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A giant creature with a "toilet seat-shaped" head and huge fangs was a top predator 40 million years before the first dinosaurs evolved, new research reveals.
The skull alone of Gaiasia jennyae was over 2ft long, say scientists.
The salamander-like animal lived in swampy waters 300 million years ago with its jaws wide open, preparing to clamp down its interlocking jaws on any unsuspecting prey unwise enough to swim past.
Study co-lead author Dr Jason Pardo, of the Field Museum in Chicago, USA, said: “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.
“It’s a big predator, but potentially also a relatively slow ambush predator.”
He explained that the fossilised predator is named after the Gai-as Formation in Namibia where it was found, and Jenny Clack, a palaeontologist who specialised in the evolution of early tetrapods - the four-limbed vertebrates that gave rise to amphibians, reptiles, birds, and mammals.
Study co-lead author Professor Claudia Marsicano, of the University of Buenos Aires, Argentina, and her colleagues found the fossil.
She said: “When we found this enormous specimen just lying on the outcrop as a giant concretion, it was really shocking.
"I knew just from seeing it that it was something completely different. We were all very excited.
“After examining the skull, the structure of the front of the skull caught my attention.
"It was the only clearly visible part at that time, and it showed very unusually interlocking large fangs, creating a unique bite for early tetrapods.”
The team, whose findings were published in the journal Nature, unearthed several specimens, including one with a well-preserved, articulated skull and spine.
Dr Pardo said: “We had some really fantastic material, including a complete skull, that we could then use to compare with other animals from this age and get a sense of what this animal was and what makes it.
"It turns out, there’s a lot about the creature that makes it special."
He explained that while today, Namibia is in south west Africa, it was even further south 300 million years ago - near the 60th parallel, almost level with the northernmost point of Antarctica today.
At that time, the Earth was nearing the end of an ice age.
Dr Pardo says the swampy land near the equator was drying up and becoming more forested, but closer to the poles, the swamps remained, potentially alongside patches of ice and glaciers.
In the warmer, drier parts of the world, animals were evolving to new forms.
Dr Pardo says early four-legged vertebrates, known as stem tetrapods, branched out and split into lineages that would one day become mammals, reptiles, and amphibians.
But on the fringes, in places such as what’s now Namibia, more ancient forms remained.
Dr Pardo said: “Gaiasia is a stem tetrapod - it’s a holdover from that earlier group, before they evolved and split into the groups that would become mammals and birds and reptiles and amphibians, which are called crown tetrapods.
“It’s really, really surprising that Gaiasia is so archaic. It was related to organisms that went extinct probably 40 million years prior.
“There are some other more archaic animals still hanging on 300 million years ago, but they were rare, they were small, and they were doing their own thing.
“Gaiasia is big, and it is abundant, and it seems to be the primary predator in its ecosystem.”
He says Gaiasia jennyae yields "big-picture information" for palaeontologists studying how the world was changing during the Permian period.
Dr Pardo said: “It tells us that what was happening in the far south was very different from what was happening at the Equator.
"And that’s really important because there were a lot of groups of animals that appeared at this time that we don’t really know where they came from.
“The fact that we found Gaiasia in the far south tells us that there was a flourishing ecosystem that could support these very large predators."
He added: "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.”
