Washington,
DC (3/20/98)- New prehistoric finds in Madagascar and the Mongolian
desert provide valuable new evidence for the dinosaur-bird link hypothesis.
In Madagascar, a team of researchers led by paleontologist/anatomist
Catherine Forster of the State University of New York (SUNY) at Stony Brook
found fossil remains of a sickle-clawed bird bearing a close relationship
to therapod dinosaur anatomy.
The discovery of the new raven-sized fossil bird "is a wonderful
example of how the fossil record provides the basic data for formulating,
testing, and revising ideas about life through time," says Chris Maples,
director of National Science Foundation's geology and paleontology program,
which funded the research.
The fossil bird, dubbed Rahona ostromi (Ostrom's menace from
the clouds), is 65 to 70 million years old, dating from the Late Cretaceous
period.
The forearm bone of Rahona is long and shows anatomic evidence of well-developed
feathers, indicating it was a capable flyer. Perhaps the most amazing observation
is the finding of a large, sickle-like killing claw at the end
of a thick second toe on the hind foot. This unique toe and claw is
identical to the one carried by a group of fast,
predaceous theropod dinosaurs called "maniraptorans". Viewers of
'Jurrasic Park' may remember this feature on the hook-clawed velociraptors.
"This new fossil is one of the strongest last nails in the coffin of
those who doubt that dinosaurs had anything to do with the origin of birds.
Rahona was at the base of the bird family tree, right next to Archaeopteryx.
It had a feathered wing and many bird features in its hips and legs, including
a perching foot. But it also kept the big killing claw of its theropod
ancestors," Forster said.
"Paleontologists have suggested that theropods gave rise to birds, and
the presence of this "maniraptoran" toe and claw on the Malagasy
bird "clinches it for us. This discovery lends a lot of weight to the idea
that birds are a side-branch of the theropod family tree," she added.
More Clues from Bizarre Fossils in the Gobi Desert
A team of researchers from the American Museum of Natural History and George
Washington University made another very important find in Mongolia- the
first known skulls of an unusual group of prehistoric creatures called
the Alvarezsauridae. This find provides further evidence in support
of the theory that birds evolved from dinosaurs, revealing an advanced
stage in this transition. Numerous physical characteristics in the fossil
skulls show that these strange creatures were actually early birds. Their
unusual appearance also challenges the traditional view that all primitive
birds looked similar to their modern-day cousins.
The new fossils were found in the Gobi Desert and, like Rahona ostromidate,
date from the late Cretaceous Period (approximately 70 million years ago).
The researchers named the ancient bird Shuvuuia deserti, from the
Mongolian word shuvuu, meaning "bird," and the Latin for desert, in reference
to the ancient climate in which the animals lived. The flightless bird
was about the size of a turkey, walked on two legs and had a long tail
and neck. However, unlike most primitive birds, it had stubby forearms
that ended in a single, blunt claw. The exact purpose of this appendage
remains a mystery.
Paleontologists have found fossil remains of animals similar to Shuvuuia
deserti, including the early bird Mononykus, in Mongolia, Argentina, and
North America, but never a skull. Skulls contains key physical characteristics
for tracing evolutionary history.
The skull of Shuvuuia deserti reveal an important physical characteristic
found only in birds: the animal was capable of "prokinesis," the movement of the snout up and down independently
of the rest of the skull. This allowed the animal to open its mouth quite wide enough to eat very large dinners.
Shuvuuia's diet might have included insects, lizards and even small mammals.
These newly discovered fossils are the most primitive known fossil birds
with the exception of the Archaeopteryx (pictured above). Interestingly,
the more ancient Archaeopteryx resembles modern birds more closely than
the more advanced Shuvuuia deserti. This riddle illustrates the
complexity of the evolution of birds and is certain to stir debate.
Forster's article appears in the March 20, 1998 issue of the journal
Science. The Shuvuuia deserti discovery is described in the March
19, 1998 issue of the journal Nature.
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