LATE PALEOZOIC DIADECTIDAE (COTYLOSAURIA: DIADECTOMORPHA) OF NEW MEXICO AND THEIR POTENTIAL PREFERENCE FOR INLAND HABITATS

Diadectidae is a diverse group of terrestrially-adapted reptiliomorphs known from Late Pennsylvanian-Early Permian (Kasimovian-Kungurian) strata of the Euramerican equatorial part of Pangea. Usually regarded as the earliest herbivorous tetrapods, their close phylogenetic relationship to Amniota supports the idea that diadectids laid amniote eggs. Given their primary plant diet, possible reproduction on land, and large abundance of fossils in intracontinental red-beds, it has proposed that diadectids preferentially inhabited inland to upland environments. To test this hypothesis we studied the distribution of diadectid body- and ichnofossils from New Mexico. Late Pennsylvanian-Early Permian strata of New Mexico represent depositional settings ranging from tropical tidal flats (northern margin of the Hueco seaway) to alluvial aprons around highland areas (ancestral Rocky Mountains). Diadectid skeletal remains are known from six locales (El Cobre Canyon, Arroyo del Agua, Pecos River Valley, Jemez Springs, Sierra Lucero, Socorro) and, with exception of Late Pennsylvanian finds from Sierra Lucero, all come from inland alluvio-fluvial red-beds. Diadectid footprints are known from four locales (Pecos River Valley, Abo Pass, Sierra Lucero, Socorro) and all represent Permian alluvio-fluvial red-beds that accumulated at least 120 km landward from the nearest marine shoreline. The majority of diadectid footprints is from the Pecos River Valley area in rocks deposited in the Permian Taos trough of the ancestral Rocky Mountains. No record exists from the dozens of contemporaneous track sites with coastal plain and peritidal deposits of today's south-central New Mexico (e.g., Caballo Mountains and Robledo Mountains). Thus, at least the Permian data strongly support the assumption that diadectids preferred inland habitats and avoided coastal lowlands.