In a fascinating new twist in the evolutionary tale, American Scientists now say that the development of eyes led vertebrates out of the sea, rather than the development of legs.

By analysing fossil data records, researchers from Northwestern University have discovered that the eyes of aquatic vertebrates increased dramatically in size in the era just preceding the first forays on land some 385 million years ago. This has led them to theorise that improved ability to spot prey on land led vertebrates ashore, and that limb development came as an evolutionary necessity some time after.

Another interesting by-product of this research is the suggestion that improved visual ability also led to greater cognitive ability, as animals moved from split-second reactions in poor-vision surroundings to being able to consider reactions over time at a much greater distance on land.

Sources:

1. PNAS:
   Massive increase in visual range preceded the origin of terrestrial vertebrates.

2. The Independent:
   Eyes, not legs, prompted animals to move from sea to land 385 million years ago.