In days of old, the cats were gold, and their teeth were used for stabbing: that’s the picture paleontologists once painted of Smilodon fatalis, the saber-toothed cat that roamed North America until its extinction 11,000 years ago. Hunting alone, the tan-colored cat raced its hapless prey across grassy plains and then plunged its vicious, daggerlike fangs into the neck of its quarry.