Evolution in the sabertooth cat, Smilodon fatalis, in response to Pleistocene climate change

The late Pleistocene was a time of environmental change, culminating in an extinction event. Few fossil localities record a temporal series of carnivore fossil populations from this interesting interval as well as Rancho La Brea (RLB). We analyzed mandibles of Smilodon fatalis from RLB using 2D geometric morphometrics to examine if, and how, mandibular shape changes through time. S. fatalis shows mandibular evolution with oscillations between a small, ancestral-type morph in pits 77 (≈37 Kybp) and 2051 (≈26 Kybp), a larger, more derived morph in pits 91 (≈28 Kybp) and 61-67 (≈13.6 Kybp), and an intermediate morph from pit 13 (≈17.7 Kybp). These oscillations end in pit 61-67, where Smilodon exhibits its greatest body size, widest gape, and lowest bite forces. Additionally, variation is lowest in pit 61-67, which was deposited concurrent with the Bølling-Allerød warming event, which may have important implications for the timing or conditions during the extinction event. Contra to a temporal Bergmann’s rule, such rapid warming events appear to be correlated with larger, derived, morphologies while static, cooler, climates correlate with gracile, ancestral morphologies.