Organic-walled microfossils of possible dinoflagellate affinity from the Lower Permian of Sonora (northwest Mexico)

Shallow-water carbonates from the Lower Permian of Sonora, northwest Mexico , have yielded small organic-walled microfossils that show several features characteristic of dinoflagellates. The oldest unequivocal dinoflagellate f ossils, however, presently known come from the Middle Triassic. Earlier rep orts of microfossils with possible dinoflagellate affinity from the Paleozo ic and Neoproterozoic, together with dinoflagellate-specific biomarkers fou nd in Early Cambrian rocks and molecular phylogenetic analyses, suggest the presence of an intermediate stage of evolution, or protodinoflagellate gro up in pre-Mesozoic times. (C) 2000 Elsevier Science B.V. All rights reserve d.