Big Old Mammal .

Last week Chicago's Field Museum of Natural History placed on exhibition a unique skeleton: that of Titanoides faberi, earliest mammal of its size known to exist on Earth.

Like birds, mammals are revealed in the fossil records as descendants of reptiles. As long as 200,000,000 years ago some clumsy reptiles like Cynognathus ("Dog-Jaw") were already showing mammalian quirks around the mouth. By 100,000,000 years ago a few small creatures had probably crossed the mammalian line. Waiting for the gaudy Age of Reptiles to ring down its curtain, the little mammals had promising new equipment--hair for warmth, hot blood for cold weather, milk to feed their young on the move. Their brains grew bigger. When the mighty lizards died out, they were ready to spurt.

Sixty million years ago--the dawn of their Age--Titanoides was the biggest of mammals, about the size of a polar bear. Stout, thick-legged, big-tailed, weighing half a ton, probably a fine swimmer, Titanoides liked swamps, crushed lush water plants in his none too capable teeth. Prior to 1932 the only evidence of him was a single jawbone. Then Bryan Patterson of the Field Museum found three skeletons, two fragmentary, one almost complete, near Grand Junction, Colo. The excellent specimen put on show in Chicago last week is the only one of Titanoides visible in any of the world's museums.

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