World / Science & Health

South Africa tetrapod fossil find blows myth that fish ancestors walked ashore in tropics only

AFP-JIJI

The discovery of two Devonian tetrapods in South Africa suggests that the evolution of these creatures from water to land could have occurred anywhere else, and not only in the tropics as was previously thought, a study has established.

The evolution of tetrapods — four legged vertebrates — from fishes was a key event in human ancestry and for a long time scientists have assumed that they had originated in Laurasia — the smaller supercontinent, which included modern-day North America, Greenland and Europe.

The discovery of Tutusius umlambo and Umzantsia amazana in the coastal Eastern Cape province, near polar latitudes, suggests that four-limbed animals were more widespread in their early stages of evolution, contrary to widespread views that the ancestors of all vertebrates — the amphibious, aquatic tetrapods that first colonized the land — evolved in warm tropical environments.

“Now we have evidence of two types of Devonian tetrapod from the other end of Gondwana, on the other side of the South Pole, in the Antarctic Circle,” Dr. Robert Gess, one of the leading researchers, told AFP.

“These are our ancestors. It’s now equally possible that they came from here than from the other side of the world.

The complete study will be released Friday.

Although the fossils are incomplete, alive these creatures would have resembled a cross between a crocodile and a fish, sporting a crocodile like head, stubby legs and a tail with a fish-like fin.

Twelve Devonian tetrapods have previously been described, all of which came from the Devonian tropics, between 30 degrees north and south of the equator.

All but two of them came from Laurasia.

Only one Devonian tetrapod jaw came from Gondwana — the supercontinent that incorporated present-day Africa, South America, Australia, Antarctica and India. This was found in Eastern Australia, which was on the extreme northern tropical coast of Gondwana.

It was then deduced that all Devonian tetrapods were tropical, with a tropical origin, and that the move onto land probably occurred in tropical environments.

The conditions in Devonian tropical lakes and estuaries therefore seemed to hold the key to understanding the causes of this pivotal macroevolutionary transition.

“So we now know that tetrapods, by the end of the Devonian lived all over the world, from the tropics to the Antarctic circle. So it’s possible that they originated anywhere and that they could have moved onto land anywhere. It really broadens the scope of possibilities.” said Gess.

The latest fossil discovery of the meter long Tutusius umlambo, which is named after Nobel Peace Prize winner Archbishop Emeritus Desmond Tutu, and Umzantsia amazana means their terrestrialization could have happened anywhere.

Gess explained that when naming the creature Desmond Tutu came to mind because this was the type of creature that “ultimately pioneered the way for our ancestors up out of a somewhat anoxic, dangerous, swampy world into the sunshine and a bright new future. ”

The study was jointly conducted by South Africa’s University of the Witwatersrand and Sweden’s Uppsala University

South Africa holds one of the most comprehensive databases of human evolutionary history in the world. This includes the Cradle of Humankind, the world’s richest early hominin site and is home to around 40 percent of the world’s known human-ancestor fossils.