Many turtles can fit in the palm of your hand. Wade into deep oceans, however, and the sizes rapidly grow. The mighty leatherback sea turtle, can reach about 1.75 m (5.7 ft) in shell length. That's big enough to make it the world's largest turtle and one of its biggest reptiles around. But its size has nothing on its prehistoric turtle relatives.
A newly announced turtle shell fossil of Stupendemys geographicus reveals quite a beast indeed.
A rival to Archelon
S. geographicus lived between 12 and 5 million years ago. This animal had a shell that was 2.4 m (8 ft) in length. And that's just the shell — the animal itself would've been even longer! It is estimated to have weighed about 1,145 kg (2,500 lbs).
Estimates of Archelon, another giant dinosaur-era turtle, put it at about 4.6 m (15 ft) in total length and 2,200 kg (4,900 lbs) — so in the size department, it does sounds like this creature wins the battle for biggest turtle. But ...
We don't have as many S. geographicus fossils to study as we do Archelon. Its true size could still be a mystery. S. geographicus was a freshwater turtle, not an ocean-dwelling one like Archelon or the present-day leatherback. And modern freshwater turtles are usually much smaller than their ocean cousins.
In short, even if S. geographicus may not have been the biggest turtle to have ever lived, but it was certainly remarkable. And this particular shell fossil is also the largest, most complete turtle shell fossil ever found.
We can see why a paleontologist thought to include the word "stupendous" (meaning: extremely impressive) into its Latin name!