Just after The Origin of Species debuted in 1859, T.H. Huxley wrote his friend Charles Darwin, "I am sharpening up my claws and beak in readiness." Huxley, with his jaw thrust out combatively and muttonchop whiskers abristle, defended evolution on the public lecture circuit, the 19th-century equivalent of the television talk show. He pounced on the discoveries of the dinosaur-like bird Archaeopteryx and the bird-like dinosaur Compsognathus in the 1860s as evidence of a missing link between birds and dinosaurs. A decade later, he added to his arguments Othniel C. Marsh's reconstructions of fully feathered Cretaceous birds with crocodile teeth.

Anatomical similarities to birds implied that at least some dinosaurs must have been warm-blooded like birds. Chicken-sized Compsognathus was clearly built for speed and no one denied it. Edward D. Cope's vision of the larger Laelaps, relative of the venerable Megalosaurus, was that of an aggressive, leaping fighter. It would need more than a lizard's passive solar heat to make it the energetic predator Cope imagined.

All the while, Victorian paleontologists nursed an acute case of ambivalence. When Huxley went so far as to propose a new classification of the dinosaurs in 1869 that emphasized their avian, rather than reptilian features, he was ignored. The great sauropods such as Apatosaurus just seemed too unbelievably large not to be sluggish and therefore cold-blooded. Marsh passed up sauropod characteristics that screamed "bird," such as air-filled bones, to fixate on their tiny heads. "The very small head and brain, and slender neural chord, indicate a stupid, slow moving reptile," he wrote in 1883.

Marsh's judgment of the failings of a small brain was perfectly plausible in an era when phrenology--the measurement of human cranial capacity to determine intelligence and character--was all the rage among psychologists and anthropologists.