Science: 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...

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