Meet Gaiasia Jennyae, the swamp creature with a toilet seat head

Forty million years before the dinosaurs appeared, there was a ferocious predator that lived in swampy areas. With a skull measuring over two feet long, it waited patiently with its mouth wide open, ready to seize any unsuspecting prey that crossed its path. Meet Gaiasia Jennyae, the swamp creature with a head that looks like a toilet seat.

“Gaiasia jennyae was considerably larger than a human and probably lived deep in swamps and lakes. Its head is large, flat, and shaped like a toilet seat, allowing it to open its mouth and suck in its prey. It has enormous fangs; the entire front of its mouth is made up of giant teeth,” says Jason Pardo, an NSF postdoctoral researcher at the Field Museum in Chicago and co-senior author of the Nature study. “It’s a large predator, but it can also be a relatively slow ambush predator.”

The Gai-as Formation in Namibia, where the fossil was discovered, gave it its name. It is also named after Jenny Clack, a paleontologist who focused on the early evolution of tetrapods, which refers to four-limbed vertebrates that evolved from lobe-finned fish and eventually led to the development of amphibians, reptiles, birds and mammals.

The fossil was discovered by Claudia Marsicano of the University of Buenos Aires and her colleagues, who are co-authors alongside Pardo.

“When we discovered this huge specimen sitting on the outcrop as a giant concretion, it was a real shock. I knew, just by seeing it, that it was something completely different. We were all very excited,” Marsicano said. “After examining the skull, it was the structure of the front part that caught my attention. It was the only part clearly visible at the time, and it featured very large, interlocking fangs, which created a bite unique to early tetrapods.”

The research team discovered several specimens, including one containing a well-preserved articulated skull and vertebral column.

“When we discovered this huge specimen sitting on the outcrop as a giant concretion, it was a real shock. I knew, just by seeing it, that it was something completely different. We were all very excited,” Marsicano said. “After examining the skull, it was the structure of the front part that caught my attention. It was the only part clearly visible at the time, and it featured very large, interlocking fangs, which created a bite unique to early tetrapods.” It seems that this animal has many distinctive characteristics.

Namibia, which is now just north of South Africa, was even further south 300 million years ago. Specifically, it was near the 60th parallel, almost at the northernmost point of Antarctica today. At that time, the Earth was nearing the end of an ice age. The marshy terrain near the equator was drying out and becoming more forested, while closer to the poles, marshes persisted, perhaps alongside ice pockets and glaciers.

In the warmer, less humid regions of the globe, animals adapted and evolved into new species. The first four-legged vertebrates, called stem tetrapods, diversified and split into lineages that gave rise to mammals, reptiles, and amphibians. However, in peripheral regions, in places like present-day Namibia, more primitive forms persisted.

“Gaiasia is a stem tetrapod – it’s a remnant of that earlier group before they evolved and split into groups that would become mammals, birds, reptiles and amphibians, called crown tetrapods,” said Pardo. “It’s really quite surprising that Gaiasia is so archaic. It was related to organisms that went extinct probably 40 million years ago.”

Besides, for a strange relic from an even older time, Gaiasia seemed to be doing rather well. “There are other, more archaic animals that survived 300 million years ago, but they were rare, they were small, and they did their own thing.” said Pardo. “Gaiasia is large, abundant and appears to be the top predator in its ecosystem.”

Furthermore, Gaiasia jennyae, although only one species, provides valuable information to paleontologists studying global changes during the Permian period.

“This shows us that what was happening in the far south was very different from what was happening at the equator. And that’s very important because many groups of animals appeared at that time, and we don’t really know where they came from,” said Pardo. “The fact that we found Gaiasia in the far south tells us that there was a thriving ecosystem that could support these very large predators. The more we look, the more answers we’ll find about these large groups of animals that interest us, like the ancestors of modern mammals and reptiles.”

Journal reference:

1. Claudia A. Marsicano, Jason D. Pardo, Roger M. H. Smith, Adriana C. Mancuso, Leandro C. Gaetano, and Helke Mocke. A giant stem tetrapod was an apex predator in the Gondwana Ice Range during the late Paleozoic. Nature, 2024; DOI: 10.1038/s41586-024-07572-0