Acanthochaetetes huauclillensis nov. sp. (Porifera: Demospongiae) from the Lower Cretaceous of Oaxaca, Mexico, and its palaeoecological, palaeobiogeographic and stratigraphic implications

摘要

A new species of chaetetid demosponge, Acanthochaetetes huauclillensis nov. sp., is described from the Upper Hauterivian to Lower Barremian of Santiago Huauclilla, Oaxaca State, Southern Mexico. The presence of tylostyle spicule pseudomorphs allowed its assignment to the Demospongiae. Criteria which allowed the proposal of this new taxon were: the presence of a scalariform arrangement of tabulae in adjacente calicles, which is observable in longitudinal section and the dimensions of calicles and tabulae in cross and longitudinal sections. These two characters make Acanthochaetetes huauclillensis nov. sp. unique among Acanthochaetetidae.The finding of microbialites growing on top of specimens of Acanthochaetetes huauclillensis nov. sp, in addition to their association to rudist faunas and the lack of associated algae allow the determination of its palaeoecological settings as coming from a cryptic reef-like environment.Further assessements include the palaeogeographic implications of this finding, which extends the distribution of ancient Acanthochaetetidae to the Western Tethyan Realm. The westward broadening of the distribution area of this family would have thus allowed its diversification and thus the development of a new species, in addition to filling the hiatuses in occurrence between the Oxfordian (oldest record for Acanthochaetetidae) and the Lower Albian, when they started their major diversification.