Dinosaurs Without Bones (10 page)

Although this might seem odd to people outside of paleontology, nine years passed from the discovery of this world-class tracksite until paleontologists arrived to evaluate them. Nonetheless, this lag time reflected the reality of how long it took news to travel from rural Queensland to the “ivory towers” of academia, especially in the days before such academics could be contacted more easily by e-mail. The only hint of the trace fossils’ presence was conveyed a few years after their discovery. In this instance, Ron McKenzie, a station hand of Mr. Seymour’s, took natural casts of the tracks to the Queensland Museum and had them confirmed as dinosaur tracks.

Otherwise, nothing much in a scientific sort of way happened until 1971, when Mr. McKenzie and Mr. Knowles took paleontologists to
the site: Richard T. Tedford of the American Museum of Natural History, Alan Bartholomai of the Queensland Museum, Patricia (Pat) Vickers-Rich of Monash University, and her husband Thomas (Tom) Rich of the Museum of Victoria. Nonetheless, despite the presence of so many prominent paleontologists in that part of Queensland, they weren’t there to look at dinosaur tracks. Instead, they were prospecting for body fossils of Cretaceous mammals, whose remains are much smaller and rarer than dinosaur tracks. Nonetheless, the tracks, mentioned by Mr. Knowles in conversation with the paleontologists, made for an interesting non-mammalian fossil diversion, and they readily agreed to look at the site where the tracks had been discovered.

Once these paleontologists visited this place with Mr. Knowles, Dr. Tedford, through application of his well-practiced geological reasoning, traced the small outcrop of the track-bearing layer into an adjoining hillside. He figured that the stratum continued underneath the surface of the hill, which they tested by walking to the other side of the hill. Sure enough, the same track bed was there, just where Dr. Tedford predicted it would occur. Thus the entire track-bearing bed was likely more extensive than originally surmised, and would need to be excavated before it could be investigated in detail.

This is all well and good, but still does not tell how the track-site gained its current nickname of “Lark Quarry.” When paleontologists from the University of Queensland and Queensland Museum—Drs. Tony Thulborn and Mary Wade—decided to study the site in the mid-1970s, one of their most dedicated volunteers was Malcolm Lark, a local resident. Accordingly, they named the site in his honor. The “quarry” part of its moniker came from what these paleontologists and volunteers did during the field seasons of 1976 and 1977. In order to expose and see more of the track-bearing surface, they had to strip off a 30-cm (12-in) thick sandstone bed overlying the tracks. By the time they finished, these industrious folks estimated that they’d moved more than 50 tons of rock, which revealed an area of 210 m
²
(2,250 ft
²
) holding more than 3,300
dinosaur tracks. This was a hard-earned mother lode of dinosaur trace fossils.

You might think that such a concentration of dinosaur tracks—on average about 15 tracks per square meter—would be enough in itself to guarantee everlasting paleontological fame. But it got even better. Once the surface was cleared of its overburden and its tracks could be mapped and described in detail, a remarkable story came to life. And storytelling is what ichnology is all about, and why it is probably among the oldest sciences known to humankind. Moreover, science ideally should surprise us, and these tracks certainly astonished the original investigators, along with succeeding generations of paleontologists and the public afterwards.

Based on Thulborn and Wade’s analysis of the site, the area was a lakeshore that had been submerged regularly by a nearby stream emptying into it. Fluctuations between submergence and emergence of the shoreline could be discerned from alternating sand and mud layers in the rock, as well as long parallel grooves caused by logs that dragged across the lake bottom during flooding of the stream and lake. Once emergent, this shoreline would have served as a water source for local animals, and its moist, silty, and sandy sediments may have registered tracks over the course of several days or weeks. The tracks would have dried slightly underneath the warmth of the Cretaceous sun, but not so long as to bake them and cause them to crack around their edges. A minor flood from the lake or stream later covered the tracks with a protective layer of sand, which, along with the track-bearing layer, hardened and became part of the geologic record.

