Sunday, December 26, 2010

The Mystery of Lark Quarry

One of the most famous dinosaur tracksites in the world – Lark Quarry Conservation Park in central Queensland – is protected from the elements of the Australian outback by a beautiful, spacious, and environmentally friendly building. But how comfortable would it be to spend a night there, alone with the dinosaur tracks? I was about to find out, having been accidentally locked in, and just after the departure of the last tour of the day.

Lark Quarry has gorgeous dinosaur tracks, and lots of them. But would you sleep with them?

Before talking about that embarrassing episode from the first time I visited Lark Quarry in 2007, let’s go back to justifying why these dinosaur tracks deserve such renown, including why they have their own building – in the proverbial “middle of nowhere,” about 110 km (65 miles) from the nearest town of Winton – and National Heritage status in Australia.

The eco-chic Lark Quarry Conservation Centre, one of the few buildings anywhere in this part of Queensland and made to preserve one of the best dinosaur tracksites in the world, while serving as a valuable educational resource. I should point out, though, that despite the energy efficiency of this building, and construction that used recycled materials and local labor, I saw no shade-grown coffee, cruelty-free eggs, or free-range tofu on the premises.

How often do you get to pose with a sign that has the words “Dinosaur Stampede” on it, and it’s not a joke? Photograph by Ruth Schowalter.

I remember first learning about Lark Quarry as a geology graduate student, soon after beginning my studies in ichnology while at the University of Georgia (USA) in the mid 1980s. Imagine how thrilling it was for a nascent ichnologist in Georgia to read about a site that held more than 3,000 Cretaceous dinosaur tracks in faraway Queensland, Australia. What an amazing place, worthy of communal worship in the Church of Ichnology! I likewise dreamed of the ichnological ecstasy that would result from a pilgrimage to see it in person. This aspiration became real for the first time in 2007 (that’s when I got locked in) and was fulfilled again in 2010, although that time with my wife Ruth along to gaze admirably at this hallowed ground. She also successfully kept us from being trapped in the building.

How was such an incredible site discovered? As is still typical for fossil finds in Queensland, it was spotted by a sharp-eyed amateur, cattle-station manager Glen Seymour. (And just as a grumpy aside, academic paleontologists everywhere are too busy nowadays sitting behind computer screens, replying to e-mails, and serving on committees to find much of anything. Consequently, we depend even more on amateurs with “eyes on the ground,” who we very much appreciate.) When Mr. Seymour saw the tracks in the 1962, only a few were visible on a rock surface sticking out of a hillside; I imagine that their resemblance to emu or brush turkey tracks caught his eye, honed by much time outdoors and looking at the ground.
The rolling red hills of the Queensland outback. Somewhere out there are more dinosaur tracks, waiting to be discovered, and make the Cretaceous rocks of Australia even more famous.

Indeed, he later said he considered them as fossil bird tracks, and was flabbergasted when local grazier, photographer, and naturalist Peter Knowles indentified them as dinosaur tracks. I also can’t help but think, though, that the indigenous people of this area and other parts of Australia, many of whom were expert trackers, probably noticed these marks of long-gone animal life in the Cretaceous rocks and incorporated these trace fossils into Dreamtime stories.

Now, this might seem strange to people outside of paleontology, but nine years passed from the discovery of this world-class tracksite until academic paleontologists arrived to evaluate them. Nonetheless, this lag time reflected the reality of how long news took to travel from outback Queensland to the “ivory towers” of academia. Several years after their discovery, Ron McKenzie (a station hand of Mr. Seymour’s) had taken natural casts to the Queensland Museum and had them confirmed as dinosaur tracks, but nothing much happened after that.

Finally, in 1971, Mr. McKenzie and Mr. Knowles took paleontologists to the site, including Richard H. Tedford of the American Museum of Natural History, Alan Bartholomai of the Queensland Museum, Patricia (Pat) Vickers-Rich of Monash University, and Thomas Rich of the Museum of Victoria. Oddly enough, they weren’t in the area to look at dinosaur tracks, but instead were more interested in Cretaceous mammals. The dinosaur tracks, brought up by Mr. Knowles in conversation with the paleontologists, nonetheless made for an interesting non-mammalian diversion. Once they visited the site, Dr. Tedford traced the track-bearing layer into an adjoining hillside, meaning the entire layer was more extensive than originally surmised, and would need to be excavated before it could be investigated scientifically.

