New insight into tetrapods
Eastern Cape fossil find set to turn theories on head
The groundbreaking discovery outside Grahamstown of Africa’s first tetrapod fossils, hailing from the Devonian era, is likely to turn on their head theories on the evolution of four-legged vertebrate animals from fishes.
Palaeontologist pioneer from the Albany Museum Dr Rob Gess made the revolutionary discovery in rocks from Waterloo Farm, an exceptional fossil site just outside Grahamstown which preserved a wide range of fish, plant and invertebrate fossils from 360 million years ago.
Gess said the evolution of tetrapods from fishes during the Devonian period was a key event in our distant ancestry.
The discovery of the fossils – published today in the journal Science – is likely to force a major reassessment of this event.
“Whereas all previously found Devonian tetrapods came from localities which were in tropical regions during the Devonian period, these specimens lived within the Antarctic circle,” the article’s authors – Gess and fellow palaeontologist from Uppsala University in Sweden, Prof Per Ahlberg – said.
This means Devonian tetrapods were not restricted to warm environments, as previously believed, and suggests they may have been spread globally.
At the time, Africa was part of the vast continent of Gondwana, made up of what are now South America, Australia, Antarctica, India and Madagascar.
At that time, what is now South Africa was in the Antarctic Circle.
Until now almost all of the sparse records of Devonian tetrapods came from the other large Devonian continent, Laurussia, which comprised what is now North America, Greenland and Europe.
This continent was almost entirely within the Devonian tropics, and all the tetrapod remains came from the tropical region.
Only two species were reported from outside Laurussia, but these two were also from within the ancient tropics, leading to the belief that tetrapods lived in tropical environments and probably originated in Laurussia.
“This discovery totally disrupts this view,” Gess said.
“It shows that tetrapods lived all over the world by the end of the Devonian period, even down to high latitudes.
“It also implies that tetrapods could have originated anywhere, and that the next step, the move onto land, could also have occurred anywhere.”
The two new species, named Tutusius and Umzantsia, are now Africa’s earliest known four-legged vertebrates by a remarkable 70 million years.
The about-metre-long Tutusius umlambo – named in honour of Archbishop Desmond Tutu – and the smaller Umzantsia amazana are both incomplete.
Tutusius is represented by a single bone from the shoulder girdle, whereas Umzantsia is known from a greater number of discovered bones, but they both appear similar to previously known Devonian tetrapods.
Alive, they would have resembled a cross between a crocodile and a fish, with a crocodile-like head, stubby legs, and a tail with a fish-like fin.
The Waterloo Farm fossil site was revealed in 1985 after controlled rock-cutting by the South African National Roads Agency (Sanral) along the N2 highway south of Grahamstown.
This cutting exposed dark grey mudstones of the Witpoort Formation that represent an ancient environment of a brackish, tidal river estuary and contain abundant animal and plant fossils.
The discovery means South Africa can add insight into the emergence of land animals to its incredible fossil record, which also includes transition to mammals from reptile-like ancestors and the evolution of humans.
“There is probably not another country that so fully documents the long and dramatic evolutionary history of our own lineage,” Gess said.
The research was supported by the South African DST-NRF Centre of Excellence in Palaeosciences, based at the University of the Witwatersrand, and the Millennium Trust.