At the time of their excavation, the forms and sizes of the tracks pointed toward four species of bipedal dinosaurs as the track-makers: a medium-sized ornithopod, about the same mass as a hefty heifer; a smaller ornithopod, close to the size of a modern emu; a much smaller theropod, only slightly bigger than a chicken; and the source of dramatic tension in the story, a large
Allosaurus
-scale carnivorous theropod. Most of the tracks on the surface were from the small theropods and ornithopods, and they were not
lolling about in idyllic harmony at the lakeshore. Instead, these dinosaurs were running flat-out, clearly motivated by something that caused all of them to move in the same direction at high speed.

Drs. Thulborn and Wade came up with this scenario once they measured the directions of the individual trackways and distances between tracks within each trackway. Using the formula devised by R. McNeil Alexander for calculating dinosaur speed based on track length, hip height, and stride, they figured these dinosaurs were moving at about 12 to 16 kph (7.5–10 mph), which is quite fast for short-legged dinosaurs. Furthermore, the tracks mostly showed toe-tips touching the ground instead of entire digits. Lastly, some tracks were greatly elongated, indicating that slipping and sliding happened during their journeys. Very simply, when small animals take big strides, get up on their toes, and lose their footing on moist ground, they are running. To find out just how many dinosaurs were involved in this collective action, they walked a line perpendicular to the direction of movement and counted a minimum of 130 animals; about 55% of these were theropods and 45% ornithopods.

So instead of my recounting more of their evidence, I will let words from Drs. Thulborn and Wade’s first research paper about the site, published in 1979, speak for the feelings these tracks evoked. In reading this, note how they broke an unspoken rule in paleontology, in that they expressed an emotional empathy with animals from nearly a hundred million years ago:

Persuasive circumstantial evidence leads us to conclude that they represent a stampede—that is, a wild, unreasoning and panic-stricken rush to escape the threat of danger. What could have caused such presumed panic?

It was a great question, and in their attempt to answer it Thulborn and Wade pointed to the large three-toed tracks that entered the scene from the left. These tracks originated from the same direction taken by more than a hundred small dinosaurs, some of which ran
around and onto the tracks of the big dinosaur, interpreted by the paleontologists as those of a big theropod. How big? As mentioned before, dinosaur sizes can be estimated by their tracks: just multiply the length of the footprint by 4.0, and you have the approximate hip height of the dinosaur. In this instance, the best-preserved track was 64 centimeters (25 inches) long, so its hip was about 2.5 meters (8.3 feet) off the ground. Just to put this in perspective, this is higher than the tallest basketball player in the NBA, and would have been big enough to make you and me run, too. So imagine the fright felt by a much smaller ornithopod or theropod from the approach of such an imposing predator.

Compounding this effect would have been the contagious fear spreading instantly through a sizeable group of small dinosaurs, instigating a chain reaction of similar behaviors. Think of the arrival of a fox in a chicken yard, or even a human walking up to a group of shorebirds, and how the jittery reaction of one bird is enough to spook the others, thus causing all to share the terror.

Bolstering this idea of a panic-inducing theropod was its trackway pattern, which was unusual. Based on their measurements, Thulborn and Wade figured it was moving slowly, at only 8 kph (5 mph), and because it crossed its right foot over its line of travel, then its left foot, it may have even paused at some points before picking up speed and turning sharply to the right. Frustratingly, this is also the point where the trackway reaches its end, forever eroded. This odd trackway pattern, expressed by only eleven footprints, led Thulborn and Wade to propose that the theropod might have been stalking, looking for prey in a target-rich environment.

Thulborn and Wade’s map of the tracksite and other analyses of the tracksite constituted a masterpiece of meticulousness, supplying a wealth of data to support their interpretations. From their work they published two peer-reviewed papers, the first with the provocative title of “Dinosaur Stampede in the Cretaceous of Queensland,” published in 1979. The second, published in 1984, was a much longer and more detailed report modestly titled “Dinosaur Track-ways in the Winton Formation (Mid-Cretaceous) of Queensland.”

