The bottom line? You wouldn't want to meet a theropod in a dark alley. The research, to be published in this week's issue of the journal Science, offers insights into dinosaur metabolism, the warm-blooded versus cold-blooded debate, the question of whether or not dinosaurs might have been the ancestors of birds, and the biology that helped them dominate the world -- and eventually may have led to their extinction.

"This exquisitely preserved fossil shows that theropod dinosaurs had the ventilatory machinery to support periods of high activity, but that they lacked bird-style lungs or other anatomical features suggestive of a sustained high metabolic rate," according to Zoe Eppley, program director in NSF's division of integrative biology and neuroscience, which funded the research. "This find adds further support to the view that these dinosaurs were not warm-blooded."

This fossil is helping confirm that "the dinosaurs were indeed, by definition, cold-blooded, and that in all likelihood, birds are not the descendants of any known group of dinosaurs," said Nicholas Geist, a paleobiologist at OSU. "The extraordinary condition of this fossil allows us to 'hang some meat on the bones' of these animals and bring them back to life a bit. It's almost like a dinosaur dissection."

What that analysis reveals, Geist said, is an animal that had the best of both worlds. Like other cold-blooded animals, theropod dinosaurs had low metabolic rates while at rest, an excellent strategy for conserving energy. But their enhanced lung ventilation capacity gave them the potential for the aggressive, extended activity typical of birds and mammals. "Theropod dinosaurs were fast, dangerous animals," Geist said, "certainly not slow or sluggish. They could conserve energy much of the time and then go like hell whenever they wanted to. That might go a long way towards explaining why they were able to dominate mammals for 150 million years."

Geist and OSU colleague Terry Jones made these observations after study in Salerno, Italy, of a fossil first discovered just a few years ago of a baby Scipionyx, a meat-eater that lived about 110 million years ago and bore some similarity to a velociraptor. "Besides an intact skeleton, this fossil shows remnants of liver, large intestine, windpipe and even muscles," Jones said. "The baby dinosaur probably died in a shallow, still, saltwater marsh that preserved its structure incredibly well. It's like a Rosetta stone for paleontology, and shows us more about dinosaur biology than we ever knew before."

This type of physiology would provide some metabolic advantages unlike that of any animal still alive today, Jones said. "But for various reasons it only works well in a warm climate, which most of the world had during the age of dinosaurs. When the climate turned colder or more seasonal variation developed, what had once been the advantage of the dinosaurs became their problem."

Adds Geist, "A lot of people who only see cold-blooded reptiles moving slowly in temperate zones have no concept of what they can do in warmer climates and how well they can function. Then if you add in the lung capacity that we're finding for meat-eating dinosaurs, what you have is a turbocharged reptile. If you could go back in time and see one, that's probably the last thing you'd ever see."

Editors: Two color photographs in digital format of the Scipionyx fossil can be obtained by contacting Ute Vergin at 541-737-0785, or downloading directly from the Web at: http://www.osu.orst.edu/dept/ncs/photos/index.html

Note: If no author is given, the source is cited instead.

• Dinosaurs
• Paleontology
• Early Mammals
• Fossils
• Tyrannosaurus Rex
• Origin of Life

• Paralititan
• Feathered dinosaurs
• Brachiosaurus
• Archaeopteryx
• Hadrosaurus
• Velociraptor