New Mexico Geological Society Annual Spring Meeting — Abstracts

New Mexico Museum of Natural History (NMMNH) locality 3380 (discovered by R. Dello-Russo) is located on the western flank of the Lucero uplift in central New Mexico. This site is stratigraphically low in the Bluewater Creek Formation near the base of the Chinle Group (Adamanian -latest Carnian) and is approximately 228 Ma. The site has produced an astonishing amount of fragmentary fossils, including bones of phytosaurs (probably Rutiodon-grade), Metoposauridae indet, rare bones of the diminutive metoposaurid amphibian-Apachesaurus sp., several teeth of the lungfish Arganodus sp., and numerous indeterminate reptiles, principally archosaurs, as well as coprolites. The fossils occur over a large area (approximately 1000 m²) and are weathering out of fine-grained overbank deposits and in some instances occur in sandbars in shallow channel deposits. None of the fossils are articulated or associated. The bones themselves display stage 3 to stage 4 weathering with splintered ends and longitudinal cracks along the bone shafts, indicating that they were subaerially exposed to decay and weathering for a long period of time prior to burial. Fossils recovered include scutes, limb bones, and more than 200 phytosaur teeth.

In direct contrast to L-3380 is the younger Snyder quarry (NMMNH locality 3845), located in north-central New Mexico. The Snyder quarry is in the Petrified Forest Formation of the Chinle (Revueltian -early-mid Norian age) and is approximately 210 Ma. The quarry is smaller than L-3380 with an approximate excavated area of 50 m². Thousands of bones have been recovered from this quarry, including the remains of phytosaurs, aetosaurs, coelophysoid dinosaurs, semionotid and colobodontid fish, temnospondyl amphibians, and a procolophonid reptile. The bones, which include skulls, teeth, vertebrae, ribs, scutes, and limb elements, were deposited in a broad, shallow channel and are in excellent condition with no evidence of either weathering or extensive scavenging. The skeletal elements are associated with rare instances of articulation. Snyder quarry bone densities range from 6 bones/m² to 70 bones/m², whereas L-3380 bone densities are estimated at an average of 20 bones/m². These two localities provide an opportunity to contrast two very different taphonomic settings. The Snyder quarry represents a catastrophic event, most likely a forest flre, while NMMNH L-3380 represents an attritional accumulation of corpses on a floodplain.