SYDNEY, June 22 (UPI) -- When fish that can travel across dry land and exist outside of water for more than a few moments are discovered, they're usually presented as a rare phenomenon.
While they're in the minority, especially among modern fish species, new research suggest such fish are more common than previously thought.
When looking at evolutionary history more broadly, fish adapted to dry land aren't all that exceptional.
"Amphibious behavior has evolved repeatedly in a wide diversity of present day fish, and the move onto land does not appear to be as difficult as has been presumed," researcher Terry Ord, an evolutionary ecologist at the University of New South Wales, explained in a news release.
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Ord and his UNSW colleague Georgina Cooke analyzed the evolutionary relationships between fish species with out-of-water adaptations, and also looked at the ecological and evolutionary conditions that might inspire fish to move from water to land.
The pair identified 33 fish families with at least one species that showcases amphibious tendencies. They published their findings in the journal Evolution.
"These forays onto land have occurred in fish that live in different climates, eat different diets and live in range of aquatic environments, from freshwater rivers to the ocean," atted Ord. "While many species only spend a short time out of water, others, like mudskippers and some eels can last for hours or days."
The new study also documents a unique group of intertidal fish called blennies, which includes several species that hop around on land full-time as adults, staying within the vicinity of crashing waves and hiding in the crevices of wet rocks at low tide.
"In this one family of fish alone, an amphibious lifestyle appears to have evolved repeatedly, between three and seven times," added Ord.
Though the movement of several species from sea to land is thought to have given rise to all land vertebrates, scientists have presented the transition as rare -- citing the challenge of breathing, moving and mating on land as too great of a barrier.
The latest findings suggest these challenges aren't all that problematic.
"The real difficulty in developing a fully-fledged terrestrial lifestyle may be in preventing drying out," Ord said. "This has direct consequences for them breathing on land because they still require their gills, which need to stay moist to function properly."
