Raptorex
Raptorex is a dubious genus of tyrannosaurid dinosaur. Its fossil remains consist of a single juvenile specimen probably uncovered in Mongolia, or possibly northeastern China. The type species is R. kriegsteini, described in 2009 by Sereno and colleagues. The genus name is derived from Latin raptor, "robber", and rex, "king". The specific name honours Roman Kriegstein, a survivor of the Holocaust, whose son Henry Kriegstein donated the specimen to the University of Chicago for scientific study.[1][2]
While initially considered to have come from the Yixian Formation of China, dated to approximately 125 million years ago during the early Cretaceous period, later studies showed that such an early date for the fossil are unlikely, and given its extremely close similarity to juvenile tyrannosaurids of the late Cretaceous, it probably came from the Iren Dabasu or similar formation. Because the specimen is a juvenile, and the changes undergone by tyrannosaurids during growth are not yet well understood, many researchers now consider it to be a nomen dubium, because it cannot be confidently paired with an adult skeleton (though it is extremely similar to juvenile Tarbosaurus bataar skeletons of the same size and age).[3]
The only known Raptorex specimen shows the same basic proportions as juvenile tyrannosaurids: a comparatively large and solidly-constructed skull, long legs with adaptations for running, and tiny, two-fingered forelimbs. This is in contrast with more basal tyrannosauroids such as Dilong, which retained features characteristic of more basal coelurosaurs such as a small head and long, three-fingered forelimbs.[1]
The specimen is a very small juvenile, estimated at 3 m (9.8 ft) long and about 65 kg (143 lb). The holotype (LH PV18) measured about 2.5 m (8.2 ft) and died in its third year.[3]
According to Peter Larson, who attempted to re-trace the origins of the specimen, the holotype fossil of Raptorex (currently designated LH PV18 and housed in the collections of the Long Hao Institute of Geology and Paleontology in Hohhot, Inner Mongolia, China) was purchased from a Mongolian fossil dealer by an American businessman in Tokyo, Japan, and subsequently taken to the United States, where it was again put up for sale at the Tucson, Arizona Gem, Mineral and Fossil Show. There it was sold by Hollis Butts to Dr. Henry Kriegstein, an ophthalmologist and fossil collector. Up until this point, the specimen had been identified as a juvenile specimen of Tarbosaurus, which had been collected from Mongolia. Kriegstein notified American paleontologist Paul Sereno of the specimen, who proposed it represented a subadult of a new species from the Yixian Formation of China. Sereno arranged to publish a description of the specimen and to have it sent to China, from where he assumed it had been smuggled.[3]
In Sereno's description of the specimen, he and his co-authors interpreted it as a near-adult aged about six years. Sereno initially stated to the press that numerous index fossils present in the rock slab surrounding the specimen showed it belonged to Early Cretaceous. In an interview with the Chicago Tribune, Sereno said “From sediments, fossil fish bones, turtles, clam shells and other fauna we recovered from the rock matrix alongside the Raptorex fossil, we could generally pinpoint where it had been dug up in an area along the border with Inner Mongolia."[4] However, only a single fish vertebra and a crushed, unidentifiable mollusk shell were actually present alongside the Raptorex specimen.[1][3] Sereno and colleagues identified the fish vertebra as being similar to the genus Lycoptera, a key index fossil of the early Cretaceous Yixian formation.[1] However, they did not describe the bone or note any features in common with known Lycoptera specimens.[3]
