DIETARY MODIFICATIONS OF THE TEETH IN THE EARLY MIOCENE STENOMYLINE CAMELS (CAMELIDAE: ARTIODACTYLA)

The stenomylines were a small group of early Miocene gazelle-like camels that developed extremely hypsodont, or high-crowned teeth. Previous authors measured the tooth crown height and mesowear of Stenomylus itself, but did not include a study of the even more hypsodont genera Rakomylus and particularly Blickomylus. We measured the height index (HI = total tooth height of unworn m3/transverse width of m3) and estimated the mesowear of early camelids such as Poebrotherium, plus the basal stenomyline Pseudolabis, which had brachydont teeth (HI < 2) and relatively high cusp relief. As previously reported, Stenomylus has a HI as high as 4 and slightly more mesowear (levels 3-4). Similarly, Rakomylus has a HI = 4 and mesowear values around 5. But, Blickomylus was dramatically more hypsodont, with a HI as high as 6.5 on the least-worn teeth (the same as the most hypsodont horses of the later Miocene), and a mesowear index of 6 (completely flat tooth-crowns with no cusp relief). This suggests that Blickomylus had an extremely abrasive diet, like the most hypsodont horses and ruminants of the Miocene. In fact, it is the most hypsodont animal of the early Miocene, at a time when horses like Parahippus had low-crowned teeth. It is unclear why such high-crowned teeth were selected for in Blickomylus in the early Miocene, as they would have been high-crowned before the extensive savanna grasslands had appeared. However, it is striking that this only occurs in the Zia Sand of New Mexico and in central Utah, but is unknown in High Plains deposits of Nebraska, Colorado, and South Dakota, which yields the greatest diversity of Hemingfordian mammals, including many other camel groups. Possibly, Blickomylus lived on a diet of plants covered with abrasive materials in New Mexico and Utah, but not in the northern High Plains.