Earliest 4-legged Animal Fossil Discovered

The Chinese Academy of Sciences released a computer generated image of the stem-tetrapod. [File photo/Xinhua]

Chinese scientists have unearthed a skull fossil of a fish-like stem-tetrapod that could extend the earliest record of tetrapods by some 10 million years, according to a research paper published Tuesday in the online journal "Nature Communications."

The stem-tetrapod, discovered in southwest China, will increase scientists' understanding of the fin-to-limb evolutionary transition, the paper said.

Living tetrapods, such as frogs, turtles, birds and mammals, comprise just one subgroup of the tetrapod superclass, which also includes finned and limbed stem-tetrapods.

Some stem-tetrapod species are believed to have moved onto land about 370 million years ago and gradually evolved into the earliest terrestrial vertebrates and eventually humans.

Previously, there was a gap of at least 16 million years from the oldest fossil record of the lungfish lineage to the earliest known stem-tetrapod Kenichthys, a finned stem-tetrapod.

The report said the new discovery pushes the fossil record of tetrapods back by some 10 million years and, as a result, the first appearance of the tetrapod superclass has been drawn far closer to the estimated time of the lungfish-tetrapod split.