Museum Victoria, and personnel from Parks Victoria—succeeded in carrying out his quixotic goal. With the help of a front-end loader and heaps of cooperation, this block of rock with dinosaur tracks was transported safely off the beach. It and the other slab of rock with dinosaur tracks next to it was then put on the back of a flatbed truck and deposited in Museum Victoria in Melbourne, where both are now stored for future reference and further study.

Oh yeah, there was another rock, also with dinosaur tracks. Greg discovered that one, handily providing yet another reason why academic paleontologists are so dependent on non-academic folks to make significant contributions to our science. Greg’s discovery was also a lesson in hubris for me. I was so giddy (and more than a little fulsome) about finding the first block, I hadn’t even bothered to look around to see if any more like it were nearby.

Fortunately, he did. So while I was writing field notes about the tracks on the first block and imagining future fame—perhaps an appearance on Comedy Central, which represents the pinnacle of public acclaim for scientists in the U.S.—he was looking at every nearby boulder. Suddenly, at some point he started acting like a larrikin, running around the beach and looking for a piece of driftwood. In less than a minute, he found a 2”
3
4” board (you’d be surprised at what washes up on these beaches) and quickly placed one end under a boulder only a few feet away from where I sat. Clearly channeling the spirit of Archimedes, he began flipping the rock, using the board as a lever.