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Fagaceae fossil of Patagonia
The Fagaceae oak family is thought to have an evolutionary origin in the temperate forests of the north and in south-east Asia. Wilf et al. now report fossils dating back 52 million years from the southern hemisphere belonging to the still living genus Castanopsis. The assumptions of Fagaceae origin focused solely on the northern hemisphere. Ancestral Castanopsis can represent one of the many kinds of Paleo-Antarctic plants encountered with Castanopsis today in the tropical forests of Southeast Asia.
Science, this number p. eaaw5139
Structured abstract
INTRODUCTION
The family of Fagaceae flowering plants includes all oaks, beeches, chestnuts, holm oaks and allies of 10 genera and more than 900 species. The family is distinguished by its very high biomass and dominance of forests from the northern temperate zone to the tropics, particularly the South East Asian (SE) tropics. Many Fagaceae are key species that define the structure of the forest, provide important food reserves through their nutritious fruits, and have considerable economic and cultural importance. So far, no living or fossil members of Fagaceae have been found south of the Malay Archipelago and, therefore, the southern hemisphere has not been seriously considered in the history of the family (beech southern, Nothofagus, belongs to a separate family).
REASONING
We discovered two fossiliferous fossils of Fagaceae, a mature and an immature with> 110 preserved fruits, as well as abundant fagaceae leaves in the Laguna del Hunco flora of the ebony (52 million years ago) from Chubut, south of Argentina. This assemblage of very diverse fossils represents the vegetation of the rain forest of the terminal phase of Gondwana; South America, Antarctica and Australia had not yet separated and the global warmth allowed for floral and wildlife exchanges between these landmasses. Subsequently, Australia moved north and eventually collided with Southeast Asia, initiating new biotic exchanges. The flora of Laguna del Hunco reflects these terrestrial processes, preserving many taxa that persist in Australasia and Southeast Asia, many of which are distinctively associated with tropical Fagaceae and provide a rich biogeographic context in the world. discovery. Examples include Eucalyptus (gum), Gymnostome (rhu), engelhardioid Juglandaceae (walnut family), ceratopetalum (coachbuilder), Lauraceae (laurels), Ripogonum (Supplejack) Agathis (kauri), various podocarps (yellowwoods), Papuacedrus (a New Guinea cypress), and Todea (king fern)
RESULTS
We place the new fossil infructescences in the Fagaceae and the living Asian genus Castanopsis, close relative of the chestnuts, because of the preservation of the cupule-fruit complexes with lateral solitary placement on their axis in tip-shaped infructescence; complete closure of (only) nut; (two) asymmetrical valves; squamous ornament; perianth lobed; and three linear styles with unexpanded stigmas. Fossil leaves are also compatible with Castanopsis and likely represent the same source plant as the infructescences; both are in the same strata as the taxa listed above which are local living associates Castanopsisparticularly in the mountainous rainforests of New Guinea. The new fossils represent a major extension south of the historical range of the Fagaceae, as well as the oldest record, about 8 million years old, of the genus. Castanopsis, which has about 120 living species and dominates at low elevations, from New Guinea to the Himalayas and Japan.
CONCLUSION
The diagnostic characteristics of fossils, the early Eocene age and the presence of floral associations very similar to those of today suggest that Castanopsis evolved in the southern hemisphere, probably from an ancestor who had dispersed earlier from North America and followed the southern route to Asia with the taxa of associated survivors. This discovery greatly enhances Gondwana's known heritage in Asia and Malaysia and shows the persistence of surviving lineages, which have followed their preferred wet and humid rainforest environment across time and space, from Gondwana. in Asia. Modern analogue forests, often located in areas of biodiversity-rich watersheds, are now threatened by anthropogenic changes that occur more rapidly than in the past in an order of magnitude. The abundant fossilized leaves bearing the marks of various insects, large walnuts and associated flora all indicate that ancient trees were essential species in the Eocene oak forests of Patagonia. Castanopsis is today in Asia. Thereafter, Castanopsis and many other rainforest taxa seem to have disappeared in Patagonia with the early phases of Antarctic separation and drying up of regional climates.
(Top) Fossil lakes from the beginning of the Eocene to Laguna del Hunco. (Bottom) From left to right: photos of discovery of the land of Castanopsis mature (large walnut length, 17 mm) and immature (length, ~ 15 cm) segments, a fagaceae (length, 18.5 cm), one Eucalyptus Caldericola infructescence (length, 8.2 cm), and a Papuacedrus prechilensis leafy branch (length, 10.2 cm).
Abstract
The family of Fagaceae beech-trees dominates the forests of the northern temperate zone in tropical Asia and Malaysia, where it reaches its southern limit. We report Eocene infructescences of Castanopsis, a diverse and abundant fagus genus of Southeast Asia, and competing leaves of the 52-million-year-old Laguna del Hunco flora of southern Argentina. The assemblage of fossils includes many plant taxa associated with Castanopsis aujourd & # 39; hui. The discovery reveals the new history of Gondwana among the Fagaceae and the characteristic tree communities of the tropical rainforests of the low mountain region of Southeast Asia. Living diaspora associations persisted as a result of Cenozoic climate change and plate movements as constituent lineages followed post-Gondwana mesic biomes for thousands of kilometers, highlighting their current vulnerability to rapid climate change and loss of life. 39; habitat.
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