Andrewsarchus

Andrewsarchus Temporal range: Middle Eocene PreꞒ Ꞓ O S D C P T J K Pg N
Holotype skull of Andrewsarchus mongoliensis
Scientific classification
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
Other species
†Andrewsarchus crassum Ding, Zheng, Zhang, & Tong, 1977[3]
Synonyms
Genus synonymy Paratriisodon Chow, 1959[4] Species synonymy A. mongoliensis Paratriisodon henanensis Chow, 1959[5] Paratriisodon gigas Chow, Li, & Chang, 1973[6]

Andrewsarchus (/ˌændruːˈsɑːrkəs/), meaning "Andrews' ruler", is an extinct genus of artiodactyl (even-toed 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, and may have been a distant relative of entelodonts.^[7] Known from a largely complete skull, most of a lower jaw and isolated teeth, it is notable for being historically reputed as the largest terrestrial, carnivorous mammal.^[1]

The holotype of Andrewsarchus mongoliensis, a partial skull (AMNH-VP 20135),^[8] was recovered from the lower Irdin Manha Formation of Inner Mongolia.^[1][9] It was named in honour 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.^[1] A second species, A. crassum, was named by Ding Suyin and colleagues in 1977 on the basis of two premolars from the Dongjun Formation of Guangxi.^[10][5]

Paratriisodon henanensis was named by Minchen Chow in 1959 for a 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.^[11] Both species are considered junior synonyms of A. mongoliensis.^[5]

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 a 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 more like them and less like mesonychids, and that Osborn's estimates were inaccurate.^[2]

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. The snout is greatly elongated, one-and-a-half times the length of the basicranium,^[1] and the portion of the snout anterior to the canines is entelodont-like.^[2] The sagittal crest is reduced, suggesting a weak temporalis muscle and a relatively weak bite force.^[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 upper incisors are arranged in a semicircle, a trait shared with entelodonts. The second is enlarged, and is 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]

Andrewsarchus was originally assigned to the family Mesonychidae,^[1] and Paratriisodon was classified as a member of the family Arctocyonidae.^[11] In 1966, Andrewsarchus became the sole member of its own subfamily, Andrewsarchinae,^[12] within Mesonychia. Andrewsarchinae was elevated to family level by Philip D. Gingerich in 1998.^[13] Paratriisodon was first synonymised with Andrewsarchus by Leigh Van Valen in 1978,^[14] and the latter genus was reassigned to the subfamily Triisodontinae within Arctocyonidae.^[5][14] More recently, Andrewsarchidae was revived. Since then, Andrewsarchus has been recovered as a member of Cetancodontamorpha, most closely related to entelodonts, hippos, and whales.^[15][7] In Yu et al. (2023), it was recovered in a polytomy with Achaenodon and Erlianhyus.^[7]

Below is a simplified cladogram based on the results of Spaulding et al. (2009) and Yu et al. (2023).^[7][15]

The Irdin Manha Formation, from which the holotype of Andrewsarchus was recovered, consists of Irdinmanhan strata dated to between 47.8–37.71 mya.^[16] Andrewsarchus itself comes from the IM-1 locality, dated to the lower Irdinmanhan,^[17] from which the hyaenodontine Propterodon, the mesonychid Harpagolestes, the perissodactyls Deperetella and Lophialetes, the omomyid Tarkops, the glirian Gomphos, the rodent Tamquammys, and various indeterminate glirians are also known.^[16][17]

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.^[7][15]

• Achaenodon
• Entelodontidae
• Triisodontidae

Wikimedia Commons has media related to Andrewsarchus.

1. ^ ^{a b c d e f g h i} Osborn, H.F. (1924). "Andrewsarchus, giant mesonychid of Mongolia". American Museum Novitates (146): 1–5. hdl:2246/3226.
2. ^ ^{a b c d e f} 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.
3. ^ 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.
4. ^ ^{a b c} Chow, M.M. (1959). "A new arctocyonid from the Upper Eocene of Lushih, Honan" (PDF). Vertebrata PalAsiatica. 3 (3): 133–138.
5. ^ ^{a b c d} 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.
6. ^ 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.
7. ^ ^{a b c d e} 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.
8. ^ O'Leary, Maureen A.; Gatesy, John (7 August 2008). "Impact of increased character sampling on the phylogeny of Cetartiodactyla (Mammalia): combined analysis including fossils". Cladistics. 24 (4): 397–442. doi:10.1111/j.1096-0031.2007.00187.x. ISSN 0748-3007.
9. ^ "PBDB Collection". paleobiodb.org. Retrieved 18 August 2024.
10. ^ Ding, S.Y.; Zheng, J.J.; Zhang, Y.P.; Tong, Y.S. (1977). "The age and characteristics of the vertebrate fauna from Liuniu and Oongjun Formations of the Bose Basin, Zhuang autonomous region". Vertebrata Palasiatica. 15: 35–44.
11. ^ ^{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.
12. ^ Zhou, X. (1995). Evolution of Paleocene-Eocene Mesonychidae (Mammalia, Mesonychia) (PhD dissertation). University of Michigan. hdl:2027.42/129581.
13. ^ 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
14. ^ ^{a b} Van Valen, Leigh (1978). "The Beginning of the Age of Mammals" (PDF). Evolutionary Theory. 4: 45–80.
15. ^ ^{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.
16. ^ ^{a b} "PBDB Collection". paleobiodb.org. Retrieved 18 August 2024.
17. ^ ^{a b} Wang, YuanQing; Meng, Jin; Beard, Christopher K.; Li, Qian; Ni, XiJun; Gebo, Daniel L.; Bai, Bin; Jin, Xun; Li, Ping (1 December 2010). "Early Paleogene stratigraphic sequences, mammalian evolution and its response to environmental changes in Erlian Basin, Inner Mongolia, China". Science China Earth Sciences. 53 (12): 1918–1926. doi:10.1007/s11430-010-4095-8. ISSN 1869-1897.