Abstract Detail

Fossil plants at the intersection of evo-devo and phylogeny: celebrating the contributions of Gar W. Rothwell to biodiversity and evolution

Wilf, Peter [1].

The First Gondwanan Fagaceae: Early Eocene Castaneoids from Patagonia and the Paleo-Antarctic Component of Southeast Asian Tropical Rainforests.

The beech family (Fagaceae s.s.), with eight genera and over 900 species, is one of the most ecologically and economically important plant groups in the world. The known extant and fossil distributions of the family have been confined to the Northern Hemisphere and the tropics. In montane, aseasonal areas of SE Asia, the diverse castaneoid genera Castanopsis and Lithocarpus often form co-dominant associations with several conifer taxa that have well-known Gondwanan origins. Based on the fossil record, these living associations were classically considered as a mix of Laurasian and Gondwanan elements (castaneoids and conifers, respectively). Here, I report the first Gondwanan Fagaceae s.s., early Eocene (52.2 Ma) castaneoid fossils from Laguna del Hunco in Patagonian Argentina. Notably, this site has produced rare South American fossil records of several genera whose extant ranges include SE Asian rainforests and associations with castaneoids, such as Agathis (Araucariaceae); Dacrycarpus, Phyllocladus, and Podocarpus (Podocarpaceae); and Gymnostoma (Casuarinaceae). The new castaneoid fossils include ca. 90 leaves, a spike-like infructescence bearing dozens of immature solitary fruits, and an axis with four maturing solitary fruits. The leaves have several fagaceous features, including long petioles with expanded bases; bristle-tipped, regular teeth each associated with a single craspedodromous secondary vein; and fine, closely spaced, strongly percurrent tertiary veins. The immature fruits show early stages of cupule and scale development and bear three styles with punctiform stigmas as in Castanopsis and Lithocarpus. The maturing fruits have asymmetrical, two-cuspidate-valved cupules that fully enclose a single nut, a characteristic combination today for Castanopsis. However, the cupule ornamentation of helically arranged, imbricate, symmetrical scales without spines or tubercles is more similar to Lithocarpus. The cumulative evidence indicates the presence of castaneoid Fagaceae in Eocene Patagonia with close affinity to Castanopsis (Asia and New Guinea, ca. 140 living species). Thus, the castaneoid Fagaceae had a previously unknown Gondwanan history. Castaneoids have associated with the same conifer and other taxa for tens of millions of years, apparently tracking mesic rainforest environments together in response to climate change and plate movements over thousands of kilometers. Other fossil occurrences of castaneoids, all from the Northern Hemisphere, do not include any of the same characteristic associations. Thus, today’s SE Asian rainforests co-dominated by castaneoids and “southern” conifers appear to indicate considerably more Gondwanan historical connections than previously thought, and this surviving floral association from the paleo-Antarctic represents a significant piece of SE Asian tropical biomass and biodiversity.

Related Links:
Patagonia Paleofloras Project on Google Scholar

1 - Pennsylvania State University, Geosciences, 537 Deike Bldg., University Park, PA, 16802, United States

Asian rainforests

Presentation Type: Colloquium Presentations
Abstract ID:236
Candidate for Awards:None

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