Phylogeny and systematics of early Paleogene bats

Bats appear in the fossil record on multiple continents during the early Eocene. More than seventy Eocene bat species have been named to date, including stem bats, probable members of crown families, and others of uncertain affinity. Most phylogenetic analyses of Eocene bat relationships have focused on the handful of taxa known from nearly complete skeletal material, whereas the taxonomic relationships of more incomplete fossils have been based largely on phenetic similarities. Here we evaluate the evolutionary relationships of over 60 species of Eocene bats—including many taxa known only from fragmentary craniodental remains—in an explicitly phylogenetic context. Our analysis is based on nearly 700 morphological characters scored in 82 taxa, including 20 extant species representing all living bat families other than Pteropodidae. We found that phylogenetic relationships of Eocene bats are more complex than previously thought. Numerous families (e.g., †Archaeonycteridae, †Mixopterygidae, †Palaeochiropterygidae) and genera (e.g., †Archaeonycteris, †Icaronycteris, †Carcinipteryx) were found to be non-monophyletic as previously recognized, requiring adjustments to chiropteran taxonomy. Four major clades of stem bats were recovered in our analyses. †Microchiropteryx folieae (~ 54 Ma, India) was recovered as the earliest crown bat, occurring as the most basal lineage of Vespertilionoidea, whereas many putative crown bats were recovered among stem Chiroptera. †Tachypteron franzeni was found to be a crown bat in our analyses, as in previous studies, but it was recovered unexpectedly as a stem miniopterid. The phylogenetic relationships presented here represent the most comprehensive analysis of Eocene bat relationships completed to date, substantially improving our understanding of the position of many fossil taxa within Chiroptera and providing a foundation for future analyses of bat evolution.