Fossil fruits of a new Attaleinae (Cocoseae, Arecaceae): Evidence of a palm grove community during the Early Miocene in northern Patagonia, Argentina

Abstract

Premise: Palms can develop a wide variety of fruit shapes and sizes. Species in the Cocoseae tribe possess an evident synapomorphy: the presence of three “eyes” or germination pores in their endocarp, probably best known by the widespread monotypic extant Cocos nucifera. There is little consensus on the biogeographic history of the cocosoid palms, there being few previous world-spread fossil records, some of which require further study in order to establish a clear taxonomic assignment. Methods: Anatomy of permineralized fruits (pyrenes) from the Miocene in northern Patagonia, Argentina, was studied using thin sectioning and polished surfaces observed under transmitted and epifluorescence microscopy. Some fossils were analyzed under X-ray micro-tomography. Results: We report a new palm fruit fossil record based on anatomical studies of >30 specimens. These were assigned to a new fossil taxon within the subtribe Attaleinae (Tribe Cocoseae, Arecoideae). Furthermore, the presence of an unusual character as endocarp intrusions suggests a close anatomical relationship with the extant Syagrus romanzoffiana. Conclusions: The new fossil taxon is one of the best-preserved fossils of the Cocoseae worldwide and is the first unambiguous fossil record for Attaleinae from southern South America. The extremely high concentration (hundreds to thousands) of pyrenes within several strata of the basal section of the Chichinales Formation and their wide distribution in the study area allow for the interpretation of a palm grove community. This record represents the most austral occurrence of the Attaleinae in South America, indicating that subtropical climatic conditions extended into northern Patagonia almost to the Early Miocene.