Oral Paper

         Paleobotany

A new species of Acmopyle (Podocarpaceae) with preserved accessory transfusion tissue from the early Eocene of Argentinean Patagonia

Presenting Author
Ana Andruchow-Colombo
Description
Acmopyle is one of the 18–20 genera with extant representatives of the conifer family Podocarpaceae. The genus comprises two extant species with restricted rainforest ranges, A. pancheri (New Caledonia, Near Threatened) and A. sahniana (Fiji, Critically Endangered), along with a rich fossil record in Australia since the Paleocene and a few prior reports from Antarctica and South America. Here, we report a new Acmopyle fossil species from the early Eocene (52.2 Ma) Laguna del Hunco locality, Chubut, Argentina, based on 42 compression specimens of leafy shoots (expanded photosynthetic units). As the extant species of the genus, the new fossil taxon is heterophyllous, being characterized by three distinct leaf types: (1) scale-like leaves that are mostly bifacially flattened; (2) transitional leaves that are tetragonal in cross-section to bilaterally flattened; and (3) mature, highly coriaceous, robust and expanded leaves that are bilaterally flattened and show a two-ranked secondary arrangement over their branches. The new species uniquely preserves coalified but distinctive remains of accessory transfusion tissue (ATT, an extra-venous water conducting tissue), an important physiological adaptation of extant Acmopyle. Some fossil specimens also have possible reproductive buds. To test the placement of the new Patagonian Acmopyle, we included it in a total evidence phylogenetic analysis, together with extant and extinct members of the Podocarpaceae and Araucariaceae families and recovered it in a polytomy with the two extant Acmopyle species. Additionally, we report herbivory damage, including margin feeding (DT12), apex feeding (DT13), hole feeding (DT01), and circular punctures (DT47). The presence of Acmopyle in the early Eocene of Argentina is significant because of the previously demonstrated drought intolerance of the genus, which stems from the high collapse risk of the ATT. Thus, the new fossils provide direct physiological evidence of ever-wet rainforest environments in Patagonia during the early Eocene Climatic Optimum and the final stages of Gondwana.