Scientists close to solving age-old turtle shell mystery
London, Oct 9 : Discovery of a new fossil could help scientists in unravelling the
biggest mysteries of evolution-how the turtle got its shell.
The researchers discovered a fossil from a 210-million year-old, land-dwelling reptile,
called Chinlechelys tenertesta-Latin for thin-shelled turtle-from New Mexico, and
discovered that the earliest turtles didn't have a shell at all.
It is now believed that in the course of millions of years, rows of protective armour
plates gradually fused together over the reptile's vertebrae, which ultimately resulted
into a complete shell.
"Turtles ultimately originated from something that looked like an armadillo," New
Scientist quoted lead author Walter Joyce, a palaeontologist at the Peabody Museum of
Natural History in New Haven, Connecticut, as saying.
It was his colleague Spencer Lucas, of the New Mexico Museum of Natural History and
Science in Albuquerque, who had earlier found a neck-bone fragment of the new reptile. But
Joyce said that the small size of the skeleton made its provenance debatable.
But, recent erosion has uncovered enough pieces of Chinlechelys tenertesta, that
scientists can easily trail the origin of the shell.
Joyce said that triassic turtles are few and far between, quite unlike fossils dating
from the later Jurassic era, which he claims are "so common people stopped collecting
them".
And he believes that this is the reason why they resided on land, where fossilisation
is far less likely to happen.
"This one's by far the thinnest ever found," said Joyce.
The animal is about 30 centimetres long, with a shell only a millimetre wide. In fact,
its dorsal ribs aren't fully fused to its shell - or carapace - much like in later fossils
and in modern turtles.
"This is a crucial new discovery. This new guy is an animal that belong to the lineage
of turtles, it's a proto-turtle in a way," said Guillermo Rougier, at the University of
Louisville in Kentucky, who uncovered the first Triassic turtles in northwest Argentina.
These and other early turtles had already gained their carapaces and offered few clues as
to its origin.
However, C. tenertesta, indicates towards the body form that must have given rise to
the shell. But, Joyce believes that it is still unclear as to why turtles evolved their
shell.
They speculate that a full shell might offer added protection and stability, the proof
of which lies in the pudding - their body plan is the world's oldest, changing little over
200 million years.
"For some reason just being a turtle is an idea that came along and just really works,"
he said.
--ANI
