New Mexico Geological Society Annual Spring Meeting — Abstracts

The Lamy amphibian quarry, located near Lamy in Santa Fe County, New Mexico (sec. 7, TI2N, RIlE), is in the Garita Creek Formation of the Chinle Group, which is of Adarnanian age (-215-220 Ma). The quarry is dominated by the remains of large metoposaurid amphibians assigned to Buettneria perfecta, and has long been considered to have been produced by drastic drought conditions. However, an examination of the original field data together with specimens from the quarry reveal that the Lamy amphibian quarry is, in fact, a hydrodynamically sorted, semi-attritional accumulation. The quarry is in fine-grained sediments that lack mudcracks and fine laminations that· would be expected in a pond that has dried up. The fossil bones show a strong preferred long-axis orientation, which is indicative of interaction of the fossil material with a strong current of water. The material is also hydrodynamically sorted, with the assemblage consisting of predominantly large, flat skeletal elements such as skulls, mandibles, and pelvic and shoulder girdle elements. The skulls and girdle elements are often imbricated, providing further evidence for the transport of the material in a current. The population is dominated by adult animals, which raises the potential of an earlier catastrophic event affecting a population of metoposaurs. There are no signs of scavenging, nor of advanced weathering on the bones. The best explanation of the taphonomic data is that a catastrophic mortality event killed a group of metoposaurid amphibians, and the corpses were subsequently quickly disarticulated and transported over a significant distance prior to deposition in a topographic low. There is no evidence, however, for the drought hypothesis that has long been advocated to explain the Lamy amphibian quarry.