Tuesday, 25 November 2014

Supplejack leaves from the Early Eocene of Patagonia.


Australia and Antarctica are remote from one-another today, but share many common floral and faunal elements. This is because they are both former parts of the ancient continent of Gondwana, and along with Antarctica were the final parts of the ancient supercontinent to break apart. Antarctica today is a frozen continent, with life only clinging on around its coasts, but in the warmer climate of the Eocene supported a far richer fauna and flora, and provided a land bridge between Australia and South America.

In a paper published in the journal Palaeontologica Electronicaon in October 2014, Raymond Carpenter of the School of Earth and EnvironmentalSciences at the University of Adelaide, Peter Wilf of the Department of Geosciences at Pennsylvania State University, John Conran of the AustralianCentre for Evolutionary Biology and Biodiversity at the University of Adelaide and Rubén Cúneo of the Museo Paleontológico Egidio Feruglio of the Consejo Nacionalde Investigaciones Científicas y Técnicas describe the discovery of leaves attributed to a Supplejack plant from the Early Eocene of Patagonia.

Supplejacks, Ripogonaceae, are today found only in Australia, New Zealand and Papua New Guinea. They are prickly vines or shrubs found in the understory of rainforests, and produce robust abundant leaves, which they shed each year, giving them good potential for producing fossils. Genetic studies have shown Supplejacks to be closely related to Chilean Bellflowers, Philesiaceae, which have similar habits but which are restricted to the temperate Valdivian rainforests of Chile.

The new species is named Ripogonum americanum, as it was the first member of the group recorded from the Americas. It is described from two specimens, one leaf preserved as part and counterpart, the other as a single sided impression only. Both were recovered from the Laguna del Hunco caldera-lake beds of Chubut in Argentinean Patagonia, which has produced a varied palaeorainforest flora, and which contains volcanic tuff layers which have enabled the dating of the fossils to about 52.22 million years old (Early Eocene).

(1) Ripogonum americanum from Laguna del Hunco and (2)extant Ripogonum album from Queensland, Australia. Note that although the petiolar region is not preserved, a decurrent pair of suprabasal secondary veins andbasal pair of submarginal veins are clearly visible. Note also the tertiary veins, higher order reticulate venation, veinloops between the secondary vein pairs, and looped ultimate veins at the margins (arrowed). Note virtually identical details on the recent leaf to those visible in the fossil. Scale bars equal 10 mm. Carpenter et al. (2014).

Previous fossils attributed to Ripogonum have been found in Tasmania and New Zealand, but this is the first specimen from the Americas. The Laguna del Hunco  deposits have also yielded specimens attributed to the Philesiaceae, suggesting that the two groups were living alongside one-another at the time, and that Ripogonum had a distribution that ranged from Patagonia across Antarctica to Australia and New Zealand.

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