Discovery of swamp monster that predates dinosaurs rewrites evolutionary history

Claudia Marsicano studying the prepared stem-tetrapod fossil in Cape Town before it was transported back to Namibia. (Image credit: Roger Smith)

In the scorching deserts of Namibia, an international team of scientists came across an exciting (and monstrous) discovery that’s shaking up our understanding of early vertebrate evolution. After three years of painstaking research, they’ve 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 dinosaurs.

Meet Gaiasia jennyae, a newly discovered species of basal tetrapod that lived approximately 280 million years ago. With a “toilet seat-shaped” skull over two feet long and a body stretching to nearly 10 feet, 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 where it was found and what that means for our understanding of early tetrapod evolution.

“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,” says Professor Claudia Marsicano from the University of Buenos Aires, one of the study’s lead authors, in a statement. “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.”

Basal tetrapods are early four-limbed vertebrates that represent a crucial step in the transition of life from water to land. They’re the ancient ancestors of all modern land-dwelling vertebrates, including amphibians, reptiles, birds, and mammals. Until now, fossils of these early tetrapods were primarily found 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 widely distributed than previously thought, with well-established populations in the southern hemisphere as well.

‘Whole front of mouth is just giant teeth’

The fossil was discovered in the Ugab River valley in Damaraland, a region now known for its arid climate and rugged beauty. But 280 million years ago, this area was part of a very different world. Namibia was located 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 equatorial regions were becoming drier and more forested, the polar regions remained swampy, possibly alongside patches of ice and glaciers.

It was in this cold, swampy environment that Gaiasia jennyae thrived. Dr. Jason Pardo, an NSF postdoctoral fellow at the Field Museum in Chicago and co-lead author of the study, vividly describes the creature: “Gaiasia jennyae was considerably larger than a person, and it probably hung out near the bottom of swamps and lakes. It’s got a big, flat, toilet seat-shaped head, which allows it to open its mouth and suck in prey. It has these huge fangs, the whole front of the mouth is just giant teeth.”

Unearthing Gaiasia is significant not just because of its size and location, but also because of its evolutionary position. Despite living 280 million years ago, Gaiasia shows features of much older, less evolved tetrapods. In fact, it’s related to organisms that were thought to have gone extinct around 40 million years earlier. This makes Gaiasia a “living fossil” of its time – a holdover from an earlier era that somehow managed to survive and thrive long after its relatives had disappeared.

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 fair bit 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 which fitted together – and then a third,” says Sibusiso Mtungata, a skilled fossil technician from the Iziko Museum. “I called [co-author Roger Smith] over to help me find more, and as we walked upslope, he spotted a large flat rock which 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 searching 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 that 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 being crushed 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 skull block and moved downslope. The fossil was then taken to the Iziko South African Museum in Cape Town, where it underwent two years of painstaking preparation in the Karoo Fossil Laboratory.

The fossil’s size presented unique challenges during preparation. It was too large to CT scan, so the preparators had to work carefully, 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-dwelling 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 mostly based on fossils from the northern hemisphere.

Professor Marsicano emphasizes that this discovery proves the early history of tetrapods in Pangea during the Palaeozoic was much more complex than previously thought. It suggests that while more advanced forms were evolving in the warmer, drier parts of the world, more ancient forms persisted in the colder, swampier regions near the poles.

The name Gaiasia jennyae honors both its place of discovery and a pioneering researcher in the field. “Gaiasia” refers to Gaias, a nearby desert spring where the fossil was found, while “jennyae” pays tribute to Professor Jennifer Clack, a world-renowned expert in early tetrapod evolution who passed away 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, we might find more answers about these major animal groups that we care about, like the ancestors of mammals and modern reptiles,” says Pardo.

The fossil has now been returned to Namibia, where it will soon be 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.