December 9, 2009
When the big-screen adaptation of Jurassic Park premeired in 1993, “raptors” instantly became some of the most popular dinosaurs. For scientists, though, they posed a troublesome problem. There were only a few types of raptor, technically called dromaeosaurs, known at the time, and paleontologists were unsure how they evolved.
But since then paleontologists have found numerous new kinds of dromaeosaur, many of which had been covered in feathers in life. The latest dinosaur to be added to this group is a small, 125-million-year-old raptor from China named Tianyuraptor ostromi. Described in the journal Proceedings of the Royal Society B by a team of Chinese scientists, this small predator is helping scientists to understand how dromaeosaurs evolved.
While dromaeosaurs in the movies are shown as big animals, about the size of an adult human or bigger, many of them were quite small. They would have been not much bigger than the traditional Christmas goose (a living relative of theirs), and Tianyuraptor is no exception. As with many other groups of predatory dinosaurs it appears that the dromaeosaurs started off small, and only a few later forms (such as Deinonychus and Utahraptor) grew to very large size.
Yet Tianyuraptor differs from other dromaeosaurs in an important way. Its arms are relatively short. Most raptors have long forelimbs that are about 70 percent of the length of their hindlimbs, suggesting that the arms of these dinosaurs were important to catching prey and, in some species, even flying. Tianyuraptor, however, has arms that are only about half the length of its legs, meaning that it might have been doing something slightly different with its arms.
The precise relationships among the earliest known dromaeosaurs are still difficult to tease out, but Tianyuraptor is significant to the evolution of the raptors. Not only was it an early form, but it was different from other dromaeosaurs that lived in the area at about the same time. It appears that by 125 million years ago there was already a diverse array of small raptor dinosaurs, part of an evolutionary radiation in which some groups became extinct and others persisted. While probably not the great-great-great grandaddy of Velociraptor, Tianyuraptor does help us better understand the origins of some of its more famous cousins.
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