Wuerhosaurus

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 Roman 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.

Description

Wuerhosaurus homheni was probably a broad-bodied animal, reaching 7 m in length and 4 MT in body mass. 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.

In contrast, W. ordosensis was much smaller, estimated by Paul to have been 5 m long and weigh 1.2 MT. It had a relatively long neck with a broad pelvis, but the neural spines are shorter.

Classification

Phylogeny

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

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.

Paleoecology

The type species, W. homheni, is known from the Tugulu Group, while W. ordosensis is known from the Ejinhoro and Luohandong Formations. 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. Uranium-lead dating has shown that the age of Wuerhosaurus in the Lianmuqin Formation of the Tugulu Group is slightly younger than 135.2 million years old, while Wuerhosaurus in the Ejinhoro Formation is from the Barremian. Stegosaur footprints from the Tugulu Group in Xinjiang Province, China, have been attributed as registered by W. homheni individuals. These tracks include the world's smallest stegosaur tracks, measuring 5.7 cm in length, indicative of a dinosaur that was approximately cat-sized.

References

References

1. (2018-12-01). "First Record of Stegosaur (Ornithischia, Dinosauria) from the Aptian–Albian of Mongolia". Paleontological Journal.
2. (2024-01-31). "A new stegosaur from the late Early Cretaceous of Zuoyun, Shanxi Province, China". [[Historical Biology]].
3. Dong, Z.. (1973). "Reports of Paleontological Expedition to Sinkiang (II): Pterosaurian Fauna from Wuerho, Sinkiang". Memoirs of the Institute of Vertebrate Paleontology and Paleoanthropology, Academia Sinica.
4. Dong, Z.. (1990). "Dinosaur Systematics: Approaches and Perspectives". Cambridge University Press.
5. 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.
6. (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.
7. Paul, G.S.. (2016). "The Princeton Field Guide to Dinosaurs". Princeton University Press.
8. (1999). "The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals". Marshall Editions.
9. (1993). "The Age of Dinosaurs". Publications International, LTD.
10. (2001). "The Armored Dinosaurs". Indiana University Press.
11. (2007). "New evidence of shared dinosaur across Upper Jurassic Proto-North Atlantic: ''Stegosaurus'' from Portugal". Naturwissenschaften.
12. (2017). "A new phylogeny of Stegosauria (Dinosauria, Ornithischia)". Palaeontology.
13. Maidment, Susannah C.R.. (2008). "Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia)". Journal of Systematic Palaeontology.
14. Carpenter, K.. (2010). "Species concept in North American stegosaurs". [[Swiss Journal of Geosciences]].
15. (July 2017). "内蒙古鄂尔多斯盆地下白垩统罗汉洞组剑龙类化石新材料". Geological Bulletin of China.
16. Donovan, T.. (2002). "RE: Tsagantsabian age". Cleveland Museum of Natural History.
17. (2021). "Calibrating the Early Cretaceous Urho Pterosaur Fauna in Junggar Basin and implications for the evolution of the Jehol Biota". GSA Bulletin.
18. (2021-02-28). "Stegosaur Track Assemblage from Xinjiang, China, Featuring the Smallest Known Stegosaur Record". PALAIOS.
19. "Tiny cat-sized stegosaur leaves its mark".