Weltrichia magna sp. nov., a new record for the Middle Jurassic of Oaxaca, México

Abstract

The Jurassic locality San Juan Mixtepec (Zorrillo Formation in the state of Oaxaca) contains fossil plants of the order Bennettitales, mainly of the genus Zamites, as well as reproductive structures of the genera Williamsonia, Williamsoniella and Weltrichia, but male reproductive structures of the latter genus are scarce and almost restricted to the south of Mexico; they have also been reported in the Triassic of the north of Mexico. Here we report a new record for this locality and a new species of male reproductive structure of the genus Weltrichia. We recovered half of an adpression in fine-grained sandstone with the positive and negative of the adaxial part of the male reproductive structure, which when open measures 22.6 cm in diameter. A reconstruction suggests the presence of ten centrifugal rays that become thinner towards the acute apex and are fused in a central basal cup. The structure exhibits complete centrifugal rays with basal structures that are interpreted as insertion sites for pollen sacs. We employed acetate peel, mechanical separation and hydrofluoric acid (HF) maceration techniques for extraction of anatomical samples. We compared 13 morphological and 10 anatomical characters with previous records from localities in México, Europe, Asia and other parts of the world. We observed epidermal cells and syndetocheilic stomatal apparatuses, which corroborate an epidermal affinity to the Bennettitales. This new record would be the largest male reproductive structure found in the region thus far, and increases the distribution of Weltrichia in the Jurassic of Oaxaca.