Feathered non-avian theropods found

Jeff Poling

Scientists reported in the June 25, 1998, edition of the journal Nature the discovery of two new fossils from Liaoning, China. The early Cretaceous Liaoning site is already known for its spectacularly preserved fossils of soft tissue including feathers on specimens of Confuciusornis and possible protofeathers on Sinosauropteryx. The two new animals, named Protarchaeopteryx robusta (robust first ancient-wing) and Caudipteryx zoui (Zou Jiahua's tail feather), also have feathers preserved but add to the list of incredible Liaoning discoveries for a different reason: they are, according to the authors, the first dinosaurs preserved with unambiguous feathers that are not in the clade Aves, the clade commonly referred to as "birds."

The animals were covered with feathers, including down, like those of Archaeopteryx and modern birds, with central rachis, radiating vanes and barbules. Unlike those of Archaeopteryx and all flying birds, the primary feathers of Protarchaeopteryx and Caudipteryx were symmetrical, indicating they were incapable of sustained powered flight. The feathers covered their bodies and formed "wings" on their forelimbs and large fans on their tails.

Protarchaeopteryx and Caudipteryx were approximately turkey-sized with long legs suitable for swift running.

Neither animal had the fully reversed first toe held close to the ground that Archaeopteryx and modern birds have, an adaptation for perching. Instead, the toe was farther up the foot in a position typical of non-avian theropod dinosaurs.

Both animals had U-shaped furculas typical of those known from both avian and non-avian theropods.

Both fossils were found with gastroliths, or "stomach stones," like those found in modern birds and some predentatan dinosaurs, but never before found in theropods.

Both animals had gastralia, or belly ribs, typical of those of non-avian theropods and early birds.

The teeth of Protarchaeopteryx were serrated, unlike those of all known birds, including Archaeopteryx. The teeth of Caudipteryx were confined to the premaxillary, and were elongate and spike-like, unique among all theropods.

Both animals had the semilunate (half-moon) shaped bone in the wrist typical of birds and other maniraptoran theropods such as the dromaeosaurs, which includes animals like Velociraptor. Their unfused fingers also had the typical theropod and early bird phalangeal formula (number of bones in the fingers) of 2-3-4-x-x. All fingers supported claws, with keratinous sheaths preserved on two claws of Protarchaeopteryx.

The tail of Protarchaeopteryx was comprised of up to 28 vertebrae, similar to non-avian theropods, while Caudipteryx's tail was comprised of 22 vertebrae like that of Archaeopteryx.

The forelimbs of Protarchaeopteryx were shorter, compared with the femur, than in birds but was longer than those of long-armed non-avian coelurosaur theropods such as the dromaeosaurs. The forelimbs of Caudipteryx were shorter relative to the femur than in both birds and non-avian coelurosaurs.

Because of the lack of the perching adaptation and the other synapomorphies that uniquely identify Aves (not listed here for brevity), both animals have been placed outside of the birds. The fossils do, however, have the characters typical of theropod dinosaurs. On the dinosaur family tree, Caudipteryx is placed very close to, but more primitive than, Archaeopteryx and all other birds while Protarchaeopteryx is considered to be closely related to the dromaeosaurs.

Many paleontolgists and enthusiasts feel the presence of confirmed feathers on non-avian dinosaurs should remove any lingering doubts that birds are dinosaurs. "It is a historic moment when a controversy is resolved," Dr. Phil Currie of the Royal Tyrrell museum in Alberta, Canada, said at a National Geographic Society news conference. "This shows that dinosaurs are not extinct, but are well-represented by 10,000 species of birds."