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Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation


Bats (Chiroptera) represent one of the largest and most diverse radiations of mammals, accounting for one-fifth of extant species1. Although recent studies unambiguously support bat monophyly2,3,4 and consensus is rapidly emerging about evolutionary relationships among extant lineages5,6,7,8, the fossil record of bats extends over 50 million years, and early evolution of the group remains poorly understood5,7,8,9. Here we describe a new bat from the Early Eocene Green River Formation of Wyoming, USA, with features that are more primitive than seen in any previously known bat. The evolutionary pathways that led to flapping flight and echolocation in bats have been in dispute7,8,9,10,11,12,13,14,15,16,17,18, and until now fossils have been of limited use in documenting transitions involved in this marked change in lifestyle. Phylogenetically informed comparisons of the new taxon with other bats and non-flying mammals reveal that critical morphological and functional changes evolved incrementally. Forelimb anatomy indicates that the new bat was capable of powered flight like other Eocene bats, but ear morphology suggests that it lacked their echolocation abilities, supporting a ‘flight first’ hypothesis for chiropteran evolution. The shape of the wings suggests that an undulating gliding–fluttering flight style may be primitive for bats, and the presence of a long calcar indicates that a broad tail membrane evolved early in Chiroptera, probably functioning as an additional airfoil rather than as a prey-capture device. Limb proportions and retention of claws on all digits indicate that the new bat may have been an agile climber that employed quadrupedal locomotion and under-branch hanging behaviour.

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Figure 1: Holotype of Onychonycteris finneyi (ROM 55351A).
Figure 2: Relative sizes of cochlea in extant and fossil bats.
Figure 3: Limb proportions in Onychonycteris compared with those of other bats and selected non-volant mammals.
Figure 4: Phylogenetic position of Onychonycteris and other Eocene fossils with respect to extant bat lineages.

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We thank I. Morrison for preparing the holotype specimen of Onychonycteris finneyi; A. Aase and H. Galliano for help in obtaining photographs and casts of the paratype; B. Miljour and P. Wynne for their assistance with figures; B. Boyle for photographs; and P. Myers, L. Grande, W. Simpson, M. Engstrom, J. Eger, S. Woodward, S. Schaal, G. Storch, N. Micklich, D. Lunde, E. Westwig and C. Norris for access to specimens. Students sponsored by the Undergraduate Research Opportunities Program (UROP) at the University of Michigan were involved in data acquisition and compilation. Funding was provided by the United States National Science Foundation and Deutsche Forschungsgemeinschaft DFG.

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Correspondence to Nancy B. Simmons.

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Morphological data used in phylogenetic analyses are deposited in MorphoBank and can be obtained at

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This file contains Supplementary Tables 1-3, Supplementary Figures 1-10 with Legends and additional references. (PDF 1884 kb)

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Simmons, N., Seymour, K., Habersetzer, J. et al. Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation. Nature 451, 818–821 (2008).

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