They call 55-million-year-old Diatryma gigantean a terror bird. And the evidence is compelling.

This flightless species stood some seven feet (two meters) tall and was armed with a strong beak and powerful clawed feet. In North America and western Europe, scientists say, Diatryma likely took over as top predators once the dinosaurs had died offpossibly even hunting ancestors of today's horses.

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