Page:The Outline of History Vol 1.djvu/72

has not yet revealed a single complete skeleton in the whole vast record of the Mesozoic rocks by which to check these guesses.

These little Theriomorphs, these ancestral mammals, developed hair. Hairs, like feathers, are long and elaborately specialized scales. Hair is perhaps the clue to the salvation of the early mammals. Leading lives upon the margin of exist-