Lower Cretaceous marine isopods (Isopoda: Cirolanidae, Sphaeromatidae) from the San Juan Raya and Tlayúa formations, Puebla, Mexico

Abstract

The fossil record of marine isopods is rather scarce and specimens are frequently incomplete. Our research for the paleobiota of the San Juan Raya Formation led to the finding of three species of marine isopods whose age, based on nannoplankton biostratigraphy, is interpreted as early Cretaceous (Valanginian-Hauterivian) at a new fossiliferous locality, Barranca El Gavilán (Puebla, Mexico). Most of the specimens are posterior molts and a few others seem to be incomplete bodies. Some of the isopods were found associated with juvenile stages of a mecochirid lobster. One unidentified species of cirolanid is reported and a new species of NatatolanaBruce, 1981 (Cirolanidae, Cymothoidea) is described, the first fossil cirolanid attributed to that genus. The oldest record of the fossil sphaeromatid Archaeoniscus H. Milne Edwards, 1843 in the Americas is documented, and specimens are compared with type and new material of A. aranguthyorumFeldmann, Vega, Applegate & Bishop, 1998 from the upper Albian Tlayúa Formation of Tepexi de Rodríguez, Puebla. One sphaeromatid specimen from the Tlayúa Formation is illustrated and compared to similar, undescribed specimens from the upper Albian Sierra Madre Formation in Chiapas, Mexico