Systemodon, Cope, 1881

Froehlich, David J., 2002, Quo vadis eohippus? The systematics and taxonomy of the early Eocene equids (Perissodactyla), Zoological Journal of the Linnean Society 134 (2), pp. 141-256 : 148

SYSTEMODON

Systemodon is a name first used by Cope (1881) for his taxon, Systemodon tapirinum from the San Jose formation. Both Wortman (1896) and Granger (1908) referred this taxon to Hyracotherium . These specimens have been tentatively removed from the rest of the equids because they possess a very different wear pattern in which lateral-wear surfaces on the lower teeth form a continuous shearing surface on the paracristid and cristid obliqua, a possible autapomorphy for the OTU. Two distinct groups, informally named San Jose lophoid and Bighorn lophoid, were scored for the matrix of the equid analysis. These two OTUs scored identically except that they are slightly different sizes and were condensed in the actual analysis into a single element in the matrix. The San Jose lophoid OTU was scored based on the following specimens collected from the Regina Member of the San Jose Formation on the southern end of the Jicarilla Indian Reservation, north of Regina, New Mexico: AMNH 48996, NMMNH P9238, P9402, and USNM 1064. Like other San Jose material, this sample is either late Greybullian or early Lysitean (late Wa 5 or early Wa 6). The Bighorn lophoid OTU was scored using USGS 2395, 19528, 20569, 21036, 21037, 21038, 21049, 21051, 21104, 21296, 24206, 24207, and 24459, all collected from localities approximately 450 m above the base of the Willwood Formation in the central Bighorn Basin. The temporal distribution of this taxon is difficult to determine; however, it appears to be middle or late Wasatchian (Wa 4 –Wa 7).