New Mexico Geological Society Annual Spring Meeting — Abstracts

The presence of tetrapod footprints in the Abo Formation of the Fra Cristobal Mountains has been in the geological literature since the 1980s, but we have only recently been able to confirm and better document earlier reports. An extensive assemblage of tetrapod tracks is present in the Red Gap area in the lower part of the Abo Formation, ~20 m above the Bursum-Abo contact. The footprints occur in a 1-1.5-m thick bed of thin bedded, ripple-laminated sandstone that can be traced laterally for at least 1 km. Vertebrate footprints in this bed can be referred to three ichnotaxa: Batrachichnus delicatulus (Lull), Dromopus Marsh and Limnopus Marsh. Also present are conifer impressions (Walchia) and a single invertebrate bedding-plane burrow that is simple lined with meniscate backfill and regular curved branches along one side; it appears to represent the ichnogenus Cladichnus D'Allesandro & Bromley.

In the track-bearing interval, Batrachichnus delicatulus is extremely abundant, whereas other ichnotaxa are relatively uncommon. Individual tracks of Batrachichnus delicatulus range in size from 3-7 mm in length. Most tracks are preserved as digitigrade undertracks, some showing long drag marks indicating that they were made in a soft, wet substrate. Mid-line drag marks and indistinct trampled surfaces also occur. Mud cracks are present and indicate subaerial conditions at the time of track making.

The vertebrate ichnofauna in the Abo Formation at Red Gap shows low diversity when compared to other New Mexico Lower Permian track sites. Dimetropus and Gimoreichnus, common elements that are attributed to large and small pelycosaurs, appear to be absent from the Red Gap ichnofauna. However, the Red Gap site may not yet have been adequately sampled and/or it may represent a facies different from other known Abo tracksites in New Mexico.