Hero in a half-formed shell: Early ancestor of turtles with a bony belly but bare back lived 240 million years ago.
The fossilised remains of a primitive turtle with a long tail and no hard shell that roamed Earth 240 million years ago has been unearthed in Germany.
The creature, which lived in the Middle Triassic period at around the time the dinosaurs were beginning to appear, provides new clues about the origin of turtle’s protective shell.
Although it did not have the characteristic hard shell on its back seen in modern turtles, palaeontologists say it did have a hard wall of bones along its belly.
The fossil of Pappochelys, shown above, grew to around eight inches and lived along the shores of a lake in the Middle Jurassic period 240 million years ago. Palaeontologists say it was an early ancestor of modern turtles and the shape of its skull suggests these reptiles are more closely related to dinosaurs and birds than snakes
Researchers also say the shape of its skull suggests turtles were more closely related to archosaurs like dinosaurs and birds rather than sitting on their own branch of the evolutionary tree.
They have named the new species Pappochelys – from the Greek for ‘grandfather’ and ‘turtle’- and believe it may have lived in an aquatic or semi-aquatic environment on the shores of a lake.
TURTLES LINK TO BIRDS
Turtles may look like the hard-shelled relatives of lizards and snakes, but their DNA suggests they have far more in common with birds.
Scientists in the US used a new genetic sequencing technique called Ultra Conserved Elements (UCE) to examine turtle evolution.
The results revealed turtles belong to a large group along with their relatives birds, crocodiles and dinosaurs.
They proposed turtles and dinosaurs should be grouped together in a taxonomic group known as called ‘Archelosauria’.
The findings also resolved an evolutionary mystery surrounding soft-shell turtles – a bizarre group of scale-less turtles with snorkel-like snouts.
Until now, studies linked softshell turtles with a smaller semi-aquatic group called mud turtles, despite the fact that softshells appear in the fossil record long before their mud-loving counterparts.
The study placed softshells in a league of their own on the evolutionary tree, quite far removed from any turtle relatives.
It suggests the distinctive shells of later turtles may then have evolved as protection and as a ‘bone ballast’ for controlling buoyancy while in the water.
Writing in the journal Nature, Dr Rainer Schoch, from the State Museum of Natural History Stuttgart, and Dr Hans-Dieter Sues at the Smithsonian National Museum of Natural History in Washington, said: ‘Pappochelys provides a new stage in the evolution of the turtle body plan and critical evidence for the diapsid relationships of turtles.’
The fossilised remains of many Pappochelys were discovered in rock in Schumann quarry on the outskirts of the village of Eschenau near Nuremberg in Germany.
In the Middle Triassic period this area was thought to have been covered with a lake.
The researchers say the creature probably grew to around eight inches (20cm) as adults and appears to have had jaws bearing teeth, unlike modern turtles which have beaks.
They say it bears some resemblance to two other turtle ancestors – the 220 million year old Odontochelys found in China and the 260 million year old Eunotosaurus from South Africa.
The researchers said: ‘Pappochelys is the most common reptile in the Vellberg lake deposit known so far, and is represented by various growth stages, which suggests that it either lived along the lakeshore or frequently entered the lake.
‘Under a scenario that the turtle shell initially evolved in an aquatic setting, the plastron (breastplate) on the underside of the turtle shell may have first developed as protection and ‘bone ballast’ for controlling buoyancy.
Pappochelys did not have the full shell seen in modern turtles but did have a bony plate, shown in red above, on its underside that scientists believe was the early stages of evolution of a shell. They say it may have helped provide protection and acted as a bouyancy aid for the creature in the watery environment where it lived
Researchers say the new fossil can help fill a 40 million year gap in the evolution of turtles and suggests their shells evolved in an aquatic environment before the creatures moved to the oceans, like the green turtle above
‘The thick gastralia (bones on the abdominal wall) and ribs in Pappochelys are consistent with aquatic or semi-aquatic habits.
‘Although the oldest fully shelled turtles were probably terrestrial Odontochelys apparently lived in deltaic or lagoonal settings along a coastline.’
The discovery has helped to close a gap of 40 million years in the fossil record and suggests birds, crocodiles and dinosaurs are the closest relatives of turtles, rather than other reptiles.
The primitive turtle also had thick ribs that are typical of other animals that live in aquatic or semi aquatic environments, as can be seen in the diagram above, which were separate from the bony plate shown in red