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| November 2009 |
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New flying reptile discovered
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 Darwinopterus hunting a small feathered dinosaur (Anchiornis). Picture credit: Mark Witton, University of Portsmouth |
An international group of researchers from the University of Leicester (UK), and
the Geological Institute, Beijing (China) have identified a new type of flying
reptile – providing the first clear evidence of an unusual and controversial
type of evolution.
Pterosaurs, flying reptiles, also known as pterodactyls, dominated the skies
in the Mesozoic Era, the age of dinosaurs, 220-65 million years ago. Scientists
have long recognized two different groups of pterosaurs: primitive long-tailed
forms and their descendants, advanced short-tailed pterosaurs some of which
reached gigantic size. These groups are separated by a large evolutionary gap,
identified in Darwin’s time, that looked as if it would never be filled – until
now.
Details of a new pterosaur, published in the Proceedings of the Royal
Society B: Biological Sciences fits exactly in the middle of that gap.
Christened Darwinopterus, meaning Darwin’s wing, the name of the new pterosaur
honours the 200th anniversary of Charles Darwin’s birth and the 150th
anniversary of the publication of On the origin of species.
Gaps in the fossil record are common – only a tiny proportion of all the
animals and plants that ever lived were fortunate enough to become fossilised,
and only a tiny proportion of these have been collected so far. Consequently,
our understanding, both of the history of particular groups such as pterosaurs,
and of the evolutionary processes that generated those histories, is still
patchy and often controversial.
 Fossil skeleton of Darwinopterus (skull 185 mm long). Picture credit: Lü Junchang |
More than 20 fossil skeletons of Darwinopterus, some of them complete, were
found earlier this year in north-east China in rocks dated at around 160 million
years old. This is close to the boundary between the Middle and Late Jurassic
and at least 10 million years older than the first bird, Archaeopteryx. The long
jaws, rows of sharp-pointed teeth and rather flexible neck of this crow-sized
pterosaur suggest that it might have been hawk-like, catching and killing other
contemporary flying creatures. These included various pterosaurs, tiny gliding
mammals and small, pigeon-sized, meat-eating dinosaurs that, aided by their
feathered arms and legs had recently taken to the air, and would later evolve
into birds.
“Darwinopterus came as quite a shock to us” explained David Unwin part of the
research team and based at the University of Leicester’s School of Museum
Studies. “We had always expected a gap-filler with typically intermediate
features such as a moderately elongate tail – neither long nor short – but the
strange thing about Darwinopterus is that it has a head and neck just like that
of advanced pterosaurs, while the rest of the skeleton, including a very long
tail, is identical to that of primitive forms”.
 Evolution in action. Primitive long-tailed pterosaur (top), advanced, short-tailed pterosaur (bottom). Darwinopterus (middle) exhibits features of primitive pterosaurs such as the body (monochrome) and tail (blue) and advanced pterosaurs including the skull (red) and neck (yellow). Arrow denotes direction of evolution. Picture credit: Dave Unwin |
Dr Unwin added: “The geological age of Darwinopterus and bizarre combination
of advanced and primitive features reveal a great deal about the evolution of
advanced pterosaurs from their primitive ancestors. First, it was quick, with
lots of big changes concentrated into a short period of time. Second, whole
groups of features (termed modules by the researchers) that form important
structures such as the skull, the neck, or the tail, seem to have evolved
together. But, as Darwinopterus shows, not all these modules changed at the same
time. The head and neck evolved first, followed later by the body, tail, wings
and legs. It seems that natural selection was acting on and changing entire
modules and not, as would normally be expected, just on single features such as
the shape of the snout, or the form of a tooth. This supports the controversial
idea of a relatively rapid “modular” form of evolution.
The research team warns that much more work is needed to substantiate this
idea of modular evolution but, if it proves to be true, then it might help
explain not just how primitive pterosaurs evolved into more advanced forms, but
many other cases among animals and plants where we know that rapid large scale
evolution must have taken place. The extraordinary evolutionary radiation of
mammals following the extinction of dinosaurs is just one of many examples.
Said Dr Unwin: “Frustratingly, these events, which are responsible for much
of the variety of life that we see all around us, are only rarely recorded by
fossils. Darwin was acutely aware of this, as he noted in the Origin of species,
and hoped that one day fossils would help to fill these gaps. Darwinopterus is a
small but important step in that direction.” - U. Leicester
More information:
University of Leicester - Times Higher Education University of the Year
2008/09
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