Wings over Spain

Luis M. Chiappe

Recently I learned that The Valley of Gwangi, a 1969 "lost world" movie that featured Mexican cowboys battling vicious dinosaurs and pterosaurs, was largely filmed in and near the picturesque medieval town of Cuenca, in central Spain. What the filmmakers couldn't have foreseen was the discovery in the mid-1980s of a real and more exciting prehistoric realm buried in a small pocket of limestone at a site near Cuenca. Fossils from this site, which the locals call Las Hoyas, preserve the remains of an array of creatures that lived in and near a freshwater lake some 115 million years ago.

Today, this region is hilly and arid, with occasional rock outcrops surrounded by pines and other trees. The thin-layered rocks of Las Hoyas, which cover an area of just a couple of acres, are known as lithographic limestones, the kind once used by printmakers; they preserve the remains of ancient animals in exquisite detail. Over the past decade, Jose L. Sanz and his associates, from the Universidad Autonoma in Madrid, have excavated an entire Mesozoic ecosystem--including insects, crustaceans, fishes, amphibians, and dinosaurs--from the Las Hoyas limestones. Among the most precious finds are fossils of primitive birds, which I have had the privilege to study with my Spanish colleagues.

The detailed fossils reveal not only the small, delicate bones of birds but also their feathers, and in one case the remains of a last meal--seafood--in the stomach. But the bird that never had the chance to digest that supper has a bigger claim to fame. It has given us new clues as to how and when in their evolutionary history early birds fine-tuned their ability to fly. The impressions of this bird's wing plumage included a small tuft of feathers attached to the "thumb." Immediately recognizable as the bastard wing, or alula, this feature is a characteristic of many modern birds but had never before been encountered in a fossil bird from the Mesozoic. The new bird was christened Eoalulavis, "early bird with alula." The presence of the little tuft shows that fully 115 million years ago, the finch-sized bird was able to fly and maneuver almost as well as its modern counterparts.

The bastard wing functions like the wing flap on an airplane. When a bird wants to reduce its speed or make a landing, it increases the angle of its wing to the horizon. The drag produced by this wing position helps the bird slow down. But when the angle between the direction of the airflow and the wing surface gets too steep, turbulence over the wing increases until the bird loses the lift necessary to maintain flight. Like an airplane under similar circumstances, the bird is in danger of stalling in midair. The bastard wing then comes to the rescue. By raising this small appendage, the bird creates a slot between it and the main part of the wing, similar to what happens when a pilot deploys a craft's wing flaps. The slot allows air to stream over the main wing's upper surface, easing turbulence and allowing the bird (or plane) to brake without stalling.

The primitive birds from Las Hoyas are not the only ones known from Spain. For the past century, bird feathers have been found in the lithographic limestones of the Montsec range of Catalonia, in the north. These deposits are older than those of Las Hoyas, and they too once formed the bottom of a freshwater lake. A recent and extraordinary find (made by an amateur fossil hunter, who presented the specimen to a Catalonian museum) proved to be the remains of a 135-million-year-old hatchling, the most ancient ever found.

Like any modern hatchling bird, this as-yet-unnamed relative of Eoalulavis has a large head with enormous eye orbits. But other aspects of its skull--such as the presence of teeth, the relative size of the braincase, and the ample space for the attachment of jaw muscles--are reminiscent of Archaeopteryx and birds' dinosaurian ancestors. Where the hatchling is far more advanced than Archaeopteryx, however, and closer to modern flying birds is in its specializations for powered flight--the design and proportions of its wings and shoulder. (As an older but close relative of Eoalulavis, it may also have had a bastard wing, although this is not evident in the fossil.) So, despite its toothy, dinosaurian-looking head, this bird, in adult form, probably flew as well as Eoalulavis.

During the early history of birds, evolution focused primarily on the development of flight. The 150-million-year-old Archaeopteryx, the earliest-known and most primitive fossil bird, was probably not an accomplished flyer. Yet by 115 million years ago, or possibly even 135 million years ago, some primitive birds not only flew but flew well, having developed novel structures they used aerodynamically.

