Gastropods from the Paso Hondo Formation (lower-middle Permian) of Chiapas, Mexico: Stratigraphical and paleobiogeographical considerations

The specimens herein studied were recollected in strata from the Paso Hondo Formation (lower-middle Permian), which are outcropping in the Chicomuselo region, southeast of Chiapas state, limiting with the frontier of Guatemala. The material studied consists of 13 species: four determined to a specific level (Bellerophon deflectus, Discotropis sulcifer, Omphalotrochus cochisensis, and Donaldospira geminocarinata), five conferred to other species (Warthia cf. W. welleri, Warthia cf. W. waageni, Euomphalus cf. E. kaibabensis, Worthenia cf. W. crenulata, and Glabrocingulum cf. G. coronatum), three described to genus level (Glyptospira sp., Naticopsis sp., and Stephanozyga sp.), and one assigned, doubtfully, to the genus Pharkidonotus. This community constitutes the most diverse gastropod fauna from the Permian of Chiapas known to date. Although the material is scarce and poorly preserved, the association allowed relating the age of the bearing rocks to the Kungurian-Roadian (late Cisuralianearly Guadalupian), coinciding with previous data obtained employing other invertebrates and fusulinids. Moreover, the taxa described can be associated with coeval marine faunas from the southern United States (Texas, New Mexico, and Arizona), which are recognized as geographical regions where the Grandian Province's biota was established. This information suggests that, during the early-middle Permian, those territories were connected with Chiapas through epicontinental seas formed in the equatorial region.