Shape evolution and sexual dimorphism in the mandible of the dire wolf, Canis dirus, at Rancho La Brea.

摘要

The Rancho La Brea tar pits are a classic fossil lagerstatten, famous for the deposition of episodic accumulations of large numbers of fossils over short intervals in the late Pleistocene. I analyzed 157 Canis dirus (dire wolf) hemi-mandibles from Rancho La Brea through a 2D landmark-based morphometric analysis to test for size and shape changes through time. I scored 16 landmarks on each mandible gathered from four pits of different ages: 61/67 (∼13--14 thousand years ago [ka]), 13 (∼17--18 ka), 2051 (∼26 ka), and 91 (∼28 ka). Analyses indicate size does change through time, and shares a broad correlation with climate change. A principal components analysis revealed shape variables also fluctuated from pit to pit. Other environmental effects, such as competition, nutritional stress, and prey-preference, may also vary through time. These effects, along with climate, must be considered in determining the causalities of the size and shape changes we see in the dire wolf jaws. In addition, some sexually dimorphic signals are also distinguishable among the mandibles, and are similar to those seen in the extant gray wolf (Canis lupus).