XPost: bit.listserv.skeptic, sci.paleontology
By Pallab Ghosh
Science correspondent, BBC News
The first dinosaurs may have originated in the Northern Hemisphere,
possibly in an area that is now Britain.
This is one of the conclusions of the first detailed re-evaluation of the relationships between dinosaurs for 130 years.
It shows that the current theory of how dinosaurs evolved and where they
came from may well be wrong.
This major shake-up of dinosaur theory is published in this weeks's
edition of the journal Nature.
"We may be looking at the possibility that the very earliest dinosaurs
were roaming an area that has become Britain and the group itself could
have
originated on these shores" - Matthew Baron, Cambridge University
The reassessment shows that the meat eating beasts, such as Tyrannosaurus
rex and Velociraptor, have been wrongly classified in the dinosaur family
tree.
One of the implications is that dinosaurs first emerged 15 million years earlier than previously believed.
And the fossil evidence suggests that this origin may have occurred
further north than current thinking suggests - possibly in an area that is
now the UK, according to the new study's lead author, Matthew Baron of Cambridge University.
"The northern continents certainly played a much bigger role in dinosaur evolution than we previously thought and dinosaurs may have originated in
the UK," he told BBC News.
The previous version of the dinosaur family tree was developed 130 years
ago by Harry Govier Seeley, a palaeontologist also working at Kings
College, London.
By comparing the size, shapes and arrangements of fossilised bones of
different species of dinosaurs and how they changed over time, he devised
a theory of how they were related and how they evolved.
He concluded that there were two main groups of dinosaurs: those whose hip bones were like those of modern-day birds, which Seeley called
Ornithischia, and those whose hip bones were more reptile-like, which he
named Saurischia.
The bird-hipped group were all exclusively plant-eaters and included
familiar creatures such as Stegosaurus and Triceratops.
The lizard-hipped group had two branches: the plant-eaters, such as Brontosaurus, and the meat-eaters, such as T. rex.
This organisation has been unchallenged until now.
In redrawing the relationships, researchers studied many more bones and included more species, quite a few of which have been discovered only in
the past 30 years.
The team's analysis suggests that Seeley got it wrong.
The new approach argues for the meat-eaters, a group known as theropods,
to be moved into the same classification as the bird-hipped dinosaurs.
Fossil of SalltopusImage copyrightBBC NEWS
Image caption
This fossil found in Lossiemouth in Scotland is of a dinosaur the size of
a cat. It is now thought to be close to the base of the new dinosaur tree, raising the possibility that these iconic creatures may have had their
origins in the UK
Cambridge's Prof David Norman, who supervised the study, said it
represented a major departure from past thinking.
"All the major textbooks covering the topic of the evolution of the
vertebrates will now need to be re-written if this suggestion survives
academic scrutiny and becomes accepted more widely," he explained.
"It seems that the dinosaur family tree is being shaken quite firmly. It
will be interesting to see what drops from its branches in years to come."
All the major text-books covering the topic of the evolution of the
dinosaurs will now need to be re-written
Prof David Norman, Cambrdige University
The reason that the Northern Hemisphere, and the UK in particular, has
become more likely to be the place for the emergence of the first
dinosaurs is the fact that two crucial fossils were found in Scotland and England.
For decades they were dismissed as unimportant species, but following the redrawing of the dinosaur tree they are now placed close to its base.
The Scottish and English finds suggest that it is now more likely that the first dinosaurs emerged 245 million years ago in the northern part of the planet on a land mass called Laurasia, rather than 230 million years ago
on a more southerly unit called Gondwana.
Matthew Baron said the results came as a "shock".
"A British scientist, Sir Richard Owen, gave the word dinosaur to the
world. Now we may be looking at the possibility that the very earliest dinosaurs were roaming an area that has become Britain and the group
itself could have originated on these shores."
The researchers involved cautioned, though, that the fossil record for
early dinosaurs is so sparse that it would be difficult to make any firm
claims at this stage for their origins. But the team hopes that its
findings will spur palaeontologists to search for more fossil evidence to
back up the new ideas.
A challenge to one of main theories of dinosaur evolution is bound to be controversial.
Now we have our new tree we can use it as a foundation to understand how dinosaur features evolved
Prof Paul Barrett, Natural History Museum
Prof Hans Sues of the Smithsonian Museum in Washington DC, US, said that
the findings had to be tested and corroborated.
"I am sceptical as none of the other recent analyses obtained similar
results - but I keep an open mind," he told BBC News.
Prof Paul Barrett of London's Natural History Museum, who was involved in
the study and came up with the idea of testing Seeley's old theory, said
that the new family tree seemed more logical than the previous one.
"Now we have our evolutionary tree, we can use it as a foundation to
understand how dinosaur features evolved over time, and it is already
beginning to help us explain some questions that have puzzled us," he
added.
Among those questions is the fact that birds are thought to have evolved
from meat-eating dinosaurs. But under the old scheme, they were not in the bird-hipped group.
The new tree fits more neatly with the observation that many meat-eating species and bird-hipped dinosaurs had feathers. The fact that previously
they were in separate groups led some to speculate that all dinosaurs, including the long-necked sauropods were feathered. But there has been no fossil evidence for this, and it is a suggestion that never really took
hold.
The latest work also indicates that dinosaurs evolved into meat-eaters on
two separate occasions during their evolution and it even implies that the
very first dinosaur was omnivorous and therefore ate both plants and meat. Dinosaur HipsImage copyrightDAVID NORMAN
Image caption
Up until now dinosaurs were either classified as bird-hipped or
Lizard-hipped
There was, however, one potentially disastrous consequence of the new
scheme.
It could have meant that the long-necked dinosaurs such Brontosaurus and Diplodocus would not strictly speaking be classed as dinosaurs. But
anxious not to be known as the people who expelled the Natural History
Museum's emblematic Dippy the Diplodocus skeleton from the status of
dinosaur, Matt Baron and his fellow researchers carefully reworded the definition.
"I didn't want to make Dippy not a dinosaur. That would have created a lot
of upset. They are a very well known group and everyone has recognised
them to be dinosaurs. To be truthful, I didn't want to be chased out of
every conference I went to for the rest of my career."
Huxley's triumph
Mr Baron's new family tree has similarities to ideas developed by the
biologist Thomas Henry Huxley in 1870. He believed, correctly as it turns
out, that birds descended from meat-eating dinosaurs and he included them
then with the bird-hipped dinosaurs in a group he named Ornithoscelida, or bird-limbed.
At the time Huxley's ideas were roundly dismissed and eclipsed by
Seeley's.
As an acknowledgement of Huxley's contribution, the team has revived the
name of Ornithoscelida for his new combined group.
As well as being a remarkable piece of research in itself, the work is a vignette of the scientific process itself - how challenging old, well-established ideas with a fresh eye is always worthwhile and can often bring new insights.
"We've proved Huxley right," said Mr Baron. "We didn't pay any attention
to any of the dogma of the past 130 years. We tried to incorporate no
prior assumption and so we have pulled apart the tree and reassembled it
and have come up with solutions to questions that have been troubling scientists for a very long time."
http://www.bbc.com/news/science-environment-39305750
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