Who Made the Three-Toed Dinosaur Track?

In paleontology, occasionally a scientific hypothesis rules for several decades or more and enters the public realm, becoming part of popular lore. Nonetheless, science is always changing, which means that what we took for granted as a “true” story can be upended in a way that surprises everyone, perhaps even the paleontologists doing the revising. Such is the situation with the “giant-stalking-theropod-dinosaur-causing-a-dinosaur-stampede” story of the Lark Quarry dinosaur tracksite in Queensland (Australia). This tale has been reigning for more than 30 years and is known worldwide by paleontologists and laypeople alike, but now faces a makeover in the light of new evidence.

Here are some dinosaur tracks from Queensland, Australia. The dinosaurs that made them had three toes on their rear feet, and walked only on those two feet (bipedally). So were these from theropod dinosaurs or ornithopod dinosaurs? Don’t know? Then I guess you’ll have to read more, won’t you? Display is at the Museum of Tropical Queensland in Townsville, Queensland (Australia). Note the stylish sunglasses (lower right) for scale.

The Case of the Mistaken Dinosaur

Like all stories in paleontology, that of Lark Quarry – a world-famous dinosaur tracksite in Queensland, Australia - starts in the geologic past; in this instance, during the Cretaceous Period, about 98 million years ago. The cast of this tale consisted of about 150 dinosaurs, played by:

• One species of a large herbivorous dinosaur (an ornithopod), who was a mere bit actor, making a cameo appearance before the main act.

• Two species of small dinosaurs – one a theropod and the other an ornithopod – who made up most of the cast; and

• The star of the show, a tyrannosaur-sized theropod, who made a grand entrance toward its climatic finish.

The story is filled with dramatic flourishes, of a tranquil scene shattered by brutal carnivory, and of a quiet Cretaceous lakeshore becoming a killing ground. The former lakeshore, though, left no bodies, only tracks. So we have to reconstruct what happened there by using the oldest science known to humankind, ichnology: the study of modern and fossil traces.

A small sample of the 3,300 dinosaur tracks of Lark Quarry in Queensland, Australia, showing evidence for three species of dinosaurs that either walked or ran along a Cretaceous lakeshore 98 million years ago. Who made these tracks,  what behaviors do they represent, and how were the trackmakers’s behaviors related to one another? That is the mystery – and now the controversy - of Lark Quarry.

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?

Cretaceous Oz: North by Northwest

Following field work in Victoria, Ruth and I went on holiday for our last few weeks in Australia, first to Sydney (New South Wales), then to Queensland. As Ruth and many other spouses/partners can attest, though, there’s one drawback with going on vacation with geologists or paleontologists. And that’s their insatiable drive to see more rocks or fossils. In that respect, then, Sydney seemed safe, being a big city with heaps of concrete and steel covering the good bits (geologically speaking). But Sydney also has great (and free!) museums, containing all of the items that catch the attention of the earth-inclined, and even has some outcrops of cross-bedded Triassic sandstone along its world-famous shorelines, including in front of the Sydney Opera House.

Why do photographs of the Sydney Opera House always omit the Triassic sandstone in front of it? This just goes to show you how even geologists can be temporarily distracted by dazzling architecture.

But how could a geologist not notice that the oldest brewpub in Australia – The Lord Nelson Brewery – is located in a part of Sydney called The Rocks? Out of a sense of scientific duty, we had to go there and sample a few of their brews, too.

A close-up of some of the local Triassic sandstone along a stairway in The Rocks part of Sydney, showing a transition from planar to rippled to some gorgeous convoluted bedding, the last a result of soft-sediment deformation, made before the sediment was cemented into rock. I can’t remember if this was seen and photographed before or after the visit to the brewery, which de facto means it was after.

