New Mexico Geological Society Annual Spring Meeting — Abstracts

The Alamo Wash local fauna refers to the vertebrate fauna derived from the Naashoibito Member ofthe Upper Cretaceous Kirtland Formation, San Juan Basin, New Mexico. Recent field work and analysis ofcollections made from the Kirtland Fonnation and accompanying locality infonnation indicates that several dinosaur taxa have been incorrectly referred to the Alamo Wash local fauna including the chasmosaurine ceratopsian Pentaceratops, the lambeosaurine hadrosaur Parasaurolophus, and the hadrosaurine hadrosaur Naashoibitosaurus. Pentaceratops is found stratigraphically no higher than the De-na-zin Member (= upper shale member) of the Kirtland Formation. The holotype of Kritosaurus navajovius is a nomen dubium and was recovered from the De-na-zin Member. Hadrosaur material from the Naashoibito Member that has previously been referred to Kritosaurus is not diagnostic to the generic level. Parasaurolophus tubicen (the holotype and New Mexico Museum of Natural History specimen P-25 100) and the holotype of Naashoibitosaurus ostromi are also from the De-na-zin Member.

The dinosaur taxa that can be confirmed from the Naashoibito Member are the titanosaurid sauropod Alamosaurus sanjuanensis, the chasmosaurine ceratopsian Torosaurus cf T. utahensis, indeterminate hadrosaur, indeterminate ankylosaur, a large tyrannosaurid similar to Tyrannosaurus rex and a small theropod tentatively identified as a dromaeosaur. The dinosaurs of the Alamo Wash local fauna are distinctly different from those of the underlying De-na-zin Member suggesting that there is a significant disconformity underlying the base of the Naashoibito Member. The presence of Torosaurus and possibly also T. rex in the Alamo Wash local fauna suggests a late Maastrichtian (Lancian) age.