Convergence of specialised behaviour, eye movements and visual optics in the sandlance (Teleostei) and the chameleon (Reptilia)

Chameleons have a number of unusual, highly specialised visual features, in cluding telescopic visual optics with a reduced lens power, wide separation of the eye's nodal point from the axis of rotation, a deep pit fovea, rapi d pre-calculated strikes for prey based on monocular depth judgements (incl uding focus), and a complex pattern of partially independent alternating ey e movements. The same set of features has been acquired independently by a teleost, the sandlance Limnichthyes fasciatus. Despite its underwater lifes tyle, this fish displays visual behaviour and rapid strikes for prey that a re remarkably similar to those of the chameleon [1], In a direct comparison of the two species, we have revealed other, previously unsuspected, simila rities, such as corneal accommodation, which was unknown in teleosts, as we ll as bringing together, for the first time, data collected from both speci es, The sandlance is the only teleost, among thousands studied, that has co rneal refraction, corneal accommodation and reduced lens power, as well as sharing the other specialised optical features seen in chameleons, The inde pendent eye movement pattern in the sandlance is also unusual and similar t o that of the chameleon. The selection pressures that have produced this re markable example of convergence may relate to common visual constraints in the life styles of these two phylogenetically disparate species.