Cuneo, Nestor , Hermsen, Elizabeth J. , Gandolfo, Maria A. .
First fossil record of the aquatic fern Regnellidiumin the Late Cretaceous of South America.
Fossils representing vegetative remains and dispersed spores with clear affinities to extant Regnellidium (Salviniales, Marsileaceae)are reported for the first time from Late Cretaceous sediments of southern South America. Organs are preserved as compression-impression fossils and include leaflets, stems, rhizomes, and sporocarps which occur in attachment and represent a whole plant. The fossils are consistent with extant Regnellidium on the basis of macromorphological characters such as leaflet shape and venation pattern; internal organization of the stem, petiole and rhizome; and structure of the sporocarp. Associated dispersed megaspores referable to the Cretaceous taxon Molaspora and microspores with close affinities tu Crybeloporites are also comparable to those of extant Regnellidium in shape,sculpture, and wall microstructure. Given that the fossils are consistent in all known respects with extant Regnellidiumdiphyllum, they can undoubtedly be included in the extant genus. We suggest, however, that they represent a new species based on differences in the megaspore size and exine sculpture, rhizome organization and sporocarp size. Significantly, this report not only constitutes the first record of Regnellidium-like fossil vegetative structures from South America,but along with similar spores from a contemporaneous locality in Patagonia, the first reports of the widespread, primarily Late Cretaceous megaspore taxon Molaspora. Macrofossil remains of Regnellidium are almost unknown in the fossils record, with the only other described vegetative remains being from the Eocene of Amur Oblast, Russia. The Patagonian fossils clearly demonstrate thatplants with macromorphology characteristic of Regnellidium were present by the Late Cretaceous, and could have been stem members of the modern Regnellidium lineage. While the megaspore record is much more complete than the macrofossil record, there is evidence that the Molaspora-Regnellidium megaspore morphology is plesiomorphic among the morphologies represented among the extant genera of Marsileaceae. Due to the ambiguity of the fossil record of the Regnellidium lineage, therefore, it is difficult to draw strong biogeographic conclusions from the fossil record at this time. Perhaps Regnellidium and its direct antecedents have indeed been present on the South American continent continuously for over 65 million years, although more data are needed to corroborate that hypothesis.
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1 - MEF AV. FONTANA 140, TRELEW-CHUBUT, N/A, 9100, Argentina
2 - Cornell University, Department of Plant Biology, 412 Mann Library Building , Ithaca, NY, 14853, USA
3 - Cornell University, L. H. BAILEY HORTORIUM, 410 Mann Library Building, ITHACA, NY, 14853-4301, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Union A/Hyatt
Date: Wednesday, July 11th, 2012
Time: 8:45 AM