Abstract

The bat genus Myotis is represented by 120+ living species and 40+ extinct species and is found on every continent except Antarctica. The time of divergence of Myotis has been contentious as has the time and place of origin of its encompassing group the Vespertilionidae, the most diverse (450+ species) and widely distributed extant bat family. Fossil Myotis species are common, especially in Europe, beginning in the Miocene but earlier records are poor. Recent study of new specimens from the Belgian early Oligocene locality of Boutersem reveals the presence of a relatively large vespertilionid. Morphological comparison and phylogenetic analysis confirms that the new, large form can be confidently assigned to the genus Myotis, making this record the earliest known for that taxon and extending the temporal range of this extant genus to over 33 million years. This suggests that previously published molecular divergence dates for crown myotines (Myotis) are too young by at least 7 million years. Additionally, examination of first fossil appearance data of 1,011 extant placental mammal genera indicates that only 13 first occurred in the middle to late Paleogene (48 to 33 million years ago) and of these, six represent bats, including Myotis. Paleogene members of both major suborders of Chiroptera (Yangochiroptera and Yinpterochiroptera) include extant genera indicating early establishment of successful and long-term adaptive strategies as bats underwent an explosive radiation near the beginning of the Early Eocene Climatic Optimum in the Old World. A second bat adaptive radiation in the New World began coincident with the Mid-Miocene Climatic Optimum.

Highlights

  • Bats make up over one fifth of all living mammal species [1]

  • With the Mid-Miocene Climatic Optimum, after their ancestors arrived in the New World in the latest Eocene or early Oligocene [81,82]

  • Taxon-character matrix utilized in phylogenetic analysis in TNT format. (TNT) S2 File

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Summary

Introduction

Bats make up over one fifth of all living mammal species [1]. They occupy nearly every corner of the Earth and exploit a wide variety of habitats and climatic zones. We demonstrate the late Paleogene occurrence of the well-known living bat genus Myotis and document the first occurrences of extant bat and other mammalian taxa in the fossil record. The vespertilionid bat genus Myotis is virtually ubiquitous with over 120 known extant species distributed around the Earth and found in nearly every geographic province except the poles and some oceanic islands [1]. Myotis is viewed as a relatively unspecialized taxon that retains a primitive dentition [2] and, like most vespertilionids, Myotis lacks exaggerated morphological specializations (greatly enlarged cochlea) associated with advanced echolocating abilities [3]

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