December 21, 2010

Study Claims Bird-Like Dinosaurs Were Plant Eaters

While dinosaurs such as the Tyrannosaurus rex have long been assumed to be carnivorous, many of them were, in fact, vegetarians, according to a new study set to be published in the journal Proceedings of the National Academy of Sciences (PNAS).

Paleontologists from the Field Museum in Chicago, Illinois, used statistical analysis in order to discern the dietary preferences of 90 species of theropods--bipedal, bird like dinosaurs that first appeared in the late Triassic period. Of those theropods, they discovered that many members of the group known as coelurosaurs survived largely on a plant-based diet.

According to a Field Museum press release, scientists Lindsay Zanno and Peter Makovicky collected dietary data from nearly 100 coelurosaur species and studied an array of different fossil types. The duo then tested whether or not certain skeletal traits, including tooth-loss or long necks, "could be found to correlate with direct evidence of plant eating among coelurosaurian dinosaurs."

They discovered nearly two dozen anatomical features that they claim can be "statistically linked to direct evidence of herbivory," and further went on to find that 44 theropod species in six different lineages--including the ancestors of most modern birds--were not solely carnivores, but at the very least omnivores. Of course, the T. rex and the Velociraptor of Jurassic Park fame were undeniably meat-eaters, but Zanno says that they should be looked at "more as the exception than the rule."

"Most theropods are clearly adapted to a predatory lifestyle, but somewhere on the line to birds, predatory dinosaurs went soft," Zanno told the AFP on Monday

"Once we linked certain adaptations with direct evidence of diet, we looked to see which other theropod species had the same traits"¦ then we could say who was likely a plant eater and who was not," she added. "This new research firmly supports what we've have been speculating about for some time"¦ it's time to start seeing these animals in a new evolutionary context."

Given that coelurosaurs gave rise to birds, Zanno said in the press release that studying their dietary habits could provide valuable keys to understanding how and why that evolution occurred. If they were plant eaters, the scientists state, it is possible that they first gained the ability to fly in order to reach food in the trees. However, that is just "one of many possibilities," Zanno concluded.


Image Caption: New research by Field Museum scientists finds widespread herbivory in bird-like theropod dinosaurs. Four of the 90-theropod species involved in the study shown with dietary interpretations. All four species derive from the famous feathered dinosaur beds of the Early Cretaceous Yixian Formation, P. R. China, leading the scientists to speculate that dietary diversity may have contributed to the large numbers of contemporaneous theropods in ecosystems like those of the Yixian. Credit: Dennis Finnin and Roderick Mickens, copyright American Museum of Natural History


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