Fossils of two new feathered dinosaurs
The origin of birds has been much in the news these past 2 years because of new fossil discoveries in China. Kevin Padian (University of California Berkeley, US) presents a short review of the most recent findings of Ji et al (4 authors at 3 install- ations, CN CA US). Padian makes the following points:
1) Among all living creatures, only birds have feathers. The discovery of a single isolated feather in the mid 19th century in Late Jurassic rocks of Bavaria was enough to demonstrate the remote ancestry of birds (approximately 150 million years ago). The discovery of the skeleton of Archaeopteryx in the same area in 1861 confirmed the idea of a feathered ancestor of birds, but little else in the skeleton appeared related to living birds.
2) Ji et al now describe two small theropod dinosaurs from geological beds in the Liaoning province of China, the age of the beds disputed but apparently Late Jurassic/Early Cretaceous (about 145 million years ago). These theropods have down-like and vaned barbed feathers on the body, arms, legs, and tail. But these animals were clearly not birds, and they were clearly not capable of flight.
3) If these are true feathers -- and the evidence indicates they are indeed true feathers -- we are forced to revise our idea of the association of feathers with the animals we call birds.
4) By admitting that plumage did not first spring full-blown on the wings of Archaeopteryx, we are free to examine how feathers evolved in the first place.
5) The evolution of carnivorous dinosaurs through basal (relatively "primitive") *coelurosaurs into birds shows some unmistakable trends in the morphology of wishbones, breastbones, hollow bones, long arms, hands, etc.
6) Padian concludes: "The work of Ji et al should lay to rest any remaining doubts that birds evolved from small coelurosaurian dinosaurs. These new discoveries will excite the public and scientists alike by showing that down-like and later vaned body feathers evolved before flight feathers, and that a full complement of feathers was present in coelurosaurs before birds were invented."
QY: Kevin Padian <firstname.lastname@example.org>
QY: Philip J. Currie <email@example.com>
(Nature 25 Jun 98 393:729,753) (Science-Week 17 Jul 98)
*coelurosaurs: These are a group of relatively small and lightly built dinosaurs
in the suborder Theropoda having long necks and narrow pointed
ON THE ORIGINS OF BIRDS AND BIRD-FLIGHT
In paleontology, the theropods are dinosaurs with four or fewer
toes on the hind feet, a suborder of bipedal reptiles that first
appeared in the Upper Triassic period (about 215 million years
ago) and culminated in the Upper Cretaceous period (about 70 million
years ago). A difficult problem in paleontology has been the tracing
of the evolution of birds, with most paleontologists believing
birds evolved from dinosaurs. The first feathered bird- like fossils
are classified as Archaeopteryx and were found in Upper Jurassic
deposits dating at about 150 million years ago, but unfortunately
there are no feathered intermediates yet dis- covered between
these fossils and any dinosaur ancestors. Birds are rather unique
in several aspects: feathers, toothless beaks, hollow bones, perching
feet, etc., with a combination of skeletal features unknown in
other living animals. ... ... Padian and Chiappe (2 installations,
US), in a review of extant data and the controversies concerning
the evolution of birds, conclude there is no reasonable doubt
that all groups of birds, living and extinct, are descended from
small meat-eating therapods, and that "in fact, living birds are
nothing less than small, feathered, short-tailed therapod dinosaurs."
QY: Kevin Padian, Univ. of Calif. Berkeley 510-642-5130.
(Scientific American February 1998) (Science-Week 23 Jan 98)
THERAPOD DINOSAURS AND THE ORIGIN OF FEATHERS
Chen et al (3 authors at 3 installations, CN) describe two nearly
complete skeletons of a small therapod dinosaur, Sinosauropteryx.
The specimen has the longest tail of any known therapod, a 3-
fingered hand dominated by the first finger, and integumentary
structures that could be related to the origin of feathers. The
larger specimen has stomach contents and two eggs in the abdomen.
The authors suggest the integumentary structures indicate that
avian feathers may have evolved from simpler branched structures
appearing in non-avian therapod dinosaurs, possibly for insulation.
QY: Pei-ji Chen <firstname.lastname@example.org>
(Nature 8 Jan 98) (Science-Week 23 Jan 98)
FOSSIL EVIDENCE LINKS BIRDS AND DINOSAURS
Most paleontologists agree that birds are descendants of dinosaurs,
but the precise linkage is still to be determined, and many questions
remain. Now paleontologist Fernando Novas (Museo Argentino de
Ciencias Naturales, Buenos Aires AR) has unveiled a reconstruction
of a 90 million year old fossil of a meat-eating dinosaur found
in Argentina, the most birdlike dinosaur ever discovered. The
fossil's structure provides a link between dinosaurs and birds,
and will help explain how dinosaur limbs evolved into bird wings.
The creature was almost four feet tall at the hip, and nearly
seven feet long. It has been named Unenlagia comahiensis.
(Nature 22 May 97)
NEW FOSSIL EVIDENCE FUELS BIRD-DINOSAUR LINKAGE DEBATE
Paleobiologists continue to debate whether birds evolved from
dinosaurs or from earlier reptiles. This week Jose L. Sanz et
al (Autonomous University of Madrid ES, Smithsonian Institution,
Washington DC US, University of Barcelona ES) report the discovery,
in the Pyrenees of northern Spain, of a well-preserved nestling
bird dating from approximately 135 million years ago, the specimen
the earliest hatchling bird yet discovered, apparently existing
only 10 million years after Archaeopteryx, considered the first
undisputed bird. The hatchling is reported to show a mix of primitive
and advanced features, and is the second claimed bird-dinosaur
link in two weeks. Those who dispute the bird-dinosaur link, however,
say the hatchling provides no evidence one way or the other. But
partisans on both sides of the issue admit this is an important
find because it is indeed a hatchling.
(Science 6 Jun 97)