Pleistocene subtribe Terminaliinae (Combretaceae) fossils in the middle-lower Uruguay river basin, South America

Abstract

The El Palmar Formation is a lithostratigraphic unit deposited by the Uruguay River and has an extensive Upper Pleistocene fossil record. The aims of this study are i. to describe in detail three new silicified wood specimens recovered in the Punta Viracho and Santa Ana fossiliferous localities that have the diagnostic features of the Combretaceae, and ii. to add new data to their significance of palaeoenvironmental and phytogeographical implications. Through the study of wood anatomy, the taxonomic identification of fossil woods is carried out. The mesomorphy and the efficiency of the water conduction system in the fossil woods are calculated. The Nearest Living Relatives (NLRs) method by Mosbrugger (1999) based on assemblage taxa is used to obtain paleoenvironmental data. This work provides three new fossil species related to Terminalia sensu lato (Combretaceae) based on fossil wood specimens. Features such as simple perforation plate, short vessel elements, density and diameter of the vessels suggest a strictly mesomorphic structure; where water conductivity efficiency was the predominant condition of these trees. The nearest living relatives of the fossils currently occur in the Atlantic forest in Brazil but are not present in the study area. We conclude that the present-day Atlantic woodland where these species coexist was more widespread in the Upper Pleistocene, reaching higher latitudes to the south (ca. 32° S).