March 2nd, 2013 by James Ayre
The discovery of a new species of herbivorous dinosaur has been made by researchers at the South Dakota School of Mines & Technology. The discovery also provides the first fossil evidence that prehistoric crocodyliforms (crocodiles and related animals) feed on small and juvenile dinosaurs. It’s easy to imagine large prehistoric crocodiles taking down dinosaurs in much the same way that they do large wildebeest and other mammalian herbivores today.
“Research by Clint Boyd, Ph.D., provides the first definitive evidence that plant-eating baby ornithopod dinosaurs were a food of choice for the crocodyliform, a now extinct relative of the crocodile family. While conducting their research, the team also discovered that this dinosaur prey was a previously unrecognized species of a small ornithopod dinosaur, which has yet to be named.”
The fossils were discovered in what is currently known as “the Grand Staircase Escalante-National Monument in southern Utah dates back to the late Cretaceous period, toward the end of the age of dinosaurs.” They consist primarily of tiny pieces of dinosaur bones that were found at four separate locations within the park, all within the Upper Cretaceous (Campanian) Kaiparowits Formation.
The evidence that these dinosaurs were preyed on by crocodyliforms is partially provided by the clear bite marks found on many of the bone joints. But even more substantially, by the discovery of a crocodyliform’s tooth that had apparently broken off during its attack and was left embedded in one of the dinosaur’s femurs.
This discovery is considered very important because researchers have generally considered dinosaurs to be the “dominant” species. But as this discovery shows, the ecosystems present during the time of the dinosaurs may have been a great deal more complex than they are generally assumed to have been. “The traditional ideas you see in popular literature are that when little baby dinosaurs are either coming out of a nesting grounds or out somewhere on their own, they are normally having to worry about the theropod dinosaurs, the things like raptors or, on bigger scales, the T. rex. So this kind of adds a new dimension,” Boyd said. “You had your dominant riverine carnivores, the crocodyliforms, attacking these herbivores as well, so they kind of had it coming from all sides.”
Not that it is all that surprising that crocodyliforms were successful back then, especially when you are familiar with their representatives in the world today. Crocodiles are impressive animals, featuring a very advanced sensory system that it uses to be one of the most successful hunters alive in the world.
“Based on teeth marks left on bones and the large amounts of fragments left behind, it is believed the crocodyliforms were also diminutive in size, perhaps no more than 2 meters long. A larger species of crocodyliform would have been more likely to gulp down its prey without leaving behind traces of ‘busted up’ bone fragments.”
The only evidence for interactions between the two that researchers had before this discovery was for the “very large crocodyliforms” interacting with the “very large dinosaurs.”
“It’s not often that you get events from the fossil record that are action-related,” Boyd said. “While you generally assume there was probably a lot more interaction going on, we didn’t have any of that preserved in the fossil record yet. This is the first time that we have definitive evidence that you had this kind of partitioning, of your smaller crocodyliforms attacking the smaller herbivorous dinosaurs.” This is actually only the second known case of a fossil crocodyliform tooth being found still embedded in a fossil of a prey animal.
“A lot of times you find material in close association or you can find some feeding marks or traces on the outside of the bone and you can hypothesize that maybe it was a certain animal doing this, but this was only the second time we have really good definitive evidence of a crocodyliform feeding on a prey animal and in this case an ornithischian dinosaur,” Boyd said.
Because of the very high concentrations of very small dinosaur bones present, the scientists involved are of the opinion that the crocodyliforms were very likely targeting the small dinosaurs. “Maybe it was closer to a nesting ground where baby dinosaurs would have been more abundant, and so the smaller crocodyliforms were hanging out there getting a lunch,” Boyd added.
“When we started looking at all the other bones, we starting finding marks that are known to be diagnostic for crocodyliform feeding traces, so all that evidence coming together suddenly started to make sense as to why we were not finding good complete specimens of these little ornithischian dinosaurs,” Boyd continued. “Most of the bites marks are concentrated around the joints, which is where the crocodyliform would tend to bite, and then, when they do their pulling or the death roll that they tend to do, the ends of the bones tend to snap off more often than not in those actions. That’s why we were finding these fragmentary bones.”
“In the process of their research, the team discovered through diagnostic cranial material that these baby prey are a new, as yet-to-be-named dinosaur species. Details on this new species will soon be published in another paper.”
The new research was just published in the online journal PLOS ONE.
Image Credits: South Dakota School of Mines & Technology; Kaprosuchus via Wikimedia Commons
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