|Restoration of W. homheni with low plates|
Wuerhosaurus is a genus of stegosaurid dinosaur from the Early Cretaceous Period of China and Mongolia. As such, it was one of the last genera of stegosaurians known to have existed, since most others lived in the late Jurassic.
Discovery and species
Wuerhosaurus homheni is the type species, described by Dong Zhiming in 1973 from the Tugulu Group in Xinjiang, western China. The generic name is derived from the city of Wuerho. Three separate localities in the Wuerho Valley were discovered to contain material from the new stegosaur: 64043-5, 64043 and 64045. The remains consisted of the holotype, Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) V.4006, a skull-less fragmentary skeleton, and the paratype IVPP V.4007. Holotype material includes a mostly complete pelvis and sacrum lacking the ischium, the first caudal vertebrae, two dorsal vertebrae, a scapulocoracoid, humerus and phalanx, as well as two dermal plates. Three posterior caudal vertebrae from the tail and a partial ulna of a second individual form the paratype, and Dong referred a partial ischium from a third locality to Wuerhosaurus.
A smaller stegosaur from the Ejinhoro Formation in the Ordos Basin in Inner Mongolia, was found in 1988. When the specimen (IVPP V.6877) was described by Dong in 1993, it was named W. ordosensis, as it was from a similar age and had a similar anatomy. The holotype of the species includes a nearly complete torso, consisting of three cervical vertebrae, all eleven dorsal vertebrae (with attached ribs), a complete sacrum with a right ilium, and the first five caudal vertebrae, all articulated. An additional dorsal vertebra and dermal plate were referred to the taxon when it was named. In 2014 Ulansky named a new species of Wuerhosaurus, "W. mongoliensis" for vertebrae and pelvic material, but the name is an invalid nomen nudum. It was formally described as Mongolostegus in 2018.
Wuerhosaurus homheni was probably a broad-bodied animal. Gregory S. Paul in 2016 estimated the length at 7 m (23 ft) and the weight at 4 tonnes (630 st). Only a few scattered bones have been found, making a full restoration difficult. Its dorsal plates were at first thought to have been much rounder or flatter than other stegosaurids, but Maidment established this was an illusion caused by breakage: their actual form is unknown. W. homheni had a pelvis of which the front of the ilia strongly flared outwards indicating a very broad belly. The neural spines on the tail base were exceptionally tall.
W. ordosensis was estimated by Paul to have been 5 m (16 ft) long and weigh 1.2 tonnes (190 st). It too has a broad pelvis but the neural spines are shorter. The neck seems to have been relatively long.
Wuerhosaurus is one of the most derived stegosaurians, being closely related to either Dacentrurus and Hesperosaurus, or Hesperosaurus and Stegosaurus, depending on phylogenetic analysis. Carpenter et al. (2001) recovered Wuerhosaurus in the former relationship, close to Hesperosaurus and Dacentrurus as basal in Stegosauridae. Wuerhosaurus was recovered in a different position by Escaso et al. (2007), still related to Hesperosaurus, but basal to a clade of Lexovisaurus and Stegosaurus. Maidment et al. (2008) recovered a different placement with Wuerhosaurus as being in a clade of taxa in derived Stegosaurinae, most closely related to Hesperosaurus and then Stegosaurus. More recently, Maidment (2017) elaborated upon her earlier analyses, and instead resolved Wuerhosaurus as closest to Stegosaurus, with Hesperosaurus being more closely related to Miragaia. These results are shown below.
Synonymy with Stegosaurus
Maidment and colleagues proposed in 2008 that Wuerhosaurus was a junior synonym of Stegosaurus, with W. homheni being renamed Stegosaurus homheni, and W. ordosensis being a dubious taxon. W. homheni was synonymized because the holotype that could be located was similar to Stegosaurus, and because of its phylogenetic position. Wuerhosaurus placed between Stegosaurus and Hesperosaurus, the latter being considered a species of Stegosaurus because of its age, location, and anatomy. Since Wuerhosaurus placed between two possible Stegosaurus species, Maidment et al. synonymized the taxon as well. Wuerhosaurus ordosensis was considered to be a nomen dubium because the holotype could not be found in the IVPP collections. The original description did not mention any valid diagnostic traits, and no other description provided features either, so Maidment et al. considered the taxon undiagnostic. This opinion has been contested, however, by Carpenter (2010). He discussed how the diagnoses and features used by Maidment et al. were inconsistent and generalized, with Wuerhosaurus homheni bearing numerous differences. As such, Carpenter advocated for the separation of both Hesperosaurus and Wuerhosaurus from Stegosaurus, and the separation of the different Stegosaurus species from S. armatus.
