Permian ammonoids from the Guadalupian (Wordian–Capitanian) of Las Delicias, Coahuila state, Mexico: new biostratigraphical and paleobiogeographical insights

This work describes and discusses Permian ammonoid faunas collected in two stratigraphic sections from the Las Delicias Formation of Coahuila state, northern Mexico. The taxa identified comprise 18 species, including Demarezites quirozii new species, as well as Mexicoceras smithi (Miller and Furnish, 1940), a variety of Mexicoceras guadalupense (Girty, 1908) here upgraded to specific status. The systematic analysis of the species found allowed us to recognize two middle Permian faunal zones, represented in ascending order by the Waagenoceras dieneri - Adrianites elegans Biozone from the Wordian and the Timorites schucherti - Cibolites uddeni Biozone from the Capitanian. Thus, the relative age of the Las Difuntas-18 section is established as Wordian (middle Guadalupian), whereas the Las Manuelas I section is Wordian–Capitanian (middle–upper Guadalupian). Both ammonoid zones are correlated with those recorded in Guadalupian outcrops from the southern USA, northeastern Japan, and southern China. This faunal resemblance between Mexican ammonoids and those taxa reported in these regions (USA, Japan, and China) supports the proposal that during the middle Guadalupian there was a marine corridor through the Panthalassa Ocean, which could have connected the Paleotethys and North American regions. It should be noted that ammonoids of both studied sections from the Las Delicias Formation were correlated better with West Texas (USA) and British Columbia (Canada) faunas, which are included in the North American Realm. UUID: https://zoobank.org/60c6c43c-6536-4fbf-a372-c610bec86626