Permineralized conifer-like leaves from the Jurassic of Patagonia (Argentina) and its paleoenvironmental implications

Abstract: Anatomically preserved conifer-like leaves from the Middle Jurassic La Matilde Formation at the Barda Blanca locality in the Gran Bajo de San Julián area, southern Patagonia are described here. Leaves are assigned to conifers based on the following foliar features: thick-walled epidermal cells, a sclerenchymatic hypodermis, resin canals and transfusion tracheids associated with the vascular bundle. General mesophyll anatomy and inferred foliar morphology suggest a similarity to large, broad, linear-lanceolate, multi-veined conifer-like leaves. The general foliar habit indicates an affinity with the large, multi-veined leaves of the Araucariaceae; especially with those exhibited by the species of the Araucaria sections, Araucaria and Bunya. Anatomically, the permineralized leaves exhibit xeromorphic foliar features, including thick-walled epidermal cells, an isobilateral mesophyll with well-developed palisade cells and mechanical tissue. The general leaf anatomy shown by the Patagonian specimens along with sedimentological data may suggest that during the deposition of the La Matilde Formation at the Barda Blanca locality, the parent plant was well adapted to the environmental conditions, which probably consisted of a high light intensity with an adequate quantity of water in the soil, which increased the maximum leaf conductance of CO2.