A previously unknown species of primitive turtle made the move from land to water 164 million years ago, fossils found on the Isle of Skye indicate.
Excavations on the island have yielded the remains of at least six turtles that learnt to swim during the age of the dinosaurs.
Eileanchelys waldmani, the species that started swimming in the island’s lakes and lagoons, represents the missing link in the evolution of turtles that palaeontologists have long sought.
Its limbs were similar to those of modern freshwater turtles rather than the flippers of sea-going species, but are likely to have had webbing between the claws.
Scientists concluded that the newly discovered species was aquatic because the fossils were found in rock that once formed the bottom of a lake or lagoon, and because unlike the remains of contemporary land animals, which were fragmented having been washed into a pool, the turtles were relatively complete and articulated.
“Eileanchelys waldmani can be plausibly interpreted as the earliest known aquatic turtle,” researchers concluded in their report published in the journal Proceedings of the Royal Society.
Although Skye is swept by often ferocious Atlantic storms today, the conditions were markedly different during the Middle Jurassic, when the turtle evolved. Then, the island was part of a coastal region of a much bigger land mass, dotted with low salinity lagoons and freshwater lakes and ponds.
The weather was much warmer than today, and other fossil remains have shown that the turtle lived alongside creatures such as salamanders, sharks and crocodiles.
Jérémy Anquetin, of the Natural History Museum and one of the researchers who analysed the fossilised turtles, said: “Although the majority of modern turtles are aquatic forms, it has been convincingly demonstrated that the most primitive turtles from the Triassic, about 210 million years ago, were exclusively terrestrial.
“Until the discovery of Eileanchelys, we thought that adaptation to an aquatic habitat might have appeared among primitive turtles but we had no fossil evidence of that.
“Now we know for sure that there were aquatic turtles around 164 million years ago. This discovery also demonstrates that turtles were more ecologically diverse early in their history than had been suspected before.”
The turtle fossils were recovered from a slab of rock cut out in 2004. Each was encased in the slab and it took months to release them. They were analysed by researchers from the Natural History Museum and University College London, and the fossils are now in the collection of National Museums Scotland.