EARLY CRETACEOUS DINOSAUR FOOTPRINTS FROM CERRO DE CRISTO REY, DOÑA ANA COUNTY, NEW MEXICO

Dinosaur tracks and reptile swimming traces occur at two localities in the latest Albian “Anapra Sandstone” (=Sarten Member of Mojado Formation, Bisbee Group) at Cerro de Cristo Rey in southernmost Doña Ana County, New Mexico. At one locality, numerous underprints (~ 400) of the ichnogenus Caririchnium (an ornithopod dinosaur) are preserved in concave relief on top of a hematized, bioturbated sandstone bed in the lower part of the Anapra, ~ 9 m above its base. The exposure is approximately 400 m2, although ~150 m2 is partially covered by erosional debris. These tracks are relatively large (footprint length up to 65 cm), tridactyl, and have wide, blunt toes and a square to bilobate heel. The second locality exposes two track-bearing beds, 9 m apart stratigraphically, in the upper third of the Anapra Sandstone. The lower bed of the second locality also preserves large Caririchnium tracks in concave relief with small manus impressions. Large (footprint length=40-60 cm) tracks of the ichnogenus Magnoavipes (theropod dinosaur), characterized by extremely thin, pointed toes, are preserved in convex epirelief. The upper bed preserves Caririchnium tracks in convex epirelief as well as numerous reptile swimming traces—scratch marks and other parallel, linear grooves. These two upper Anapra track beds can be traced over a strike of ~ 750 m and preserve as many as 350 distinct footprints, including at least 12 pairs of swimming traces. The Anapra Sandstone is of latest Albian age (Plesioturrillites brazoensis ammonite zone), so the Cerro de Cristo Rey tracks are slightly younger than the well known late Albian tracksites of northeastern New Mexico, which are in strata equivalent to the Mortoniceras equidistans ammonite zone or slightly younger. At Cerro de Cristo Rey, the dominance of ornithopod tracks and absence of sauropod tracks fits regional patterns of late Albian-Cenomanian track distribution consistent with a North American extirpation of sauropods before late Albian time. The deltaic/coastal plain depositional setting of the Anapra Sandstone is also remarkably similar to the track-bearing late Albian-Cenomanian sandstones of NE New Mexico, Oklahoma and SE Colorado, which also have a tetrapod footprint ichnofacies dominated by ornithopod (Caririchnium) tracks.