Dinosaurs Without Bones (42 page)

“Greg, what are you doing?” I asked, as Tom and I watched him.

“This rock is the same as that one!” he shouted.

Tom and I swiveled our heads back and forth between the slab with the dinosaur tracks and the one Greg was attempting to turn over. He was right. They matched perfectly, although the one he was flipping was upside-down, its uppermost surface hidden from view. We ran over to help, and soon we were looking at its other side.

We gaped accordingly, as on the top surface of the rock were more dinosaur tracks. I pulled a small brush from out of my field vest and cleaned off the beach sand from the rock surface, and we stared at the lithified sand from a Cretaceous river floodplain, some of which had molded into the three-toed shapes of dinosaur feet. Just three hours beforehand, when we first descended onto Milanesia Beach, only two confirmed dinosaur tracks had been found in the Eumeralla Formation of western Victoria, and four in all of southern Australia. We now had twenty-four in front of us. You could say we were having a good day.

The most brilliant methods are often the simplest, and the one Greg used for finding the tracks handily fulfilled that dictum. He had noticed the thickness of the first block, as well as its thinly interlayered sandstones and siltstones. Within these alternating layers—a little more than halfway down its thickness—was a gray siltstone, looking much like a different flavor in an otherwise monochrome layer cake. He then glanced around to see if any other nearby boulders shared those traits, and matched one with the one I had discovered. Seeing that the gray siltstone bed was less than halfway down its thickness, he correctly surmised that it was wrong side up, and intuited that the dinosaur tracks could be on its top surface. He was right.

However, there was little time to revel and otherwise pat each other on our backs, as it was now mid-afternoon on a near-winter day. This meant we were losing our sunlight, and we still had a long uphill hike ahead of us back to the car park. Tom quickly measured the second slab’s dimensions and figured out its weight. He reckoned it was about 400 kg (880 lbs), smaller than the first one but still too massive for any (or all) of us to haul up the trail.

I hurriedly photographed the overall surface and started sketching the forms and locations of the tracks on the surface. I also noted any similarities or differences between these newly found tracks and the ones found a few hours earlier. One of the last items on the agenda was to record a few digital video clips of me talking about the dinosaur tracks, which I knew later could be edited into an informative video to accompany a press release. Looking at those clips later was amusing, because you could see that I was trying very hard to be informative and objective but also couldn’t help but show how thrilled I was with what had just happened.

Greg again assisted me in recording measurements as I used the digital calipers to gather data on the dinosaur tracks from this second block: number of toes, length, width, depth, and so on. He wrote down the numbers in my field notebook as I read them aloud. Only then did I take close-up photographs of individual tracks with a photo scale next to each, documenting their dimensions and other details. Much later, back in the comfort of my office at Emory
University in Atlanta, Georgia, I re-measured the tracks from photographs to double-check these results, just in case I had misspoken or Greg had miswritten the data that afternoon. Because I did not know whether I would see these tracks again—notwithstanding Tom’s relentless plotting to acquire them for his museum—I was being extra careful in ensuring that the results could be repeated, checked by others, and otherwise pass peer review in the future.

As the sunlight faded, we decided we had had enough and vowed to come back the next week to better assess the geological context of the tracks, study and photograph them more, and figure out how to recover them from this high-energy, wave-filled place. Milanesia Beach had been generous to us that day, and as we all trudged up the steep trail, we were filled with laughter and excitement about these gifts offered by the dinosaurs, the Cretaceous floodplains, and, much more recently, coastal erosion.

The three of us came back the next week, along with Monash University geologist Mike Hall and my wife Ruth, who had just arrived in Australia to join me. Once we relocated the tracks, I recorded more measurements and descriptions while the others conducted a reconnaissance of the nearby cliff face and looked for the probable source of the dinosaur-track-bearing bed. They had a merry adventure doing this, climbing over hill and dale, while I, doing my best Marlin Perkins
Wild Kingdom
impression, stayed safely on the beach, waving to them once in a while as I looked up and saw their tiny figures crawling along the outcrop. Ultimately, they were able to narrow down the likely zone from where the tracks came, but it was inaccessible, on a sheer vertical face that kept saying “You’ll all die!” if anyone tried to approach it. (This one needed no warning signs.) So gravity had been our friend, and I expect it will continue to be, as we can simply wait for it to provide us with more dinosaur tracks on Milanesia Beach in the future.

