12 March 2012

Fossil Vertebrate of the Month: Panthera atrox

P. atrox in the Natural History Museum of L.A. County
John Orcutt, 2010
At least in Oregon, this March has certainly come in like a lion, which inspired this month's FVOTM: Panthera atrox, the American lion.  There has recently been some debate over whether or not this common name is correct: while very lion-like, Per Christiansen and John Harris have suggested that it was actually more closely related to jaguars.  I come down on the other side of the debate: the morphological data are, at best, ambiguous (and I would argue that they tend to favor the interpretation of P. atrox as a true lion) and molecular data from subfossil specimens indicate that P. atrox was very closely related to both modern lions and to European cave lions (in fact, some have argued that all three species really should be lumped into one).  Panthera atrox is best known from the "tar" seeps of Rancho La Brea, where it is the most common conical-toothed cat (though not the most common cat; that honor goes to the saber-toothed Smilodon).  Because it is less common than its machairodontine "cousin," it has been suggested that, unlike modern lions, P. atrox might have been solitary; this should come as no surprise as modern lions are very unusual among cats in living in large social groups.  Panthera atrox certainly would have been large enough to tackle prey on its own.  In fact, with the largest individuals weighing in at somewhere around 350-400 kg, it was probably the largest conical-toothed cat ever, and would have been in the same size range as the largest saber-tooths (as well as a few species of bear).

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