THE CONTINUING SIGNIFICANCE OF SIBLEY RANCH LOCALITIES (CULBERSON COUNTY, TEXAS) TO GUADALUPIAN (MIDDLE PERMIAN SERIES) AMMONOID RESEARCH

Ammonoids from the Cherry Canyon and Bell Canyon formations (Guadalupian Series) at Sibley’s Last Chance Ranch have been important to ammonoid research for over a century. The ranch lies on basinal deposits roughly twenty miles from the Capitan Reef front. Ammonoid specimens are abundant on the ranch at numerous localities, and most assemblages are relatively diverse. The faunas have historically been used to help characterize the Wordian and Capitanian stages. At least ten species among eight genera are represented.

Sibley’s Last Chance Ranch includes the type localities of three ammonoid taxa: Newellites richardsoni, Roadoceras beedei, and Palermoceras fisheri. Newellites richardsoni is the genotype and sole formally recognized species of its genus, considered an advanced offshoot from Waagenoceras. The locus typicus has confusingly been cited in the literature as belonging to several different Wordian and Capitanian units, but we confirm that it is the Manzanita Member (Wordian Stage). Casey’s Hill at Sibley Ranch is the only known locality at which both western hemisphere species of Timorites, T. uddeni and T. schucherti, occur together. Palermoceras fisheri is known by only two specimens from a single locality at Sibley Ranch, which is the only occurrence of Palermoceras in the western hemisphere.

Recently, the authors described four previously undocumented ammonoid localities at Sibley Ranch. Two previously published localities were confirmed and updated with GPS technology, including the locus typicus of N. richardsoni. In addition, two other previously described but unpublished localities have been confirmed and multiple new localities have been documented. We present them here for the first time.