Sometimes people think evolution only happened in the past. A species of fish evolved legs hundreds of millions of years ago and these eventually evolved into land mammals. Much later, some land mammals re-entered the water and these evolved into whales, etc. Skeptics about evolution often ask why we don’t see the same thing happening today. Or, what good is a half-fin, half-leg? But in fact everything is always evolving, even today, and we do see all kinds of transitional forms in our current world, just as we do in the fossil record. We see mammals today with a wide spectrum of adaptations for water, for example. Polar bears, otters, beavers, hippos, seals, and sea lions show all stages of adaptation to water, from very rudimentary to exquisite, with feet and ears and other body parts nicely covering the range between those of typical land mammals and typical fully-aquatic ones. Similarly there are many fish today that have a range of transitional features giving them some ability to move on land.
This armored catfish found in our Rio Anzu Reserve is a weird example. It has four modified fins that give the fish support as it climbs on rocks near water. Note the hair-like spiky growths near the tips of the fish’s pectoral fins. If the world were not already populated with terrestrial tetrapods, these fish might have evolved in the future to fill the vacant niches on land.
The fish’s mouth does most of the work, though, acting as a suction cup that keeps the fish attached to the rock.
These things can climb near-vertical surfaces:
It grazes on algae, with a rasping mouth. like a snail’s.
This fish was found during a fish investigation of our Rio Zunac and Rio Anzu reserves by Ernesto Rodríguez, partly supported by a science grant from Henri Botter and Ardy van Ooij. When I get the final report of this investigation I’ll post more fish pictures, something we don’t often get on this blog!