The La Brea asphalt seeps have me trapped. It seems I can’t visit Los Angeles without stopping by the Ice Age treasure trove to pester the paleontologists at Project 23 about what they’re finding and wander among the chocolate-colored skeletons inside the Page Museum. And in those halls, there’s one exhibit that never ceases to amaze me. Lined up behind glass are Smilodon skulls with two sets of fangs.

It’s actually not surprising that young sabercats temporarily carried two sets of upper canines. If you’ve ever raised a kitten, you may have noticed when their permanent teeth started to erupt and push their milk teeth out of the way. That’s a standard mammalian feature, as true for Smilodon as