A new rhynchonellid fauna (Brachiopoda) from the Wordian (middle Permian) of Coahuila, Mexico: Stratigraphy and paleoenvironments

Seven brachiopod species of the order Rhynchonellida of a new locality (Las Margaritas I section) from the Las Delicias Formation in Coahuila, Mexico are described. The fauna includes four taxa identified as Bryorhynchus bisulcatum, Leiorhynchioidea schucherti, Leiorhynchoidea amygdaloidea, and Paranorella imperialis, as well as three species assigned with open nomenclature: Leiorhynchioidea cf. scelesta, Stenoscisma sp., and Rhynchopora sp. The brachiopod fauna identified, together with the record of different middle Permian ammonoids allowed us to establish a Wordian (middle Guadalupian) age for the Las Margaritas I section. The assignment of this relative age enabled restricting the stratigraphic range of Leiorhynchioidea schucherti and Paranorella imperialis to the middle Guadalupian since previously had only been related inaccurately to the middle Permian. The record of the species Bryorhynchus bisulcatum, Leiorhynchioidea cf. scelesta, and Leiorhynchoidea amygdaloidea, as well as the genus Stenoscisma is the first in Mexico. The preservation of specimens, lithological features, and associated fauna suggest that rhynchonellid brachiopods were deposited in different platform facies: shallow lagoonal or offshore, characterized by low to medium energy, stenohaline conditions, and continuous terrigenous input.