Crotalus oreganus

Pook et al. (2000), Ashton and de Queiroz (2001), and Douglas et al. (2002) analyzed mtDNA sequence data and concluded that Crotalus viridis comprised at least two clades, C. viridis and C. oreganus, with C. cerberus being the sister taxon to populations of C. oreganus. The former two studies did not formally recognize C. cerberus as a species, although both suggested that it was distinct based on sequence differences and allopatry. The latter study did recognize C. cerberus as well as four other taxa. Although the studies relied on the same locus, Crother (2017) conservatively conclude that the congruence among all three studies might suggest the recognition of C. viridis, C. oreganus and C. cerberus. An unpublished study (Goldenberg 2013) suggests a unique lineage, that has not yet been named, occurs in the southern part of the nominate species' range, and that the subspecies as currently recognized do not correspond with the actual species-level divergences in the group (Crother 2017).

The traditional view of rattlesnake taxonomy that recognizes the two monophyletic sister genera Crotalus and Sistrurus (e.g. Brattstrom 1964) has recently been challenged. Stille (1987) and McCranie (1988) presented data that suggested Sistrurus is not monophyletic and rendered Crotalus paraphyletic. Parkinson (1999) found Sistrurus monophyletic but its position rendered Crotalus paraphyletic. Knight et al. (1993) used mtDNA to defend the traditional generic taxonomy, but in order to do so ignored the most parsimonious tree. The genus Crotalus is monophyletic when including the Mexican C. ravus (Murphy et al. 2002), and is supported as such in most recent phylogenies, as well as being the sister taxon to a monophyletic Sistrurus (e.g., Pyron et al. 2013) (Crother 2017). Davis et al. (2016) used mtDNA and morphometric analyses that resolved six species within the C. viridis complex, which Crother (2017) don't follow pending further analyses with nDNA.

This species, recently separated from Crotalus viridis, ranges from southern British Columbia to central Baja California, and east to the Rocky Mountains (Pook et al. 2000), Ashton and de Queiroz 2001, Douglas et al. 2002). The ranges and relationships of Crotalus oreganus and Crotalus viridis in the Four Corners region and in northwestern Colorado have not been precisely defined and need further clarification (Hammerson 1999; Brennan and Holycross, 2004, Herpetol. Rev. 35:190-191). Elevational range extends from sea level to around 3,355 meters (11,000 feet) but most localities are below 2,745 meters (9,000 feet) (Basey 1976, Stebbins 2003, Campbell and Lamar 2004).

This species is represented by a large number (hundreds) of occurrences (subpopulations) (Campbell and Lamar 2004).

No major threats are known. Locally, populations are being reduced as a result of persecution and habitat loss and degradation from residential, commercial, and agricultural development.