Dinosaur Tales

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While the Pompeii layer preserved natural body postures, it was too coarse to take imprints of soft tissues and delicate structures, so there's no way of knowing whether Mei long had feathers. But other strata of the Liaoning fossil beds are much finer grained. That's where paleontologists found the feathered tyrannosaur, which Xu and Norell named Dilong paradoxus ("surprising emperor dragon"). It's one of the oldest known tyrannosaurs, and one of the emu-size specimens has unmistakable traces of primitive feathers on its tail and jaw. Those filaments, which are about three-quarters of an inch long and branched like modern feathers, are the first direct evidence that tyrannosaurs sported plumage. Because Dilong paradoxus is one of the earliest tyrannosaurs, Norell and his colleagues infer that its larger, more advanced relatives, including T. rex, must have had feathers for at least part of their life span.

That notion is reinforced, albeit indirectly, by the growth analysis Norell and a group of American and Canadian scientists published in Nature in August. By looking at growth lines — skeletal marks, analogous to tree rings, that show how much bigger a dinosaur got from year to year — the scientists were able to estimate that T. rex packed on weight at a blistering pace, sometimes as much as 5 lbs. a day. That also supports the idea of warm-bloodedness, which means baby T. rex had to have a way to retain body heat. As the dinosaur shot toward adulthood, however, it would have developed the opposite problem: shedding the excess heat pumped out by an active, 11,000-lb. body. Norell and Xu theorize that T. rex probably lost its feathers as it matured, just as growing elephants lose their body hair.

Impressive as these new discoveries are, they hardly mean that all the details of the dinosaur-bird link have been ironed out. While current thinking favors speedy predators like velociraptors as the direct ancestors of modern birds, both Chiappe and Norell argue that the birds' forebears could just as easily have been troodontids like Mei long or even oviraptors, another related type of dinosaur. (Several years ago in Mongolia, Norell and colleagues unearthed a fossil oviraptor sitting on its egg-filled nest.) And then there's also the open question of how flight evolved. Mei long, says Chiappe, was clearly sleeping on the ground. But if flight began as flying-squirrel-like glides out of trees, he wonders, "wouldn't it have been safer resting in a tree?"

Those are important points, and they may take years to work out. But the fact that paleontologists are focusing on such details makes it clear that the dinosaur-bird connection, so bitterly controversial just a few short years ago, is no longer in dispute.