“How vision may have driven fishes onto land
The big implication of this research is the effect it all had on our brains with the shift in behaviour and cognition that accompanied this transition onto land.
About 375 million years ago, certain fishes had developed powerfully strong paired fins that were capable of transporting them out of the water and onto land…A new theory says it was improved vision, as shown by dramatic increases in eye size and visual acuity, that enabled fishes peeping upwards at the waterline to spot prey on land. This would have motivated them to venture out of the water to hunt for food.
…fishes underwent a series of visionary improvements in stages moving from water to land. The first step was when they began to look upwards towards light. Ambush predators, which surprise their prey by a rapid attack coming up from underneath, do this…The second stage was when fishes took to surfacing and poking their eyes above water to peer through the air at the environment around them. It was found that after the emergence of vision, from the fully aquatic vision to totally aerial vision, there was a five million fold increase in the total amount of space monitored by vision…..
Fully formed rows of fingers and toes would be clearly more advantageous for moving on land, though some of the first tetrapods had evolved digits whilst living in water.
With larger eyes, vertebrates began long range sensing for the first time. To sneak up on prey successfully implies they must have been planning an ambush attack, such as creeping up from behind. Otherwise the prey would see them coming and escape if they approached directly.
In living fishes and amphibians the time between prey detection and escape is reduced by about 6 microseconds through using a single large cell called a Mauthner neuron cell to initiate the escape plan. This neural circuity enables ultra-fast reactions to stimuli. These Mauthner command cells are today only found in fishes and amphibians. Later, more efficient nerves in the spine displaced the need for Mauthner cells.”