The Year in Science: Paleontology

Sunday, January 08, 2006

Fresh Meat: T. rex Bone Yields Soft Tissue But No DNA

In March and June of this year, paleontologist Mary Schweitzer of North Carolina State University published two papers that rocked the world of dinosaur research. Studying fragments of a two-ton Tyrannosaurus rex femur found in Montana, she found soft tissue that apparently had survived roughly 68 million years.

Schweitzer's first find was a thin layer of medullary bone, a structure that identified the T. rex as female. Medullary bone is an inner layer that serves as a quick calcium source for egg-laying females. But until Schweitzer's discovery, it had been found only in female birds. The find adds weight to the theory that birds evolved from some dinosaurs.

Schweitzer's next find was more surprising. "The thought is that in dinosaur bone, all the organics are gone and replaced by minerals," she says. But by applying a dilute acid solution—a technique normally used only on fresh tissue—a lab technician exposed flexible fragments that look like modern tissue. Surprisingly, they included vessel-like structures with possible red blood cells inside. "It was just kind of like Christmas," Schweitzer says.

Although the ancient tissues look fresh, a closer look reveals that "they were altered," she says. That's bad news for finding dinosaur DNA. "I certainly don't think we'll be able to clone dinosaurs," she says. Was this a freak occurrence, or do other fossils lying in museum back rooms shelter soft tissue? How much has the T. rex tissue changed over time? Schweitzer is bent on finding out. "It's really fun," she says. "I'm excited."  —Elise Kleeman

Dino Hunters Find Bizarre Omnivore

Fleet, feathery, and wielding a wicked set of 4-inch-long claws, the 13-foot-long dinosaur had another intriguing trait: It apparently craved leafy greens as much as meat. Falcarius utahensis was unearthed from the Cedar Mountain Formation about a dozen miles southeast of Green River, Utah. In May the discovery team from the Utah Geological Survey and the Utah Museum of Natural History at the University of Utah dubbed the dinosaur "a missing link between small-bodied predatory dinosaurs and the highly specialized and bizarre plant-eating therizinosaurs."

Therizinosaurs are classified as maniraptorans, which probably evolved into birds during the Jurassic Period 150 million years ago. Falcarius had a sizable gut designed to ferment plants, and teeth better suited for shredding leaves than biting another animal. But it was also agile enough to hunt for meat. "This guy has a big brain and an incredible sense of smell," says James Kirkland, Utah's state paleontologist and leader of the study that announced the discovery. "Why does it need such a good sense of smell if it's a vegetarian? It has to be becoming a vegetarian because it has adaptations for digesting plants and consuming plants."

Falcarius's neck was elongated, perhaps for ease in browsing tree branches, and it tromped about in a landscape lush with vegetation, says Lindsay Zanno, a University of Utah doctoral student. Zanno is piecing together and analyzing the dinosaur's skeleton as well as conducting isotope tests on its teeth to narrow down its diet. That work, she believes, will help "redefine the evolution of the entire group of therizinosaurs."  —Kurt Repanshek

Oldest Embryos Suggest Dinosaurs Were Caring Parents

Scientists cracked open a pair of fossilized dinosaur eggs from South Africa and in July reported a momentous discovery. The eggs not only contained the oldest and best-preserved dinosaur embryos ever found but also offered the earliest evidence yet that dinosaurs may have nurtured their young.

A construction project unearthed a trove of six 190-million-year-old dinosaur eggs in Golden Gate Highlands National Park in South Africa nearly three decades ago, but the 2.4-inch-long fossils were embedded in fine-grain siltstone and too fragile to handle with the tools available at that time. A team led by paleontologist Robert Reisz of the University of Toronto at Mississauga excavated two of the eggs using miniature jackhammers and dental drills and revealed two specimens of baby Massospondylus carinatus, the predecessor of the giant long-necked sauropods, such as Brachiosaurus and Apatosaurus.

Although the dinos seemed to be just shy of hatching, they had no teeth. That suggests they had no way of feeding themselves and would have been tended by their mother—a level of after-birth care not previously seen in such ancient dinosaurs. The awkward body proportions of the baby dinos provided another surprise. The adult Massospondylus, which was typically 5 feet tall and had an 8-foot-long tail, walked on its hind legs and had short forelimbs. But the 6-inch-long hatchlings had four legs of equal length, a short tail, and an oversized head. Reisz theorizes that the dinos may have begun life on four legs and grew to be two-legged. If correct, this is a pattern of development unlike anything seen before.  —Kathy A. Svitil

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