Saurornithoides

Saurornithoides

Saurornithoides Fossil range: Late Cretaceous, 75 Ma
Holotype skull of Saurornithoides mongoliensis, AMNH
Right side of a cast of the only known skull of Saurornithoides mongoliensis.
Scientific classification
Class	Reptilia
Superorder	Dinosauria
Order	Saurischia
Suborder	Theropoda
Family	Troodontidae
Genus	Saurornithoides Osborn, 1924
Species	S. mongoliensis Osborn, 1924 (type)

Saurornithoides is an extinct genus of troodontid maniraptoran dinosaur, living during the Late Cretaceous period. These creatures were predators, which could run fast on their hind legs and had excellent sight and hearing. The name is derived from the Greek stems sauros (lizard), ornithos (bird) and oid (form), an appropriate name for a creature close to the ancestry of birds.

Description

Saurornithoides, like others in its family, was probably predominantly carnivorous. Estimates of its length range from 2 to 3 meters (6.6 to 9.8 feet) and weight from 23 to 54 kilograms (51 to 120 lbs). It had large eye sockets and stereoscopic vision, allowing for good depth perception. It probably had good vision in light and very good night vision. It had a long, low head, a depressed muzzle, sharp teeth and a relatively large brain. Swift and smart, like its North American cousin Troodon, Sauronrnithoides probably scoured the Gobi Desert, looking for small mammals or reptiles to eat. Scientists speculate that it used its long 'arms' and grasping 'hands' to seize live prey, which would have consisted of small animals. Like other troodontids, it had an especially large claw on the second toe of each foot.

A single specimen of this theropod has been found in the Djadochta Formation of Mongolia. Saurornithoides was named by paleontologist Osborn in 1924. The type and only species is S. mongoliensis. A second species, S. junior, was named by Rinchen Barsbold in 1974, based on a specimen from the Nemegt Formation thought to be more closely related to S. mongoliensis than to other troodonts. However, a 2009 review of the genus found that the support for this idea was lacking, and re-classified S. junior in the new genus Zanabazar.

History of Discovery

Originally, only one or possibly two individuals of Saurornithoides were known, closely associated within the same layer of the Djadochta Formation of Mongolia. The fossils were found on 9 July 1923 by a Chinese employee of an American Museum of Natural History expedition, Chih. The material contained a single skull and jaw in association, and vertebrae, a partial pelvis, hindlimb and foot associated nearby. More bones were initially included but later shown to belong to Protoceratops. Henry Fairfield Osborn at first intended to name the animal "Ornithoides", the "bird-like one", and in 1924 mentioned this name in a popular publication but without a description so that it remained an invalid nomen nudum. He then formally described the remains in the same year, finding them to be a new genus and species, which he named Saurornithoides mongoliensis. The generic name was chosen because of the bird-like bones of the taxon, which was thought to represent a megalosaurian, translating as "saurian with bird-like rostrum". Saurornithoides was noted to resemble Velociraptor, although more sluggish according to Osborn. The holotype specimen is AMNH 6516. This specimen was the first troodontid skeleton found, though at the time the connection with Troodon, then known only from its teeth, was not realized.

In 1964, another specimen was described from the Late Cretaceous of Mongolia. The first specimen ever collected by a professional Mongolian palaeontologist, it was given the specimen number IGM 100/1. In 1974, it was described by Rinchen Barsbold as a new species, Saurornithoides junior. It was assigned to the genus based on cranial comparisons, as well as the similar provincialism. However, since the description, many more troodontids have been described with cranial material, and as such, a 2009 study on Saurornithoides reassigned this species to its own genus, Zanabazar.

In 1993, a juvenile specimen of S. mongoliensis was described. The highly ossified hindlimb suggested that Saurornithoides and other troodontids were well developed at birth and that they probably required little to no parental care.

Several other Saurornithoides species were named, though none of these is today seen as valid. In 1928, baron Franz Nopcsa coined Saurornithoides sauvagei. However, this was the result of a printing error: he had planned to name a Teinurosaurus sauvagei. In 1982, Kenneth Carpenter renamed Stenonychosaurus inequalis Sternberg 1932 into Saurornithoides inequalis. Today this is usually seen as a junior synonym of Troodon formosus. In 1991, George Olshevsky renamed Pectinodon asiamericanus Nesov 1985 into Saurornithoides asiamericanus. In 1995 he made it a Troodon asiaamericanus. In view of its provenance from the Cenomanian of Uzbekistan, it is usually seen as a different taxon from Saurornithoides. In 2000, Olshevsky renamed Troodon isfarensis Nessov 1995 into Saurornithoides isfarensis. In 2007, this was shown to have been a hadrosaurid fossil.

References

• Fantastic Facts About Dinosaurs (ISBN 0-7525-3166-2)
• Lessem, Don Dinosaurs A to Z. Page 170, 2003. (ISBN 0-439-16591-1).