December 19, 2008
When Jurassic Park was released into theaters, scientists were quick to point out that the film featured super-sized Velociraptor. Even the largest of the dromaeosaurs then known, like Deinonychus, were puny compared to their on-screen cousins. The same year that the film was released, however, the first remains of an enormous, 21-foot-long dromaeosaur named Utahraptor were recovered in, you guessed it, Utah. Velociraptor may have been small, but there were giants in its family tree. Now another “raptor,” just as enormous, named Austroraptor has been announced in the Proceedings of the Royal Society B [Biological Sciences].
Even though many dromaeosaurs are known from the Northern Hemisphere, primarily North America and Asia, they did have some odd cousins that lived in what is now South America. A particular group of these Southern Hemisphere raptors, the Unenlagiinae, had very long snouts and relatively short arms compared to other dromaeosaurs, and Austroraptor falls into this strange group. Even though much of the skeleton is still missing, the recovered skull, leg, vertebrae, and arm bones have told paleontologists a lot about this narrow-snouted predator, which lived 70 million years ago.
Many dromaeosaurs have very long arms, but the humerus of Austroraptor indicates that it had shorter arms more similar in relative size to Allosaurus or Carcharodontosaurus. This is consistent with a trend seen widely among carnivorous theropods; as bodies get bigger, arms get shorter. The leg bones of Austroraptor are also strikingly large, and this also has to do with scaling. Larger animals require thicker and stronger bones to hold themselves up; Austroraptor is not simply a scaled-up version of its smaller relatives like Buitreraptor.
The discovery of Austroraptor has revealed that South America was a center of diversification for predatory dinosaurs. Not only does it illustrate the variety of dromaeosaurs present in South America during the Cretaceous, but it shows that these dinosaurs grew to large sizes and probably came into competition with other predators like the Abelisaurids, theropods like the recently-announced Skorpiovenator. South America during the Cretaceous was definitely a dangerous place to live.
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