Dinosaur type linked
Garrison Hilliard
Researchers have discovered a fossil skeleton that appears to link the
earliest
dinosaurs with the large plant-eating sauropods.
This could help to bridge an evolutionary gap between the two-legged
common
ancestors of dinosaurs and the four-legged giants, such as diplodocus.
The remarkably complete skeleton shows that the creature was bipedal but
occasionally walked on all four legs.
The team reports its discovery in the Royal Society journal Proceedings B.
"What we have is a big, short-footed, barrel-chested, long-necked,
small-headed
dinosaur," explained Adam Yates, the scientist from the University of
Witwatersrand in Johannesburg who led the research.
"The earliest ancestral dinosaur - the great grand-daddy of all dinosaurs
-
walked on two legs. This [one] is intermediate between those bipedal forms
and
the true gigantic sauropods."
The skeleton was discovered at a site in the Senekal district of South
Africa.
Dr Yates explained that features of its feet and jaw, as well as its size,
gave
away its significance.
The dinosaur, Aardonyx celestae was a heavy, slow-moving animal.
"It had a lot of features we see on sauropods," explained Dr
Yates. "Short,
broad feet and a big, broad gut, so it was clearly a plant-eater that was
bulk-feeding.
"And the anatomy of the jaw shows it had a wide gape - to stuff more food
in."
It also had, he said, "sauropod-like front feet".
"Its toe bones were very robust and solid, so its weight was being born on
the
inside of the foot. It was still bipedal, but it may have been going down
on to
all fours to browse."
'Living fossil'
The dinosaur dates from the early Jurassic period - about 200 million
years ago.
"Although structurally it's intermediate, it lived too late to be an
actual
ancestor, because true sauropods already existed [then].
"So, at the time, it was a living fossil - the transition must have
happened
much earlier."
Dr Yates stressed that the site where the fossil was discovered provided
an
abundance of valuable knowledge about dinosaur evolution.
"If you want to study how the dinosaurs became giants," he said. "You have
to
come to South Africa."
Dr Paul Barrett - a palaeontologist from the Natural History Museum in
London
said that the discovery of Aardonyx helped "fill a marked gap in our
knowledge
of sauropod evolution".
"[It shows] how a primarily two-legged animal could start to acquire the
specific features necessary for a life spent on all fours.
"Evolution of this quadrapedal gait was key in allowing the late sauropods
to
adopt their enormous body sizes."
Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/8353114.stm
Published: 2009/11/11 01:11:32 GMT
(Sketch at http://news.bbc.co.uk/2/hi/science/nature/8353114.stm)