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| Summary of the interdigital webbing hypothesis, showing the proposed evolutionary trajectories of the Yangochiroptera, Rhinolophoidea and Megachiroptera. in Anderson & Ruxton, 2020. DOI: 10.1111/mam.12211 |
Abstract
Bats (order Chiroptera) are the only mammals capable of powered flight, and this may be an important factor behind their rapid diversification into the over 1400 species that exist today – around a quarter of all mammalian species. Though flight in bats has been extensively studied, the evolutionary history of the ability to fly in the chiropterans remains unclear.
We provide an updated synthesis of current understanding of the mechanics of flight in bats (from skeleton to metabolism), its relation to echolocation, and where previously articulated evolutionary hypotheses for the development of flight in bats stand following recent empirical advances. We consider the gliding model, and the echolocation‐first, flight‐first, tandem development, and diurnal frugivore hypotheses. In the light of the recently published description of the web‐winged dinosaur Ambopteryx longibrachium, we draw together all the current evidence into a novel hypothesis.
We present the interdigital webbing hypothesis: the ancestral bat exhibited interdigital webbing prior to powered flight ability, and the Yangochiroptera, Pteropodidae, and Rhinolophoidea evolved into their current forms along parallel trajectories from this common ancestor. Thus, we suggest that powered flight may have evolved multiple times within the Chiroptera and that similarity in wing morphology in different lineages is driven by convergence from a common ancestor with interdigital webbing.
Keywords: bats, Chiroptera, echolocation, evolution of flight, interdigital webbing, pterosaurs, Scansoriopterygidae
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| Fig. 1: Phylogenetic groupings of chiropterans, showing the relevant subdivisions of the Chiroptera into the Megachiroptera/Microchiroptera and the Yinpterochiroptera/Yangochiroptera. |
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| Fig. 2: Summary of the interdigital webbing hypothesis, showing the proposed evolutionary trajectories of the Yangochiroptera, Rhinolophoidea and Megachiroptera. |
CONCLUSION:
The ability of some vertebrates to take flight has been studied in a range of scientific disciplines, and yet the evolutionary journey of chiropterans from small arboreal mammals to the adept flyers we know today has never been laid out definitively. The story is inherently more complex than that of other vertebrate flyers such as birds, thanks to the close coupling of flight and echolocation in many bat species, and the evolution of flight in bats cannot be uncovered without taking this into account. With advances in molecular analyses, the phylogenetic tree of chiropterans is becoming clearer; the Rhinolophoidea is emerging as unique, not only in morphology and behaviour, but also in phylogeny.
Many hypotheses for the evolution of flight in bats remain viable, but we present a novel hypothesis which synthesises current understanding of chiropteran flight, phylogeny and evolution: that the ancestral bat exhibited interdigital webbing, and that the Yangochiroptera, Pteropodidae, and Rhinolophoidea evolved into their current forms along parallel trajectories from this common ancestor. Drawing on comparisons from the vertebrates, and in the light of the recently published description of the membrane‐winged dinosaur Ambopteryx longibrachium, this interdigital webbing hypothesis provides a biologically satisfying narrative for the evolution of flight in bats, from arboreal mammals to the fastest‐flying vertebrates that we know of. In comparison with some previous hypotheses, this novel hypothesis may be less parsimonious, but we feel it offers the best fit to currently available empirical evidence. Further evidence could strengthen support for this hypothesis, or falsify it.
Sophia C. Anderson and Graeme D. Ruxton. 2020. The Evolution of Flight in Bats: A Novel Hypothesis. Mammal Review. DOI: 10.1111/mam.12211
