Resolving Australian analogs for an Eocene Patagonian paleorainforest using leaf size and floristics

Abstract

Vein scaling is valuable for improving the resolution of fossil leaf-size distributions by including fragmented specimens. The legacy of LH is evident not only in subtropical and tropical Australia but also in tropical montane Australasia and Southeast Asia, reflecting the disparate histories of surviving Gondwanan lineages.

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

“…Both A. pichileufensis and A. huncoensis are on the small end of leaf size for living Sect. Eutacta (Fig A; consistent with Merkhofer et al., ). Araucaria pichileufensis has leaves similar in size to A. humboldtensis J. Buchholz , A. heterophylla (Salisb.)…”

The last Patagonian cycad,Austrozamiastockeyigen. et sp. nov., early Eocene of Laguna del Hunco, Chubut, Argentina

“…With Austrozamia, the Encephalarteae join many other taxa with significance to Gondwanan biogeography that make their last (or only) South American appearances at Laguna del Hunco or the early middle Eocene Río Pichileufú site. The living relatives of these associated taxa have defined the modern analog environments for Austrozamia stockeyi as relatively cool, everwet rainforests like those found in the subtropical Border Ranges of Australia, Southeast Asian tropical mountains, and elsewhere (Wilf et al 2009;Kooyman et al 2014;Merkhofer et al 2015).…”

“…Hill 1998;Heibloem 1999) that broadly fit recent paleoenvironmental interpretations of ancient Laguna del Hunco (Wilf et al 2009;Carvalho et al 2013). Both Lepidozamia species and several Macrozamia species inhabit Australian rainforest areas that Merkhofer et al (2015) identified as particularly rich in Laguna del Hunco "survivor" taxa. Remarkably, the fossil osmundaceous fern Todea amissa M. Carvalho associated with Austrozamia at Laguna del Hunco (Carvalho et al 2013), and extant Todea barbara (L.) T. Moore associates not only with Lepidozamia and Macrozamia in Australia (K.D.…”

“…However, it is now recognized as an assemblage of >200 species and morphotypes of early Eocene plant organs from ca. 6000 recently collected specimens, dominated by angiosperms but also including ferns and gymnosperms (Wilf et al 2005;Carvalho et al 2013;Merkhofer et al 2015). The gymnosperm flora, which we contribute to here, primarily represents living Old World rainforest taxa that are also known as fossils elsewhere in Gondwana, especially southeastern Australia (e.g., Hill and Brodribb 1999 (Wilf et al 2005(Wilf et al , 2009Wilf 2012).…”

“…The assemblage represents the early Eocene climatic optimum, the terminal phase of Gondwana, and the western end of an extinct, trans-Antarctic rainforest biome; thus, the Laguna del Hunco flora is uniquely relevant to studies of Gondwanan paleobiogeography and evolutionary timing, among many other topics (Romero 1978;Wilf et al 2013;Kooyman et al 2014;Merkhofer et al 2015;Wilf and Escapa 2015 Knight and Wilf 2013); and the eudicots Akania (Akaniaceae), Eucalyptus (Myrtaceae), and Gymnostoma (Casuarinaceae; Romero and Hickey 1976;Gandolfo et al 1988Gandolfo et al , 2011Zamaloa et al 2006;Hermsen et al 2012).…”