Entombed in fine-grained sediments of volcanic ash that preserve minute details, the skeleton of the still-nameless dromaeosaur is haloed with fibers and filaments. It measures about two feet long from head to tail. A small fish is visible near one foot.

Over the past ten years, discoveries from China’s Liaoning Province have been giving us rare glimpses of a fossil community near the boundary of the Jurassic and Cretaceous periods. These glimpses just keep getting better. Known as the Jehol biota, these ancient plants and animals are embedded in fine-grained sediments that preserve details: the veins of leaves and insect wings, the patterning of skin, and the filaments of feathers. Some of the fossils are proving pivotal in testing the hypothesis that birds are the living descendants of dinosaurs.

Liaoning’s farmers have been collecting fossil fish and insects in the area for decades. The Chinese government now regulates fossil collection and while paleontological excavation has taken place sporadically for years, most specimens are still unearthed by local people. The Jehol fossils are enclosed in gray volcanic ash that was deposited on the bottom of shallow lakes. They are the remains of a varied community of plants and animals that perished in or near the lakes and were quickly buried. The most abundant fossils are arthropods, but plants and fishes are also common. Rarer fossils include dinosaurs, turtles, pterosaurs, lizards, and early mammals. Some specimens reveal fossilized stomach contents and skin shaded in patterns. We cannot tell what colors the patterns represent, but we do know that some Jehol animals, including insects, fish, and small dinosaurs, were spotted or striped, like their living relatives.

Not a bird: The juvenile dromaeosaur from Liaoning Province, China, is covered with feathery filaments from head to ankle (only the feet are bare). The relatively large head indicates that it was a young animal when it perished about 130 million years ago.

Among the first of the remarkable fossils of land-dwelling vertebrates to emerge at Liaoning in the 1990s were creatures called protobirds. They are more closely related to modern birds than is Archaeopteryx from southern Bavaria, but more primitive than birds alive today. Protobirds such as Confuciusornis had the same kind of feathers as modern birds; some specimens even display long tail feathers reminiscent of tropic birds and birds of paradise.

In 1996 the fossil of a small theropod—a bipedal, birdlike dinosaur—came to light and made news in the popular press as well as the scientific community. Named Sinosauropteryx, this creature was the first nonbird whose fossil included featherlike structures. The subsequent discovery of other small dinosaurs with feathery appendages—Caudipteryx, Protarchaeopteryx, Beipaosaurus, and Sinornithosaurus—was seen by most paleontologists as evidence supporting several hypotheses: birds are the living descendants of theropod dinosaurs; birds are not the sole feather-bearing creatures; featherlike structures preceded flight and hence did not evolve in connection with it. Some scientists accept the presence of feathers on Confuciusornis but reject the idea that other Jehol theropods were feathered. They suggest that these creatures are actually primitive birds, or that the featherlike impressions are from a bird that became mixed in with the skeleton during burial, or that they are internal structures related to tail or body musculature. To clinch the argument, we needed a fossil that unambiguously showed a nonavian dinosaur with a feathery body covering.

Crowning glory: Featherlike structures on the top of the head are not the impressions of a crest or head plume, because within the fossil, several layers of the filaments are present and separated by sediments. The entire head is covered by a thick mat of the short filaments.

A new specimen—for now known as NGMC 91—is that kind of fossil. I examined this specimen with colleagues from the Chinese Academy of Sciences. We know that it is a dromaeosaur, a theropod and relative of Velociraptor. We are confident about this assignment because NGMC 91 has several features present only in dromaeosaurs, notably the second toe modified into a sickle claw and the series of elongated connections between tail segments, which serve as stiffening rods. The head, tail, and much of the body are covered with single small fibers. Other parts of the body are covered with tufts or sprays of filaments. On the back of the “arms,” branched structures lie parallel to one another, just like the barbs of a modern bird feather.

On the “arms” and tail, the featherlike structures are bunched, originating and radiating from a single point. Except at the tip, the long tail has short filaments.