Nonetheless, our main reason for going to Sydney was to view art, which was already plentiful, but made more so by a biannual art event named (oddly enough) The Biennale. Venues hosting art associated with this event were scattered throughout parts of the central business district (CBD) of Sydney, but most works were either at the Museum of Contemporary Art or on Cockatoo Island, which is located just north of the Sydney Harbor Bridge. For those of you who revel in using both sides of your brain and want to learn more about an artist’s perspective on this year’s artworks, please read Ruth’s take on it (written under her persona of Hallelujah Truth).

We also took in a few hours of the Australian Museum, which has a nicely done section on Australian indigenous cultures (including art styles of different regions), and the obligatory dinosaur hall, which seem to be required of all major natural-history museums. Nonetheless, I was pleased to see how the dinosaur-hall exhibit – which thankfully was not just about dinosaurs, but included other biota, even from outside of the Mesozoic Era – included much information based on the Cretaceous of both Victoria and Queensland.

A reconstruction of Qantassaurus intrepidus, the only dinosaur named after an airline (Qantas), but more importantly is a small ornithopod dinosaur that lived in southern Victoria during the Early Cretaceous Period, about 105 million years ago. Sadly, this detailed reproduction is mostly speculative, as this species is represented by only a few isolated bones, which also took considerable human labor to uncover.

A reconstruction of another small ornithopod from the Early Cretaceous of Victoria, Leaellynasaura amicagraphica. Unlike Qantassaurus, this dinosaur was named after a person (Leaellyn, daughter of paleontologists Tom Rich and Pat Vickers-Rich) and the friendship of the National Geographic Society, respectively. Also unlike Qantassaurus, Leaellynasaura is represented by a partial skull, as well as bones from below the skull.

Note the presence of a villainous raptorial claw entering the frame, about to victimize this poor, defenseless little dinosaur. Might be a good idea to duck into a burrow for safety, eh?

An ankylosaur is loose in the Australian Museum! What a waste! Oh, the humanity! The ankylosaur is Minmi, named in honor of creator spirits in indigenous cultures of northern Australia. Minmi is the most complete ankylosaur in Australia, and its skeleton was discovered in Early Cretaceous rocks of central Queensland, dating from about 95 million years ago.

As loyal readers know, I now have a little bit of experience with the Cretaceous rocks of Victoria after walking over a great amount of these (hmmm, some of those key words might be worked into the name for a blog some day). In contrast, I have much less experience with the Cretaceous of Queensland, which actually is far more extensive and produces vastly greater numbers of fossils than Victoria.

Now, I am not being disloyal to Victoria when I make such a statement: it’s just a fact, supported by the near-constant discovery and recovery of skeletons of large dinosaurs and marine reptiles. For example, last year the world learned about just how special Queensland dinosaurs were, when the Australian Age of Dinosaurs Centre unveiled three new species: two beautiful sauropods and one very nasty-looking theropod (and I mean “nasty” in a good, wholesome Janet-Jackson sort of way). Much, much more about those dinosaurs and the Centre will be discussed in a future entry.

But long before dinosaur bones were found in abundance in Queensland and new dinosaur species were described, people had found something even more important in central Queensland, and I say that with the fully biased opinion of an unrepentant ichnologist. That would be the Lark Quarry dinosaur tracksite, located about 110 kn (60 miles) south of Winton.

This tracksite is arguably one of the most important in the world (and yes, I will argue in favor of that designation, and yes, you will lose if you take up a contrary view). In a relatively small area on a single bedding plane are more than 3,000 dinosaur tracks preserved in natural relief. That in itself is remarkable, but the tracksite also records a few moments of dinosaurian behavior not interpreted from anywhere else in the world. More about that will be explored later, too.

So the following entries, based on our two weeks in Queensland, might be more aptly titled: The Great Cretaceous Drive, as not so much walking was done while we drove many kilometers in the outback. Fortunately for marital stability, there was a lot of paleontologically inspired art along the way too. So Ruth and I were able to combine our interests to each learn about why the Cretaceous of this part of Australia is also rich in stories that inspire our creative juices. So stay tuned for some juicy revelations, coming up soon!