Leaf measurements from New Caledonian conifers

Premise: The archipelago of New Caledonia contains one of the world's most distinctive biotas. The presence of notable paleoendemic taxa suggests Gondwanan vicariance may have played an important role in the formation of New Caledonia's biota, but geological evidence indicates that the landmass was submerged until the Oligocene and its flora resulted from more recent long-distance dispersal events. The lack of a fossil record contributes to uncertainties inherent in both interpretations, but newly discovered fossil plant assemblages may help to clarify the origins of the New Caledonian flora.

Methods: We use standard paleobotanical techniques to prepare and describe leafy conifer shoots from an early Miocene deposit (~19 Ma) on the Pindaï Peninsula of western New Caledonia. To determine affinities of the fossil material, we compare it to herbarium collections of extant New Caledonian conifers and the broader macrofossil record.

Results: Fossil leaves contain cellular-level details of leaf morphology and epidermis anatomy, which are consistent with the conifer family Podocarpaceae, particularly the extant genus Dacrycarpus. Stomata in the fossils are arranged in crowded complexes unlike those of any described Podocarpaceae taxon, however, and we assign this material to a new extinct genus Dacrycarpoides.

Conclusions: New Caledonia is a hotspot of modern conifer biodiversity and was home to now-extinct lineages as well. The presence of extinct conifers on Miocene New Caledonia is consistent with floras from neighboring landmasses and highlights the role of extinction in shaping the modern flora of New Caledonia and other Australasian landmasses.

Methods
To compare fossil material with living and extinct taxa, we examined leaf morphology and epidermal anatomy in published descriptions and compilations of Southern Hemisphere conifers in the families Araucariaceae, Cupressaceae, and Podocarpaceae (e.g., Florin, 1931; Stockey and Ko, 1986; Hill and Brodribb, 1999). We also compared our fossil material with herbarium specimens of extant New Caledonian species that produce awl-shaped leaves comparable to those of the fossils, including Dacrycarpus vieillardii (Parl.) de Laub., several species of Dacrydium Sol. ex G. Forst. (D. balansae Brongn. & Gris, D. guillauminii J. Buchholz, D. araucaroides Brongn. & Gris,), and two species of Araucaria Juss. that have relatively small leaves (A. bernierii J. Buchholz, A. subulata Vieill.). This material was supplied by loan from The Huntington Library, Art Museum, and Botanical Gardens in San Marino, California, USA.