Hello tweets,

this story was emailed to me a little while ago. I
thught you'd all be interested to read it, too!
=======
http://news.nationalgeographic.com/news/2004/10/1021_041021_bird_embryo.html

Earliest Unhatched-Bird Fossil Found-Old as Dinosaurs

John Roach
for National Geographic News
October 21, 2004

Paleontologists in China have unearthed a
121-million-year-old fossil bird embryo that is likely
the world's oldest. (See URL for story and pictures.)
The bird was found scrunched in an oval-shaped space
slightly smaller than a chicken egg-one of several
clues that suggest the bird never hatched.

More important, scientists say, is the evidence that
the embryonic bird had feathers, a large skull, and
hardened bones. The findings support the notion that
early birds, like dinosaurs, were well developed at
birth and able to move and forage on their own from
the get-go.

The same theory suggests that birds that give birth to
helpless, naked young evolved much later.

Paleontologists Zhou Zhonghe and Zhang Fucheng
discovered the fossil in Liaoning Province in
northeastern China. Employees of the Institute of
Vertebrate Paleo-anthropology at Beijing's Chinese
Academy of Sciences, the researchers describe their
find in tomorrow's issue of the journal Science.

The bird is preserved in a space that measures
approximately 1.4 by 0.8 inches (35 by 20
millimeters), which is bigger than a robin's egg. No
eggshell was preserved.

"We did think about the possibility of the fossil not
in an egg. However, several lines of evidence appear
to exclude this," Zhou said.

The fossil's egglike shape provides one bit of
evidence. Another is that the fossilized bird rests in
a "tucked" posture that is consistent with a
late-stage embryo rather than a hatchling, the
researchers said. They also note that the bird's
feathers did not differentiate into barbs (the side
structures of a feather that branch from the shaft),
which is typical of a late embryo and not a hatchling.


"It is admittedly still a mystery why no eggshell was
preserved," Zhou said.

Kevin Padian is a professor in the department of
integrative biology and curator of the Museum of
Paleontology at the University of California,
Berkeley. He agrees that the fossil is likely that of
a bird embryo and not a recent hatchling.

Common Bird

Zhou believes the bird is an enantiornithine, the most
common bird type found during the early Cretaceous
period in China. The Cretaceous period spanned from
bout 145 million to 65 million years ago.

Zhou said several other enantiornithine species are
known from the deposit where the latest fossil was
found, but that it was difficult to link the embryo to
a specific genus or species.

Padian, however, is less certain of the
identification, noting that half of the fossil's
characteristics are not exclusive to enantiornithines.
He added that characteristics that would identify the
fossil an enantiornithine are "either dubious or not
well preserved on the specimen."

"But then, what else could it be?" Padian asked.

According to Zhou and Zhang, the bird embryo had a
large skull, feathers, and a hardened skeleton. The
features signal that the bird was precocial, or mature
enough to move and feed independently upon hatching.


Finding such an ancient, well-developed, unhatched
bird supports the idea that Earth's first birds were
also precocial when young. Bird species with helpless,
naked young, known as altricial species, evolved
later, according to the paleontologists.

"The fact that there are bones at all at that stage of
development is a basis for saying that the skeleton is
relatively ossified [or hardened] and is therefore a
precocial bird, said Padian, the Berkeley
paleontologist.

He noted, however, that "it's not clear what degree of
ossification [or skeletal hardening] would be expected
in precocial versus altricial birds. It's a spectrum,
not a dichotomy. But the inference seems justified."


Zhou and Zhang also suggest that the fact that early
birds had well-developed young suggests it was a trait
derived from dinosaur ancestors-that this species may
have evolved from dinosaurs. For example, research
suggests that Troodon, a fast moving, meat-eating
theropod dinosaur from the Cretaceous, developed
precocially.

"Several previously known theropod embryos and the
late Cretaceous avian embryos all seem to be preocial
animals, judged purely from skeletal evidence," Zhou
said.

Egg Tooth

Some modern bird embryos have a special structure on
the top of their bills known as an egg tooth, which
they use to break open their eggs while they hatch.
The egg tooth drops off soon afterward.

The unhatched bird in the newly discovered fossil
lacks an egg tooth, which suggests the feature evolved
later, according to the paleontologists. Instead of an
egg tooth, the bird has long, curved nails, which it
probably used to break open the shell, Zhou said.

The claws also suggest the bird was adapted to living
in trees. A hundred and twenty-one million years ago,
Liaoning Province in northern China was a forested
landscape dominated by active volcanoes and sprinkled
with lakes and streams.

According to Zhou, the unhatched bird likely lived in
a tree near the water. Its nest, he suspects, fell
directly into a lake and was quickly buried. The
specimen's intact preservation excludes the
possibility that it was transported for a distance
before being buried.

"A volcanic eruption might have caused the fast
burial, but it is difficult to imagine what really
happened to this embryo," he said.


=====
Devorah A. N. Bennu, PhD
Independent Scholar and
Research Associate,
American Museum of Natural History
birdologist [at] yahoo [dot] com
public blog: http://girlscientist.blogspot.com

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