Ammonoids of the Middle Permian Reef Trail Member, Uppermost Bell Canyon Formation, Guadalupe Mountains National Park, West Texas

The Reef Trail Member is the uppermost lithostratigraphic unit of the Capitanian Stage in the Guadalupe Mountains region (where the Type Middle Permian Series GSSPs are being established). It is immediately overlain by evaporites of the Castile Formation (Lopingian Stage, Upper Permian Series). That transition is widely considered to mark a significant mass extinction event, so faunal composition of the Reef Trail Member is important to know. The only ammonoid commonly associated with the Reef Trail is Strigogoniatites fountaini. Although long considered to be in the underlying Lamar Limestone Member, the locus typicus of Strigogoniatites fountaini lies within the Reef Trail Member. This thesis documents a diverse fauna of juvenile ammonoids from a limestone bed approximately three meters below the Reef Trail/Castile contact in Reference Section SC1, located in the Patterson Hills within Guadalupe Mountains National Park, West Texas. These specimens represent several ammonoid families, including Cyclolobidae, Adrianitidae, Paragastrioceratidae, Paraceltitidae, and Medlicottiidae. The juvenile specimens were mostly recovered from acid residues. Regarding taphonomy, many of the juvenile specimens as well as larger specimens from other toe-of-slope localities are crushed on one side, indicating that the conchs had rested on their sides on the sea floor prior to burial. Rugose coral epibionts on one large specimen indicates that residence time on the sea floor was significant. The Reef Trail ammonoid fauna is much more diverse in both taxonomy and preservation than previously recognized, even near the top of the section and purported end-Capitanian mass extinction event.