The basic geological principle of lateral continuity, using a tilted layer (bed or stratum) of Cretaceous-age sandstone from coastal Victoria, Australia. This bed should continue laterally unless interrupted by erosion or some other geological process. This is how you can predict the extent of a bed that contains dinosaur tracks, and is exactly what Richard Tedford did to find the extent of the Lark Quarry tracksite.

How did the site get 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 local resident Malcolm Lark. The “quarry” part came from what these paleontologists and volunteers did during the field seasons of 1976 and 1977 to better see more of the track-bearing surface: strip off the 30-cm (12 in) thick sandstone overlying the tracks. These hard-working folks estimated that more than 50 tonnes of rock were moved, which exposed more than 200 m2 (= 650 feet2) and 3,300 dinosaur tracks. This site was a motherlode of dinosaur trace fossils.

Lark Quarry toward the end of the field season in 1976, with the piles of rubble showing just how difficult it was to get to the dinosaur tracks, while also demonstrating how ichnology sometimes requires “digging,” too. Photo by the Queensland Museum, and lifted from the Australian Age of Dinosaurs Journal, Issue 2, p. 23. To compensate for my shameless borrowing of this photo, everyone reading this should subscribe to the award-winning magazine from which it originated:

You would think that such a concentration of dinosaur tracks (on average, about 17 tracks per m2) would be enough in itself to guarantee everlasting paleontological fame. But it got even better. Once the surface was clear and its tracks could be mapped and described in detail, a remarkable story emerged. And storytelling is what ichnology is all about, and why it is probably among the oldest sciences known to humankind. Moreover, any science worth mentioning should astonish us, and these tracks certainly surprised its original investigators, as well as more than a generation of paleontologists and the public afterwards.

The original environment in this area about 98 million years ago was a lakeshore that had been submerged by a nearby stream emptying into it. Fluctuations between submergence and emergence of the shoreline can 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 a flood.
Those long grooves were not caused by dinosaur tails dragging along a muddy surface, but by logs or some other inert objects pushed by a current. You may now instead stare at the dinosaur tracks, especially the really big ones to the right.

When emergent, this shoreline would have served as a waterhole for local animals; its moist, muddy sediments may have registered tracks over the course of several days or weeks. The tracks would have dried slightly underneath the warmth of a Cretaceous sun, but not so long as to bake them and cause mudcracks to radiate from the tracks. A small amount of flooding from the lake or a nearby stream later covered the tracks with a protective layer of sand, which, along with the track-bearing layer, hardened and became part of the fossil record.

Ah, the calm before the storm, the salad days, if you will. Wait, did someone hear something? Artwork on display at the Lark Quarry Conservation Centre.

At the time of their excavation, the forms and sizes of the tracks pointed toward three species of two-legged (bipedal) dinosaurs as the main trackmakers: a small herbivorous ornithopod, about the size of a modern emu; a much smaller theropod dinosaur (only slightly bigger than a chook); and the source of drama in the story, a large carnivorous theropod.

Size differences between the three trackmakers at Lark Quarry can be figured out by looking at their tracks; their overall forms also indicate three species of dinosaurs. Do you see all three represented here as three-toed tracks? The smallest are from chook-sized theropods, the slightly larger ones from emu-sized ornithopods, and the big one is from, well, something different from the other two.

The vast number of tracks on the surface originated from the small ornithopods and theropods, and they were not lolling about in idyllic harmony at the lakshore. 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 realized this scenario once they measured the directions of the individual trackways and distances between tracks within each trackway. Furthermore, the tracks mostly showed toe-tips touching the ground, instead of entire digits. Lastly, some tracks were greatly elongated, indicating a little bit of slipping and sliding. Very simply, when small animals take big steps, get up on their toes, and start to lose their footing, they are running.

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 evoked by the tracks. Note here how they broke an unspoken rule in paleontology: they expressed an emotional empathy with animals from nearly 100 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?

To answer this question, Thulborn and Wade pointed to the large, three-toed tracks that entered the scene from Stage Left, exactly the direction taken by more than a hundred small dinosaurs that ran around and onto the tracks of the big dinosaur. Based on size and overall outline, the paleontologists interpreted the large tracks as those of a big theropod. How big? Dinosaur sizes can be estimated by track sizes: 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 at about 2.5 meters (8.3 feet) off the ground.

Yes, this would have been big enough to make you and me run, so imagine the fright felt by a little ornithopod or theropod from the approach of a predatory dinosaur this large. Compounding this effect was the contagious fear that would have spread instantly through the sizeable group of small dinosaurs, causing a chain reaction in 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 all sharing the terror.

