VERTEBRATE FOSSILS OF THE LOWER PERMIAN ABO FORMATION, ABO PASS, NEW MEXICO

The Lower Permian Abo Formation was named by Lee in 1909 for exposures at the southern end of the Manzano Mtns. in Abo Canyon. A type section was formally described by Needham and Bates in 1943 in Abo Canyon. The Abo has been littologically divided into two members. The lower unit termed Scholle Member consist of covered slopes of mudstone and siltstone intercalated with channelform trough-cross bedded fine grained sandstone and conglomerates. The upper Canon de Espinosa Member consist of thick intervals of mudstone and siltstone interbedded with sheets of fine grained sandstone and rare conglomerates. The paleoenvironment inferred from the deposits are of a low relief floodplain with numerous stream channels. Also indicated is a trend towards a more arid climate from the Carboniferous into the Permian. The first vertebrate fossil retrieved from the Abo Formation were burrows and bones of the aestivating lungfish (Dipnoa) Gnatorhiza bothreta found near the easten flanks of the Los Pinos Mtns. The first tetrapod fossil was found in 2009 when one of us (HWM) visited the Abo mine area. It was retrieved from the Canon de Espinosa Member and consists of a nueral spine fragment with the distinctive figure eight shape of the eupelycosaur Dimetrodon. Additional fieldwork by one of us discovered the highly fossiliferous Scholle copper mine site. The deposit is in a channel lag in the Scholle Member at the open pit mine. Vertebrate fossils are found in both the unconsolidated mudstone and sandstone. The tetrapod taxa retrieved including the eupelycosaurs Sphenacodon and Dimetrodon. These fossils indicate a pelycosaur dominated terrestrial ecosystem of Coyotean (probably middle Wolfcampian) age.