Escapa, Ignacio , Cuneo, Nestor .
Osmundaceae in the Mesozoic of Gondwana: new evidence from the Jurassic of Patagonia, Argentina.
Osmundaceae is a small family of leptosporangiate ferns classically considered the sister group to the remaining leptosporangiate ferns as suggested from several molecular phylogenetic studies. The family has been considered a morphological evolutionary intermediate between the eusporangiate and the leptosporangiate ferns and its suggested divergence age is early Permian or even late Carboniferous. Irrespective of some controversies it is generally accepted that the extant species are grouped in four genera: Osmunda, Todea, Leptopteris and the monotypic Osmundastrum. In the southern hemisphere, the presence of the family can be traced back to the Triassic of Antarctica, with a Osmunda species morphologically related to some extant representatives of the genus, and perhaps to the late Permian through the record of Paleosmunda from Australia. In the Mesozoic of South America permineralized stems (Osmundacaulis) and compression-impression fronds (Cladophlebis) with a few of them preserving fertile parts, mostly represent the family In the present contribution, two new species of osmundaceous ferns assigned to Todites and Osmundopsis are described from the Early Jurassic of Chubut province, in NW Patagonia. The materials consist of well-preserved vegetative and fertile fronds, which show reproductive and leaf characters of relevance in the understanding and diversification of this fern family in the southern hemisphere. The presence of fertile fronds with pinnules completely covered by abaxial spherical sporangia characterizes Todites sp., while Osmundopsis sp. shows slightly reduced fertile pinnules with distally dehisced sporangia disposed on the abaxial side of fertile pinnules; both species bearing Cladophlebis-like vegetative fronds. The two species represent each of the two main lineages interpreted for the family in recent phylogenetic hypothesis, suggesting that osmundaceous ferns were well established and diversified in the southern hemisphere, in particular during the late Triassic and early Jurassic.
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1 - MEF- Kansas University
2 - CONICET-Museo Paleontologico Egidio Feruglio
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Superior A/Cliff Lodge - Level C
Date: Wednesday, July 29th, 2009
Time: 9:00 AM