Abstract
BackgroundEven if they are considered the quintessential “living fossils”, the fossil record of the extant genera of the Cycadales is quite poor, and only extends as far back as the Cenozoic. This lack of data represents a huge hindrance for the reconstruction of the recent history of this important group. Among extant genera, Bowenia (or cuticles resembling those of extant Bowenia) has been recorded in sediments from the Late Cretaceous and the Eocene of Australia, but its phylogenetic placement and the inference from molecular dating still imply a long ghost lineage for this genus.ResultsWe re-examine the fossil foliage Almargemia incrassata from the Lower Cretaceous Anfiteatro de Ticó Formation in Patagonia, Argentina, in the light of a comparative cuticular analysis of extant Zamiaceae. We identify important differences with the other member of the genus, viz. A. dentata, and bring to light some interesting characters shared exclusively between A. incrassata and extant Bowenia. We interpret our results to necessitate the erection of the new genus Eobowenia to accommodate the fossil leaf earlier assigned as Almargemia incrassata. We then perfom phylogenetic analyses, including the first combined morphological and molecular analysis of the Cycadales, that indicate that the newly erected genus could be related to extant Bowenia.ConclusionEobowenia incrassata could represent an important clue for the understanding of evolution and biogeography of the extant genus Bowenia, as the presence of Eobowenia in Patagonia is yet another piece of the biogeographic puzzle that links southern South America with Australasia.
Highlights
Even if they are considered the quintessential “living fossils”, the fossil record of the extant genera of the Cycadales is quite poor, and only extends as far back as the Cenozoic
Our results revealed that the fossils are different from the type of Almargemia, necessitating us to erect the new genus Eobowenia to accommodate leaves that share some important characters with extant Bowenia
The specimens examined for Almargemia incrassata are stored in the Natural History Museum (NHM), London, UK, to which they were donated as duplicates by Sergio Archangelsky in 1960, under accession numbers v52264 and v52265
Summary
Even if they are considered the quintessential “living fossils”, the fossil record of the extant genera of the Cycadales is quite poor, and only extends as far back as the Cenozoic. This lack of data represents a huge hindrance for the reconstruction of the recent history of this important group. The Cycadales have been regarded for their phylogenetic position and their number of plesiomorphic characters as the only group of pteridosperms that survived up to the present [1, 2] They play a crucial role in our understanding of the evolution of seed plants [1, 3]. The results of recent molecular dating seem to indicate that most of the extant species diversity in cycads originated during the Late Miocene and Pliocene [16,17,18], and well after the Mesozoic
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