EUSUCHIAN CROCODILIANS FROM THE FRUITLAND AND KIRTLAND FORMATIONS, SAN JUAN BASIN, NEW MEXICO
Thomas E. Williamson
New Mexico Museum of Natural History and Science, 1801 Mountain Road, NW, Albuquerque, NM, 87104
Late Cretaceous eusuchian crocodilians are generally rare in the Upper Cretaceous (late Campanian - Maastrichtian) Fruitland and Kirtland Formations. They are represented primarily by isolated teeth, osteoderms, and postcranial fragments. Previously, these have been referred to Allognathosuchus, Brachychampsa, Crocodylus, and Leidyosuchus..However, these diagnoses are based on inadequate material. A partial skull and skeleton (NMMNH P-27840) from the De-na-zin Member, Kirtland Formation and other specimens representing isolated and associated skeletal elements are here referred to eusuchia indet. P-27840 is represented by portions of the skull roof including much of the frontal and parietals, and other regions of the skull including the jugal, basioccipital, quadrate, fragments of the maxillae, and portions of both dentaries. The postcranial skeleton is represented by fragmentary vertebrae, limb fragments, a partial ilium and osteoderm fragments. The lack of occlusion pits medial to the maxillary teeth suggests that P-27840 does not represent an alligatoroid. Other less complete specimens from the Fruitland and Kirtland Formations in the NMMNH collection may belong to the same taxon. These are characterized by relatively anteroposteriorly elongate osteoderms that lack keels and have broad overlap regions, and dorsal vertebrae with procoelus centra. P-26260 is a partial left dentary that closely resembles those of P-27840. It includes the roots of 6 teeth, one complete tooth, and portions of the symphyseal region.
A possible second eusucruan taxon from the De-na-zin Member is represented by a single specimen (P-26234) that includes a nearly complete osteoderm and an associated femur. The osteoderm of this specimen bears a relatively high, narrow, and posteriorly pointing median ridge and is similar to those pertaining to the crocodylian Akanthosuchus from the lower Paleocene Nacimiento Formation of the San Juan Basin. Isolated bulbous teeth probably represent posterior crusrung teeth of an alligatoroid, suggesting that the second eusuchian above is an alligatoroid, or that there is at least a third eusuchian crocodylian present in Late Cretaceous faunas of the San Juan Basin.
Keywords:
Eusuchian
pp. 63 2001 New Mexico Geological Society Annual Spring Meeting April 7, 2000, Macey Center