New Mexico Geological Society Annual Spring Meeting — Abstracts

History, 1801 Mountain Road NW, Albuquerque NM 87104 New Mexico's fossil record contains two endemic occurrences of syncarid crustaceans, both from the extinct Paleozoic order Palaeocaridacea. Uronectes kinniensis Schram & Schram, 1979, is known from the upper Virgilian Kinney Quarry Lagerstiitten, and Erythrogaulos carrizoensis Schram, 1984, is known from the upper Virgilian to lower Wolfcampian Carrizo Arroyo section. An addition to this important record comes from New Mexico Museum of Natural History locality 4667, in the Upper Pennsylvanian (Missourian) strata of the Atrasado Formation (Madera Group), near Tinajas Arroyo, Socorro County. Six specimens representing a new syncarid genus with uncertain family assignment have been found. Characteristic features include a reduced first thoracomere, circular thoracomere ornamentation, a spines cent spatulate telson, long caudal rami, and distally rounded uropods bearing strong median ribs. It is distinctive in possessing welldeveloped furca near the terminus of the te1son, a feature placing it outside of the Palaeocaridacea and making it the only Paleozoic syncarid known to have preserved this primitive crustacean structure. This sync arid may belong to the extant order Anaspidacea, from which only one fossil anaspidid anaspidacean, Anaspidites antiquus Chilton, is known from the Triassic of Australia.

The syncarid fossils at locality 4667 occur in a 4-meter thick unit of thinly laminated black shale. The paleoenvironment is interpreted as being lacustrine. Darwinuloid ostracods and conchostracans assigned to Pseudestheria sp. are highly abundant, indicating alkaline conditions at the time of deposition. A maxillopodan crustacean and a phyllocarid crustacean, both showing soft-bodied preservation, are known from single occurrences. Other faunal elements are low in abundance, including paleoniscoid and coelacanth scales, isolated fish bones and coprolites. A sparse paleoflora that consists primarily of seed ferns is also present.