Run away! Run away! Diorama at the Corfield and Fitzmaurice Building in Winton, Queensland, showing little theropods and ornithopods running around the leg of a massive and presumably hungry theropod.

Thulborn and Wade’s map and analysis of the tracksite was a masterpiece of meticulousness, providing a wealth of data supporting their interpretation. They published two peer-reviewed papers about the tracksite, the first with the provocative title of Dinosaur Stampede in the Cretaceous of Queensland, published in the journal Lethaia in 1979. The second was a much longer and more detailed report in Memoirs of the Queensland Museum, modestly titled Dinosaur Trackways in the Winton Formation (Mid-Cretaceous) of Queensland and published in 1984.

I still point to the 1979 paper as one of the most compelling I have ever read in ichnology, and I often re-read it to remind myself of what constitutes a “gold standard” in the 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, GPS, GIS, image analysis, laser scanners, 3-D rendering, Internet, or other technological short-cuts that would have made such a study a lot 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 us.

This story of a dinosaur stampede in Queensland became so intriguing, it is rumored to have inspired one of the more spectacular scenes in the movie Jurassic Park (the first one, 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 a large carnivorous dinosaur (who happens to be the most redeeming character in that movie), Tyrannosaurus rex, also from the Late Cretaceous. (Both dinosaurs also illustrate why Jurassic Park should have been titled Cretaceous Park). Unfortunately for the prey, but fortunately for the predator, one of the flock is separated from its group and singled out for sacrifice while the others continue running for safety. (No mateship in Cretaceous dinosaurs, that’s for sure.)

A brief clip from the “documentary film” Jurassic Park, likely inspired by the Lark Quarry tracksite in Queensland. Did you notice the most unrealistic part of this scene? You got it:  the paleontologist does not have a beer in his hand.

Perhaps more than a hundred million people have seen this scene, but I’ll bet less than 1% of these people know about the connection between it and Lark Quarry. Of course, locals in Winton know about it, and I have heard them joke about how nice it would have been for the Lark Quarry Conservation Centre to receive a very small royalty from the film profits (indeed). Regardless, Ruth and I were pleased to contribute in a non-Spielberg way to the local Winton economy by visiting the tracksite, staying four nights in a Winton pub hotel, purchasing pub meals, singing Waltzing Matilda, and of course quenching our thirst with XXXX beer.

Oh yes: you’re wondering how I got trapped in the building with the dinosaur tracks? In July 2007, I had driven six hours from Townsville, Queensland to Winton, then another hour to Lark Quarry. I made it to the last afternoon tour of the day, and after it ended, I purposefully dawdled, waiting for other people in the tour to leave so I could soak in the beauty of these trace fossils in silence. I took many photographs and otherwise gazed longingly at the tracks, beheld at long last after reading about them for more than 20 years. However, while in this ichnologically induced nirvana-state-of-mind, I neglected to hear the clicking of the entrance, now locked by the tour guide, who had not bothered to check whether anyone was still inside with the tracks.

The immoveable door invoked a panic akin to that experienced by the small dinosaurs there more than 95 million years ago (although, on the bright side of things, I was not locked in overnight with a multi-tonne predator). Fortunately, my primate brain kicked into gear, and I recalled how the tour guide had used a portable PA (public-announcement) system. I quickly commandeered this unit, and after much hooting and hollering at its highest volume, I managed to attract the attention of the tour guide, who was about to leave for Winton. Saved! However appealing it might have been in a spiritual way to spend a night with these much-adored tracks, I was also happy to say “goodbye for now” and hope that I would see them another day. Which I did, in July 2010.

So next week, with stories of Lark Quarry anxieties dancing in our heads, we will reconsider the original dinosaurian tale told here, and think about how science can change stories. Even ones we really, really like.

Sources of information about Lark Quarry you should read (please don’t believe anything I just wrote):

Thulborn, R.A., and Wade, M., 1979. Dinosaur stampede in the Cretaceous of Queensland. Lethaia 12, 275-279.

Thulborn, R.A., and Wade, M., 1984. Dinosaur trackways in the Winton Formation (mid-Cretaceous) of Queensland. Memoirs of the Queensland Museum 21, 413–517.

Meiklejohn, D., and Elliott, J. 2004. The ghosts of Lark Quarry. Australian Age of Dinosaurs Journal, Issue 2: 18-31.