Weltrichia xochitetlii sp. nov. (Bennettitales) from the Middle Jurassic of northwestern oaxaca, Mexico: First paleobotanical evidence from the Tecomazúchil Formation

Abstract

The Jurassic flora of southern Mexico represents a key phytogeographic element in North America, where vegetative organs (leaves) of Bennettitales are the most abundant and best preserved. In this region, valid species of reproductive organs of the genus Weltrichia (Williamsoniaceae) have only been recorded in Mexico. These are three species from the Jurassic in northwestern Oaxaca and are restricted to the Ayuquila Formation (Bajocian/Bathonian). Here we present Weltrichia xochitelii, a new fossil-species discovered in the Tecomazúchil Formation (Callovian). This new species is established based on diagnostic characters that differ from other species, such as the external outline diameter of the organ, the basal cup diameter, the number of centrifugal rays, and the shape, position, and size of the pollen sacs. Weltrichia xochitetlii and W. microdigitata comprise the group of smallest reproductive organs of the family Williamsoniaceae (Bennettitales) worldwide. We also provide a stratigraphic and sedimentary description of the first fossiliferous locality of the Tecomazúchil Formation, a comment on its paleobotanical content, and a comparison with records from other localities in southern Mexico. The Ayuquila and Tecomazúchil formations were deposited in the Ayuquila BBasin. This new record broadens the stratigraphic range of Weltrichia up to the Callovian in northwestern Oaxaca. In addition, it increases the number of species of this fossil-taxon in the region, which corresponds to the highest richness in North America from the Jurassic.