ADDITIONS TO THE VERTEBRATE FOSSIL RECORD OF THE MOENKOPI FORMATION (MIDDLE TRIASSIC: ANISIAN), NORTHERN NEW MEXICO

Andrew B. Heckert1, S. G. Lucas2 and J. W. Estep2

1Dept. of Earth and Planetary Sci, Univ. of New Mexico, Albuquerque, NM, 87131 2New Mex. Mus. of Nat. History & Sci., 1801 Mountain Road NW, Alb., NM, 87104

Two fossil specimens from the Anton Chico Member of the Moenkopi Formation near Dilia, Guadalupe County in northern New Mexico greatly expand our understanding 6f the Middle Triassic tetrapod fauna in New Mexico. The first specimen, New Mexico Museum of Natural History and Science (NMMNH) P-27269, is the partial skeleton of a large erythrosuchid archosaur. The disarticulated skeleton was found in a greenish gray, smectitic mudstone near the middle of the Anton Chico Member at NMMNH locality 3642. The skeleton consists of skull fragments, a tooth, 41 partial vertebrae (including cervical, dorsal, sacral, and caudal vertebrae), gastralia, osteoscutes, the proximal humerus, and incomplete femora, tibiae, and fibulae. The centra are amphicoelous and deeply excavated laterally. These features and others support assignment of NMMNH P-27269 to the Erythrosuchidae. The New Mexico erythrosuchid closely resembles Shansisuchus shansisuchus Young from the upper Ermaying Formation of China and is from an animal about the same size (i.e., body length about 3 m). The only previously reported erythrosuchid form North America is Arizonasaurus babbiti Welies from the Holbrook Member of the Moenkopi Formation in Arizona. The Holbrook and Anton Chico Members are temporally correlative (early Anisian). However, there is no anatomical overlap of the holotype skull fragment of A. babbiti and the New Mexico erythrosuchid, so whether or not they represent the same taxon is uncertain. The presence of a Shansisuchus-like erythrosuchid in the North American lower Anisian establishes greater cosmopolitanism of the Erythrosuchidae and supports correlation of the upper Ermaying and upper Moenkopi Formations.

NMMNH P-27270 is the partial skeleton of a medium-sized (approx. 1 m) capitosauroid amphibian. The partial skeleton consists primarily of skull fragments with some partial postcrania, including a fragmentary interclavicle and clavicles. Although generically indeterminate, these specimens are identifiable as capitosauroid. The capitosaurid amphibian Eocyclotosaurus, recovered previously from the Anton Chico Member at another locality, indicates an early Anisian age for the Anton Chico Member of the Moenkopi Formation in New Mexico.

Keywords: vertebrate paleontology

pp. 51 1998 New Mexico Geological Society Annual Spring Meeting April 9, 1998, Macey Center