Original paper

Middle Pennsylvanian bryozoans of Cerros de Tule, Sonora, Mexico

Ernst, Andrej; Vachard, Daniel

Abstract

A rich bryozoan assemblage of Cerros de Tule contains 10 species including two cystopo rates, one trepostome, two rhabdomesine cryptostomes and five fenestrates. The age of this assemblage was determined on the basis of associated fusulinds Beedeina as late middle Desmoinesian (probable equivalent of the Podolskian substage of the Moscovian stage). Two species are new: Fabifenestella almazani sp. nov. and Acupipora mexicana sp. nov. The assemblage displays a mixed taxonomic com- position containing North American and Russian taxa. Two species are encrusting and eight species develop arborescent colonies. Ecologically, the fauna corresponds to a heterozoan community indicat- ing decreased water energy, low sedimentation rate and presence of stable hard to soft substrates. The presence of this heterozoan fauna implies a period of cooling which could be explained by climate change, glacio-eustatic sea-level variations, deepening of the basin, or upwelling.

Keywords

palaeobiogeographystratigraphybryozoataxonomypennsylvanian