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The Journal of Experimental Biology 205, 439-441 (2002)
© 2002 The Company of Biologists Limited

Commentary

Why did some ichthyosaurs have such large eyes?

Stuart Humphries1,2,* and Graeme D. Ruxton1

1 Division of Environmental and Evolutionary Biology, Graham Kerr Building, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK and
2 The Freshwater Biological Association, Ferry House, Far Sawrey, Ambleside, Cumbria LA22 0LP, UK
The authors contributed equally to this work

*Author for correspondence (e-mail: s.humphries{at}bio.gla.ac.uk)

Accepted 15 November 2001

Many species of extinct marine ichthyosaurs had much larger eyes for their body size than would be expected of extant marine mammals and reptiles. Sensitivity to low light at great depth for the deep-diving genus Ophthalmosaurus has recently been suggested as the reason for the large eyes of these animals. Here, we discuss the implications for vision at such depths and consider other optical factors determining eye size. We suggest that the large eyes of ichthyosaurs are more likely to be the result of simultaneous selection for both sensitivity to low light and visual acuity. The importance of the evolutionary history of extant marine mammals and extinct ichthyosaurs is discussed, as are ecological factors driving both acuity and sensitivity.

Key words: vision, eye size, vertebrate, dive depth, ichthyosaur.






© The Company of Biologists Ltd 2002