Feathers fly in first bird debate
A chicken-sized dinosaur fossil found in China may have overturned a
long-held theory about the origin of birds.
For 150 years, a species called Archaeopteryx has been regarded as the first
true bird, representing a major evolutionary step away from dinosaurs.
But the new fossil suggests this creature was just another feathery dinosaur
and not the significant link that palaeontologists had believed.
The discovery of Xiaotingia, as it is known, is reported in Nature magazine.
The authors of the report argue that three other species named in the past
decade might now be serious contenders for the title of "the oldest bird".
Archaeopteryx has a hallowed place in science, long hailed as not just the
first bird but as one of the clearest examples of evolution in action.
Discovered in Bavaria in 1861 just two years after the publication of
Darwin's Origin of Species, the fossil seemed to blend attributes of both
reptiles and birds and was quickly accepted as the "original bird".
But in recent years, doubts have arisen as older fossils with similar
bird-like features such as feathers and wishbones and three fingered hands
were discovered.
Now, renowned Chinese palaeontologist Professor Xu Xing believes his new
discovery has finally knocked Archaeopteryx off its perch.
His team has detailed the discovery of a similar species, Xiaotingia, which
dates back 155 million years to the Jurassic Period.
By carefully analysing and comparing the bony bumps and grooves of this new
chicken-sized fossil, Prof Xu now believe that both Archaeopteryx and
Xiaotingia are in fact feathery dinosaurs and not birds at all.
"There are many, many features that suggest that Xiaotingia and
Archaeopteryx are a type of dinosaur called Deinonychosaurs rather than
birds. For example, both have a large hole in front of the eye; this big
hole is only seen in these species and is not present in any other birds.
Several species discovered in the past decade could now become contenders
for the title of most basal fossil bird.
Epidexipteryx - a very small feathered dinosaur discovered in China and
first reported in 2008 (above). It had four long tail feathers but there is
little evidence that it could fly.
Jeholornis - this creature lived 120 million years ago in the Cretaceous. It
was a relatively large bird, about the size of a turkey. First discovered in
China, and reported in 2002.
Sapeornis - lived 110 to 120 million years ago. Another small primitive bird
about 33 centimetres in length. It was discovered in China and was first
reported in 2002.
"Archaeopteryx and Xiaotingia are very, very similar to other
Deinonychosaurs in having a quite interesting feature - the whole group is
categorised by a highly specialised second pedo-digit which is highly
extensible, and both Archaeopteryx and Xiaotingia show initial development
of this feature."
The origins of the new fossil are a little murky having originally been
purchased from a dealer. Prof Xu first saw the specimen at the Shandong
Tianyu Museum. He knew right away it was special
"When I visited the museum which houses more than 1,000 feathery dinosaur
skeletons, I saw this specimen and immediately recognised that it was
something new, very interesting; but I did not expect it would have such a
big impact on the origin of birds."
Other scientists agree that the discovery could fundamentally change our
understanding of birds. Prof Lawrence Witmer from Ohio University has
written a commentary on the finding.
"Since Archaeopteryx was found 150 years ago, it has been the most primitive
bird and consequently every theory about the beginnings of birds - how they
evolved flight, what their diet was like - were viewed through the lens of
Archaeopteryx.
"So, if we don't view birds through this we might have a different set of
hypotheses."
There is a great deal of confusion in the field says Prof Witmer as
scientists try to understand where dinosaurs end and where birds begin.
"It's kind of a nightmare for those of us trying to understand it. When we
go back into the late Jurassic, 150-160 million years ago, all the primitive
members of these different species are all very similar.
"So, on the one hand, it's really frustrating trying to tease apart the
threads of this evolutionary knot, but it's really a very exciting thing to
be working on and taking apart this evolutionary origin."
Such are the similarities between these transition species of reptiles and
birds that other scientists believe that the new finding certainly will not
mean the end of the argument.
Prof Mike Benton from the University of Bristol, UK, agrees that the new
fossil is about the closest relative to Archaeopteryx that has yet been
found. But he argues that it is far from certain that the new finding
dethrones its claim to be the first bird.
"Professor Xu and his colleagues show that the evolutionary pattern varies
according to their different analyses.
"Some show Archaeopteryx as the basal bird; others show it hopped sideways
into the Deinonychosaurs.
"New fossils like Xiaotingia can make it harder to be 100% sure of the exact
pattern of relationships."
According to Prof Witmer, little is certain in trying to determine the
earliest bird and new findings can rapidly change perspectives.
"The reality is, that next fossil find could kick Archaeopteryx right back
into birds. That's the thing that's really exciting about all of this."
http://www.bbc.co.uk/news/science-environment-14307985
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