to the mesonychid Mesonyx. However, since the known morphology of Andrewsarchus is entelodont-like and consequently very different from mesonychids in habits and likely in body proportions, according to Szalay and Gould (1966) if a size estimate has to be made it would be more appropriate to follow the proportions of entelodonts. The type skull of Andrewsarchus mongoliensis (AMNH 20135) is in basal length, with a long snout comprising 60% of that measurement. The orbits of the eyes are set low and widely separated from one another by the snout, the sagittal crest is small, and the articulation for the mandible is shallow. Andrewsarchus mongoliensis has a complete placental tooth formula with 3 incisors, 1 canine, 4 premolars and 3 molars in each side of the jaws, as in entelodonts. The incisors are arranged in a semicircular configuration, the second and third premolars are elongated and single-cusped, the crowns of the molars are heavily wrinkled, and the first and second molars are much more heavily worn than the precedent and subsequent teeth. In fact, the molars are so similar to those of entelodonts it has been suggested that had they been found in isolation, they would have been classified as such. There are also greatly enlarged second incisors, as big as the canines, which despite not being preserved can be estimated from the diameter of their tooth sockets. They were proportionally small compared to the whole dentition and the size of the skull according to Szalay and Gould, contrary to Osborn's description. References Cetancodontamorpha Eocene even-toed ungulates Mammal enigmatic taxa Eocene mammals of Asia Lutetian genus first appearances Priabonian genus extinctions Fossil taxa described in 1924 Taxa named by Henry Fairfield Osborn Prehistoric even-toed ungulate genera