Eocene Plant Diversity at Laguna del Hunco and Río Pichileufú, Patagonia, Argentina

Abstract

The origins of South America's exceptional plant diversity are poorly known from the fossil record. We report on unbiased quantitative collections of fossil floras from Laguna del Hunco (LH) and Río Pichileufú (RP) in Patagonia, Argentina. These sites represent a frost-free humid biome in South American middle latitudes of the globally warm Eocene. At LH, from 4,303 identified specimens, we recognize 186 species of plant organs and 152 species of leaves. Adjusted for sample size, the LH flora is more diverse than comparable Eocene floras known from other continents. The RP flora shares several taxa with LH and appears to be as rich, although sampling is preliminary. The two floras were previously considered coeval. However, (40)Ar/(39)Ar dating of three ash-fall tuff beds in close stratigraphic association with the RP flora indicates an age of 47.46+/-0.05 Ma, 4.5 million years younger than LH, for which one tuff is reanalyzed here as 51.91+/-0.22 Ma. Thus, diverse floral associations in Patagonia evolved by the Eocene, possibly in response to global warming, and were persistent and areally extensive. This suggests extraordinary richness at low latitudes via the latitudinal diversity gradient, corroborated by published palynological data from the Eocene of Colombia.

No post-Cretaceous ecosystem depression in European forests? Rich insect-feeding damage on diverse middle Palaeocene plants, Menat, France

“…To underscore this point, we note that the richest Palaeocene or Eocene lacustrine leaf flora known from the USA is the early Eocene Republic flora from Washington State (Wolfe & Wehr 1987;Pigg et al 2007). When sampled using very similar collecting methods, Republic yielded a much lower total of 58 dicot-leaf species from approximately 1000 specimens, equivalent to 51.6 + 4.3 species when rarefied to the sample size of Menat (Wilf et al 2005).…”

Richness of plant–insect associations in Eocene Patagonia: A legacy for South American biodiversity

“…These sediments were deposited 52 million years ago (35,36), during the early Eocene global climatic optimum (37). At this time, thermophilic organisms reached middle and high latitudes of both hemispheres (38-42), and the LH flora contains a large proportion of tropical as well as temperate lineages (34)(35)(36)39). Our unbiased macrofloral sample, in which all material was collected or tallied, totals 6,521 specimens from 25 quarries, of which 4,303 specimens (66%) are identifiable to 186 species of plant organs.…”

“…Adjusted for sample size by using rarefaction, the LH flora is more speciose than comparable Eocene assemblages known from other continents (35,36). Relatively rare fossil insects are also preserved, including several phytophagous taxa (43).…”

“…All voucher specimens from LH are deposited at the Museo Paleontológico Egidio Feruglio, as described in ref. 36.…”

Phylogeny and Character Evolution in the New Zealand Endemic Genus Plagianthus (Malveae, Malvaceae)

“…We placed an exponential prior distribution of 3 with a zero offset of 44.7 million years ago (Ma) with a probability distribution that tails off to 60 Ma for the most recent common ancestor (mrca) of Lawrencia spicata and Hoheria angustifolia. In our analyses this prior corresponds to the Eocene appearance of fossils attributed to the Malveae in Australia, New Zealand, and South America ( Mildenhall 1980 ;Pocknall 1982 ;Zamaloa and Romero 1990 ;Barreda 1993 ;Macphail 1997 ;Dettmann and Clifford 2000 ;Mautino et al 2004 ;Wilf et al 2005 ;Barreda et al 2007 ;Iglesias et al 2007 ). A second prior, with a log-normal distribution of 13.5 Ma with 95% confidence intervals of 12.4-14.6, was placed on the node separating the western Australian endemic Lawrencia helmsii from L. squamata, which is widely distributed across southern Australia.…”