The fossil flip‐leaves (Retrophyllum, Podocarpaceae) of southern South America

Abstract

Retrophyllum is considerably older than previously thought and is a survivor of the end-Cretaceous extinction. Much of the characteristic foliar variation and pollen-cone morphology of the genus evolved by the early Eocene. The mixed biogeographic signal of R. spiralifolium supports vicariance and represents a rare Neotropical connection for terminal-Gondwanan Patagonia, which is predominantly linked to extant Australasian floras due to South American extinctions. The leaf morphology of the fossils suggests significant drought vulnerability as in living Retrophyllum, indicating humid paleoenvironments.

EoceneAraucariaSect.Eutactafrom Patagonia and floristic turnover during the initial isolation of South America

“…Conifer taxa previously described from the Eocene fossil caldera‐lake deposits of Laguna del Hunco (~52.2 Ma), Chubut, Argentina, and Río Pichileufú (~47.7 Ma), Río Negro, Argentina (Fig. ; Berry, ; Wilf et al., , ; Wilf, ; Wilf et al., 2017a, b), illustrate a complex biogeographic history of Old World (mostly Australasian/SE Asian) and New World survival patterns following the early Cenozoic isolation of Antarctica and onset of global cooling (Zachos et al., ; Lauretano et al., ).…”

“…All images of fossil and herbarium specimens were annotated and organized using a common set of keywords in Adobe Bridge CC (version 9.0.1.216, Adobe Inc., San Jose, California, USA) to expedite comparison of a unified set of morphological characters in a large sample (after Wilf et al., ). Full‐resolution images of fossil specimens are deposited open‐access at FigShare (see Data Availability below).…”

“…), including the discoveries reported here of previously undescribed pollen cones, one of these attached to a leafy branch; in situ fossil pollen; and, rarely, in situ leaf cuticle, greatly increasing the number of characters that can be used to diagnose the fossils. Notably, fossil Araucaria from Laguna del Hunco, which has not been formally studied until now, has also been thought to represent A. pichileufensis in the absence of any previously observed differences from the Río Pichileufú material (Wilf et al., , ). The abundant Laguna del Hunco Araucaria material also includes preservation of leafy branches, OCs, and pollen cones (Wilf et al., , ).…”

“…However, until now there has been no detection of a significant change in species composition of the prevalent conifers between the two localities, and abundant Araucaria fossils at both sites are considered to have affinities with Araucaria Sect. Eutacta (e.g., Wilf et al, ) but have not been formally investigated since the 1940s (Berry, ; Florin, ).…”

“…Eutacta . Modern excavations at Río Pichileufú (Wilf et al., , ) have significantly increased the sampling of A. pichileufensis (fossil material shown in Figs. ), including the discoveries reported here of previously undescribed pollen cones, one of these attached to a leafy branch; in situ fossil pollen; and, rarely, in situ leaf cuticle, greatly increasing the number of characters that can be used to diagnose the fossils.…”