Recent Progress and Future Prospects in Fossil Xenarthran Studies, with Emphasis on Current Methodology in Sloth Taxonomy

Abstract

Among the several positive developments in xenarthran studies over the past 20 years have been the training of and active participation by many new researchers, prospecting of previously unexplored or poorly known localities in northwestern South America, pioneering and expansion of paleobiological studies, and revisiting of classic sites in Argentine Patagonia. While these developments have resulted in much new information, including description of new taxa, correlation with faunas previously known from the classic regions of Argentina and Brazil, and enhanced understanding of the modes of life of extinct vertebrates, there remain several areas of research that require more effort from our community. Among these are the need for improved descriptions and illustration of skeletal structures such as those of the auditory and basicranial regions of the skull and the vertebral and autopodial elements. Although perhaps the more difficult and less well-documented regions, much is to be gained for phylogenetic and taxonomic analyses by enhanced efforts in these regards, and several recent publications help provide standard references to their description and illustration. Also, as alpha taxonomy forms the foundation of higher-level analyses, more attention must be paid to intraspecific variation and the quality of specimens in the recognition of diagnostic characters in descriptions of new taxa. Critical assessment of such variation and specimen choice in several recently erected taxa is conducted here, with the goal of inspiring more cautious assessment of characters and relying on a population rather than typological approach in reaching decisions on potential new taxa.