Temporal range: Late Cretaceous, 75Ma
|Holotype skull, AMNH 6516|
|Species:||† S. mongoliensis|
Saurornithoides (// saw-ROR-ni-THOY-deez) is a genus of troodontid maniraptoran dinosaur, which lived 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), referring to its proximity to the ancestry of birds.
Saurornithoides is a troodontid, a group of small, bird-like, gracile maniraptorans. All troodontids have many unique features of the skull, such as closely spaced teeth in the lower jaw, and large numbers of teeth. Troodontids have sickle-claws and raptorial hands, and some of the highest non-avian encephalization quotients, meaning they were behaviourally advanced and had keen senses. Estimates of its length range from 2 to 3 metres (6.6 to 9.8 ft) and weight from 23 to 54 kilograms (51 to 119 lb). 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, Saurornithoides 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.
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 material included a single skull and jaw in association, and vertebrae, a partial pelvis, hindlimb and foot associated nearby. Henry Fairfield Osborn described these remains in 1924, 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.
In 1964, another specimen was described from the 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 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.
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 larger 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.
A juvenile of Saurornithoides was described in 1993. It is known from leg, assigned to Saurornithoides by the length of the metatarsals. The individual is more than twice as small as the holotype, yet has a similar degree of ossification. This might mean that troodontids were independent soon after hatching.
- Junchang Lü, Li Xu, Yongqing Liu, Xingliao Zhang, Songhai Jia, and Qiang Ji (2010). "A new troodontid (Theropoda: Troodontidae) from the Late Cretaceous of central China, and the radiation of Asian troodontids." (PDF). Acta Palaeontologica Polonica 55 (3): 381–388. doi:10.4202/app.2009.0047.
- Osborn, H.F. (1924). "Three new Theropoda, Protoceratops zone, Central Mongolia" (PDF). American Museum Novitates (144): 12.
- Norell, Mark A.; Makovicky, Peter J.; Bever, Gabe S.; Balanoff, Amy M.; Clark, James M.; Barsbold, Rinchen and Rowe, Timothy (2009). "A Review of the Mongolian Cretaceous Dinosaur Saurornithoides (Troodontidae: Theropoda)". American Museum Novitates 3654: 63. doi:10.1206/648.1.
- Turner, A. H.; Makovicky, P. J.; Norell, M. A. (2012). "A Review of Dromaeosaurid Systematics and Paravian Phylogeny". Bulletin of the American Museum of Natural History 371: 1. doi:10.1206/748.1.
- Currie, P.J.; Peng, J.-H. (1993). "A juvenile specimen of Saurornithoides mongoliensis from the Upper Cretaceous of northern China". Canadian Journal of Earth Sciences 30 (10): 2224–2230. doi:10.1139/e93-193.