Batrachopus from the southwestern United States, and a revision of some Early Mesozoic crocodylomorph ichnogenera

Introduction During the field season of 1983, a field party from the University of California investigated the faunas of the Kayenta and Moenave formations in northeastern Arizona, on lands of the Navajo and Kaibab-Paiute nations. This fieldwork was a continuation of paleontological, sedimentologic, and biostratigraphic reconnaissance of the region begun in 1981 and supported by grants from the National Geographic Society and the Museum of Paleontology of the University of California (UCMP). Work to date has been summarized by Clark and Fastovsky (Chapter 23) and by Padian et al. (1982). The tracks described here were discovered by J. M. Clark, and collected by Clark, K. Padian, S. M. Gatesy, and E. Cobabe. Upon arrival at Berkeley, the sandstone slabs bearing the footprints were washed and cleaned with a soft brush to remove dirt; latex molds of the best preserved individual tracks and trackways were made by Kyoko Kishi. The purpose of this chapter is to describe these tracks, the first southwestern records of the crocodylomorph ichnogenus Batrachopus. To do so, however, it has proved necessary to revise the ichnogenus Batrachopus and other named ichnogenera, mostly from the Newark Supergroup of eastern North America. We also review the stratigraphic distribution of trackways comparable to Batrachopus, and we conclude that the basis of first records suggests correlation of the Dinosaur Canyon Member of the Moenave Formation with the Early Jurassic horizons of the Newark Supergroup. The trackways described here were collected from two different areas in the Dinosaur Canyon Member of the Moenave Formation. The first locality, V85012, is some 500 m east of the type locality of Protosuchus richardsoni (UCMP locality V3828) near "Protosuchus Pillar," worked by Barnum Brown and field crews from the American Museum of Natural History (AMNH) in 1931 and 1934. As Colbert and Mook (1951) noted, eight Protosuchus specimens came from the "Protosuchus Pillar" area in Dinosaur Canyon during those years; seven are AMNH specimens, and the eighth is a UCMP specimen (36717) discovered by Dr. S. P. Welles (locality V4120). From this same region, less than half a kilometer south-southeast of Protosuchus Pillar, six protosuchian skeletons and the first set of footprints mentioned above were discovered within 100 m of each other by James M. Clark in 1983. The tracks came from the base of a cross-bedded orangered sandstone bed, 1.5-3.0 m thick, with blue-white spheres and burrows; the crocodile skeletons were higher in this bed. Clark (UCMP field notes, 1983) determined that the type specimen of Protosuchus is from the next higher sandstone horizon, similar to the lower bed but without cross bedding, and separated from it by one meter of shaly sandstone, brown with green-white spheres and tunnels. Clark concluded, and we agree, that all the Protosuchus localities in this area are much higher in the Moenave Formation than Colbert and Mook (1951) realized: Locally, the Moenave is a graded sandstone terrace, above which the talus and cliffs of Dinosaur Canyon rise. The cliffs are primarily formed of Kayenta rocks, with a cap of Navajo Sandstone, and the Moenave-Kayenta contact is probably within fifteen meters of the highest occurrence of Protosuchus. The second footprint locality, V84239, is about two miles (3.5 km) south-southeast of the Landmark, north of Tanahakaad Wash, Coconino County, Arizona, near the base of the Adeii Eechii Cliffs. [A third record of Batrachopus, uncollected, occurs in the Dinosaur Canyon Member of the