The Lark Quarry ‘Dinosaur Stampede’ Debate Continues
Palaeontologists aim to extract the maximum amount of information about extinct animals from the remains they leave behind. However, one type of information that is more difficult to obtain is their behaviour. Did T-rex hunt in packs? Did the Neanderthals use language? Questions regarding behaviour are often difficult to answer as there is little or no trace of it left behind. One of the best sources of behavioural information on extinct creatures comes from their trackways; the footprints that the animals leave behind can not only reveal information about the locomotory capabilities of the individual animal, but can also inform us on the composition of ancient communities and their palaeoecology.
One of the most famous trackways is Lark Quarry, in central-western Queensland, Australia. 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 made by dinosaurs around 94 million years ago. The traditional interpretation of the trackways suggests that a dinosaur stampede of 150 smaller individuals had occurred, triggered by the approach of a larger theropod (Thulborn & Wade, 1984). This can be seen in the YouTube video below, it definitely makes for great entertainment! However a study released in 2013 examined the trackways and found that any interaction between the larger and the smaller trackmakers was highly unlikely (Romilio et al. 2013). The topic has been a contentious one, with plenty of debate going on between supporters of the contrasting hypotheses, which I have blogged about in the past (here and here).
Now however, Anthony Romilio and his PhD supervisor Steven Salisbury, both from the University of Queensland, have went back and documented the 3D morphology of the tracks of the largest Lark Quarry trackmaker, along with associated surface structures using objective methods that retain 3D track information. This has been done in order to determine how well these trackways have been approximated in the original published 2D track outlines of Thulborn and Wade (1984). This paper was published in the journal Cretaceous Research last month.
What they’ve found is that the morphology of the tracks obtained from their photogrammetry models differ from the original published 2D track outlines. Some of the original outlines were found to be over 20% larger than the actual tracks. They also once again conclude that the large trackmaker was a large ornithopod rather than a theropod, determining that the larger tracks lack any discernable claw marks or digital pad impressions that would indicate the presence of a theropod.
Furthermore, they find that there is a lack of evidence to suggest that both types of dinosaurian track types formed (near) simultaneously, as Dr. Salisbury states: “The 3D models show that there are pressure bludges surrounding the large footprints, and that many of these are cut by the drag marks caused by partially floating vegetation. This indicates that water covered the site after the large tracks were made. The pressure bulges and drag marks are also dotted with smaller footprints, indicating that Lark Quarry’s small-bodied dinosaurian trackmakers traversed the site sometime after the drag marks for formed, and definitely after the large ornithopod walked through. Based on our earlier research, we know some of these smaller dinosaurs were swimming. The time over which various tracks were made at the site could range from a few hours to several days. It’s definitely not a ‘moment’ frozen in time.”
So, rather than a dinosaur stampede, Romilio and Salisbury are arguing that Lark Quarry represents a complex time-averaged assemblage of multiple dinosaurian trackways that occurred over hours – days and also that the water level varied during this time period. Time will tell what hypothesis is closest to the truth. In the meantime though, the debate is certain to continue, with advocates of the stampede theory still arguing their case, in what is an excellent example of a spirited scientific discussion.
Dr. Salisbury's quotes are taken from the University of Queensland press release (see here)
Anthony Romilio, Steven W. Salisbury, Large dinosaurian tracks from the Upper Cretaceous (Cenomanian–Turonian) portion of the Winton Formation, Lark Quarry, central-western Queensland, Australia: 3D photogrammetric analysis renders the ‘stampede trigger’ scenario unlikely, Cretaceous Research, Volume 51, September 2014, Pages 186-207, ISSN 0195-6671, http://dx.doi.org/10.1016/j.cretres.2014.06.003.
Thulborn, R. A., and M. Wade. 1984. Dinosaur trackways in the Winton Formation (mid-Cretaceous) of Queensland. Memoirs Queensland Museum 21:413–517.