New Mexico Geological Society Annual Spring Meeting — Abstracts

In 1929, Robert Abercrombie discovered parts of at least five mammoth skeletons near Mesa Redonda, Quay County, New Mexico. Nelson Vaughn of the Colorado Museum of Natural History (now the Denver Museum of Nature and Science) supervised the excavation of these mammoths in 1930. Many of the Mesa Redonda mammoth fossils were transferred to the New Mexico Museum of Natural History in 1985 where they were used to construct a composite mounted skeleton now on display. The Mesa Redonda mammoth site is located in and along the eastern bank of a small, unnamed arroyo that flows NE from the base of Mesa Redonda, ~23 km S of Tucumcari. The bone-bearing stratum is a 1.0-1.5-m thick layer of friable, light brown to moderate reddish-brown, very fine-grained to fine-grained, muddy sandstone. This bed rests directly on Upper Triassic bedrock of the Redonda Formation of the Chinle Group. Above the bone layer is a 0.3- to 0.5-m thick sedimentary breccia with imbricated clasts of Mesozoic sandstone and limestone that indicate paleoflow to the NE. Lenses of such breccia also occur in the bone-bearing sandstone layer. Pedogenesis at the top of the bone-bearing sandstone locally has produced a 0.2-m thick layer of pale yellowish-brown sandy clay. The top of the section at the mammoth site is an unconsolidated, light brown eolian sand of probable Holocene age. The geometry and lithotypes of the Quaternary sediments at the Mesa Redonda mammoth site clearly were part of an alluvial fan system that flowed N/NE from the Mesa during part of the Pleistocene. The bone-bearing sandstone probably represents inter-channel portions of the fan, and bank deposition related to lower energy discharge and/or stream meander.

Measurements of three Mammuthus M3s from Mesa Redonda are: length, 241-257 mm; width, 92-101 mm; crown height, 187-271 mm; enamel thickness, 2.3-3.0 mm; 17-19 plates; and lamellar frequency (plates/100 mm) of 6-8. The measurements and morphology of these teeth support their assignment to the advanced species M. columbi. The presence of M. columbi and the associated fauna of extant terrestrial gastropods indicates a late Pleistocene (late Rancholabrean) age for the Mesa Redonda fauna. The gastropod assemblage suggests a relatively mesic, riparian habitat of grasses and woody, deciduous vegetation.