'Living Fossil' Reveals How Animals Transitioned from Sea to Land with its Primitive Colon

When it comes to understanding the process of evolution, "living fossils" may just provide the key. Scientists have taken a closer look at the skate and its primitive colon in order to understand how animals first emerged from water in order to live on land.

"I'm particularly interested in how land animals stay hydrated, even though we don't have a hard shell that prevents us drying up like raisins in the sun," said Nicole Theodosiou, one of the researchers, in a news release. "The colon is an important organ that helps us retain and absorb water, but how exactly did we come to have this organ?"

The skate hasn't changed much in about 450 million years, which makes it a living fossil when it comes to studying animals that lived in the ancient past. The skate is also isotonic with its environment, which means that concentrations of things like salt inside its body are in exact balance with concentrations outside its body. This means that the skate is never thirsty or in danger of not getting enough to drink. Surprisingly, though, it does have a rudimentary colon that soaks up water.

"Fish aren't supposed to have the ability to absorb water in their intestines, they just don't really need to," said Theodosiou. "The fact that skates do absorb water, and have the cell types and water channels to facilitate water absorption, means that animals were potentially 'primed,' in a way, to survive on land."

In fact, the new colon finding shows how animals may have first evolved to cope with land conditions. Not only that, but it shows that the colon existed even before animals made this transition.

"That's new," said Theodosiou. "People think that animals move to a new environment and they evolve to survive. But maybe sometimes in evolution you need to be ready to accept the change that comes."