Unprecedented numbers of Mesozoic birds discovered worldwide over the past twenty years have contributed to a revolution in evolutionary thought among paleontologists. The fossil record has shown birds to be the direct heirs of bipedal dinosaurs (see "First Came Feathers," facing page, and "Origins of the Feathered Nest," Natural History, June 1995). We also now know that birds were a large and diverse group, even in their early evolutionary history (see "A Diversity of Early Birds," Natural History, June 1995). The early birds from Spain take their place in this growing roster and show us that the airspace above the large land dinosaurs was full of flapping wings.

RELATED ARTICLE: First Came Feathers

Our language has its share of sayings when it comes to birds. Birds of a feather flock together. If it walks like a duck and quacks like a duck, it must be a duck. These are a couple that come to mind. For better or worse, these old saws might require some revision, based on discoveries of two new fossil animals from northeast China.

The two turkey-sized creatures were found m fine-grained lake sediments, estimated to be 135 million to 122 million years old, near Beipiao City, in Liaoning Province. They belong to the coelurosaurs, a group of theropod dinosaurs that now includes birds. The Chinese fossils have a whole slew of features--hollow bones, flexible wrists, and wishbones, to name a few--that ally them with birds, and whose presence in other coelurosaurs have for mine time indicated to paleontologists that birds are the descendants of coelurosaurian dinosaurs. Other features--including an opposable hallux (or back toe) and smooth-enameled teeth--are characteristics of Mesozoic birds and are not present in the Liaoning animals. But the new fossils consist of more than bones and teeth; they contain remarkably well preserved feathers. The presence of feathers in animals that are not birds forever blurs the distinction between birds and their closest relatives and indicates that feathers alone are not sufficient evidence for calling something a bird.

Named Protoarchaeopteryx and Caudipteryx (tail feather), the Chinese animals have feathers that are quite similar to those of modern birds. The feathers cover the entire body and have central shafts with branching barbs. Scanning electron microscopy shows that the barbs are held in alignment by smaller barbules--tiny, Velcro-like hooks that give feathers their neat appearance, even after a fair amount of ruffling. As in modern birds, the long arm feathers (preserved in Caudipteryx but not in Protoarchaeopteryx) emanate from the hand, although the primary feathers of modern flying birds tend to be even longer. In the dinosaurs, the barbs are distributed symmetrically on either side of the shaft, unlike the asymmetric, and more aerodynamic, distribution of barbs found in the wing feathers of modern birds. Both Protoarchaeopteryx and Caudipteryx have long tails covered in feathers with a flourish at the tip: a clump of feathers that form a fan.

Although fully feathered, neither Protoarchaeopteryx nor Caudipteryx could fly. The origin of feathers and the origin of flight are separate issues. Likely scenarios for the evolution of feathers concern their use for display or insulation. Patches of downlike feathers on some parts of the Chinese animals appear, in my opinion, to support the insulation argument, as does the remarkable fluffy covering of another, much more primitive coelurosaur from the same deposits, Described in 1997, Sinosauropteryx is known from several specimens, all of which show this covering. While not consisting of true feathers, this feature is also powerful evidence that its coelurosaurian relatives, such as Velociraptor, Troodon, and even Tyrannosaurus, were also cloaked in protofeathers.

How bird flight originated is still a wide-open question, but proponents of the "trees down theory" (a hypothesis that holds that flight developed after an intermediate gliding stage) cannot be too pleased to learn that both Caudipteryx and Protoarchaeopteryx, while feathered, were flightless ground-dwelling runners. This fact does not close the argument, but it does lend support to the idea that flight arose from the ground up rather than from trees down.

What do these discoveries ultimately mean? To me, it is a matter of perception. If we could travel back in time to the late Mesozoic, some animals would be familiar, others alien. But if we focused only on early birds and their close dinosaur relatives and compared them, we would find little outward difference between these avian and nonavian dinosaurs. This is what the fossils are telling us in the strongest statement yet: the dinosaurs are still among us in the form of the feathered bipeds we call birds.

Mark Norell is a curator and chairman of the Department of Verrtebrate Paleontology at the American Museum of Natural History in New York.

Vertebrate paleontologist Luis M. Chiappe is a research fellow and associate in the Department of Ornithology at the American Museum of Natural History in New York.

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