September 15, 2011
Raptors are total media hogs. Ever since the big screen adaptation of Jurassic Park came out in 1993, the sickle-clawed carnivores have cast a disproportionately large shadow over the rest of their dinosaurian kin, especially their close relatives the troodontids.
If you’re any kind of dinosaur fan, chances are good that you have at least seen a troodontid dinosaur before. The genus Troodon is a common staple of dinosaur books and documentaries (including Dinosaur Revolution), and it looks like a more slender version of more imposing predators such as Deinonychus. There’s a good reason for this. Together Troodon and Deinonychus represent the two branches of the sickle-clawed dinosaur group known as the deinonychosauria: Troodon represents the troodontids and Deinonychus carries the banner for the dromaeosaurids. Among the things that distinguished troodontids from their dromaeosaurid relatives were relatively big brains, big eyes, an increased number of smaller teeth, and smaller sickle claws that, in some species, could not be retracted as far as in their cousins such as Velociraptor.
Troodon is only the most famous of its kind—perhaps because it has been known for the longest time—but many other troodontid dinosaurs have been named from sites in North America, Asia, and Europe. The latest dinosaur to join the family is Linhevenator tani from Inner Mongolia, China. The dinosaur was described by paleontologists Xing Xu, Qingwei Tan, Corwin Sullivan, Fenglu Han and Dong Xiao in the journal PLoS One.
Dating back to somewhere between 84 million to 75 million years ago, Linhevenator is just one of several recently described theropod dinosaurs to be recovered and described from Inner Mongolia. (The other two, appropriately enough, were the alvarezsaurid Linhenykus and the dromaeosaurid Linheraptor.) The skeletal material which represents the new dinosaur includes the skull and jaws, several vertebrae, the right shoulder blade and upper arm bone, part of the hips, a left thigh bone, the left foot and a few other fragmentary parts. Some of these bones were found articulated with each other, others not, but as troodontid dinosaurs go, Linhevenator is one of the more complete dinosaurs yet found.
What makes Linehvenator particularly unusual are some of the details of its limbs. Compared to other troodontids, Linhevenator had a relatively long shoulder blade, a relatively short and thick humerus, and its second toe was tipped in a specialized, retractable claw like that seen in Troodon but not in some earlier members of the group. This is a curious suite of characteristics. Whereas Linhevenator appears to have had a killing claw similar to that of its dromaeosaurid cousins like Deinonychus, the newly described dinosaur may have had proportionally short and strongly muscled arms. This may hint that Linhevenator was not using its arms to capture prey in the same way as dromaeosaurids or earlier troodontid dinosaurs, even if it did have a specialized killing claw. Instead, Xu and co-authors argue that the dinosaur may have had arms adapted to digging, climbing, or something else entirely, although testing these hypotheses is difficult at present. With any luck, additional discoveries of troodontids will help flesh out what these peculiar dinosaurs were like in life.
Xu, X., Tan, Q., Sullivan, C., Han, F., & Xiao, D. (2011). A Short-Armed Troodontid Dinosaur from the Upper Cretaceous of Inner Mongolia and Its Implications for Troodontid Evolution PLoS ONE, 6 (9) DOI: 10.1371/journal.pone.0022916
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