How vision may have driven fishes onto land | 3/8/2017 | Staff
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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.

These fishes would eventually evolve into the first truly terrestrial animals, called tetrapods. They had four limbs bearing digits – fingers and toes – to help them when they walked around around on land.

Mysteries - Scientists - Fishes - Water - Land

But one of the biggest mysteries for scientists is figuring out what could have driven such fishes out of the water and onto land in the first place.

Was it availability of new food sources, or perhaps their need to escape from predators in the water?

Theory - Vision - Increases - Eye - Size

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. The new research is published today by Malcolm MacIver from Northwestern University in the US and colleagues. They have named this the "Buena Vista" hypothesis, from the Spanish for "good view".

Team - Eye - Sizes - Kinds - Fishes

The team measured the eye sizes of many kinds of fossil fishes and early tetrapods that lived between 390 million and 250 million years ago to show a dramatic increase in eye size just before the most advanced fishes, called elpistostegalians, left the water to evolve into the first tetrapods.

While fossil eyeball capsules are sometimes preserved perfectly in 3-D, most fossil eyes are reconstructed from the shape of the curved sclerotic ring bones that surround the eye, combined with size and shape of the orbit, which is the hole in the skull that envelops the eyeball.

Increase - Size - Skulls - Fishes - Amphibians

The increase in eye-socket size as measured from fossil skulls of fishes and early amphibians corresponds to a three-fold increase in eye size.

Experimental models of visual ability...
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