Claudia Marsicano examines the prepared fossil of the stem tetrapod in Cape Town before it was transported back to Namibia. (Photo: Roger Smith)
In the burning deserts of Namibia, an international team of scientists has made a thrilling (and monstrous) discovery that is turning our understanding of early vertebrate evolution on its head. After three years of painstaking research, they have unearthed the fossilized remains of a colossal creature that once ruled ancient swamps and lakes—a fearsome predator that existed long before the age of the dinosaurs.
Meet Gaiasia jennyaea recently discovered species of basal tetrapod that lived about 280 million years ago. With a “toilet seat”-shaped skull measuring over two feet long and a body that stretched nearly 10 feet in length, this ancient carnivore was larger than most humans and would have been the apex predator of its time. But it’s not just the creature’s size that has scientists excited—it’s also where it was found and what that means for our understanding of early tetrapod evolution.
“When I saw this huge animal, I knew it was a different species. There is no record of giant basal tetrapods during the Carboniferous-Permian transition (about 299 million years ago) anywhere in the world, let alone the southern continents that formed Gondwana,” said University of Buenos Aires professor Claudia Marsicano, one of the study’s lead authors, in a statement. “What caught my attention next was the structure of the frontal part of the skull, which was sticking out of the ground. It showed unusually interlocking large canine teeth.”
Basal tetrapods are early four-legged vertebrates that represent a crucial step in the transition from water to land. They are the ancient ancestors of all modern land-dwelling vertebrates, including amphibians, reptiles, birds, and mammals. Until now, fossils of these early tetrapods have been found mainly in the Northern Hemisphere, leading scientists to believe that this is where they first evolved and diversified.
The discovery of Gaiasia jennyae in Namibia – part of the ancient supercontinent Gondwana – challenges this long-held belief. It suggests that these early land-dwelling creatures were more widespread than previously thought, with well-established populations in the southern hemisphere.
‘The entire front of the mouth is made up of gigantic teeth’
The fossil was discovered in the Ugab River Valley in Damaraland, a region now known for its dry climate and rugged beauty. But 280 million years ago, this area was part of a very different world. Namibia lay much further south, near the 60th parallel—about as far south as the northernmost point of Antarctica is today. The Earth was emerging from an ice age, and while the equatorial regions became drier and more forested, the polar regions remained swampy, possibly adjacent to ice sheets and glaciers.
It was in this cold, swampy environment that Gaiasia jennyae thrived. Dr. Jason Pardo, an NSF postdoctoral researcher at the Field Museum in Chicago and co-lead author of the study, describes the creature vividly: “Gaiasia jennyae was considerably larger than a human, and probably hung out on the bottom of swamps and lakes. It has a big, flat, toilet-seat-shaped head, which it uses to open its mouth and suck in prey. It has these huge canines, the entire front of its mouth is made up of giant teeth.”
The excavation of Gaiasia is significant not only because of its size and location, but also because of its evolutionary position. Despite living 280 million years ago, Gaiasia shows characteristics of much older, less developed tetrapods. It is even related to organisms that were thought to have gone extinct about 40 million years earlier. This makes Gaiasia a “living fossil” of its time—a relic from an earlier era that somehow managed to survive and thrive long after its relatives were gone.
The research team, funded by PAST Africa and the National Geographic Society, included paleontologists from South Africa, Namibia, Argentina and the United States. Their discovery, published in Nature, was the result of meticulous fieldwork and a good dose of luck.
“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 that fit together – and then a third,” says Sibusiso Mtungata, a skilled fossil technician at the Iziko Museum. “I called [co-author Roger Smith] to help me find more, and as we were walking uphill he saw a large flat rock that he recognized as the head. When we looked along the edge and saw rows of teeth, we knew we had finally found what we had been looking for – a nearly complete skull and skeleton!”
The fossil was remarkably well-preserved, thanks to the unique conditions in which it was buried. Smith, a Distinguished Professor at the Evolutionary Studies Institute at the University of the Witwatersrand and Emeritus Research Associate at Iziko Museums, says the skeleton was preserved in mudstone from an ancient freshwater lake. As the soft tissue decomposed, gases formed, causing calcium carbonate to crystallize around the bones. This created a hard crust that protected the bones from shattering as they were buried deeper over millions of years.
Extracting and preparing the fossil was a monumental task. The skeleton had already weathered out of the rock, so there was no need for excavation, but the team spent hours searching for fragments that had fallen off the cranial block and been moved down. The fossil was then taken to the Iziko South African Museum in Cape Town, where it spent two years painstakingly prepared at the Karoo Fossil Laboratory.
The size of the fossil presented unique challenges during preparation. It was too large for a CT scan, so preparators had to proceed with caution, not knowing exactly what to expect as they removed the surrounding rock. The process created so much dust that a special extractor had to be brought in to manage it.
A monstrous impact on animal evolution
The discovery of Gaiasia jennyae provides crucial insights into the early evolution of land animals and highlights the importance of the southern continents in future research on this topic. It challenges previous assumptions about the distribution and evolution of early tetrapods, which were largely based on fossils from the Northern Hemisphere.
Professor Marsicano emphasizes that this discovery proves that the early history of tetrapods in Pangaea during the Paleozoic was much more complex than previously thought. It suggests that while more advanced forms evolved in the warmer, drier parts of the world, older forms persisted in the colder, swampy regions near the poles.
The name Gaiasia jennyae honors both the site of discovery and a pioneering researcher in the field. “Gaiasia” refers to Gaias, a nearby desert spring where the fossil was found, while “jennyae” honors Professor Jennifer Clack, a world-renowned expert on early tetrapod evolution who died in 2020.
As we continue to unearth new fossils and piece together the puzzle of early vertebrate evolution, discoveries like Gaiasia remind us that the history of life on Earth is far more complex and surprising than we often assume. “The more we look, the more answers we may find about these important groups of animals that interest us, like the ancestors of mammals and modern reptiles,” Pardo says.
The fossil has now been returned to Namibia, where it will soon go on display at the Geological Museum of Namibia. There it will stand as a testament to the incredible diversity of life that has existed on our planet and the ongoing process of scientific discovery that continues to reshape our understanding of Earth’s history.