Fish that can walk on land evolved the ability to blink like we do
Scientists have discovered that mudskippers – fish that breathe air – probably blink for the same reasons as humans
Most fish would perform pretty well in a staring competition. But not, perhaps, the mudskipper. Because unlike most fish, mudskippers can blink. And new research into how they do it provides clues to its origin in land animals such as ourselves.
Soft tissues such as eyelids and muscles are not preserved in the fossil record. Which is why biologists have turned to mudskippers for clues to how early terrestrial vertebrates evolved the ability to keep their eyeballs moist on land.
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Research published in the journal PNAS suggests that these amphibious gobies have come up with a fairly straightforward solution: they retract their eyeballs into their skull using already-existing musculature so that the surrounding tissue acts as ready-made eyelids.
“It is sufficient to achieve a bunch of functions that are associated with life on land,” says team member Thomas Stewart of Pennsylvania State University.
It may be no coincidence that many living vertebrates also have retractable eyeballs, says Stewart. “Frogs are a famous example, but rats are also kind of bug-eyed and if you watch them blinking you’ll see them retract.”
On the other hand, some amphibious fish, such as the European eel and lungfish are incapable of blinking. “Maintaining a fluid film on the eye is really important,” Stewart notes. “A lungfish might live out of water in its cocoon for weeks. One wonders how they are able to keep their eyes healthy. It’s a curious one.”
Main image: Mudskippers are amphibious fish © Afriadi Hikmal/Getty
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