Southern Hemisphere Caytoniales: vegetative and reproductive remains from the Lonco Trapial Formation (Lower Jurassic), Patagonia

Abstract

Macrofossil impressions of caytonialean leaves and micro- and megasporangiate organs from the Early Jurassic Taquetrén locality in Patagonia, Argentina, are described based on more than 300 hand specimens. Leaves of the organ-genus Sagenopteris are described using both discrete and continuous features allowing us to erect the species Sagenopteris trapialensis sp. nov. Associated microsporangiate organs of Caytonanthus type are the first recorded for South America and are characterized by a unique combination of architecture, size and type of dehiscence. Two specimens, one resembling an isolated Caytonia cupule, and the other a Caytonia axis, are also described. The availability of a collection with numerous specimens has proven to be an important tool in order to fully understand the intraspecific morphological plasticity of the studied species. The striking morphological resemblance of both vegetative and reproductive organ-genera with their Northern Hemisphere counterparts suggests that they were part of the same lineage, which was widely distributed during the Jurassic. Well-defined whole-plant concepts are still needed to advance the goal of deciphering the internal relationships of caytonialeans in particular, and their relationships with other groups of seed-plants in general, and thorough macro-morphological characterization of the organs that compose them, as we present here, may be of valuable use in achieving it.

Keywords:

• Caytoniales
• Jurassic
• Caytonia
• Sagenopteris
• Patagonia

Acknowledgements

We are grateful to Heidi M. Anderson and one anonymous reviewer whose comments and suggestions helped to improve the manuscript. We would like to thank Juan Shanahan for his hospitality during several field seasons. We also thank Ana Andruchow Colombo, Luis Miguel Sender, Cristina Nunes, Ariel Aresti, Ian Davie, Leandro Canesa, Roberto Scasso and Pablo Puerta for their assistance during several seasons of fieldwork. Special thanks to Mariano Caffa and Laura Reiner for mechanical preparation of the fossils, Eduardo ‘Dudu’ Ruigomez for the curation of the specimens and Ana Andruchow Colombo for help and valuable suggestions. We are also grateful to Ove Johansson and Anna Lindström of the Naturhistoriska riksmuseet, who kindly provided us with photographs of the type specimen of Sagenopteris nilssoniana (S087455) and other specimens from Höör. Financial support to NRC has been provided by Agencia Nacional de Promoción Científica y Tecnológica [PICT 2012-1520]. We also thank the Fundación Egidio Feruglio for additional funding.