Wuerhosaurus was lower to the ground than most other stegosaurids; scientists believe that this was an adaptation to let it feed on low-growing vegetation. Wuerhosaurus, like other stegosaurids, perhaps had a thagomizer on the end of its tail, like that of Stegosaurus which featured four bony spikes that would most likely have been used for self-defense. A single spike was found but was seen by Dong as being positioned on the shoulder.
The type species, W. homheni, is known from the Tugulu Group, while W. ordosensis was found in the Ejinhoro Formation. The approximate age of Wuerhosaurus is 130 mya, based on the approximate dating of the Tsaganstabian fauna, and thus the stegosaur would have lived in the Hauterivian era, which is roughly coeval with the Wealden group, from which other stegosaur material has been found.
- Dong, Z. (1973). "Dinosaurs from Wuerho". Reports of Paleontological Expedition to Sinkiang (II): Pterosaurian Fauna from Wuerho, Sinkiang (in Chinese). 11. Memoirs of the Institute of Vertebrate Paleontology and Paleoanthropology, Academia Sinica. pp. 45–52.
- Dong, Z. (1993). "A new species of stegosaur (Dinosauria) from the Ordos Basin, Inner Mongolia, People's Republic of China". Canadian Journal of Earth Sciences. 30 (10): 2174–2176. doi:10.1139/e93-188.
- Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 156. ISBN 1-84028-152-9.
- Dong, Z. (1990). "Stegosaurs of Asia". In Carpenter, Kenneth; Currie, Philip J. (eds.). Dinosaur Systematics: Approaches and Perspectives. Cambridge University Press. pp. 255–268. ISBN 978-0-521-43810-0.
- Galton, P.M.; Carpenter, K. (2016). "The plated dinosaur Stegosaurus longispinus Gilmore, 1914 (Dinosauria: Ornithischia; Upper Jurassic, western USA), type species of Alcovasaurus n. gen."". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 279 (2): 185–208. doi:10.1127/njgpa/2016/0551.
- Paul, G.S. (2016). The Princeton Field Guide to Dinosaurs (2 ed.). Princeton University Press. p. 248. ISBN 978-0-691-16766-4.
- Dodson, P., ed. (1993). "Wuerhosaurus". The Age of Dinosaurs. Publications International, LTD. p. 102. ISBN 0-7853-0443-6.
- Carpenter, K.; Miles, C.A.; Cloward, K. (2001). "New primitive stegosaur from the Morrison Formation, Wyoming". In Carpenter, K. (ed.). The Armored Dinosaurs. Indiana University Press. pp. 55–75. ISBN 978-0-253-33964-5.
- Escaso, F.; Ortega, F.; Dantas, P.; Malafaia, E.; Pimentel, N.L.; Pereda Suberbiola, X.; Sanz, J.L.; Kullburg, J.C.; Kullburg, M.C.; Barriga, F. (2007). "New evidence of shared dinosaur across Upper Jurassic Proto-North Atlantic: Stegosaurus from Portugal". Naturwissenschaften. 94 (5): 367–374. doi:10.1007/s00114-006-0209-8. PMID 17187254.
- Maidment, Susannah C.R.; Norman, David B.; Barrett, Paul M.; Upchurch, Paul (2008). "Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia)". Journal of Systematic Palaeontology. 6 (4): 367–407. doi:10.1017/S1477201908002459.
- Raven, T.j.; Maidment, S.C.R. (2017). "A new phylogeny of Stegosauria (Dinosauria, Ornithischia)" (PDF). Palaeontology. 2017 (3): 1–8. doi:10.1111/pala.12291. hdl:10044/1/45349.
- Carpenter, K. (2010). "Species concept in North American stegosaurs". Swiss Journal of Geosciences. 103 (2): 155–162. doi:10.1007/s00015-010-0020-6.
- Donovan, T. (2002). "RE: Tsagantsabian age". Dinosaur Mailing List. Cleveland Museum of Natural History. Retrieved 2018-01-08.