Measures of Relative Dentary Strength in Rancho La Brea Smilodon fatalis over Time

Abstract

The late Pleistocene megafaunal extinction of approximately 12,000 years ago, included the demise of Smilodon fatalis, a hypercarnivore from the Rancho La Brea deposits, which has been studied across time by looking at different deposits or pits to determine morphological size and shape changes and trends during this time. To better understand functional aspects of these changes, this study focused on a measure of jaw strength over time, which can give an indication of morphological changes within the jaw that cannot be seen using surface morphometrics. By radiographing dentaries, cortical bone can be seen, which provides an estimate of resistance to bending forces while biting, and can be measured and used as an indicator of jaw strength. Measurements were taken at repeatable locations on the dentary of the depth of the cortical bone, and of a standardized measure of cortical bone, which allows for the comparison between different individuals. Specimens included those of five different pits ranging from about 37 Kybp to 13 Kybp (just before the extinction of S. fatalis). No significant difference was found in the depth of jaws at any of the measurement points from any of the pits. However, significant differences were found in both the actual thickness of cortical bone, and the standardized thickness of cortical bone at the lower P4 between pit 13 (which had the lowest amount of bone) and pit 61/67 (which had the highest). These conclusions support other studies that have shown that individuals in pit 13 were under physiological and perhaps dietary stress, which may be reflected in the deposition of cortical bone, while the opposite trend is seen in the individuals in pit 61/67. Our results further support findings suggesting Smilodon did not appear to be morphologically most vulnerable right before its extinction.

Geomitologia da Pedra da Onça: Conservação do Patrimônio Natural e Cultural por meio da História do Gato-maracajá, o Verdadeiro Felino da Ilha do Governador, Rio de Janeiro, RJ

“…Smilodon fatalis apresentou certas adaptações no Rancho La Brea ao longo do tempo, referentes ao aumento ou redução da resistência da mandíbula e dos dentes no decorrer das sucessivas mudanças faunísticas, com modificações que foram mais favoráveis ao consumo de presas cujas carnes e ossos fossem mais rígidas ou macias (dependendo do intervalo temporal e do paleoclima observado, sendo relacionados ao tamanho e robustez do animal predado). Modificações nos ângulos de abertura da mandíbula também foram notadas, estando associadas com as alterações no tamanho da fauna (Binder, Cervantes & Meachen 2016;Meachen, O'Keefe & Sadler 2014). Ademais, a produção de espessos ossos corticais exige muita energia, além de tornar o animal mais robusto e lento.…”