Mammalian Fauna From The Fullerton Gravel Pit (Ogallala Group, Late Miocene), Morton County, Kansas

The Fullerton Gravel Pit, Morton County, Kansas is one of many sites in western Kansas at which the Ogallala Group crops out. The Ogallala Group was deposited primarily by streams flowing from the Rocky Mountains. Evidence of water transport is observable at the Fullerton Gravel Pit through the presence of allochthonous clasts, cross-bedding, pebble alignment, and fossil breakage and subsequent rounding. Fluvial mechanisms also played an important role in the distribution of fossil material. When the fossils from the Fullerton Gravel Pit are placed in Voorhies Groups, it appears that a majority of them were removed from suspension gradually and transported through traction. This interaction created a distinct bias in the accumulation of specific specimens at the site. The identity of the mammalian taxa recovered from the Fullerton Gravel Pit was determined by comparison with previously identified specimens, as well as previously utilized comparative techniques. Camels are the majority of identifiable elements at the site. In particular, the medium-sized camel, Hemiauchenia is best represented. The canid, Osteoborus, proboscideans, such as gomphotherids, and perissodactyls, predominantly horses, are also present. Conspicuous by its absence, Teleoceras, a common Miocene rhinoceros, has yet to be discovered. The absence of Teleoceras may in part be due to channel velocity and depth. The presence of the canid Osteoborus restricts the Fullerton Gravel Pit to the Hemphillian age. The biochronologic range of the camels, Aepycamelus, Protolabis, and Procamelus end in the early Hemphillian, providing evidence restricting the Fullerton Gravel Pit to an early Hemphillian age. Of the horse species found at the site, only Neohipparion trampasense partitions the Hemphillian, being confined to the late Barstovian to early Hemphillian. The biostratigraphic range of these genera results in an assignment of the Fullerton Gravel Pit to an early Hemphillian age. Within the Equidae, hypsodont dentition and muzzle width indicate that horses were grazers. However, the varying degree of hypsodonty in the Camelidae indicates they were more diverse. Whereas, Hemiauchenia, exploited a grazing niche; others such as Procamelus occupied a browsing niche. Tooth condition and the percent δ13C reinforce the interpretations obtained for camel feeding. Grazing and browsing niches are supported in a savanna-grassland environment. Grasses would have sustained the grazers, and intermittent trees and brush the browsers. This interpretation of the Fullerton Gravel Pit is in agreement with analyses describing the spread of the savanna-grassland landscape across North America during the Miocene. A number of factors influence fossil distribution at the Fullerton Gravel Pit. Niche specialization, fluvial filtering, and an evolving landscape each accounts for the abundance of camel material, as well as the distribution of other taxa.