Friday, July 05, 2024

Gondwana’s ultimate hunter – New giant fossil tetrapod found in Namibia

UNIVERSITY OF THE WITWATERSRAND

Artist/illustrator Gabriel Lio’s reconstruction of Gaiasia jennyae — IMAGE:
ARTIST/ILLUSTRATOR GABRIEL LIO’S RECONSTRUCTION OF GAIASIA JENNYAE, THE NEW STEM TETRAPOD FROM NAMIBIA, AND AN APEX PREDATOR OF THE WETLAND AREAS OF SOUTHERN GONDWANA APPROXIMATELY 280 MILLION YEARS AGO.
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CREDIT: GABRIEL LIO

After three years of meticulous study, an international team of researchers has announced the discovery of a fossilised giant basal tetrapod in Namibia's arid heartland in Nature. A basal tetrapod is an early four-legged vertebrate with fingers and toes, which lived during the transition from water to land. These ancient carnivores are among the earliest ancestors of all modern animals. This nearly complete 3-meter-long skeleton of an adult, unearthed in the Ugab River valley in Damaraland, is the largest ever discovered. This discovery is significant because it challenges previous assumptions that these early four-legged vertebrates, which lived during the transition from water to land around 280 million years ago, were only found in the northern hemisphere. The new species, named Gaiasia jennyae, provides crucial insights into the early evolution of land-dwelling animals and shows how important southern continents are in future research on this topic.

Funded by PAST Africa and the National Geographic Society, the team, comprising palaeontologists from South Africa, Namibia, Argentina, and the US, was searching for evidence of the earliest four-legged animals to set foot on land in this part of the ancient supercontinent Gondwana. Gondwana, which existed from about 550 to 180 million years ago, included what are now South America, Africa, Antarctica, Australia, and India.

The team was conducting fieldwork in Namibia, meticulously surveying the rugged terrain, when they spotted something exciting. “The nearly complete skeleton was preserved in mudstone from an ancient freshwater lake. As the soft tissue decomposed, gases formed that caused calcium carbonate to crystallise around the bones, creating a hard crust that protected them from being crushed as they were buried deeper,” explains Prof. Roger Smith, Distinguished Professor at the Evolutionary Studies Institute at Wits and Emeritus Research Associate at Iziko Museums, Cape Town.

Mr. Sibusiso Mtungata, a highly skilled fossil technician from the Iziko Museum, describes the discovery moment: “We had found isolated vertebrae of something big, so we were looking for a more complete skeleton. I came across two round cylinders of rock with bone in the middle which fitted together - and then a third. I called Roger over to help me find more, and as we walked upslope, he spotted a large flat rock which he recognised as the head. When we looked along the edge and saw rows of teeth, we knew we had finally found what we had been searching for - a nearly complete skull and skeleton!”

Prof. Claudia Marsicano from the University of Buenos Aires, Argentina, elaborates on the significance of the find. "As soon as I saw this enormous animal, I knew it was a different species. There is no record of giant basal tetrapods during the Carboniferous-Permian transition (approximately 299 million years ago) anywhere in the world, and certainly none from the southern continents that made up Gondwana. What caught my attention next was the structure of the front part of the skull, which was sticking out of the ground. It showed unusually interlocking large fangs." It was an ambush predator that ate the fish that lived in the same lake.

Collecting the fossil took some time. “The skeleton had already weathered out of the rock, so there was no need for excavation, but the whole team spent hours searching for fragments that had fallen off the skull block and moved downslope,” says Mr. Mtungata. The skeleton was then taken to the Iziko South African Museum in Cape Town to be painstakingly prepared in the Karoo Fossil Laboratory, a process that took two years. “Mechanical preparation was a challenge because it was too large to CT scan, so I didn’t know what to expect – especially in the palate where teeth of all different sizes were everywhere. And there was up to 10cm of rock around the vertebrae that needed to be drilled away, creating so much red dust that we had to bring in a special extractor,” says Mr. Mtungata.

The fossil preparation revealed that the large, flattened skull was decorated with unusual patterns and had a unique palate structure. It had enormous, backward-curved fangs in both the upper and lower jaws, making its mouth unlike anything seen before. Initially thought to be a large amphibian, further study showed that the skull had features of much older, less evolved four-legged animals, previously found only in older rocks in the northern hemisphere.

"We named the new species Gaiasia jennyae. 'Gaiasia' is after Gaias, a nearby desert spring where the fossil was found. 'Jennyae' honours Professor Jennifer Clack, a world-renowned expert in early tetrapod evolution, who passed away in 2020," explains Prof. Roger Smith.

The new findings strongly suggest that early tetrapods were well-established in the cold-temperate regions of Gondwana as early as the Carboniferous-Permian transition. “This discovery challenges previous beliefs about early tetrapod distribution and evolution, which were mostly based on fossils from the northern hemisphere,” says Prof. Marsicano. “Our research shows a well-established early Permian fauna, with Gaiasia as an apex predator, in rocks from high-latitude Gondwana, now located in central Namibia. This challenges previous ideas and proves that the early history of tetrapods in Pangea during the Palaeozoic was much more complex than we thought."