Blickomylus (Artiodactyla, Camelidae, Stenomylinae) and the Age of the Moroni Formation, Central Utah

The first, and thus far only, fossil vertebrate to be discovered in the Moroni Formation of central Utah (Fig. 1) is a new species of the Miocene stenomyline camel Blickomylus Frick and Tay lor, 1968, represented by parts of both rami, each with p4-m3, of a single individual (Fig. 2). Among the stenomylines, all of which have transversely narrow, hypsodont molars, Blickomylus is the most highly derived in the anteroposterior elongation of the third molars (Frick and Taylor, 1968). The only previously de scribed species of Blickomylus, B. galushai, has as its type speci men a crushed skull, F:A.M. 50840; the type and originally re ferred skulls, jaws, and metapodials are from Blick Quarry in the Chamisa Mesa Member of the Zia Sand Formation in Sandoval County, New Mexico (Frick and Taylor, 1968). The age of Blick Quarry is considered to be early Hemingfordian, He-1, and the genus ranges through the entire Hemingfordian (Tedford et al., 2004). Blickomylus galushai has also been reported from the Hemingfordian of the Browns Park Formation in northeastern Colorado (Honey and Izett, 1988) and the Split Rock Formation of central Wyoming (Munthe, 1988). The only other stenomyline having somewhat similar derived characteristics, although rela tively less elongated third molars, is Rakomylus Frick, 1937. The type and single known species, R. raki, is based on a skull, F:A.M. 30990, complete except for the nuchal area, and is known also from several mandibles, and metapodials from the Skull Ridge Member of the Tesuque Formation, Santa Fe Group, Santa Fe County, New Mexico, in deposits referred to the Bar stovian (Frick and Taylor, 1968; Galusha and Blick, 1971). Because the specimen from the Moroni Formation consists of rami, only characters of the lower jaw and dentition can be com pared to Blickomylus and Rakomylus. Both Rakomylus and Blickomylus exhibit dental changes after wear that tend to blur some of their generic distinctions. In topotypic specimens of B. galushai from the Blick Quarry, pl-4 are small, ml is reduced in size and laterally displaced, and m3 is more hypsodont and rela tively more elongated than in the other stenomylines. In at least one referred specimen of B. galushai from Straight Cliff Fork, F:A.M.50803, pl-3 are absent and p4 has three cusps, presum ably paraconid, protoconid, and metaconid. Rakomnylus raki ex hibits greater premolar reduction than in topotypic specimens of B. galushai, having pl vestigial or probably absent in adults, p2 absent, p3 vestigial, and p4 smaller than in B. galushai. However, the ml of R. raki is relatively well developed, and m3 is less elongated relative to m2 than in B. galushai. The stenomyline from the Moroni Formation combines features such as the re duced premolars that occur in Rakomylus with the more reduced ml and greatly expanded m3 of Blickomylus. The Moroni cam elid is smaller than B. gallishai and appears to represent a new species of Blickomylus. Institutional Abbreviations-F:AM, Frick Collection, Ameri can Museum of Natural History; CM, Carnegie Museum of Natural History.