Why did the dinosaur cross the river? Because it wasn’t a stampede.

One of Australia’s best known dinosaur sites, the Dinosaur Stampede National Monument at Lark Quarry, near Winton, Queensland has just been dramatically reinterpreted in a new paper published in the Journal of Vertebrate Paleontology.  The site, which was covered by a purpose built building in 2002 and placed on the Australian National Heritage List in 2004 preserves over 3000 individual tracks that, until recently, were believed to demonstrate evidence of a ‘jumanji-esque’ dinosaur stampede.

Where these tracks made by fleeing dinosaurs of were they trying to cross a river? Image from environment.gov.au
Were these tracks made by fleeing dinosaurs or were they trying to cross a river? Image from environment.gov.au

The new paper, by Anthony Romilio (University of Queensland), Ryan Tucker (James Cook University) and Steven Salisbury (University of Queensland) puts forward a rather different hypothesis: the tracks represent a river of varying depth that dinosaurs often had to cross.

The orthodox spin on the story identifies two ichnotaxa (taxa known only from their tracks) as the track makers. Wintonopus, a small ornithopod and Skartopus, a small theropod. This was actually used as evidence of ‘mixed herding’ where small herbivores and carnivores hung around together as protection against larger predators Thulborn and Wade (1979, 1984, 1989).

Romilio et al. disagree with this interpretation. they claim that there is in fact only a single track maker present, which would be named as Wintonopus as it was named first, with Skartopus becoming a junior synonym. They also failed to find any evidence of a single mass of running individuals leaving them with their own opinion on what was going on here. “The presence of swim traces, long stride lengths, and preferred trackway orientation indicates that the majority of Lark Quarry trackmakers moved downstream and were current assisted. The paleo-water depth would have had to vary in order to allow different-sized buoyed trackmakers to contact the substrate, indicating that animals passed through the area at different time intervals. In the absence of evidence for the single mass of running terrestrial trackmakers, we consider that Lark Quarry is not representative of a ‘dinosaurian stampede.'”

A more accurate picture? Image by Anthony Romilio.
A more accurate picture? Image by Anthony Romilio.

So, which view is more accurate? Only time, and further research will tell. But as there appears to be some friction between the authors of the new paper and Richard Thulborn (one of the authors of most of the earlier work on the trackways), one thing is for sure; this isn’t the last we’ve heard about the Lark Quarry trackway.

The paper is discussed in a little more detail by Brian Switek (@Laelaps) on his excellent blog Laelaps (one of the best palaeo blogs going).

References

Romilio A, Tucker, R. T. and S. W. Salisbury (2013): Reevaluation of the Lark Quarry dinosaur Tracksite (late Albian–Cenomanian Winton Formation, central-western Queensland, Australia): no longer a stampede?, Journal of Vertebrate Paleontology, 33:1, 102-120

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

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

Thulborn, R. A., and M. Wade. 1989. A footprint as a history of movement; pp. 51–56 in D. D. Gillette andM.G. Lockley (eds.),Dinosaur Tracks and Traces. Cambridge University Press, Cambridge, U.K.

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