Golden eye, a two-foot-long savanna monitor lizard, is about to make a contribution to science. His keeper, Tomasz Owerkowicz, sets him down on a treadmill enclosed by a large plastic box, then flips the power switch. Golden Eye’s pink, forked tongue flicks out, testing the surface of the treadmill. When Owerkowicz nudges him with his gloved hand, Golden Eye starts to trot at a steady pace. He’s my best runner, says Owerkowicz proudly. Occasionally he offers the lizard encouragement--sometimes another nudge, sometimes a cheer (Come on, sweetie pie). Soon Golden Eye is trotting faster and his throat is moving up and down. I used to think that was connected with the tongue-flicking, but it’s not, Owerkowicz says. They do it when they get tired; it’s a way to increase their oxygen intake, I think.
Owerkowicz, a graduate student in biology at Harvard, is happy to see Golden Eye getting a good workout. He is something of an animal personal trainer--every day for the last few months, he has coached savanna monitors, hedgehogs, and ground squirrels through 20-minute treadmill workouts. In their well-exercised bodies (and particularly in their bones), Owerkowicz thinks there are clues to one of paleontology’s longest, hottest, and most popular debates: Were dinosaurs warm-blooded endotherms like the hedgehogs and squirrels, or cold-blooded ectotherms like Golden Eye?
In the last decade, warm-bloodedness has gained a firm upper hand. Remember the scene in Jurassic Park in which high-energy velociraptors let out steamy breaths as they stepped into a walk-in refrigerator? Cold-blooded animals could never have done that. And though clearly the scene is Hollywood make-believe, many scientists think it has a core of truth. Over the years they’ve amassed a pile of evidence-- everything from the microscopic structure of fossilized dinosaur bones to the dinosaurs’ postures--to support the case for warm-bloodedness, and their argument has been persuasive. Textbooks now usually portray dinosaurs as hot to trot, and natural history museums are furiously revamping their displays to reflect the image makeover. Once thought of as dim-witted, sluggish, oversize reptiles, dinosaurs are now shown as highly intelligent speedsters. Triceratops eludes its predators by galloping away; herds of migrating duck-billed dinosaurs called hadrosaurs care for their young in communal nesting grounds; and a number of carnivores, including Velociraptor, leap and slash at prey with lethal, sickle-shaped claws.
Yet not everyone has been lured into the warm-blooded camp. Even as the museum technicians were starting to hike up their fossils, a small but growing coterie of paleontologists and physiologists was preparing to launch an assault against the new vision of the extinct beasts. They began questioning the claims being drawn from the fossil evidence, searching for a truly incontestable mark of endothermy. So far, these revisionists have found, all the studies suggest that dinosaurs should go back to the ectothermic fold.
A lot of this business about warm-blooded dinosaurs was just blown way out of proportion, says Alan Feduccia, an evolutionary biologist at the University of North Carolina at Chapel Hill. It was just pure hype. So I applaud these new studies. Dinosaurs are beginning again to look like reptiles--although not your everyday ones. As Owerkowicz and crew are quick to point out, a reptilian metabolism is not an insult. Dinosaurs could still be very active and agile, especially the bipedal ones, says Owerkowicz, and they could have lots of interesting behaviors, just as in Jurassic Park. But no, I don’t think they would have steamed up the refrigerator.
