Mesonyx

Mesonyx
Postcranial remains of M. obtusidens
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Placentalia
Order: †Mesonychia
Family: †Mesonychidae
Genus: †Mesonyx
Type species
Mesonyx obtusidens
Cope, 1872
Other species
  • M. nuhetingensis Tong, 1989
  • M. uqbulakensis Jin, 2012

Mesonyx ("middle claw") is an extinct genus of mesonychid, one of two families that is part of the extinct order Mesonychia. Mesonychians were a clade of hoofed mammals closely related to ungulates,[1] that first appearing in the fossil record during the Early Paleocene,[2] roughly 63 million years ago.[3] However, the order is thought to have arisen in the Late Cretaceous at least 66.7 Ma.[4][3]

Fossils of the various species in both North America and East Asia. The North American species, M. obtusidens were found in rocks dating to the early Bridgerian to middle Uintan of the Middle Eocene in North America.[5][6] On the other hand, M.uqbulakensis and M. nuhetingensis, were exclusive to the Arshantan of the Early Eocene in East Asia.[7][8]

M. obtusidens was thought to have been one of the top predators of its time along with crocodyliforms and the oxyaenid Patriofelis.[9][10]

Taxonomy

Generally accepted cladogram by Spaulding et al. (2009), Mesonyx is classified, together with other mesonychians, outside of ungulates.[1]

Description

The skull of M. obtusidens (left), compared with skulls of a wolf, brown bear, and Andrewsarchus

M. obtusidens had a basal cranium length of 27.9 cm (11.0 in).[11] 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).[12] Like other mesonychids, the toes ended in small hooves.[13] 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.[13]

Paleobiology

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.[14] These animals had a reduced sense of smell and likely relied on sight and hearing to find food.[15]

Paleoecology

Life reconstruction by Charles R. Knight

Mesonyx species have been unearthed in Colorado, Wyoming, Utah and China. An additional two species – M.uqbulakensis and M. nuhetingensis – have been described from the Early Eocene Arshanto Formation in China.[16]

M. obtusidens was first recovered in the Cottonwood Creek of the lower member of the Bridger Formation of the Bridgerian and Uintan stages.[17] The formation preserved an environment which alternated between marshlands with braided streams and vast yet shallow lakes based on depositional materials.[9][18] Plant based evidence of palms, ferns, and Sequoia suggests the Bridger Formation, was a dense, paratropical forest, which was common in North America during the global hot climate of the Eocene.[9] Also known from the lower member of the formation were the fellow mesonychid Harpagolestes, catfish, salamanders, frogs, varanid lizards, boas, turtles, several crocodyliforms[19] (including the fully terrestrial Boverisuchus vorax)[20], the primates Anaptomorphus, Notharctus, Omomys, Trogolemur, Smilodectes, and Uintasorex, the tillodonts Trogosus and Tillodon, the pholidotans (pangolin relatives) Metacheiromys and Tetrapassalus mckennai, various rodents in the families Cylindrodontidae, Paramyidae, and Sciuravidae,, the hyaenodonts Limnocyon, Sinopa, Thinocyon, and Tritemnodon, oxyaenodonts Machaeroides and Patriofelis, the carnivoraforms Miacis, Oodectes, Palaearctonyx, Uintacyon, Viverravus, and Vulpavus, the hyopsodont Hyopsodus, the dinoceratan Bathyopsis, the equid Orohippus, the brontotheres Limnohyops and Palaeosyops, the helaletid Helaletes, the hyrachyid Hyrachyus, the dichobunids Antiacodon and Microsus, and the helohyid Helohyus.[17]

References

  1. 1 2 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.
  2. ↑ Missiaen, Pieter. "亚洲早古近纪哺乳动物生物年代学与生物地理学的新认识."古脊椎动物学报 49.1 (2011). paper
  3. 1 2 Gingerich, Philip D.; Uhen, Mark D. (1998). "Likelihood estimation of the time of origin of Cetacea and the time of divergence of Cetacea and Artiodactyla". Palaeontologia Electronica. doi:10.26879/98008.
  4. ↑ Solé, Floréal; Fournier, Morgane; Ladevèze, Sandrine; et al. (2023). "New postcranial elements of mesonychid mammals from the Ypresian of France: New hypotheses for the radiation and evolution of the mesonychids in Europe". Journal of Mammalian Evolution. 30 (2): 371–401. doi:10.1007/s10914-023-09651-x.
  5. ↑ Gunnell, Gregg F.; Murphey, Paul C.; Stucky, R.K.; Townsend, Kathryn B.; Robinson, Peter; Zonneveld, John-Paul; Bartels, W. S. (2009). "Biostratigraphy and biochronology of the latest Wasatchian, Bridgerian, and Uintan North American Land Mammal "Ages"". Geology, Vertebrate Paleontology, and Biostratigraphy.
  6. ↑ Solé, Floréal; Godinot, Marc; Laurent, Yves; Galoyer, Alain; Smith, Thierry (2018). "The European Mesonychid Mammals: Phylogeny, Ecology, Biogeography, and Biochronology". Journal of Mammalian Evolution. 25: 339–379. doi:10.1007/s10914-016-9371-8.
  7. ↑ 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.
  8. ↑ Mesonyx, Paleobiology Database, collection #16240, Huerfano II site, Huerfano County, Colorado, authorized by John Alroy
  9. 1 2 3 Kort, Anne E.; Ahrens, Heather; David Polly, P.; Morlo, Michael (2021-10-01). "Postcrania and paleobiology of Patriofelis ulta (Mammalia, Oxyaenodonta) of the Bridgerian (lower–middle Eocene) of North America". Journal of Vertebrate Paleontology. 41 (6) e2045491. doi:10.1080/02724634.2021.2045491. ISSN 0272-4634.
  10. ↑ Kort, Anne E. (2019). "The Paleoecology of Patriofelis ulta and Implications for Oxyaenid Extinction (thesis)". Indiana University.
  11. ↑ Osborn, Henry Fairfield (November 11, 1924). "Andrewsarchus, giant mesonychid of Mongolia". American Museum Novitates (146). The American Museum of Natural History. Retrieved December 15, 2024.Public Domain This article incorporates text from this source, which is in the public domain.
  12. ↑ 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.
  13. 1 2 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.
  14. ↑ "Mesonyx and the other mesonychid mesonychians (mesonychians part IV)". scienceblogs.com. August 15, 2009. Retrieved 2020-02-15.
  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.
  16. ↑ 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.
  17. 1 2 Gazin, Charles Lewis (1976). "Mammalian Faunal Zones of the Bridger Middle Eocene" (PDF). Smithsonian Institution Press. 26: 1–13.
  18. ↑ Buchheim, H.P; Brand, L.R; Goodwin, H.T (2000). "Lacustrine to fluvial floodplain deposition in the Eocene Bridger Formation". Palaeogeography, Palaeoclimatology, Palaeoecology. 162 (1–2): 191–209.
  19. ↑ Kort, Anne E. (2019). "The Paleoecology of Patriofelis ulta and Implications for Oxyaenid Extinction (thesis)". Indiana University.
  20. ↑ https://www.researchgate.net/publication/306173638_Stratigraphy_and_taphonomy_of_Grizzly_Buttes_Bridger_Formation_and_the_middle_Eocene_of_Wyoming
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