Eoraptor Booted Out Of Theropod Family

Galvasean

Eoraptor (meaning 'dawn thief') was for a long time to be considered to be the earliest memberof the theropod family of dinosaurs (the one with all the meat eaters in it). However the discovery of a new type of dinosaur carnivore from the same time called Eodromaeus (meaning 'dawn runner') called for reclasification. This new dinosaur had long legs for speedy running, saber teeth and sharp claws on it's hands. By comparison, Eoraptor looks very underequiped as a predator, leading many palaeontologists to the conclusion that it is in fact a very primitive relative of the prosauropodomorphs (the family of dinosaurs that gave rise to the giant long necked sauropods).

Many palaeontologists have argued that Eoraptor was the earliest member of the theropods, but the new study suggests that this little dinosaur, toothy as it might appear, was in fact a basal sauropodomorph.

The argument for kicking Eoraptor out of the theropod lineage focuses on the fact that Eodromaeus and Eoraptor lived at the same time and that Eodromaeus has very marked theropod-like features, whereas Eoraptor not only lacks these but also has the inset lower first tooth and enlarged nostrils of a sauropodomorph.

It is also noteworthy that Eodromaeus had air sacks in it's bones, similar to those of modern birds. This shows that theropod dinosaurs started to show avian (bird-like) traits very early on in their evolution.

Read more on this interesting subject here (with comments from both Paul sereno and Mike Benton!).


Eodromaeus skeleton with palaeontologist Paul Sereno.