No Australian Tyrannosauropus After all – Lark Quarry Revisited
New Interpretation of Lark Quarry Dinosaur Trackways – Suggest no Large Theropod
Every once in while a very special type of fossil site is discovered, one that provides an exciting and unique glimpse into the ancient world of the Mesozoic. One such place is Lark Quarry, located near the small town of Winton, Queensland (Australia). The region is very famous for its Early Cretaceous dinosaur fossils. However, at Lark Quarry it is not fossilised bones that so excited researchers when they were first brought to the site, it is the presence of literally hundreds of beautifully preserved dinosaur footprints.
One set of footprints, was believed to show the presence of a large “T. rex-like” meat-eater causing smaller dinosaurs to stampede. Now some further research published in the scientific journal “Cretaceous Research” offers a new interpretation.
Lark Quarry Revisited
Many scientists have studied the extensive trace fossils, but perhaps the most famous part of the site represents the preserved evidence of what took place in perhaps less than ten seconds nearly 100 million years ago. A herd of small, plant-eaters (the footprints of which have been ascribed to Wintonopus by ichnologists), plus a large number of predatory coelurosaurs (named Skartopus) were disturbed by the approach of what was thought to be a large, carnivorous theropod dinosaur (known as Tyrannosauropus).
The large, meat-eater seemed to have the smaller dinosaurs trapped and the only chance they had to escape was to run straight past the giant predator as quickly as they could. The tracks indicate that the smaller animals sprinted past the bigger dinosaur, running at speeds in excess of 12 miles an hour as judged by the stride length.
This famous part of the trackways preserved in the fine grained sandstone of Lark Quarry was studied by doctors Tony Thulburn and Mary Wade, who published their results in 1984. They cited the evidence of the large footprints to support the theory that enormous predatory dinosaurs lived in what was to become Australia, in the Early Cretaceous. This, they thought was evidence of 11-metre-long carnivores stalking smaller dinosaurs. The Trannosauropus’s trackway actually consists of eleven footprints, (three-toed prints), some of which were interpreted as showing the marks left in the soft sand by sharp claws on the toes.
The stride length indicates that it moved at about 3-5 miles per hour – a walking speed and it seems to have weaved about slightly, with a tendency to slow down towards the end of the tracks. This was interpreted as the meat-eater lurching at the smaller dinosaurs but slowing down as it realised that its attack had been unsuccessful.
It was the large prints that were originally interpreted as being from a large, meat-eating dinosaur, however, a new study has indicated that this may not be the case.
New research by scientists at the University of Queensland suggests that the large footprints were not made by a carnivorous dinosaur at all. The prints actually represent the tracks made by a large, but definitely herbivorous dinosaur. If this new theory is accepted it means that the Lark Quarry trace fossils are not evidence of a large theropod dinosaur, something similar to a T. rex or an Allosaurus.
University of Queensland School of Biological Sciences PhD student Anthony Romilio, the lead author of the research, believes that the large prints actually represent the tracks made by an ornithopod dinosaur, perhaps something resembling a Muttaburrasaurus.
Muttaburrasaurus (M. langdoni), is known from two skeletons found in eastern Australia. This large animal has been taxonimcally classified as an iguanodont, an ornithopod.
An Illustration of Muttaburrasaurus langdoni
Picture credit: Everything Dinosaur
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Anthony came to this conclusion after comparing the characteristics of the Lark Quarry Tyrannosauropus prints with those of other theropods and known ornithopods.
“Making the distinction between the three-toed tracks of herbivorous ornithopod dinosaurs and the three-toed tracks of carnivorous theropod dinosaurs can be quite difficult. This confusion has led to numerous ornithopod dinosaur tracks being incorrectly identified as belonging to theropods, and vice versa.”
Tracks Made by a Plant-eater
For many years, these large prints from the Lark Quarry site were regarded as being from a meat-eater that had caused a dinosaur stampede, but earlier work, highlighted by Mr. Romilio does suggest a big plant-eater was the culprit.
Threshold values for specific foot proportions for both theropod and ornithopod dinosaurs enabled the Queensland team to distinguish between the tracks made by different types of dinosaur and based on this research Anthony was able to conclude:
“The footprint analysis shows overwhelmingly that the Lark Quarry tracks were made by an ornithopod dinosaur. The best preserved prints show a remarkable similarity in overall size, shape and claw outline to ornithopod tracks from Canada named Amblydactylus gethingi. These features mean that we need to re-name the large Lark Quarry tracks Amblydactylus cf. A. gethingi.”
The size of the prints and the fact that Muttaburrasaurus fossils have been found in sediments of the same age as the Lark Quarry deposit have led the team to suggest that a “Muttaburrasaurus-like” animal probably made them. Muttaburrasaurus is believed to have been a facultative biped, that is, an animal that walked on all fours for most of the time, but if the need arose it could rear up onto its hind legs and walk in a bipedal fashion.
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Anthony’s PhD supervisor, Dr Steve Salisbury stated that the previous identification of the Lark Quarry tracks as belonging to a large, meat-eating dinosaur was central to the interpretation of the track site as a stampede.
“The approach of the large dinosaur was thought to have triggered the stampede of 150-170 smaller dinosaurs across the sandy mud nearly 100 million years ago. Whether the presence of a large herbivore like Muttaburrasaurus was enough to spook a herd of smaller dinosaurs into a stampede is now unclear. Further research on the actual nature of the stampede itself is what we are now focusing on.”