Superregnum: Eukaryota
Cladus: Unikonta
Cladus: Opisthokonta
Cladus: Holozoa
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Megaclassis: Osteichthyes
Cladus: Sarcopterygii
Cladus: Rhipidistia
Cladus: Tetrapodomorpha
Cladus: Eotetrapodiformes
Cladus: Elpistostegalia
Superclassis: Tetrapoda
Cladus: Reptiliomorpha
Cladus: Amniota
Cladus: Synapsida
Cladus: Eupelycosauria
Cladus: Sphenacodontia
Cladus: Sphenacodontoidea
Cladus: Therapsida
Cladus: Theriodontia
Cladus: Cynodontia
Cladus: Eucynodontia
Cladus: Probainognathia
Cladus: Prozostrodontia
Cladus: Mammaliaformes
Classis: Mammalia
Subclassis: Trechnotheria
Infraclassis: Zatheria
Supercohors: Theria
Cohors: Eutheria
Infraclassis: Placentalia
Cladus: Boreoeutheria
Superordo: Laurasiatheria
Ordo: †Mesonychia
Familia: †Mesonychidae
Genus: †Mesonyx
Species (†4): †M. nuhetingensis – †M. obtusidens – †M. uintensis – †M. uqbulakensis
Name
Mesonyx Cope, 1872
References
Primary references
Cope, E.D. 1872. Descriptions of some new Vertebrata from the Bridger Group of the Eocene. Proceedings of the American Philosophical Society 12: 460–465.
esonyx ("middle claw") is a genus of extinct mesonychid mesonychian mammal. Fossils of the various species are found in Early to Late Eocene-age strata in the United States and Early Eocene-aged strata in China, 51.8—51.7 Ma (AEO).[1]
Description
The skull of Mesonyx (left), compared with skulls of a wolf, bear, and Andrewsarchus
Mesonyx species have been estimated as 1.25-1.5m (4.5–5 ft.) long in life, not including the tail. Weight estimates vary, from 20 to 55 kg (about 45-120 lbs).[2][3] Like other mesonychids, the toes ended in small hooves.[4]
Like other mesonychids, they had large heads and long necks in proportion to their body size, and cranial material is most often preserved. Mesonyx uintensis from the Upper Eocene of Wyoming is described as having a total cranium length of 429 mm. (17 inches) and a facial length of 206 mm (8 inches).[5] The long skull had a relatively large sagittal crest above the braincase to anchor large jaw muscles and give it a powerful bite. Brain casts show that M. obtusidens had an unusually well-developed neocortex for an Eocene mammal. Although modern Carnivora have more complex brains, their ancestors did not; Mesonyx species would have been intelligent animals for their time.[4]
Size estimates of Mesonyx were used to generate the proposal that Andrewsarchus was the largest predatory land mammal that ever lived. Since Andrewsarchus is known only from a single isolated skull, the estimate of its size was based on scaling up material from Mesonyx. However, it is now known that the two genera are not closely related,[6] their skulls indicate different lifestyles, and they likely had very different proportions in life.
Paleoecology
While this was the earliest genus of mesonychid to be named (by Edward Drinker Cope in 1872) and the group is named after it, Mesonyx was one of the most derived genera of mesonychids, evolving features for active running.[7] These animals had a reduced sense of smell and likely relied on sight and hearing to find food.[8] They were probably active hunters.[2]
Distribution and habitat
Mesonyx specimens have been unearthed in Colorado, Wyoming, Utah and China. Mesonyx uintensis is known from the Upper Eocene of northern Utah.[5] An additional two species – Mesonyx uqbulakensis and M. nuhetingensis – have been described from the early Eocene Arshanto Formation in China.[9]
Phylogeny
In the generally accepted cladogram by Spaulding et al. (2009), Mesonyx is classified, together with other mesonychians, outside of ungulates.[10]
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References
iconPaleontology portal
Mesonyx, Paleobiology Database, collection #16240, Huerfano II site, Huerfano County, Colorado, authorized by John Alroy
"Mesonyx". prehistoric-fauna.com. Retrieved 2020-02-15.
Radinsky, Leonard B. (1976). The brain of Mesonyx, a Middle Eocene mesonychid condylarth /. Chicago: Field Museum of Natural History. doi:10.5962/bhl.title.5164.
Radinsky, Leonard (1977). "Brains of Early Carnivores". Paleobiology. 3 (4): 333–349. Bibcode:1977Pbio....3..333R. doi:10.1017/S0094837300005509. ISSN 0094-8373. JSTOR 2400308. S2CID 88286017.
Osborn, Henry Fairfield (November 11, 1924). "Andrewsarchus, giant mesonychid of Mongolia" (PDF). American Museum Novitates (146). The American Museum of Natural History. Retrieved 2007-08-05.
Spaulding, Michelle; O'Leary, Maureen A.; Gatesy, John (2009-09-23). "Relationships of Cetacea (Artiodactyla) Among Mammals: Increased Taxon Sampling Alters Interpretations of Key Fossils and Character Evolution". PLOS ONE. 4 (9): e7062. Bibcode:2009PLoSO...4.7062S. doi:10.1371/journal.pone.0007062. ISSN 1932-6203. PMC 2740860. PMID 19774069.
"Mesonyx and the other mesonychid mesonychians (mesonychians part IV)". scienceblogs.com. August 15, 2009. Retrieved 2020-02-15.
Radinsky, Leonard B. (1976). The brain of Mesonyx, a Middle Eocene mesonychid condylarth /. Chicago: Field Museum of Natural History. doi:10.5962/bhl.title.5164.
Xun Jin (2012). "New mesonychid (Mammalia) material from the Lower Paleogene of the Erlian Basin, Nei Mongol, China" (PDF). Vertebrata PalAsiatica. 50 (3): 245–257.
Spaulding, Michelle; O'Leary, Maureen A.; Gatesy, John (2009-09-23). "Relationships of Cetacea (Artiodactyla) Among Mammals: Increased Taxon Sampling Alters Interpretations of Key Fossils and Character Evolution". PLOS ONE. 4 (9): e7062. Bibcode:2009PLoSO...4.7062S. doi:10.1371/journal.pone.0007062. ISSN 1932-6203. PMC 2740860. PMID 19774069.
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