Around 365 million years ago, a fishy, finned creature that resembled a small alligator clambered up on a sandbank and earned its place in evolutionary history. Researchers who recently discovered fossils of the animal, named Ventastega curonica, say it's the most primitive four-legged creature ever found. While it wasn't the first "fishapod" to lurch out of the water (that honor goes to the Tiktaalik, which accomplished the feat about 375 million years ago), its more primitive evolutionary stage gives researchers new information about the earliest four-legged creatures, or tetrapods.
Ventastega was first described from a few bone fragments unearthed in Latvia in 1994, but it took additional years of excavation and the discovery of remains from many more individuals before scientists had a good idea of what the creature looked like. The latest portrait to emerge, from an especially well-preserved find, reveals an animal with a part-fish, part-tetrapod skull and a full-fledged tetrapod body. It would have spent the majority of its time on water and been clumsy on land [National Geographic News].
The creature, described in the journal Nature, had four primitive flippers with which to waddle around, and is thought to have had as many as nine toes per foot. But despite its early success in making the transition from sea to land, researchers say the Ventastega was an evolutionary dead end, and that different species evolved into our earliest land-based ancestors. Lead researcher Per Ahlberg says:
"All these changes in these creatures are not going in lockstep; it's a mosaic with different parts of animals evolving at different rates. Ventastega has acquired some of land-animal characteristics, but has not yet got some of the other ones" [BBC News].
Image: Nature/Philip Renne
As for what it's motivation may have been for struggling up onto land, Ahlberg hypothesizes that the Ventastega could have fed on stranded fish in semi-tidal creeks. Other researchers have complementary theories for
why fish started to develop what would later become legs. Edward Daeschler, associate curator of vertebrate zoology at the Academy of Natural Sciences in Philadelphia, theorizes that the water was so shallow that critters like Ventastega had an evolutionary advantage by walking instead of swimming [AP].
