June 12, 2009
When we talk about dinosaurs, we often associate some of our favorites with the times in which they lived. Dinosaur enthusiasts know that Tyrannosaurus was a Cretaceous dinosaur, for example, but fewer people know that Tyrannosaurus only lived at the very end of the Cretaceous, about 68 to 65 million years ago. The Cretaceous as a whole lasted from about 145 to 65 million years ago, and this makes the reign of the prehistoric tyrant a relatively short one by comparison. Not all parts of the Cretaceous are equally well known, though, and in a new paper published in Naturwissenschaften, paleontologists have described a large predatory dinosaur that helps fill in a significant gap in our knowledge of Asia during the Cretaceous.
Up until now, paleontologists who have been studying the Cretaceous dinosaurs of Asia have primarily been working with the bookends to a series. The Late Jurassic, from about 161 to 145 million years ago, and Late Cretaceous in Asia are relatively well known, but there is a 60-million-year gap spanning the Early and Middle Cretaceous from which little is known. While scientists have found some smaller dinosaurs from the earlier part of the Cretaceous, remains of large predatory dinosaurs have often been so fragmentary that it has been difficult to tell what sort of theropods were roaming the landscape. Were they the ancestors of the later tyrannosaurids, or did some of these teeth and shards of bone belong to other predators?
The fossils described by the paleontologists in the new paper provide evidence that large non-tyrannosaurid theropods once hunted in the Cretaceous of Asia. The first fossils of this dinosaur were discovered decades ago and called Chilantaisaurus maortuensis, a new species within a large theropod genus known from other fossils—but there was a problem. The fossils for the new species did not match any of the bones used to describe the other Chilantaisaurus species, so researchers could not be sure if they were really belonged to the same genus of dinosaur or not.
The fossils remained in a sort of limbo for years, but last January paleontologist Steve Brusatte had another look at the Chilantaisaurus maortuensis fossils and noticed something peculiar. Different scientists had placed the species within several different theropod groups, but Brusatte saw that the fossils clearly had traits that linked it to carcharodontosaurids, large predators known primarily from Africa and South America. One from Asia had never been found before. Brusatte teamed up with Roger Benson, Dan Chure, Xu Xing, Corwin Sullivan, and Dave Hone to describe the fossil, and they came to some interesting conclusions.
The first order of business was giving this dinosaur a new name. Based upon the available skull material they rechristened the fossils Shaochilong maortuensis, the “shark tooth dragon.” But what was a carcharodonotosaurid doing in Asia? How did it get there? There are not concrete answers to these questions yet, but during the Early and Middle Cretaceous Asia may have held a curious mix of dinosaurs previously segregated in the Northern and Southern hemispheres. As paleontologist Thomas Holtz mentioned in a mailing list comment about this paper, this discovery might make possible a scenario previously regarded as fictional: large carcharodontosaurids may have hunted and eaten horned dinosaurs.
You can read more about the paper, including some background information on the re-discovery of the fossils described, at Dave Hone’s Archosaur Musings blog.
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