October 20, 2009
The Allosaurs Make a Comeback
A cast of the skull of Allosaurus, photographed at the Utah Museum of Natural History.
I have always felt a bit sorry for Allosaurus. It was one of the top predators in what would become North America during the Jurassic, but the fearsome tyrannosaurs of the late Cretaceous are much more popular. In fact, the popularity of Tyrannosaurus and its kin has created the impression that the allosaurs dwindled and died out before the end of the Age of Dinosaurs, that they just could not compete with bigger, meaner predators. But a new study published in the journal Naturwissenschaften by paleontologists Roger Benson, Matt Carrano and Stephen Brusatte shows that close relatives of Allosaurus were going strong until the very end.
Over the past several decades, numerous enigmatic theropod dinosaurs have been discovered from Cretaceous rocks outside North America. A number of these, such as the recently described Aerosteon , closely resembled Allosaurus. And Aerosteon was not alone. The authors of the new study have placed it together with the theropods Australovenator, Chilantaisaurus, Fukuiraptor, Megaraptor, Neovenator and Orkoraptor in a group called the Neovenatoridae.
If these names sound a bit unfamiliar, it’s because most relatively new dinosaurs are quite new—discovered within the last decade or so—and many of them have been hard to categorize. Megaraptor is a good example: at first, researchers thought that it was an enormous “raptor”-type dinosaur, though later studies suggested that its large claws were a sign that it was related to Spinosaurus. Now we know that it was more like Allosaurus in form and was part of a “hidden” radiation of this type of dinosaur throughout the world during the Cretaceous.
As a group, the Neovenatorid dinosaurs were smaller and more fleet of foot than their well-known relatives the carcharodontosaurids. Both groups are closely related to Allosaurus, being parts of the larger group the Allosauroidea, but they represent different sorts of adaptations. They probably played a very different role as predators in the ecosystems in which they lived.
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So it’s not just allosaurs and carcharodontosaurs? Now it’s neovenatorids, too? That’s…wierd. I’d have to see the character list. Unless more Megaraptor material is known that I’m aware of, it seems like a bold statement to suggest it was related to Neovenator and Fukiraptor moreso than megalosaurs and spinosaurs.
And sinraptorids. Don’t forget the sinraptorids. All of those critters were all together in one big, happy allosauroidea.
Megaraptor has a big, enlarged first digit with a ripping claw. Fukuiraptor and Chilantaisaurus were both mis-identified as raptors at first due to their big, ripping claws. In fact Australovenator is exactly what we would expect to confirm this family; it has an ankle bone that looks exactly like Fukuiraptor (its the new name for the “Australian Allosaur”), and yet it has hands a lot like Megaraptor.