Echolocation or flight first?


The debate continues; did echolocation or flight evolve first in bats? The discovery of a beautifully preserved Eocene bat
Onychonycteris finneyi led researchers to conclude that it lacked the morphology of the stylohyal bone (a part of the laryngeal apparatus) necessary for echolocation (Simmons et al. 2008). Thus, flight evolved before laryngeal echolocation.

Hold on a minute, say Nina Veselka and colleagues. Their 2010 reanalysis of larynx anatomy in 26 bat extant species shed new light on the old debate. Using micro-comuted tomography scans of bat heads, they reconstructed the 3D morphology of the laryngeal apparatus in both echolocating and non-echolocation bat species.



Figure. 1 The stylohyal bone in blue contacts the tympanic bones (yellow) directly in the echolocating vampire bat in part a, while the stylohyal does not lie over the tympanic bones in the tongue-clicking Rousettus aegyptiacus in part b. (From Veselka et al. 2010)

In all species of echolocating bats examined, the stylohyal bones lie across and articulate with the tympanic bones; in some cases the stylohyal is fused to the tympanic bones. In non-echolocating Pteropodidae, the stylohyal bones do not come in direct contact with the tympanic bones (including species that use tongue-clicking to echolocate).

What advantage might be conferred by the articulation of the stylohyal with the tympanic bones? The authors suggest that contact between these bones might support and anchor the larynx muscles or form a reflex mechanism to help dampen middle ear ossicle vibrations during pulse production.

Interestingly, the stylohyal bone appears to contact the tympanic bones in the fossil
O. finneyi as well, suggesting that this Eocene bat may have been capable of echolocation. Thus, the debate over which came first, echolocation or flight, continues.

References

Simmons, N.B., Seymour, K.L., Habersetzer, J. and G.F. Gunnell. 2008. Primitive early Eocene bat from Wyoming and the evolution of flight and echolocation.
Nature, 451:818-821.

Veselka, N., WcErlain, D.D., Holdsworth, D.W., Eger, J.L., Chhem, R.K., Mason, M.J., Brian, K.L., Faure, P.A., and M. Brock Fenton. 2010. A bony connection signals laryngeal echolocation in bats.
Nature, 463:939-942. doi:10.1038/nature08737.