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      Oldest Known Eucalyptus Macrofossils Are from South America

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          Abstract

          The evolutionary history of Eucalyptus and the eucalypts, the larger clade of seven genera including Eucalyptus that today have a natural distribution almost exclusively in Australasia, is poorly documented from the fossil record. Little physical evidence exists bearing on the ancient geographical distributions or morphologies of plants within the clade. Herein, we introduce fossil material of Eucalyptus from the early Eocene (ca. 51.9 Ma) Laguna del Hunco paleoflora of Chubut Province, Argentina; specimens include multiple leaves, infructescences, and dispersed capsules, several flower buds, and a single flower. Morphological similarities that relate the fossils to extant eucalypts include leaf shape, venation, and epidermal oil glands; infructescence structure; valvate capsulate fruits; and operculate flower buds. The presence of a staminophore scar on the fruits links them to Eucalyptus, and the presence of a transverse scar on the flower buds indicates a relationship to Eucalyptus subgenus Symphyomyrtus. Phylogenetic analyses of morphological data alone and combined with aligned sequence data from a prior study including 16 extant eucalypts, one outgroup, and a terminal representing the fossils indicate that the fossils are nested within Eucalyptus. These are the only illustrated Eucalyptus fossils that are definitively Eocene in age, and the only conclusively identified extant or fossil eucalypts naturally occurring outside of Australasia and adjacent Mindanao. Thus, these fossils indicate that the evolution of the eucalypt group is not constrained to a single region. Moreover, they strengthen the taxonomic connections between the Laguna del Hunco paleoflora and extant subtropical and tropical Australasia, one of the three major ecologic-geographic elements of the Laguna del Hunco paleoflora. The age and affinities of the fossils also indicate that Eucalyptus subgenus Symphyomyrtus is older than previously supposed. Paleoecological data indicate that the Patagonian Eucalyptus dominated volcanically disturbed areas adjacent to standing rainforest surrounding an Eocene caldera lake.

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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2011
                28 June 2011
                : 6
                : 6
                : e21084
                Affiliations
                [1 ]L.H. Bailey Hortorium, Department of Plant Biology, Cornell University, Ithaca, New York, United States of America
                [2 ]Departamento de Ecología, Genética y Evolución, Universidad de Buenos Aires, Capital Federal, Buenos Aires, Argentina
                [3 ]Museo Paleontológico Egidio Feruglio-Consejo Nacional de Investigaciones Científicas y Técnicas, Trelew, Chubut, Argentina
                [4 ]Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania, United States of America
                [5 ]Denver Museum of Nature and Science, Denver, Colorado, United States of America
                Raymond M. Alf Museum of Paleontology, United States of America
                Author notes

                Collected and identified specimens from field localities: MAG EJH MCZ PW NRC CCG KRJ. Drafted the original text of the manuscript and developed and scored the morphological matrix: MAG EJH. Examined and prepared the description of the specimens: MAG MCZ. Modified the molecular sequence dataset: EJH. Performed phylogenetic analyses and contributed text to the methods sections pertaining to the analyses: KCN. Photographed specimens: MAG EJH CCG. Contributed text on the biogeographical and ecological interpretations of the Laguna del Hunco flora: PW. All authors commented on and approved this version of the manuscript.

                Article
                PONE-D-11-04346
                10.1371/journal.pone.0021084
                3125177
                21738605
                cdda83bf-c273-46f2-8278-5e464f660283
                Gandolfo et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                History
                : 8 March 2011
                : 18 May 2011
                Page count
                Pages: 9
                Categories
                Research Article
                Biology
                Ecology
                Paleoecology
                Evolutionary Biology
                Evolutionary Systematics
                Taxonomy
                Plant Taxonomy
                Phylogenetics
                Organismal Evolution
                Plant Evolution
                Paleontology
                Paleobiology
                Paleobotany
                Paleoecology
                Paleontology
                Biogeography
                Paleobiology
                Paleobotany
                Paleoecology
                Plant Science
                Botany
                Paleobotany
                Plant Taxonomy
                Plant Evolution
                Plant Phylogenetics
                Plant Taxonomy
                Earth Sciences
                Paleontology
                Biogeography
                Paleobiology
                Paleobotany
                Paleoecology

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                Uncategorized

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