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Keywords:

  • Canis dirus;
  • Pleistocene;
  • jaw musculature

Abstract

The craniofacial morphology of the extinct late Pleistocene dire wolf Canis dirus was compared with that of the living gray wolf Canis lupus, the spotted hyaena Crocuta crocuta and the extinct late Miocene bone-cracking canid Borophagus secundus. Fifteen indices that have previously been shown to reflect functional significance in the skull, jaws and related musculature of carnivorans were computed from a series of measurements made on the skulls of the four species and subjected to an analysis of variance and a principal components analysis. The results indicated that the extinct dire wolf was similar to the living gray wolf in 11 of the 15 indices. The dire wolf did not differ significantly from the gray wolf in the relative length of resistance arms to various tooth positions in the lower jaw or in the relative size, mechanical advantage and moment arm of the masseter muscle. The dire wolf was characterized by a relatively larger temporalis muscle that was capable of generating more force than that in the gray wolf. The extinct late Miocene borophagine dog B. secundus was intermediate between the two wolves and the spotted hyaena in most of the cranial and jaw indices, but displayed more similarity to the latter in several key features that can be attributed to their specialization for bone cracking. Borophagus secundus and the spotted hyaena tended to have short resistance arms and large jaw muscles with increased mechanical advantage for bites at various teeth. It is inferred that the dire wolf exhibited feeding behavior that approached that of the living gray wolf, but may have differed in killing technique, where it held longer to its struggling prey.