Bennettitales from the Middle Jurassic of northwestern Oaxaca, Mexico: Diversity, sedimentary environments, and phytogeography

The Jurassic flora of Mexico represents a key element for the knowledge of the paleoflora on the western margin of equatorial Pangea because of its abundance and diversity. Bennettitales were the dominant group and are represented by leaves and reproductive organs in Jurassic outcrops from southern Mexico. This group has been historically recorded in seven lithostratigraphic units in southern Mexico in a range from the Toarcian to the Callovian. These reports have focused on morphological and taxonomical aspects for the obtention of paleofloristic listings by locality but do not provide environmental data or have any impact on biostratigraphic or phytogeographic analyses. The highest number of localities in Mexico has been reported in the state of Oaxaca, where plant fossils are more abundant and better preserved in comparison with localities of Guerrero, Puebla, Veracruz, and Hidalgo states. Therefore, in order to reinforce the paleofloristic knowledge of southern Mexico, the present study documents the diversity of Bennettitales in northwestern Oaxaca region, which is composed of 11 fossil-genera and 41 fossil-taxa, included 30 valid species and 11 species that need taxonomic revision. We provide the description of a new species, Williamsonia sanjuanensis sp. nov., new findings of Williamsonia nathorstii, and the first record of Bennetticarpus for southern Mexico. We also describe fossiliferous outcrops of the Zorrillo and Zorrillo/Taberna undifferentiated formations and propose their sedimentary environments. In addition, we provide a proposal of one biozone based on Bennettitales. Finally, we recognize six spatio-temporal distribution patterns for this plant group in northwestern Oaxaca. These new data add to a growing set of information on the Jurassic flora of Mexico and allow to substantiate the paleobotanic importance of southern Mexico within the region of North America.