FIRST OCCURRENCE OF AMPHISAUROPUS AND VARANOPUS IN THE LOWER PERMIAN ABO FORMATION, CENTRAL NEW MEXICO

At a newly discovered site 2.4 km south of the Abo type section at Abo Pass in central New Mexico, tetrapod tracks are found in a thinly bedded, fine-grained sandstone unit 141 m above the base of the Abo Formation. The track-bearing stratum is a 0.3-1.3-m-thick tabular sandstone with extensive ripple laminae. Six vertebrate ichnotaxa are present: Amphisauropus latus Haubold, Dromopus agilis Marsh, Dimetropus sp., Batrachichnus delicatulus Lull, Gilmoreichnus hermitanus (Gilmore) and Varanopus, cf. V. microdactylus (Pabst) or cf. V. curvidactylus Moodie. The Abo Pass tracksite has an abundance of Amphisauropus, and large trampled surfaces are present. The track of a presumed seymouriamorph, Amphisauropus is widely distributed in Europe, but has previously been unrecorded in the United States. Tracks from Abo Pass show diagnostic features of Amphisauropus including: manus and pes pentadactyl and broad with rounded digit tips, trackway pattern of inward-directed manus and forward-directed pes. Varanopus, a protorothyridid-captorhinid track known from the European Rotliegend and from the Lower Permian Choza Formation of Texas, also occurs for the first time in the Abo Formation at this site. Tracks show a moderate increasing length between pes digits I to IV, pes digit V is outwardly directed slightly, and the angle between the axis of pes digits I and IV is greater than 90°. Based on the proportion and position of the pes digits, we assign these tracks to Varanopus willistoni.