New Dinosaur Species was Lunch for Prehistoric Crocs

Paleontologists from the South Dakota School of Mines & Technology, the University of Tennessee and North Carolina State University, have found the first fossil evidence of prehistoric crocs feeding on baby dinosaurs, including juveniles of a previously undescribed dinosaur species.

Top: skeletal reconstruction of a new herbivorous dinosaur with known material shown in white. Bottom: dinosaur fossils with bite marks made by crocodyliforms (Boyd CA et al)

Top: skeletal reconstruction of a new herbivorous dinosaur with known material shown in white. Bottom: dinosaur fossils with bite marks made by crocodyliforms (Boyd CA et al)

A large number of mostly tiny bits of dinosaur bones dating back to the late Cretaceous period were recovered within the Grand Staircase Escalante-National Monument in southern Utah leading paleontologists to believe that crocodyliforms – a now extinct relative of the crocodile family – had fed on baby dinosaurs. Evidence shows bite marks on bone joints, as well as breakthrough proof of a crocodyliform tooth still embedded in a dinosaur femur.

The finds, described in the open-access journal PLoS ONE, are significant because historically dinosaurs have been depicted as the dominant species.

“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. You had your dominant riverine carnivores, the crocodyliforms, attacking these herbivores as well, so they kind of had it coming from all sides,” explained lead author Prof Clint Boyd of the South Dakota School of Mines & Technology.

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 6.5 feet (2 m) long. Until now, paleontologists had direct evidence only of very large crocodyliforms interacting with very large dinosaurs.

“It’s not often that you get events from the fossil record that are action-related,” Prof 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.”

The high concentrations of tiny dinosaur bones led researchers to conclude a type of selection occurred, that crocodyliforms were preferentially feeding on these miniature 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,” Prof Boyd said.

The team also 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.

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Bibliographic information: Boyd CA et al. 2013. Crocodyliform Feeding Traces on Juvenile Ornithischian Dinosaurs from the Upper Cretaceous (Campanian) Kaiparowits Formation, Utah. PLoS ONE 8(2): e57605; doi: 10.1371/journal.pone.0057605