"Zhao's small thief", after
paleontologist Zhao Xijin.
When it lived:
Liaoning , China
In 2000, paleontologists in China discovered the fossil
remains of a four-winged dinosaur with fully developed, modern
feathers on both the forelimbs and hind limbs. The six specimens were excavated from the rich fossil beds of
Liaoning Province in northeastern China. They are dated at between 128
to 124 million years old (Early Cretaceous). The new species, Microraptor gui, provides more evidence
that birds evolved from dinosaurs, and could go a long way to
answering a question scientists have puzzled over for close to 100
years: How did a group of ground-dwelling flightless dinosaurs evolve
to a feathered animal capable of flying?
Xu Xing, a paleontologist at the Institute of Vertebrate
Paleontology and Paleoanthropology in Beijing, China, and colleagues
suggest in the January 23 issue of the journal Nature that the
species is an early ancestor of birds that probably used its feathered
limbs, along with a long, feather-fringed tail, to glide from tree to
tree. They argue that the animal represents an intermediate stage in the
evolution of flight, from gliding much as flying squirrels do today to
the active wing flapping of modern birds.
"To have fully formed flight feathers on the hind legs is
fascinating," said James Clark, Ronald Weintraub Associate Professor
of Biology at George Washington University, Washington, D.C. "There were some interesting speculations about 90 years ago that
birds might have had four feathered limbs, but no one has suggested it
in recent times, since all living birds use only their forelimbs," he
said. "This find broadens the whole scope of thinking about the
origins of flight."
Much fossil evidence has been uncovered supporting the idea that
birds evolved from a group of bipedal carnivorous dinosaurs called
theropods. Within the theropod group, birds are most closely related
to dromaeosaurids. Velociraptor, a star in the movie
Jurassic Park, is probably the most famous of dromaeosaurs.
Earlier finds in Liaoning suggest that the earliest dromaeosaurs
were small, feathered animals with forelimbs similar to those of
Archaeopteryx, the oldest known bird at around 150 million years
old, and feet with features comparable to modern tree-living birds.
This species provides another link in the emerging
transition from small, meat-eating dinosaurs to birds," said
Hans-Dieter Sues, curator of vertebrate paleontology and associate
director for science and collections at the Carnegie Museum of Natural
History in Pittsburgh, Pennsylvania. "These fossils fill in a blank in
the fossil record."
Although the M. gui fossils are about 25 million years
younger than Archaeopteryx, the four-winged dinosaur is a more
primitive form derived from a very early evolutionary branch of
dromaeosaurs. The Chinese scientists suggest that the four-winged
dinosaur is the most recent known common relative shared by both birds
Smallest known dinosaurs:
Microraptor - about 16 inches (40
cm long) and may be an adult.
Compsognathus - a theropod (meat-eater) 2 feet (60 cm) long, from
145 million years ago.
It was the size of a chicken and weighed
about 6.5 pounds (3 kg).
Saltopus - 2 feet (60 cm) long insectivore (insect-eater) from
about 200 million years ago.
Lesothosaurus - a 3 feet (90 cm) long, fast running, plant-eater
from Africa, 200 million years ago.
Wannanosaurus - a 39 inches (1 m) pachycephalosaur, a
plant-eater from China, 83-73 million years ago.
Scientific American - Kate Wong
May 2001 An exquisitely complete feathered
dinosaur has emerged from the famed fossil beds of northeastern
China's Liaoning Province. The new discovery, announced today in the
journal Nature, gives further weight to the argument that birds
evolved from dinosaurs and provides the strongest evidence yet that
feathers pre-date the origin of flight.
Earlier finds from Liaoning had hinted at the presence of featherlike
structures on several dinosaur specimens, but critics charged that the
structures were instead fibers of the protein collagen or that the
fossils represented not dinosaurs but flightless birds. Opponents of
the bird-dinosaur connection also noted that no feathers were known
from dromeosaurs-a group of small- to medium-size theropod dinosaurs
that exhibit numerous traits in common with birds and are therefore
widely held to be their closest relatives.
The new fossil, however, appears to answer both of those arguments.
Paleontologist Mark Norell of the American Museum of Natural History
in New York City and his colleagues report that the
130-million-year-old specimen represents a dromeosaur covered with
filamentous structures that exhibit a branching pattern unique to
The presence of featherlike structures on such a creature indicates
that feathers must have evolved for some purpose other than
flight-perhaps to help the animal keep warm. Indeed, for modern birds,
which are warm-blooded, feathers provide critical insulation. Thus,
Norell says, non-avian dinosaurs may have developed primitive feathers
as they developed warm-bloodedness.
Microraptor zhaoianus, is also touted as the smallest non-avian
dinosaur yet discovered, and may also give key clues to the
relationships between dromaeosaurs, troodontids, and modern birds. It
was officially named by Xu and two colleagues in the December 7th
issue of the journal Nature.
Measuring in at 39
centimeters (nearly 16 inches) and possessing a tail of 24
centimeters, Microraptor was a bipedal dinosaur that may have been
adapted to live in trees. A small section of intermentary fuzz, what
scientists believe to be the precursor to feathers, was also found on
the specimen. Although it lived some 20 million years after
Archaeopteryx, the first known bird, Microraptor is being called one
of the most-bird like dinosaurs known, and many paleontologists
believe it may play a key role in proving once and for all that birds
evolved from small meat-eating dinosaurs.
"(Microraptor) shows a
number of modifications to the hips, tail and teeth which are in some
ways intermediate between those of advanced meat-eating dinosaurs and
birds. There also appears to have been feathers, adding more evidence
to the view that feathers and feather-like structures predated the
origin of birds," Dr. Paul Barrett, a professor at Oxford University
said. "It might represent the
most bird-like dinosaur, " Xu told reporters.