Bird wings clearly share ancestry with dinosaur "hands" or forelimbs. A school kid can see it in the bones. But paleontologists have long struggled to explain the so-called digit dilemma. Here's the problem: The most primitive dinosaurs in the famous theropod group (that later included Tyrannosaurus rex) had five "fingers." Later theropods had three, just like the birds that evolved from them. But which digits? The theropod and bird digits failed to match up if you number the digits from 1 to 5 starting with the thumb. Theropods looked like they had digits 1, 2 and 3, while birds have...