These New Mexican badlands were chock-full of turtle shells, gator bones, and mammal teeth. Familiar enough, but most of these mammals were barren lineages with no descendants in the modern world. Elsewhere, the earth was running truly strange experiments, straining to fill the ecological chasm left by the dinosaurs’ disappearance. In South America, there was titanoboa, a 2,500-pound snake stretching almost 50 feet. The monster snake would be matched in fearsomeness by the continent’s “terror birds,” which first evolved in the Paleocene but would later grow heads the size of horses,
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