Introduction

The phylogenetic and geographic origins of most extant mammalian orders are stillpoorly documented. Many first appear in the fossil record during thePaleocene-Eocene Thermal Maximum (PETM) at the beginning of the Eocene epochabout 55.5 million years ago (Smith et al., 2006). However,three prominent orders are exceptions to this pattern. Rodents first appeared inNorth America about 0.5–1.0 million years before the PETM, but probablyhad an Asian origin like other Glires (Meng et al., 2003). Batsand whales are not known with any certainty before Middle Ypresian, about 54mya.

The earliest known bats are small, insectivorous forms that are preserved in bothterrestrial and lacustrine fossil faunas. Their phylogenetic and geographicorigins are still unknown, although the absence of clear transitional forms inthe fossil record suggests that bat origins are potentially either quite ancientor their evolution from non-volant mammals was quite rapid. Althoughmorphological evidence has generally supported an origin from withinEuarchontoglires, sequence data from multiple genes strongly supports an originof bats from within Laurasiatheria (Springer et al., 2003;Gunnell and Simmons, 2005).

The oldest known fossil bats are early-middle Early Eocene taxa, and the firstmembers of modern bat families and superfamilies seem to appear in the fossilrecord in the Middle Eocene (Gunnell and Simmons, 2005). We thus here restrictthe term “early bats” to the species known from the Early andearly-middle Middle Eocene (Ypresian and Lutetian, and global equivalents,encompassing European mammalian reference levels MP7 through MP13). These earlybats mainly include “eochiropterans” (Eochiroptera Van Valen 1979is a controversial paraphyletic group composed of primitive taxa; see Simmonsand Geisler, 1998 for an overview) and a few taxa belonging to the first membersof modern families.