Discovered by a farmer in the winter of 2000, the fossil was acquired by the National Geological Museum of China shortly thereafter. It is now on loan to the American Museum of Natural History and will be on display until the end of August 2001. The skeleton, including the tail, is only about twenty-four inches long and is preserved on a slab and counterslab, two halves of one sheet of rock. The size of the head—large in relation to the rest of the body—indicates that this was a young animal. The serrated teeth and sharp claws show that it was a predator, and the long hind limbs suggest that it was a fast, nimble runner.

The wings of a flying insect reveal subtle shading indicative of color patterns.

Despite the specimen’s fine preservation, we are not sure to what species it belongs. A similar dromaeosaur found in the same general area and first described in 1999 was given the scientific name Sinornithosaurus. A few characteristics seem to indicate that NGMC 91 is a different species, yet until further research is done, we will wait to name it. (In the meantime, we call it Dave, a name from an old Cheech and Chong routine.) We know that if measurements of the bones of Sinornithosaurus and NGMC 91 are placed in a mathematical model that describes the growth pattern of Archaeopteryx (the most primitive of the protobirds), both animals deviate from the Archaeopteryx trajectory in the same way. So while neither grew like the protobird, they seem to have grown like each other.

Determining the age of the Jehol fossils is problematic. Groups of researchers using various techniques have come up with conflicting results. The kinds of mammals and pterosaurs found in the Jehol fossils appear to be Late Jurassic, roughly the age of Archaeopteryx. However, measurements of radioactive decay give dates of both 147 and 124 million years, a period that straddles the boundary between Jurassic and Cretaceous. This may not reflect error; the samples taken for analysis are from the same area but not the same quarry. The shallow lakes that once dotted northern China (and are now the fossil beds) were repeatedly and over long periods of time filled in with debris from erupting volcanos. Sets of plant and animal communities of several ages may be represented.

Beneath the green farm country of Liaoning, northeast of Beijing, layers of sediment preserve communities of organisms that lived in and near ancient lakes: plants, insects, small dinosaurs, birds, fish, various reptiles, and mammals.

The issue of time is important. Vocal critics of the theropod theory of bird origins often point to the lack of dromaeosaurs in sediments the same age or older than those that contained Archaeopteryx. They argue that if dromaeosaurs are birds’ closest, albeit more primitive, relatives, they should have lived at an earlier time. This argument confuses the hierarchical branching pattern of the tree of life with a direct, linear process of ancestry and descent. Taken to an extreme, this line of thought would leave one unable to explain the existence of so-called primitive mammals alive today, for example platypuses and opossums, which split off from the branch that led to placental mammals, including us, nearly 100 million years ago.

The new fossil tells us that a body covering similar to feathers was present in nonbirds. If not connected with the ability to fly, could feathers have evolved to keep animals warm? (See “First Came Feathers,” September 1998.) Modern birds are warm-blooded, and feathers play an integral role in maintaining body heat. A reasonable idea, although difficult to verify, is that theropods developed featherlike structures in tandem with warm-bloodedness. Only later were the structures co-opted for flight and display.

As more evidence of ancient life comes to light, we can refine our vision of dinosaurs and birds-as-dinosaurs. If we could see the juvenile dromaeosaur that hunted along the lakes of Liaoning, the best way we could describe it would be: Like a bird. Strange, but like a bird.

Curator and chairman of the American Museum of Natural History’s Division of Paleontology, Mark Norell has been at the forefront of documenting the evolutionary relationship of theropod dinosaurs and birds. In Mongolia, he discovered the first embryo of a carnivorous dinosaur, the theropod Shuvuuia, and the strange Mongolian bird Mononykus (see “New Limb on the Avian Family Tree,” September 1993). Norell has also analyzed the new fossil birds and dinosaurs emerging from northeastern China. Illustrator and photographer Mick Ellison, who has visited the Chinese site five times, is principal artist in the Museum’s Division of Paleontology. In addition to his work illustrating fossil creatures, he enjoys painting portraits of people.

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