The only known dinosaur stampede has turned out to be evidence of a probable river crossing rather than a mass escape, according to new Australian research using 3D analysis.
Numerous tracks dating from between 95 and 98 million years ago found at Queensland’s Lark Quarry Conservation Park were left by small, bipedal dinosaurs called ornithopods, ranging in size from chickens to emus.
“Many of the tracks are nothing more than elongated grooves, and probably formed when the claws of swimming dinosaurs scratched the river bottom,” said study lead author Anthony Romilio at the University of Queensland (UQ) in a press release.
“Some of the more unusual tracks include ‘tippy-toe’ traces–this is where fully buoyed dinosaurs made deep, near vertical scratch marks with their toes as they propelled themselves through the water.”
Skartopus australis track (3D movie) by Romilio et al 2013 from The University of Queensland on Vimeo.
If the dinosaurs were fleeing, then the tracks ought to be much flatter. Also, comparison with swim traces left by dinosaurs elsewhere suggests changes in the water level over time.
“The smallest swim traces indicate a minimum water depth of about 14 centimeters [5.5 inches], while much larger ones indicate depths of more than 40 centimeters [15.7 inches],” Romilio said. “Unless the water level fluctuated, it’s hard to envisage how the different sized swim traces could have been preserved on the one surface.”
“Some of the larger tracks are much more consistent with walking animals, and we suspect these dinosaurs were wading through the shallow water.”
The animals could have been traveling downstream, as suggested by the large intervals between tracks, leaving markings over several days or possibly even weeks.
The paper was published in the Journal of Vertebrate Paleontology.
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