I still point to the 1979 paper as one of the most compelling I have ever read in ichnology and often re-read it to remind myself of what constitutes a “gold standard” in the traditional study of dinosaur tracks. I also keep in mind that Thulborn and Wade completed their study of 3,300 tracks without the benefit of tools we now take for granted: no high-resolution digital cameras, digital calipers, global-positioning systems (GPS), geographic information systems (GIS), image analysis, laser scanners, 3-D modeling, Internet, or other technological shortcuts that would have made such a study far easier. Just heaps of hard physical labor, lots of surveying and other measurements, and scientific reasoning, served with a healthy dollop of intuition on top. And the end result was a tale that still astonishes.

This story of a dinosaur stampede in Queensland was so intriguing that it is rumored to have inspired one of the more spectacular scenes in the movie
Jurassic Park
(the first one, that is, not its awful sequels). In this scene, a flock of the Late Cretaceous theropod dinosaur
Gallimimus
(“ostrich mimic”) stampedes in fear at the nearby presence of
Tyrannosaurus rex
, the most redemptive character of the movie, and who was also from the Late Cretaceous. (The casting of both dinosaurs, along with
Triceratops
,
Paralophosaurus
, and
Velociraptor
, also illustrates why
Jurassic Park
should have been titled
Cretaceous Park
instead.) Unfortunately for the prey but fortunately for the predator, one member of the flock is separated from its compatriots and singled out for sacrifice, while the others continue running for safety.

Although perhaps more than a hundred million people have watched this scene in the movie, I’ll bet a six-pack of my favorite adult beverage that less than 1% of these people know how it mirrors the initial scientific interpretation of the Lark Quarry tracksite. Of course, locals in Winton know about this piece of fiction imitating fact, and I have heard them joke about how nice it would have been for the Lark Quarry Conservation Centre to receive a tiny royalty from the film profits as a sort of honorary tithe. Regardless, I have been pleased to contribute to the local
Winton economy in a non-Spielbergian way by visiting the tracksite, bringing others there with me, staying in Winton, purchasing pub meals, singing
Waltzing Matilda
, and of course quenching my thirst with Queensland-produced beers, all ably demonstrating some of the touristic and economic impact of dinosaur tracks, or what I like to call “ichnotourism.”

What Made the Three-Toed Dinosaur Track?

In paleontology, just like any other science, a scientific hypothesis might rule for several decades or more, enter the public realm, and become part of popular lore. Nonetheless, because the science behind such stories is always changing, this means that what we took for granted as a “true story,” even one we like very much, can be upended in a way that surprises everyone, including the paleontologists revising its narrative. Such is the situation with the “giant stalking theropod dinosaur causing a small dinosaur stampede” story of the Lark Quarry dinosaur tracksite in Queensland.

This tale, which has reigned for more than thirty years and is known worldwide by paleontologists and laypeople alike, faced a radical makeover in the light of new evidence presented in a paper published by paleontologists Anthony Romilio and Steven Salisbury in 2011. The fresh hypothesis states that the “dinosaur stampede” was not triggered by the arrival of a predator, and no stalking of other dinosaurs by a voracious predator happened either. Yet this new evidence and its accompanying explanation has not been completely accepted, and in fact is facing a fierce challenge from one of the original researchers, Dr. Thulborn. In other words, don’t grab an eraser just yet, as the controversy may not be resolved.

The story of Lark Quarry and its dinosaur tracks illustrates very well a constant feature of science, which is that it is always evolving. This basic principle certainly has been realized in a grand way with evolutionary theory, gravitational theory, plate tectonic theory, and quantum theory. Lots of testing, scrutinizing, and arguing took place before the majority of the worldwide scientific community accepted any of these broad-sweeping, unified explanations for
much of how our world works. But these theories also underwent considerable changes—an ongoing process.

The same standard applies to more focused hypotheses of all shapes and sizes, including those concerning dinosaur tracks and other trace fossils, which is that new evidence or perspectives can modify these, making for better fits. Along those lines, in science we do not prove, we disprove, meaning that old stories are sometimes revised in the face of novel finds. Furthermore, answers invariably generate more questions, meaning that although we may get ever so much closer to the truth with each investigation, we also keep in mind that we may never quite reach it absolutely, especially when we deal with events of the distant geologic past.