Cycadean diversity in the Cretaceous of Patagonia, Argentina. Three new Androstrobus species from the Baqueró Group

Abstract

Three new species of the cycadean pollen cone Androstrobus, viz. A. munku, A. patagonicus, and A. rayen, are described. All specimens are represented by microsprophylls or fragmentary cone pieces, and they have been found in the same fossil bed at the locality Bajo Grande, in Santa Cruz province, Argentina, which is referred to the Anfiteatro de Ticó Formation of Aptian age. This is the first record of the genus in Argentina and South America. The good preservation of the material allowed the study of cuticles and pollen with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is noted that Androstrobus is a poorly defined genus that needs a revision of the type material as well as new specimens from the type locality to certify the presence of pollen. Comparisons with other Androstrobus species are made, especially with those that have been described with cuticular characters and structure of pollen. Attention is paid to the similarity of the alveolate pollen ultrastructure of the Patagonian fossils with some extant cycads, especially with genera of the Zamiaceae and Cycadaceae. The variety of pollen cones found in the same bed agrees with the presence of different vegetative organs, leaves, and fronds found previously at the same place, and that were referred to the cycads on the base of their cuticular structure. The abundance of cycads during the mid-Cretaceous in southern Argentina is a contrasting evidence with the present-day absence of the group in southern South America.