New Mexico Geological Society Annual Spring Meeting — Abstracts

Dinosaur tracks and swimming traces have been discovered at three localities latest in the latest Albian "Anapra Sandstone" (= Sarten Member of the Mojado Formation, Bisbee Group) at Cerro de Cristo Rey in Sunland Park, New Mexico, southernmost Dona Ana County.
At one locality, NMMNH locality #5293, many underprints (over 400) of the ichnogenus Caririchnium (and ornithopod dinosaur) are preserved in concave relief on top of a hematized, bioturbated sandstone bed in the lower part of the Anapra ~ 9m above its basal contact with the underlying Mesilla Vally Shale. The exposure is approximately 400 m², although ~150 m² is partially covered ny erosional debris. These tracks are tridactyl, relatively large (up to 65 cm footprint length), have wide, blunt toes, and a square bilobate heel, all of which are characteristic of the ichnogenus Caririchnium.

The second and third localities are two quarries adjacent to each other and are designated NMMNH localities #5291 and #5292. These are linear quarries exposing two track-bearing beds 9m apart stratigraphically in the upper third of the Anapra Sandstone. The lower bed of this second locality also preserves large Caririchnium tracks in concave relief with small manus impressions. Also preserved are large (40-60 cm footprint length) tracks of the ichnogenus Magnoavipes (a theropod dinosaur), characterized by . extremely thin, pointed toes. These theropod tracks are preserved in convex epirelief in a hematized, bioturbated sandstone as well. The upper bed of these two localities preserves Caririchnium tracks in convex hyporelief as numerous swimming traces-possibly from reptilians. These are scratch marks and other parallel, linear grooves. These two upper Anapra track beds can be traced over a total strike of ~750 m and as many as 350 distinct footprints are exposed, 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 North American extirpation of sauropods before late Albian time. The deltaic/coastal plan 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.