Evolution in the sabre‐tooth cat, Smilodon fatalis, in response to Pleistocene climate change

Abstract

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 analysed mandibles of Smilodon fatalis from RLB using 2-D geometric morphometrics to examine whether, and how, mandibular shape changes through time. Smilodon 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, with greatest body size, and are estimated to have its widest gape and lowest bite force. 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 whereas static, cooler, climates correlate with gracile, ancestral morphologies.

The fossil record of phenotypic integration and modularity: A deep-time perspective on developmental and evolutionary dynamics

“…Thus, both size and shape changed significantly, variance increased, and magnitude of integration decreased through the last years of S. fatalis and C. dirus, but the patterns of phenotypic and developmental integration do not seem to have changed substantially and instead channeled these changes along existing directions of variation. These results are also consistent with repeated patterns of shape evolution observed in S. fatalis mandibular morphology (35) and with neotenic changes observed in C. dirus cranial morphology (36) through the same interval.…”

“…Although uncertainties in precise dates limit extrapolation to specific climatic events (35,36), our sample spans multiple episodes of climate change (Fig. 3), through which both S. fatalis and C. dirus display increasing variance over time.…”

“…Direct evidence on the timing of evolutionary changes in development in turn allows for more precise understanding of the selection pressures driving the developmental transitions that define many large clades. Lastly, fossils provide direct evidence of evolutionary responses to large-scale extrinsic factors, such as environmental change (34)(35)(36), allowing for combined studies of intrinsic and extrinsic influences on organismal evolution.…”

Cranial morphometrics of the dire wolf, Canis dirus, at Rancho La Brea: temporal variability and its links to nutrient stress and climate

“…Summary of Canis dirus cranial material used in the course of this study. Pit deposit information and dates in years before present condensed from O' Keefe et al, 2009; for calibration information see that reference and Meachen et al, 2014. The quoted pit ages are median ages in the windows of deposition, and constraint on the duration and time of each window is currently poor for most pits.…”

“…al, 2009;Meachen et al, 2014). Deposits of varying ages bracket the PleistoceneHolocene transition (Bølling-Allerod interval, Petit et al, 1999), the Younger Dryas cool interval, the Oldest Dryas cold interval, and preceding climate intervals (Kennet et al, 2008;see Table 1).…”