Paleocene Patagonian floras: in situ cuticles complement architectural data from leaf compressions of Podocarpaceae, Lauraceae, and Nothofagaceae

ARI IGLESIAS; WILF PETER; GANDOLFO M. ALEJANDRA; STEFAN LITTLE

Vancouver, Canada

Congreso; Botanic Society of America annual meeting; 2008

Botanic Society of America

To test and refine identifications based previously on leaf architectural characters, we areinvestigating cuticle remains found in situ on compressed leaves from four lower andmiddle Paleocene taphofloras from Patagonia, Argentina. This approach allows us tobetter estimate species diversity from morphotypes that could not be split usingmacroscopic architecture alone. Selected, abundant leaf morphotypes with well preservedcuticle were studied with epifluorescence, transmitted light, and scanning electronmicroscopy. Comparisons to extant and fossil cuticles validated assignments to thefamilies Podocarpaceae, Lauraceae, and Nothofagaceae. Cuticle of a morphotypearchitecturally similar to Akania, did not match extant Akania cuticles.A broad-and subopposite-leaved conifer with multiple parallel venation and no midvein(“Zamia” tertiaria Engelhardt 1891), has cuticle characters diagnostic of Podocarpaceae,allowing us to reject architecturally identical Agathis. The “Z.” tertiaria morphotyperanges from the Maastrichtian through the middle Eocene in Patagonia. Lauraceaecuticles are recognized from stomatal characters (guard cells embedded in the subsidiarycells) and presence of simple hairs. Variation in cuticle features allows more species to berecognized than predicted from leaf architecture alone, showing that Lauraceae was adiversified group during the Paleocene in Patagonia. Nothofagus is recognized based onconsistent leaf architecture and cuticular features of Berry’s 1937 “Dryophyllum”australis. This is the oldest cuticle and macrofossil record of the genus for SouthAmerica, corroborating poorly dated pollen records and providing a well-calibratedbiogeographic datum for this important Southern group. The recognition of broad-leavedPodocarpaceae, large Nothofagus leaves, and diverse and dominant Lauraceae supports ahumid, frost-free biome for these Patagonian paleofloras, as indicated by leaf margin andleaf area analyses and other proxies.