Canis dirus was a large Pleistocene (2.6mya - 11.7 kya) canid. The latin name translates literally as the "fearsome dog", but is more commonly known as the dire wolf. Fossil remains are fairly common and have been found at over 100 sites in North America and several sites in South America. Without question, the most productive site of C. dirus fossils is the Rancho La Brea Tar Pits in Southern California, where over 200,000 specimens have been recovered (Merriam, 1912; Nowak, 1979; Kurtén & Anderson, 1980; Kurtén, 1984; Stock & Harris, 1992; Dundas, 1999; Anyonge & Roman, 2006; Anyonge & Baker, 2006).
The dire wolf thrived throughout a wide range of habitats. The South American range was dominated by arid savannahs, while North American habitats were grasslands, plains and mountainous forests. Its northern range extended into Southern Canada, but fluctuated significantly with glacial activity. The dire wolf became extinct throughout its range at the end of the Pleistocene, in both North and South America (Dundas, 1999).
Canis dirus is a large canid that possessed robust, carnivorous dentition. It was an average of 1.5 meters in length (4.9 ft) and weighed between 50 kg (110 lb) and 79 kg (174 lb). This, paired with other physical evidence, provides ample evidence that C. dirus preyed upon large, herbivorous prey (Van Valkenburgh & Sacco, 2002).
There were major differences between eastern and western dire wolf populations with respect to the proportions of their skeleton. The western population (C. dirus guildayi) was smaller than the eastern population (C. dirus dirus) and is believed to have had a more recent origin than the eastern subspecies, which came about in the Sangamon interglacial stage of the Pleistocene (125,000 - 75,000 years before present)(Anyonge & Roman, 2006). The eastern subspecies was approximately 15% heavier than the western subspecies. The western subspecies itself was 25% heavier than the extant gray wolf (Canis lupus) (Kurtén 1984; Anyonge & Roman, 2006).
Canis dirus is thought to have looked very similar to a larger gray wolf (Canis lupus), but one that possessed a massive, robust skull. Its mandibles were heavy, and held large teeth. The carnassials (cutting or shearing tooth) were especially enlarged (Van Valkenburgh & Ruff, 1987). In fact, C. dirus teeth were more outwardly similar to those of hyenas and other bone-cracking species, than to modern canids (Hill, 1991). However, C. diruswas not a bone crusher. It possessed a snout that was much too long to be a durophagous carnivore (bone crusher) and lacked the underlying specializations that these requisite bone crushers possess, such as increased bite force and thickening of the enamel (Hill, 1991). Therefore, the feeding behavior was similar to that of the extant gray wolf (Canis lupus), but larger prey may have been more consistently targeted (Hill, 1991; Anyonge & Baker, 2006).
Much like modern wolves, sexual dimorphism is minimal in Canis dirus, with a slight increase in the overall body size and canine size of the male individuals (Van Valkenburgh & Ruff, 1987).
Scientists have made inference aboutCanis dirus social behavior, based upon the minimal levels of sexual dimorphism.Low levels of sexual dimorphism in canids is associated with monogamous behavior. Therefore, Canis dirus is thought to have lived in monogamous pairs within larger pack groups, much like modern gray wolves. (Van Valkenburgh & Sacco, 2002).
Canis dirus was a pack hunter of large prey species and used highly organized strategy to capture its prey. They would have filled an ecological role, similar to that of the modern gray wolf (Canis lupus), hunted larger prey (Van Valkenburgh & Sacco, 2002; Anyonge & Roman, 2006).
There are some differences in body size between the eastern and western dire wolf (Canis dirus) populations that may reflect differences in hunting behaviors and in locomotion (Anyonge & Roman, 2006). Fossil evidence suggests that Canis dirus preferred to hunt large herbivores (Anyonge & Roman, 2006). But given the ecological and morphological similarities that it shared with the extant gray wolf, it would not be drastic to assume that some of the western populations along the Pacific coast occasionally scavenged upon marine mammals and fish when other prey was scarce, much like modern Canis lupus populations (Fox-Dobbs et al., 2007).
The more gracile limbs of the eastern populations suggest a more predatory lifestyle than the western subspecies, as they were better suited for fast pursuit. Many fossil sites, such as La Brea, support this finding and suggest that the western population may have been better suited for scavenging (Kurtén, 1984).
The extinction of Canis dirus is thought to have resulted from the sudden loss of most North American megafauna and the inability to adapt to preying upon smaller prey species (Kurtén and Anderson, 1980).
A certain faction of researchers question whether C. dirus could have been a large regional variant or subspecies of C. lupus. This hypothesis has little substantiation, but it is interesting. The brief overlap of the dire wolf and the extant gray wolf (about 30,000–10,000years ago) is the only known period that two wolf species co-existed and this overlap is well represented in the fossil record (Stevenson, 1978; Arcadi, 2006).
