Somewhere in eastern Montana, in the rolling, eroded hills known as the Hell Creek formation, paleontologist Jack Horner sips a beer and looks down at the most complete Tyrannosaurus rex ever unearthed. It lies on its left side, its neck twisted back pitiably. Horner's crew has just exposed a section of pelvic bone to its first sunset in 65 million years, and someone remarks on the redness of the bone, like smoked bacon.
"It's the comet," says Horner, with a deep nod.
"That's why it's smoked," his crew chief says.
Well, O.K., maybe not. Have a beer, sit down in the...