THE FIRST NEW GENERA OF INVERTEBRATES IDENTIFIED FROM THE FAMOUS VERTEBRATE LOCALITY OF RICHARDS SPUR, OKLAHOMA: MILLIPEDS (DIPLOPODA) WITH AFFINITIES TO CARBONIFEROUS FORMS

We have identified three new genera of Early Permian helminthomorph millipeds from the Fort Sill Fissures located near Richards Spur in southwest Oklahoma. Although millipeds as well as arthropod fragments have been previously reported from the fissures, these are the first new genera (and species) of invertebrates to be identified from this site, one of the most prolific Lower Permian upland terrestrial fossil-vertebrate sites in North America. This small fauna is also one of the most diverse of the very few Permian milliped faunas described to date. The millipeds from Richards Spur are related, at higher taxonomic levels, to Carboniferous forms. The Richards Spur fauna includes a new genus with prominent paranota. This milliped has some characters in common with the Carboniferous Hexecontasoma, a rare form described from Mazon Creek, Illinois. Another milliped with oblique pleurotergal grooves, ozopores, and a distinct medial line, can be classified in the extinct superfamily Xyloiuloidea, which is represented in the Carboniferous and Permian by several described species and genera, notably Xyloiulus. The third new form, a juliform milliped with a simple pleurotergite marked with subtle ornamentation, may be related to the unornamented species “Xyloiulus” platti, a rare form found in the Carboniferous of Great Britain (but which is not a xyloiulid). The pleurotergites of the new form, however, have an anteriorly bifurcating ridge located near their lateral edge that distinguish it from “Xyloiulus” platti. Notably absent in the fauna here, as well as in at least most other Permian milliped faunas, are the archipolypodans, which are common in the Carboniferous.

Although the forms described here are distinct, the interpretation of the overall Euroamerican milliped fauna of the Permian is hampered by inadequate illustrations and descriptions of type material of Carboniferous and Permian millipeds, especially species assigned to Xyloiulus and Archiulus, extending back to the descriptions of Dawson, Scudder, and Fritsch. The occurrence of millipeds with vertebrates at Richards Spur is not unique as co-occurrences of millipeds and vertebrates have been reported from the Carbonifeous of Nova Scotia and the the Triassic of South Africa.