Andrewsarchus
| Andrewsarchus Temporal range:
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| Holotype skull of Andrewsarchus mongoliensis | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Clade: | Cetancodontamorpha |
| Family: | †Andrewsarchidae Szalay & Gould, 1966[2] |
| Genus: | †Andrewsarchus Osborn, 1924[1] |
| Type species | |
| †Andrewsarchus mongoliensis Osborn, 1924
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| Other species | |
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| Synonyms | |
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Species synonymy
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Andrewsarchus (/ˌændruːˈsɑːrkəs/), meaning "Andrews' ruler", is an extinct genus of ungulate that lived during the Middle Eocene in China. It contains two species, A. mongoliensis and A. crassum. It was formerly placed in the families Mesonychidae or Arctocyonidae, but is now the sole member of a distinct family, Andrewsarchidae. Known from a largely complete skull, most of a lower jaw and isolated teeth, it is notable for being estimated as the largest terrestrial, carnivorous mammal, but that status has been disputed.
Taxonomy
[edit]Andrewsarchus mongoliensis was named by Henry Fairfield Osborn in 1924 for a partial skull from the Irdin Manha Formation of Inner Mongolia. The genus was named in honor of Roy Chapman Andrews, the leader of the expedition on which it was discovered, with the Ancient Greek archos (ἀρχός, "ruler") added to his surname. A second species, A. crassum, was named by Ding Suyin and colleagues in 1977 for two premolars from the Dongjun Formation of Guangxi, but its specimens are too fragmentary to establish broader affinities of the genus.[6]
Paratriisodon henanensis was named by Minchen Chow in 1959 for a partial skull and mandible, a fragmentary maxilla, and several isolated teeth from the Lushi Formation of Henan.[4] A second species, P. gigas, was named by Chow and colleagues in 1973 for a molar also from the Lushi Formation. Three molars and an incisor from the Irdin Manha Formation were later referred to P. gigas.[7] Both species are considered junior synonyms of A. mongoliensis.[6]
Description
[edit]
When first describing Andrewsarchus, Osborn believed it to be the largest terrestrial, carnivorous mammal. Based on the length of the A. mongoliensis holotype skull, and using the proportions of Mesonyx, he estimated a total body length of 3.82 m (12.5 ft) and body height of 1.89 m (6.2 ft).[1] However, considering cranial and dental similarities with entelodonts, Frederick Szalay and Stephen Jay Gould proposed that it had proportions closer to those than to mesonychids, and that Osborn's estimates were inaccurate.[2]
Skull
[edit]Andrewsarchus' holotype skull has a total length of 83.4 cm (2.74 ft), and is 56 cm (1.84 ft) wide at the zygomatic arches.[1] The snout is greatly elongated, one-and-a-half times the length of the cranium.[1][2] Andrewsarchus' upper jaw possesses the typical placental tooth formula,[2] though it is not clear whether the same is true of the lower jaw. The second upper incisor is extremely elongated, almost the size of the canine. The upper premolars are elongate and unicuspid, resembling those of entelodonts. The fourth retains the protocone, which is vestigial.[1] The mandible is long and shallow, with a shallow masseteric fossa. The tooth structure of the lower jaw is difficult to determine, as nearly all are worn or broken. The third molar is large and the talonids essentially have two cusps.[4]
Phylogeny
[edit]
Andrewsarchus was originally classified as a member of the family Mesonychidae, and Paratriisodon was classified as a member of the family Arctocyonidae.[7] In 1966, Andrewsarchus became the sole member of its own subfamily, Andrewsarchinae,[8] withinMesonychia; Andrewsarchinae was elevated to family level by Philip D. Gingerich in 1998.[9] Paratriisodon was first synonymised with Andrewsarchus by Leigh Van Valen in 1978,[10] and the latter was then assigned to the subfamily Triisodontinae within Arctocyonidae.[6][10] More recently, Andrewsarchidae was revived, and Andrewsarchus has been recovered as a member of the clade Cetancodontamorpha, being most closely related to entelodonts, hippos, and whales.[11][12] In Yu et al. (2023), it was recovered in a polytomy with Achaenodon and Erlianhyus.[12]
Below is a simplified cladogram based on the results of Spaulding et al. (2009) and Yu et al. (2023).[11][12]
Palaeoecology
[edit]In his paper describing Andrewsarchus, Osborn suggested that it may have been omnivorous based on comparisons with entelodonts.[1] This conclusion was supported by Szalay and Gould, who cite the heavily wrinkled crowns of the cheek teeth as supporting evidence,[2] as well as the close phylogenetic relationship between Andrewsarchus and entelodonts.[11][12]
See also
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References
[edit]
- ^ a b c d e f Osborn, H.F. (1924). "Andrewsarchus, giant mesonychid of Mongolia". American Museum Novitates (146): 1–5. hdl:2246/3226.
- ^ a b c d e Szalay, F.S.; Gould, S.J. (1966). "Asiatic Mesonychidae (Mammalia, Condylartha)". Bulletin of the American Museum of Natural History. 132 (2): 127–174. hdl:2246/1112.
- ^ Ding, S.; Zheng, J.; Zhang, Y.; Tong, Y. (1977). "The age and characteristic of the Liuniu and the Dongjun faunas, Bose Basin of Guangxi" (PDF). Vertebrata PalAsiatica. 15 (1): 35–45.
- ^ a b c Chow, M.M. (1959). "A new arctocyonid from the Upper Eocene of Lushih, Honan" (PDF). Vertebrata PalAsiatica. 3 (3): 133–138.
- ^ Chow, M.M.; Li, C.; Chang, Y. (1973). "Late Eocene mammalian faunas of Honan and Shansi with notes on some vertebrate fossils collected therefrom" (PDF). Vertebrata PalAsiatica. 11 (2): 165–181.
- ^ a b c O'Leary, M.A. (1998). "Phylogenetic and Morphometric Reassessment of the Dental Evidence for a Mesonychian and Cetacean Clade". In Thewissen, J.G.M. (ed.). The Emergence of Whales. Springer. pp. 133–161. doi:10.1007/978-1-4899-0159-0_5. ISBN 978-1-4899-0159-0.
- ^ a b Qi, T. (1980). "Irdin Manha Upper Eocene and its mammalian fauna at Huhebolhe Cliff in central Inner Mongolia" (PDF). Vertebrata PalAsiatica. 18 (1): 28–32.
- ^ Zhou, X. (1995). Evolution of Paleocene-Eocene Mesonychidae (Mammalia, Mesonychia) (PhD dissertation). University of Michigan. hdl:2027.42/129581.
- ^ Gingerich, Philip D. (1998), Thewissen, J. G. M. (ed.), "Paleobiological Perspectives on Mesonychia, Archaeoceti, and the Origin of Whales", The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea, Boston, MA: Springer US, pp. 423–449, doi:10.1007/978-1-4899-0159-0_15, ISBN 978-1-4899-0159-0, retrieved 16 August 2024
- ^ a b Van Valen, Leigh (1978). "The Beginning of the Age of Mammals" (PDF). Evolutionary Theory. 4: 45–80.
- ^ a b c Spaulding, M.; O'Leary, M.A.; Gatesy, J. (2009). "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. PMC 2740860. PMID 19774069.
- ^ a b c d Yu, Y.; Gao, H.; Li, Q.; Ni, X. (2023). "A new entelodont (Artiodactyla, Mammalia) from the late Eocene of China and its phylogenetic implications". Journal of Systematic Palaeontology. 21 (1): 2189436. Bibcode:2023JSPal..2189436Y. doi:10.1080/14772019.2023.2189436. S2CID 257895430.