New records of Bennettitales and associated flora from the Jurassic of the Cualac Formation, Mexico

Abstract

The present work contributes to the palaeofloristic knowledge of the Jurassic in the Cualac Formation of Mexico with the first records of the genera Anomozamites, Cycadolepis, Czekanowskia, Mexiglossa, and Williamsoniella. A new species of bisexual structure, Williamsonia rosarensis, is described; the species Zamites diquiyui is emended and the cuticular characters of the dominant species Mexiglossa varia are described for the first time. These data substantially increase the plant diversity of this stratigraphic unit and provide information about the environment in which they were preserved. These new reports come from a new locality of the Cualac Formation, in the state of Oaxaca, Mexico, called Rosario. After considering some sedimentological and taphonomic aspects, it is proposed that this locality represented an alluvial fan depositional environment that evolved into a flood plain, which favored the state of preservation of the specimens, and even preserved cuticular characters that allows an updated and more detailed taxonomy of three species. A notable find is Williamsoniella rosarensis nov. sp., a genus which has been previously reported from two Middle Jurassic localities in the UK and one in Mexico. A possible organic connection between this structure and leaves of Zamites diquiyui is also proposed. The findings mentioned above indicate that Bennettitales is the most abundant order (61.4%) with eight genera and 15 species. The present contribution confirms that paleofloristic lists are still incomplete, and thus it is necessary to continue the work in the Jurassic formations described for Mexico.