Reconstructions of the earliest phases of bird evolution – of ‘near-birds’ or ‘protobirds’, if you will – are pretty familiar, and hypothetical ‘proto-pterosaurs’ are also relatively familiar thanks to their appearance in the mainstream literature (Wellnhofer 1991, Unwin 2006). However, have you ever seen a reconstruction of a proto-bat? Such creatures must have existed, of course, but I’m only aware of one published effort to visualise them. Reproduced here, these reconstructions were originally published in Smith (1977) and were later reproduced in John Hill and James Smith’s excellent Bats: A Natural History (Hill & Smith 1984).
Smith obviously assumed that bats originated from insectivore-like mammals, and did note that insectivores – as in, shrews, moles and kin – and microbats* perhaps shared an ancestry. We still know all too little about the origins of bats: molecular phylogenies indicate membership of Laurasiatheria, but also show that bats are closer to the clade that includes pangolins, artiodactyls, perissodactyls and carnivorans than to ‘core insectivores’** (Van Den Bussche & Hoofer 2004, Nishahara et al. 2006)). Nishahara et al. (2006) even went as far as proposing the name Pegasoferae for the bat-perissodactyl-carnivoran clade they recovered.
* Hill & Smith (1984) included favourable discussion of the (poorly supported and now generally abandoned) hypothesis that megabats and microbats might descend from different ancestors. It’s now firmly established that bats are monophyletic, but also that ‘microbats’ of tradition are paraphyletic with respect to megabats. For more on this subject please see We flightless primates.
** Or eulipotyphlans.
Exactly what the ancestral pegasoferaen (pegasoferan? Pegasoferine?) looked like is unclear, but it was presumably a small, relatively long-tailed, clawed quadruped – I’m imagining something like a cross between a palaeanodont (viz, a stem-pangolin) and a dichobunid-like artiodactyl. The fact that the key, characteristic chiropteran innovation – those incredibly long, slender hands and arms – might have evolved thanks to changes in a single gene (BMP2) (Sears et al. 2006) indicates that the early stages of bat evolution happened extremely quickly (potentially in less than a few million years). This rapid evolution means that those early ‘protobat’ phases were short-lived. This of course lowers the probability that we’ll find them as fossils.
Smith also produced a series of diagrams showing the hypothetical development of the bat wing from an ancestral, insectivore-like hand. Again, this transition must have happened, but the details might have been slightly different from Smith’s (1977) portrayal: Onychonycteris finneyi from the Early Eocene of Wyoming, for example, has since demonstrated that claws on all five fingers were actually retained into the ‘true bat’ condition (Simmons et al. 2008).
Anyway, all very interesting I’m sure you’ll agree. It’s possible that there are more proto-bat reconstructions out there. Let me know if you’re aware of any. I did find this one (below), from a few years ago. It’s by some guy called Naish…
For previous Tet Zoo articles on bats, see…
- Desmodontines: the amazing vampire bats
- Giant extinct vampire bats: bane of the Pleistocene megafauna
- Camazotz and the age of vampires
- Dark origins: the mysterious evolution of blood-feeding in bats
- A new hypothesis on the evolution of blood-feeding: food source duality involving nectarivory. Catchy, no?
- Oh no, not another giant predatory flightless bat from the future
- The most terrestrial of bats
- I stroked a pipistrelle
- Red bats
- We flightless primates
- Great tits: murderous rapacious flesh-rending predators!
- Big animalivorous microbats
- Hidden in plain sight: discovering cryptic vesper bats in the European biota
Refs – -
Hill, J. E. & Smith, J. D. 1984. Bats: a Natural History. British Museum (Natural History), London.
Nishihara, H., Hasegawa, M., & Okada, N. (2006). Pegasoferae, an unexpected mammalian clade revealed by tracking ancient retroposon insertions Proceedings of the National Academy of Sciences, 103 (26), 9929-9934 DOI: 10.1073/pnas.0603797103
Sears, K. E., Behringer, R. R., Rasweiler IV, J. J. & Niswander, L. A. 2006. Development of bat flight: morphologic and molecular evolution of bat wing digits. Proceedings of the National Academy of Sciences 103, 6581-6586.
Simmons, N. B., Seymour, K. L., Habersetzer, J. & Gunnell, G. F. 2008. Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation. Nature 451, 818-821.
Smith, J. D. 1976. Comments on flight and the evolution of bats. In Hecht, M. K., Goody, P. C. & Hecht, D. M. (eds) Major Patterns of Vertebrate Evolution. NATO Advanced Study Institute Series, Series A, Life Science 14. Plenum Press, New York.
Unwin, D. M. 2006. The Pterosaurs From Deep Time. Pi Press, New York.
Van Den Bussche, R. & Hoofer, S. R. 2004. Phylogenetic relationships among recent chiropteran families and the importance of choosing appopriate out-group taxa. Journal of Mammalogy 85, 321-330.
Wellnhofer, P. 1991. The Illustrated Encyclopedia of Pterosaurs. Salamander Books Ltd., London.