Résumé
The island of New Caledonia is known for its rich and endemic flora, which includes the earliest-diverging extant angiosperm lineage and one of the highest concentrations of conifer diversity in the world. The New Caledonian flora has often been regarded as containing many relictual elements, preserving Gondwanan lineages dating to before the breakup of eastern Gondwana around 80 million years ago. Geologic evidence suggests vicariance does not explain these paleoendemics, however; the current landmass of New Caledonia was submerged until approximately 37 million years ago and thus the present-day flora should be the result of relatively recent long-distance dispersal. But prior to several recent paleobotanical discoveries, the lack of a paleobotanical record on New Caledonia made understanding the history and evolution of its flora difficult. Here we describe a new fossil that sheds light on the history of New Caledonian conifers. The conifer is known from five leafy shoot fragments preserved in a thin fossil-rich bed from the Early Miocene (Burdigalian; 16-20.4 Ma) Nepoui Group exposed in the Pindai Peninsula, on the west coast of New Caledonia. Shoots are preserved as molds and ironstone permineralizations that preserve details of attached leaves and their epidermal anatomy. Small awl-shaped leaf morphology is consistent with either Dacrycarpus or Dacrydium in the Podocarpaceae family, which both have living members on New Caledonia. Cuticular anatomy, however, suggests these fossils belong to Dacrycarpus because their stomata occur in two narrow bands on either side of the leaf and epidermal cells have straight rather than sinuous walls. But leaf flattening and shoot habit in the fossil differ somewhat from extant New Caledonian Dacrycarpus (D. vieillardii), precluding definitive assignment of this material to a living species. Our fossils nevertheless place the Dacrycarpus lineage on New Caledonia by the Early Miocene and provide a new fossil calibration for Podocarpaceae.