Walking Forward, One Step at a Time

We knew that lots more science had to be done before we could share our finds with the rest of the world, but we were confident
that that day would come. Sure enough, exactly one year later, on June 14, 2011, my coauthors and I—Tom Rich, Pat Vickers-Rich, Mike Hall, and Gonzalo-Vazquez Prokopec—received the good news that our scientific article had been accepted for publication in the Australian paleontology journal
Alcheringa
. Our peers confirmed what we knew that day one year before: we had discovered the best assemblage of polar dinosaur tracks in the Southern Hemisphere, the first dinosaur trackway from the southern part of Australia, and extended the geographic range of dinosaur finds in Victoria farther to the west. It was a most pleasing outcome from an otherwise frustrating field season.

The less technical picture that emerged from this discovery was this: Imagine small theropod dinosaurs—probably adorned with colorful feathers, ranging in size from chickens to cranes—making tracks while walking around on a river floodplain after the spring floods accompanied by a polar thaw. The tracks fell into three sizes, almost like they could be fitted for shoes, one of which was quite small (those would be the “chickens”) and two others close to one another, but with one slightly larger than the other (men and women “cranes”). Although I couldn’t prove it for sure, I suspected these three sizes were from a dinosaur family, consisting of still-growing juveniles accompanied by their mother and father.

These tracks inspired a compelling vision of parents and young performing their own version of a “Great Cretaceous Walk,” leaving traces of their late spring or early summer foray on a wet, sandy floodplain next to a polar river, perhaps like the one I had studied in Alaska. Were they foraging, stopping occasionally to snack on invertebrates burrowing into the sand below their feet? Were they looking for others of their species, seeking companionship after a long dark polar winter? Or were they just reveling in the sunshine of a longer day, enjoying a warm breeze that fluffed their feathers as it wound through the river valley? That is the beauty of dinosaur tracks, as records of life as it happened while also encouraging fantasies of what once was, back then, and very close to the place where human eyes first recognized them for what they were.

So even though these tracks were only a drop in the proverbial bucket when it comes to paleontological discoveries, and still did not completely erase the reputation of Australia as a place forgotten by dinosaur trace fossils, they helped to affirm the most important point we paleontologists like to make about the fossil record: it gets better every day. Knowing this, we are encouraged to continue looking, and sometimes with the help of our friends we find what we’re looking for, dinosaur trace fossils or otherwise.

My Mesozoic Moment

The large theropod tracks were fresh, and so was its scat. I looked around me, but the tropical rainforest was too thick to see very far, effectively hiding anything as big as what I knew had to be out there. Given such limited vision, I took advantage of the eyes and ears in the trees above me, listening to the songbirds for alarm calls, scolding, abrupt silencing, or other signs of unease. Satisfied that nothing was out of the ordinary, I squatted to take a closer look at the tracks and scat and began talking about both of these with my students, who gathered around to learn.

We were together on a short loop trail in a patch of rainforest in northern Queensland, Australia, and the theropod that made the traces in front of us was the southern cassowary (
Casuarius casuarius
). The students, all Americans and from my university, had enrolled in a study-abroad program to Queensland in June–July, 2007. Part of the program was a week-long field trip through the Wet Tropics region of northern Queensland, and on that day we were near the coastal town of Mission Beach. Before taking the
students onto the trail that day, my colleague Chris Beck and I told them that the rainforest was an ideal habitat for cassowaries, which meant we might see one. However, we also warned them that we needed to be very cautious if we did, considering that they were, as my Australian friends might say, bloody dangerous.

