Andrewsarchus, 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. 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.
The holotype of Andrewsarchus mongoliensis, a partial skull (AMNH-VP 20135),[1] was recovered from the lower Irdin Manha Formation of Inner Mongolia.[2] 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. 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.[3] [4]
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. 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.[5] Both species are considered junior synonyms of A. mongoliensis.
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 and a body height of . 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.
Andrewsarchus
Andrewsarchus was originally assigned to the family Mesonychidae, and Paratriisodon was classified as a member of the family Arctocyonidae. In 1966, Andrewsarchus became the sole member of its own subfamily, Andrewsarchinae,[6] within Mesonychia. Andrewsarchinae was elevated to family level by Philip D. Gingerich in 1998. Paratriisodon was first synonymised with Andrewsarchus by Leigh Van Valen in 1978,[7] and the latter genus was reassigned to the subfamily Triisodontinae within Arctocyonidae. More recently, Andrewsarchidae was revived. Since then, Andrewsarchus has been recovered as a member of Cetancodontamorpha, most closely related to entelodonts, hippos, and whales.[8] [9] In Yu et al. (2023), it was recovered in a polytomy with Achaenodon and Erlianhyus.
Below is a simplified cladogram based on the results of Spaulding et al. (2009) and Yu et al. (2023).
The Irdin Manha Formation, from which the holotype of Andrewsarchus was recovered, consists of Irdinmanhan strata dated to between 47.8–37.71 mya.[10] Andrewsarchus itself comes from the IM-1 locality, dated to the lower Irdinmanhan,[11] 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.
In his paper describing Andrewsarchus, Osborn suggested that it may have been omnivorous based on comparisons with entelodonts. This conclusion was supported by Szalay and Gould, who cite the heavily wrinkled crowns of the cheek teeth as supporting evidence, as well as the close phylogenetic relationship between Andrewsarchus and entelodonts.