Eocene Fagaceae from Patagonia and Gondwanan legacy in Asian rainforests

Abstract

The beech-oak family Fagaceae dominates forests from the northern temperate zone to tropical Asia and Malesia, where it reaches its southern limit. We report early Eocene infructescences of Castanopsis, a diverse and abundant fagaceous genus of Southeast Asia, and co-occurring leaves from the 52-million-year-old Laguna del Hunco flora of southern Argentina. The fossil assemblage notably includes many plant taxa that associate with Castanopsis today. The discovery reveals novel Gondwanan history in Fagaceae and the characteristic tree communities of Southeast Asian lower-montane rainforests. The living diaspora associations persisted through Cenozoic climate change and plate movements as the constituent lineages tracked post-Gondwanan mesic biomes over thousands of kilometers, underscoring their current vulnerability to rapid climate change and habitat loss.

Eocene “Chusquea” fossil from Patagonia is a conifer, not a bamboo

“…However, there was no general stratigraphic section and correlation of the lake beds available in the early 1940s, and Frenguelli and Parodi (1941) more likely were referring to a relative position within a local exposure rather than the full stratigraphic sequence as later understood (Petersen 1946;Aragón and Mazzoni 1997;Wilf et al 2003). The lithology and preservation of the holotype closely resemble fossils from the horizon of what is now quarry LH4 (see Wilf et al 2003 for coordinates), which appears to have been the site of most early collections (see Wilf et al 2019). Quarry LH4 is well exposed at a comparatively accessible location, low on a local hill slope, where the underlying basal strata of the lake beds (subsection E of Wilf et al 2003) are mostly lost to a local unconformity; thus, LH4 could have appeared to be near the base of the lake beds.…”

“…The deletion of a living New World genus (Chusquea) from the overall floral list for Eocene Patagonia further weakens the New World biogeographic signal of the late-Gondwanan vegetation of South America (see Introduction), which is currently understood to have much stronger links to the tropical West Pacific as discussed extensively elsewhere (e.g., Wilf et al 2009Wilf et al , 2014Wilf et al , 2019Gandolfo et al 2011). Interestingly, when considering the full suite of specimens (Wilf et al 2017b), Retrophyllum oxyphyllum preserves morphological evidence for affinity to both Old and New World living species of Retrophyllum.…”

“…In contrast, several putative New World elements from Laguna del Hunco have been revised recently to taxa whose living members primarily inhabit the Asia-Pacific region via Gondwanan connections (e.g., Austrocedrus-Libocedrus to Papuacedrus, Fitzroya to Dacrycarpus, Zamia to Agathis; Wilf et al 2009Wilf et al , 2014Wilf 2012). Moreover, numerous additional taxa have been described from the site that also have Asia-Pacific extant distributions (e.g., Romero and Hickey 1976;Zamaloa et al 2006;Gandolfo et al 2011;Carpenter et al 2014;Gandolfo and Hermsen 2017;Andruchow-Colombo et al 2019;Wilf et al 2019). Also, monocots in the Laguna del Hunco flora are scarce in general, otherwise represented by a few leaves of Ripogonum (Ripogonaceae; Carpenter et al 2014) and rare, undescribed palm fruits and leaf fragments (Wilf et al 2005).…”

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

“…Eutacta fits biogeographically with the documented fossil assemblages from the Laguna del Hunco and Río Pichileufú floras; many of the fossil genera present have nearest living relatives in present‐day subtropical and tropical montane rainforests of Australasia and southeast Asia (Appendix S1). New Guinea montane forests are one of the closest modern analogs for Laguna del Hunco and Río Pichileufú, with a large number of shared genera (Wilf et al., ) including living Araucaria (with one species in Sect. Eutacta ), Agathis , Dacrycarpus , Papuacedrus , Castanopsis , Eucalyptus , Gymnostoma , and several other taxa from one or both of the two Eocene Patagonian floras considered here (Brass, ; Soepadmo, ; Johns, ; Enright, ; Takeuchi, ; Ladiges et al., ).…”

“…The Río Pichileufú flora (Berry, ; Wilf et al., ) represents a period of initial climatic cooling and drying following the EECO, as known from regional and global records (Pearson et al., ; Hollis et al., ; Bijl et al., ; Dunn et al., ), from a time when the earliest separation of South America and Antarctica was underway (e.g., Lawver et al., ). Comparison of the well‐studied elements of the Laguna del Hunco and Río Pichileufú floras (Appendix S1), yields evidence of turnover in the angiosperms, cycads, and ferns, suggesting some extinction and a shift in the paleoenvironment (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.…”