When compared to modern concepts of theropod dinosaurs, cassowaries come straight out of the Cretaceous Period. They can be 2 m (6.6 ft) tall and weigh as much as 80 kg (175 lbs), making them among the heaviest birds alive. Unlike most mammals, female cassowaries are larger than the males, and would look down on most human supermodels. An adult cassowary’s torso is covered with coarse black feathers, but its most eye-catching features are on its head. The head is topped with a casque, a tall, bladed crest that from the front looks as if it can saw through flesh, but also is broad when viewed from either side. The neat visual trick this accomplishes is that it makes for a more imposing profile while also increasing its height, like a Mohawk or Roman helmet. A stout but pointed beak pokes out from its face, behind which are yellow eyes dotted with black pupils, giving it an unnerving gaze. The side of its head and the skin just under its face reflects several shades of bright blue, contrasting smartly with long red-maroon flaps of skin (wattles) hanging down from the lower part of its neck.

Below, its scaly reptilian legs connect to three thick toes, all terminated by pointy claws. The inner one—digit II—really stands out, though. It is about 12 cm (5 in) long and is often described lovingly as “disemboweling,” a descriptor bestowed in recognition of how this bird defends itself by leaping claws first into an attacker. In terms of Newtonian physics, this is a fine example of mass times acceleration translating into force which, when applied to a surface, transmits stress, and I mean that in the worst way. Given their weights, and that they are capable of running 45 km/hr (28 mph) and leaping more than a meter into the air, cassowaries can concentrate that forward momentum into the tiny areas of those claws, thus better enabling the splitting of an antagonist’s soft body cavity.

Why are cassowaries so aggressive? Mostly because they feel a need to defend their territories, which could also include protecting nest sites and offspring: good reasons to give them plenty of room to roam. Incidentally, if you are chased by a cassowary and try to escape it by jumping in a nearby water body, be aware that they are also excellent swimmers and are known to venture into the sea. In fact, they are so comfortable in water that, much like human hot-tub or pool parties, their mating rituals sometimes happen while immersed. The only way this bird could be more terrifying is if it also flew. Fortunately, it and its ratite relatives—emus, ostriches, rheas, and others—are ground-dwellers, which make them even more comparable to medium-sized flightless theropods from the Mesozoic Era.

Cassowaries are omnivorous, eating fungi, forest invertebrates (insects and snails), and small mammals, but they are primarily known as terrific fruit eaters. So far, they have been documented eating fruits from more than two hundred species of plants, including a variety of figs. This cosmopolitan dining was partly evident in scat on the trail, which consisted of a dried, grayish-white, nitrogen-rich mass mixed with a variety of seeds. I was astonished at the size of their piles, which rivaled those of large mammals I’ve tracked in North America—more like black bears than turkeys. The largest pile we encountered was 15 to 20 cm (6–8 in) wide and contained seeds as big as 2.5 cm (1 in), nearly the size of ping-pong balls. Once I identified the first of such fecal masses, the students quickly recognized more along the trail in various states of disaggregation, their completeness depending on how long ago their cassowary producers had dropped them. Nonetheless, these droppings provided an ecological lesson for the students on the importance of cassowary poop as a means of fertilizing and dispersing seeds, and one communicated much more effectively than if I had droned on about it in an indoor classroom.

Although I had only been in cassowary territory once before then, my paleontological and ichnological training suited me well for detecting their tracks and other signs. Of course, their large
three-toed tracks, measuring 20 to 25 cm (8–10 in) long and tipped with big clawmarks, were unmistakable in this ecosystem. In that place and time, the tracks could only be confused with those of emus, which lived in drier savannahs far west of there. Like most birds, their walking trackways consisted of a narrow, linear series of tracks, as if they were on a tightrope. This pattern only deviated where they stopped to forage or took a moment to assess their surroundings for potential threats or violations of their territory.

Although the tracks and scat showed that cassowaries in the area were frequent users of the human trail we were using, I figured they had their own worn pathways in the forest. However, I had no intention of testing this supposition by going for a stroll deeper into the forest and perhaps accidentally stumbling onto a nest site, which would have been very bad for both me and the cassowaries.