December 4, 2012
When I think of oviraptorosaurs – feathered, beaked, omnivorous theropods–my mind immediately jumps to Mongolia’s famous brooding dinosaurs and other forms extracted from Asia’s Cretaceous rock. But these weird dinosaurs were present in North America, too. Among the latest to come to the attention of paleontologists is Hagryphus giganteus–a large oviraptorosaur known from little more than a hand and pieces of foot.
Paleontologists started to report on the oviraptorosaurs of North America’s Late Cretaceous in the 1930s. They just didn’t immediately recognize the dinosaurs for what they were. Scrappy remains of these dinosaurs were attributed to the ostrich-like ornithomimosaurs and Cretaceous birds. It was only in the 80s and 90s that researchers began to untangle the identities of these dinosaurs. Based on specimens found in Canada, Montana, and the Dakotas, there may have been at least three different genera present–Caenagnathus, Chirostenotes, and Elmisaurus–around 75 million years ago. That depends on who you ask, though. Researchers disagree about which genera are valid. The material from these dinosaurs is so fragmentary that it’s difficult to tell just how many different forms we’re looking at.
But Hagryphus, described by paleontologists Lindsay Zanno and Scott Sampson in 2005, was different. Represented by a nearly-complete left hand, part of the left radius, and fragments of the foot, this theropod lived further to the south in the 75-million-year-old swampy environment preserved in Utah’s Grand Staircase-Escalante National Monument. Much like other dinosaurs found in the same formation, and other southern species from roughly contemporaneous deposits, the known remains of Hagryphus are distinct from the equivalent bones known from the northern species. Not only was Hagryphys bigger–Zanno and Sampson estimated that the dinosaur was about 10 feet long, quite large for an oviraptorosaur–but bones in the dinosaur’s hand were much more robust.
Zanno and Sampson considered that the unique nature of Hagryphus might be because the individual was an older specimen of one of the northern oviraptorosaurs. They rejected this hypothesis, arguing the the dinosaur’s distinctive hand proportions were more consistent with being it a different taxon than changes due to growth. If they’re right, this fits the general pattern of Utah’s Kaiparowits Formation in preserving dinosaurs that were related to those found in Montana and Alberta but were unique genera and species.
So how many oviraptorosaurs were there in North America around 75 million years ago? We probably haven’t found traces of all of them, but based on what has been described so far there were probably at least two and as many as four. We need more complete skeletons to be sure.
The same problem affects other small-bodied theropod dinosaurs from the Late Cretaceous. Based on teeth and fragmentary remains, paleontologists used to think that the deinonychosaur Troodon had a range from southern Utah to Alaska. As parts of additional specimens come out of the ground, paleontologists are starting to realize that what seemed to be just one dinosaur is really a collection of different genera or species spread across the latitudes. And regardless of what Hagryphys is, the existence of an oviraptorosaur in Utah greatly extends the range of these dinosaurs during the 75-million-year-old time frame. Exposures between southern Utah and Montana may very well hold additional oviraptorosaur specimens–individuals that will be critical to understanding how these dinosaurs evolved.
This is the latest post in the Dinosaur Alphabet series.
Zanno, L., Sampson, S. 2005. A new oviraptorosaur (Theropoda, Maniraptora) from the Late Cretaceous (Campanian) of Utah. Journal of Vertebrate Paleontology. 35:4, 897-904
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