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Three basic morpho types are proposed for cats on the basis of their upper canines: 1) conical-toothed cats with short, unserrated canines having a round cross-section; 2) scimitar-toothed cats having short, broad canines, usually with very coarse serrations; and 3) dirktoothed cats having long, slender canines which usually have fine serrations. Commonly all three morphotypes occur together in the same fauna. The method of prey capture was probably different for each morphotype. Both types of saber-toothed cats appear to have specialized on large prey, but it seems unlikely that they utilized the same prey. Scimitar-toothed cats are long-limbed, and were probably pursuit predators. Dirk-toothed cats are short-limbed and must have ambushed their prey.
The separation of cats into two families, Nimravidae and Felidae, is accepted. Felid cats have a septum bullae in the auditory bulla and a cruciate sulcus on the brain. Nimravid cats generally lack complete bullae, and when they are present there is no septum. Nimravid cats also lack the cruciate sulcus on the brain.