An extinct sofa-sized turtle may have lived alongside humans

As little as 9,000 years ago, a sofa-sized turtle paddled around the Brazilian Amazon.

The finding, based on a fossilized jawbone, reveals that some of the most massive turtles ever lived relatively close to the modern day. The turtle lived so recently, in fact, it’s possible that people living in South America encountered it, researchers report in the March Biology Letters. 

In 2007, gold miners digging near the Amazonian city of Porto Velho uncovered the fossilized remains, later determined by researchers to be part of a turtle’s lower jaw. And it was big. 

“When I saw the material, I was very excited because of its size, so we managed to bring the specimen to our lab” at the University of São Paulo, says vertebrate paleontologist Gabriel Ferreira, now at the University of Tübingen in Germany.

He and his colleagues measured the fossil jawbone and compared it to both living and extinct turtles. Based on its size and shape, they determined it was a species new to science. The team named the turtle Peltocephalus maturin — “maturin” is a reference to author Stephen King’s immense, cosmic turtle character that vomited out the universe. It was a close relative of the aquatic big-headed Amazon River turtle (P. dumerilianus), which is alive today but much smaller, with a shell length of under 50 centimeters.

P. maturin’s jawbone was among the largest of any turtle, and based on comparisons with other turtles, Ferreira and his team estimate the reptile would have had a shell nearly 2 meters long.

That estimate would make P. maturin one of the largest turtles to ever exist and the second largest freshwater turtle, Ferreira says. 

But P. maturin is truly unusual for when it lived. The team’s radiocarbon and geochemical analysis of the fossil suggest it is between 40,000 and 9,000 years old. Similarly sized giant freshwater turtles all lived much earlier. For instance, Stupendemys, the largest freshwater turtle ever, also lived in South America but did so more than 5 million years ago. 

The researchers also note that because there is evidence of human habitation in the Amazon more than 11,000 years ago, it’s possible humans encountered these enormous turtles. 

Giant turtles have evolved in all turtle groups — land, marine and freshwater species — and in multiple time periods going back tens of millions of years, says Juliana Sterli, a paleontologist at the Museum of Paleontology Egidio Feruglio in Trelew, Argentina. But it’s still unclear why.

In 2023, Ferreira and other researchers published an analysis of turtle body size evolution, which suggested freshwater turtles are mostly homogeneous in size over evolutionary time, occasionally punctuated with very large species. Previously, some researchers had suggested turtle body size might be influenced by factors like environmental temperatures, similarly to patterns seen in other vertebrate groups.

“We could not find any evidence of temperature influencing the mean or maximum body size in turtles,” Ferreira says, “so we still do not know what could be driving the evolution of those giants in the past.”