Tom stepped into another scientific controversy when he proposed that the small dinosaurian ancestors of birds evolved wing feathers, not to fly, but to brood their young. Flying, according to his theory, came later.

The relationship between birds and dinosaurs has become obvious in light of fossil discoveries. Around 100 million years ago or more, animals existed that were feathered, but lacked the long wing feathers modern birds now use to fly. Theorists have divided into two camps over how non-flying dinosaurs evolved into creatures with long feathers on their forelimbs that enabled their transition from the ground into the air. The two camps are the arborialists, who hypothesize that tree-dwelling dinosaurs evolved flight by jumping and gliding from trees. Cursorialists postulate that bird flight arose from the ground up, when small, two-legged running (cursorial) animals somehow attained the feathered lift to rise into the air.

Each side of the controversy has had its merits and advocates. And each side has had its problems and detractors. Key weaknesses in both theories involve the first stages. How could animals without wings begin jumping from trees? Wouldn't they be injured or killed? On the other hand, why would wingless ground creatures ever flap their featherless arms? How could that lead to liftoff?

Such was the state of the controversy when Tom got involved. Weighing both arguments, he thought he saw more logic in the cursorial, ground-up, theory. After researching knowledge in the field, he and long-time friend Mark Orsen developed a new version of the old cursorial theory: the Brooding-to-Flight Hypothesis.

In this concept, small, two-legged running dinosaurs, which are known from fossil evidence to have had short feathers all over their bodies, evolved long feathers on their forelimbs, not to fly at first, but to brood their young. Over time, longer and longer feathers evolved, first to augment the brooding function, and then when the feathers were long enough, to augment the animal's airborn time when it leaped up from the ground (to avoid enemies, for instance).

This theory has attracted interest from paleontologists because it is the first to offer both a rationale as to why the feathers lengthened, and also a scenario in which GRADUAL lengthening makes sense: any small improvement to the ability to shelter offspring would offer an immediate survival advantage, whereas both the ground-up and trees-down flight hypotheses fail to explain the middle stages, because short or medium feathers are useless for flight.