New Permian ammonoid localities at Sibley's Last Chance Ranch, Delaware Mountains, Culberson County, Texas




Allen, Matthew L.

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Four previously undocumented ammonoid localities at Sibley Ranch in the Delaware Mountains of Culberson County, Texas, are introduced in this study. Two previously known localities at the ranch are herein described in greater detail than in previous studies. A combined 280 specimens were studied in detail from all but one locality. The locus typicus of Newellites richardsoni is confirmed.

Several new quantitative methods are introduced for sutural analysis of Cyclolobidae. These methods show potential for a more specific taxonomy of Cyclolobidae at the species level. Morphometric methods proposed by Korn (2010) for Mississippian ammonoids are applied to Middle Permian forms for the first time, and statistical analyses were conducted to distinguish taxa. Results suggest that these methods will allow for a significant improvement of accuracy in the taxonomy of Permian ammonoids.

The Sibley Ranch ammonoid fauna is characteristic of the Wordian and Capitanian stages (Guadalupian Series). The assemblage includes representatives of Mexicoceras guadalupense, Altudoceras altudense, Newellites richardsoni, Paraceltites elegans, Roadoceras beedei, Timorites schucherti, Timorites uddeni, Roadoceras roadense, Cibolites uddeni, and Eumedlicottia burckhardti, as well as congeners of some of these taxa which were unable to be classified to the species level.


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Ammonoid, Delaware Basin, Delaware Mountains, Guadalupe Mountains, Guadalupian, Permian