New whole plant reconstructions from Patagonia shed light on the biology, phylogeny, and biogeography of the conifer family Cheirolepidiaceae.

ESCAPA, IGNACIO; LESLIE, ANDREW

Fort Worth

Congreso; Botany 2017; 2017

Cheirolepidiaceae is an extinct conifer family known from the Late Triassic through the Late Cretaceous/Early Paleogene. Members of this family have distinctive reproductive morphology that includes characteristic pollen grains (Classopollis) and complex seed cones with seeds that are covered by ovuliferous scale tissue. From a phylogenetic standpoint, the unique character combination show in Cheirolepidiaceae may help to bridge some of the long morphological gaps that exist among crown group conifer clades. Here we focus on new specimens of Pararaucaria, a Jurassic cheirolepidiaceous conifer. Following the re-interpretation of this genus as a member of Cheirolepidiaceae, permineralized seed cones from Patagonia, the United Kingdom, and the United States revealed the wide biogeographic extent of the genus. New Jurassic localities from the Argentinean provinces of Santa Cruz and Chubut preserve compressions and impressions that allow us for the first time to link Pararaucaria seed cones with leaves, branches, wood, and pollen cones. These new specimens, collected from Early, Middle, and Late Jurassic sequences, nearly complete a whole-plant concept for Pararaucaria, which allows for more detailed comparisons to well-known cheirolepidiaceous remains from the Cretaceous of Euramerica. Adding impressions and compressions to the record of Paraucaria also allows for a better understanding of its geographic distribution during the Mesozoic, deeper analyses of different features with paleobiological implications (e.g., stomata structure), and more precise and solid homology discussions on its vegetative and reproductive remains. Altogether, the newly discovered Jurassic record of Cheirolepidiaceae in Patagonia represent an unique opportunity to shed light on the evolution of the family, and its role in the early evolution of modern conifer families.