Oldest record of the scale-leaved clade of Podocarpaceae, early Paleocene of Patagonia, Argentina

ANA ANDRUCHOW COLOMBO; ESCAPA I.; CARPENTER R.; HILL R.; ARI IGLESIAS; A. ARBAZUA; WILF P.

ALCHERINGA

TAYLOR & FRANCIS LTD

Lugar: Londres; Año: 2018 vol. 100 p. 1 - 19

0311-5518

A new podocarpaceous conifer is described from the early Danian Salamanca Formation (southern Chubut, Patagonia, Argentina) based on compressions of leafy branches with cuticular remains. Kirketapel salamanquensis gen. et sp. nov. has amphistomatic, scale-like leaves with marginal frills distinguishable at the apex; stomata oriented randomly in relation to the major axis of the leaf with four to five subsidiary cells and extremely reduced Florin rings; and irregularly shaped epidermal cells. We compare K. salamanquensis with extant and extinct members of the imbricate-leaved podocarps, among which it closely resembles Florin?s Dacrydium group C genera (i.e., Lagarostrobos, Manoao, Lepidothamnus, and Halocarpus). Among these genera, only Lepidothamnus has a living representative in South America, the Chilean L. fonkii, whose leaf macro- and micromorphological characters are described in detail for comparison. Overall, the Patagonian fossil species is most similar to the extant and extinct members of Lagarostrobos in its cuticular micromorphology; however, macromorphological characters, such as the leaf size, apex curvature, and mode of flattening, clearly differentiate it from the four genera of Dacrydium group C. We include K. salamanquensis in a combined molecular and morphological phylogenetic analysis conducted under the maximum parsimony criterion. The new fossil taxon is confidently recovered as part of the here defined scale-leaved clade, also containing Halocarpus, Phyllocladus, Lepidothamnus, Parasitaxus, Lagarostrobos, and Manoao, and then constituting the oldest record known for the group. The new Patagonian podocarp constitutes the first occurrence in the fossil record of this clade both in South America and outside Australasia. Furthermore, based on its oldest locality of occurrence, K. salamanquensis shows that the divergence of the total group of the scale-leaved podocarps occurred by at least 65 million years ago, adding to the growing systematic knowledge of the earliest Cenozoic macrofloras in the Southern Hemisphere.