Lithraea australis (Berry) comb. nov. (Anacardiaceae) from the upper section of Ñirihuau Formation (middle Miocene), Patagonia

Abstract

The first records of fossil plants from the Ñirihuau Formation (middle Miocene) were published by Edward Berry at the beginning of the last century. They consist of a small collection of leaf imprints obtained from the southern margin of the Ñirihuau River valley, western Río Negro, Argentina. Based on these records, Berry described a few ferns, gymnosperms and angiosperms. Among these impressions, stand out two specimens that Berry interpreted as pinnate leaves of Cycadaceae (now Zamiaceae) that he assigned to the new species Zamia australis Berry. However, after a review of Berry's original materials of Z. australis, and new specimens collected in recent years in the same fossil locality, it is concluded that these putative zamiaceous remains are in fact angiosperm leaves. They show great similarity with those of the current South American species Lithraea molleoides (Vell.) Engl. (Anacardiaceae). To encompass these remains, a new combination, Lithraea australis (Berry) is proposed. From a paleophytogeographic point of view, the recognition of a L. molleoides closely related species suggests that the plant communities of the upper section of the Ñirihuau Formation were part of the “Transitional Province” or at least constituted the ecotone between it and the “Nothofagidites” Province.