First tetrapods of Africa lived within the Devonian Antarctic Circle


Share post:

The first African fossils of Devonian tetrapods (four-legged vertebrates) show these pioneers of land living within the Antarctic circle, 360 million years ago.

First tetrapods of Africa lived within the Devonian Antarctic Circle
Full reconstruction of Waterloo Farm by Maggie Newman including Tutusius and Umzantsia
[Credit: Maggie Newman]

The evolution of tetrapods from fishes during the Devonian period was a key event in our distant ancestry. New-found fossils from the latest Devonian Waterloo Farm locality near Grahamstown in the Eastern Cape, South Africa, published in Science, force a major reassessment of this event.

“Whereas all previously found Devonian tetrapods came from localities which were in tropical regions during the Devonian, these specimens lived within the Antarctic circle,” explains lead author, Dr Robert Gess of the Albany Museum in Grahamstown, and co-author Professor Per Ahlberg of Uppsala University in Sweden. 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.

The first African Devonian tetrapods

Two new species, named Tutusius and Umzantsia, are Africa’s earliest known four-legged vertebrates by a remarkable 70 million years. The approximately metre-long Tutusius umlambo (named in honour of Archbishop Emeritus Desmond Tutu) and the somewhat smaller Umzantsia amazana are both incomplete.

First tetrapods of Africa lived within the Devonian Antarctic Circle
Cleithrum of Umzantsia amazana [Credit: Rob Gess and Per Ahlberg]

Tutusius is represented by a single bone from the shoulder girdle, whereas Umzantsia is known from a greater number of 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.

First tetrapods of Africa lived within the Devonian Antarctic Circle
Cleithrum of Tutusius umlambo [Credit: Rob Gess and Per Ahlberg]

The Waterloo Farm locality (where the tetrapods were discovered) is a roadcut first revealed in 2016 after controlled rock-cutting explosions by the South African National Roads Agency (SANRAL) along the N2 highway between Grahamstown and the Fish River. This cutting exposed dark grey mudstones of the Witpoort Formation that represent an ancient environment of a brackish, tidal river estuary that contain abundant fossils of animals and plants.

The first tetrapod found outside of tropical regions

The real importance of Tutusius and Umzantsia lies in where they were found. Devonian tetrapod fossils are found in widely scattered localities. However, if the continents are mapped back to their Devonian positions, it emerges that all previous finds are from rocks deposited in the palaeotropics – between 30 degrees north and south of the equator. Almost all come from Laurussia, a supercontinent that later fragmented into North America, Greenland and Europe.

First tetrapods of Africa lived within the Devonian Antarctic Circle
Infographic of evolution of the shoulder girdle across the fish to tetrapod transition. Includes the proposed position 
of the cleithra of Tutusius and Umzantsia [Credit: R. Gess & C. Harris (SA NRF-DST CoE in Palaeosciences)]

The much larger southern supercontinent, Gondwana, which incorporated present-day Africa, South America, Australia, Antarctica, and India, has hitherto yielded almost no Devonian tetrapods, with only an isolated jaw (named Metaxygnathus) and footprints, being found in eastern Australia. Because Australia was the northernmost part of Gondwana, extending into the tropics, an assumption developed that tetrapods evolved in the tropics, most likely in Laurussia. By extension it was assumed that movement of vertebrates from water onto land (terrestrialisation) also occurred in the tropics. Attempts to understand the causes of these major macroevolutionary steps therefore focussed on conditions prevalent in tropical water bodies.

The Waterloo Farm tetrapods not only come from Gondwana, but from its southernmost part: reconstructed to have been more than 70 degrees south, within the Antarctic circle. Abundant plant fossils show that forests grew nearby, so it wasn’t frozen, but it was definitely not tropical and during winter it will have experienced months of complete darkness. This finding changes our understanding of the distribution of Devonian tetrapods. We now know that tetrapods occurred throughout the world by the Late Devonian and that their evolution and terrestrialisation could realistically have occurred anywhere.

South Africa now adds insights 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 on the planet that so fully documents the long and dramatic evolutionary history of our own lineage.

Source: University of the Witwatersrand [June 07, 2018]



Related articles

Tropical ‘banana eater’ birds lived in North America 52 million years ago

A fossil of an ancestor of modern tropical birds has been found in North America, proving they also...

Fossil of smallest old world monkey species discovered in Kenya

Researchers from the National Museums of Kenya, University of Arkansas, University of Missouri and Duke University have announced...

A plunge in incoming sunlight may have triggered ‘snowball earths’

At least twice in Earth's history, nearly the entire planet was encased in a sheet of snow and...

DNA provides insights into penguin evolution and reveals two new extinct penguins

New University of Otago research has improved our understanding of when and why penguins evolved, and has identified...

DNA provides unique look at moa and climate change

Ancient moa DNA has provided insights into how species react to climate change, a University of Otago study...

‘Dead clades walking’: Fossil record provides new insights into mass extinctions

Mass extinctions are known as times of global upheaval, causing rapid losses in biodiversity that wipe out entire...

Fossilized tracks show earliest known evidence of mammals at the seashore

Today, the rocks of the Hanna Formation in south-central Wyoming are hundreds of miles away from the nearest...

Cutting-edge analysis of prehistoric teeth sheds new light on the diets of lizards and snakes

New research has revealed that the diets of early lizards and snakes, which lived alongside dinosaurs around 100...