Oldest bird and longest dinosaur.

Oldest bird and longest dinosaur

Just as the 150-million-year-old Archaeopteryxfossil is being reinstated as the earliest known bird after considerable controversy (SN:5/3/86, p.276), along come two crow-size skeletons that are not only 75 million years older than Archaeopteryx but also more birdlike, according to the paleontologists who discovered them. The Washington, D.C.-based National Geographic Society, which funded the work, announced this week that Sankar Chatterjee and his colleagues at Texas Tech University in Lubbock found the 225-million-year-old fossils near Post, Tex.

According to paleontologist John Ostromat Yale University, "the material is so fragmentary that the identification [as a bird] cannot be certified, but it certainly looks as though that's the right interpretation." If so, then the fossils, to which Chatterjee has given the genus name Protoavis (ancestral bird), add credence to the notion that birds originally arose from dinosaurs. Protoavis, like Archaeopteryx, has distinctly dinosaurian features, such as clawed fingers, a tail and teeth, as well as avian characteristics, such as a wishbone.

However, Chatterjee says that Protoaviswas a much more advanced bird than the Archaeopteryx fossils, which lack keel-like breastbones and were poorly suites for flight. "The wing structures of Protoavis are so well developed, there's no doubt it could fly," he adds. "And the skull is entirely like that of modern birds." Moreover, with no teeth in the back part of its jaws, Protoavis had started down the evolutionary path that enabled later birds, unencumbered by the heavy jaws needed to support teeth, to become masterful fliers, according to Chatterjee.

In Ostrom's view there is not enoughfossil evidence to say that Protoavis was indeed more advanced. But if Chatterjee is correct, his find lends support to scientists who have argued that Archaeopteryx was too primitive to be a direct ancestor of modern birds--that there was too little time for the Archaeopteryx to evolve into the great variety of birds, some closely resembling modern species, that developed in the next tens of millions of years.

"Scientists have speculated that somebodywould find [a much older bird]," says Chatterjee. "And that is where Protoavis fits in."

No impressions of feathers were foundwith the Texas fossils, but Chatterjee says there are bumps on the forearm and "hand" to which feathers were probably attached. He thinks that Protoavis could fly between trees in the tropical forest it lived in, but not much farther.

Ostrom calls the Protoavis fossils "anextraordinarily improbable discovery" because the fragil bones of birds are rarely preserved this well. Chatterjee suspects the birds were drowned in a flash flood and were not crushed or deformed because they were entombed by a blanket of mud.

At the other end of the soze spectrumfrom birds are the dinosaur giants. In recent years, scientists have unearthed the remains of Supersaurus and Ultrasaurus, animals weighing in at about 75 or 80 tons and measuring about 90 to 100 feet long. Now paleontologist David Gillette unveils Seismosaurus, or "earthshaker," a dinosaur he thinks was even longer and possibly even larger.

Seismosaurus's bones were discoveredby three hikers at a site about 60 miles northwest of Albuquerque. Last year a team led by Gillette, curator of paleontology at the New Mexico Museum of Natural History in Albuquerque, excavated eight joined vertebrae from a 10-foot midsection of the animal's tail, as well as fragments of a thighbone and other as-yet-unidentified bones. The researchers plan to excavate more bones this fall.

In an announcement last week, Gilletteestimated that Seismosaurus was 100 to 120 feet long, 18 feet tall at the shoulder and 15 feet tall at the hip, and weighed 80 to 100 tons--about 12 times heavier than a modern bull elephant. The 150-million-year-old bones were discovered in the Morrison formation, in which Supersaurus and other large, long-necked dinosaurs of the Sauropod family have been found. Paleontologists are not sure whether the recently discovered Sauropods represent new species or are just unusually large individuals of a known species. Gillette's find, says Ostrom, "reinforces the image that many dinosaurs seem to have been very large--larger than any living animal. One can't help wonder why. What's the biological importance of being so huge?"