November 15, 2010
Paleontologists are discovering dinosaur species at a dizzying pace. These days it seems that a new species is announced almost every other week. Many of these new dinosaurs are being found in China, and two different teams of scientists have recently described a pair of unique species from two locations within the country.
As described by paleontologists Nicholas Longrich, Philip Currie and Dong Zhi-Ming in the journal Palaeontology, the dinosaur Machairasaurus leptonychus was discovered in the 84- to 75-million-year-old rock near the village of Bayan Mandahu in Inner Mongolia (itself a part of northern China bordering the country of Mongolia). There was not much left of this dinosaur. All that remained was a partial right forelimb, parts of the left arm, and a few toe bones, but the lower arm bones, fingers and claws were distinctive enough to identify this as a new type of oviraptorid dinosaur.
More specifically, Machairasaurus appears to have been a small animal most similar to a subgroup of the oviraptorids called the Ingeniinae, and according to Longrich and co-authors, Machairasaurus and its close relatives had relatively robust hands that were not well-suited to grasping. Instead, the forelimbs of this dinosaur appear to have been better suited to “scratching, tearing or, conceivably, digging” than grabbing prey, and the anatomy of their mouths hints that they may have included a large amount of plant food into their diets. As paleontologists have discovered through the study of other Cretaceous dinosaurs, theropod dinosaurs can no longer be cast as a group of entirely carnivorous dinosaurs—multiple lineages of theropods switched over to plant-eating during the Cretaceous.
The second new theropod was described by a team of Chinese scientists led by Junchang Lü in Acta Palaeontologica Polonica. Named Xixiasaurus henanensis, this small animal was a troodontid dinosaur found in the circa 83-million-year-old strata of China’s Henan Province. Represented by a partial skull, lower jaw fragment and a few other bits from its lower arms, Xixiasaurus resembled other troodontids, such as Byronosaurus, in having a set of unserrated teeth which were small and closely-packed in the front of the jaw but larger and recurved in the back of the jaw. As with the forelimb specializations of Machairasaurus, the unique teeth of Xixiasaurus, Byronosaurus, and their closest relatives, Lü and colleagues suggest, may be related to a more cosmopolitan diet that included plants, but more than tooth anatomy alone will be required to investigate this hypothesis.
LONGRICH, N., CURRIE, P., & ZHI-MING, D. (2010). A new oviraptorid (Dinosauria: Theropoda) from the Upper Cretaceous of Bayan Mandahu, Inner Mongolia Palaeontology, 53 (5), 945-960 DOI: 10.1111/j.1475-4983.2010.00968.x
Lü, J., Xu, L., Liu, Y., Zhang, X., Jia, S., & Ji, Q. (2010). A New Troodontid Theropod from the Late Cretaceous of Central China, and the Radiation of Asian Troodontids Acta Palaeontologica Polonica, 55 (3), 381-388 DOI: 10.4202/app.2009.0047
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