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The Current Taxonomic Status of Crotalus and Sistrurus


Gerald Keown

As most of us who work with reptiles and/or amphibians know, keeping up with the taxonomic status and scientific names of the various species is a continuing learning experience. The taxonomic standings of many of these animals are constantly evolving as we work to better understand them and continue to learn more about them utilizing the recent technologies available to us. To futher confuse matters, as these taxonomic changes occur, they do not always catch on with all herpetologists and herpetoculturists in a timely fashion with some herpetological workers being reluctant to accept the changes for various reasons.

Rattlesnakes belong to the taxonomic family Viperidae and to the subfamily Crotalinae commonly refered to as pitvipers, a name derived from the heat sensitive pit located on each side of the head between the eye and the nostril. There are 16 genera of Crotalinae snakes represented by about 150 species scattered throughout North America, South America, Europe and across Asia. Rattlesnakes make up 2 of these genera, Crotalus which occur throughout both North and South America, and Sistrurus which occur only in North America.

Rattlesnakes have undergone several taxonomic classification changes in recent years and it is anticipated that there will additional changes in the future.

As far back as 1973 studies concluded that what was then known as the Canebrake Rattlesnake, Crotalus horridus atricaudatus was not a valid subspecies of the Timber Rattlesnake, Crotalus horridus horridus. (Pisani, Collins, & Edwards. 1973. Transactions of the Kansas Academy of Science, 75:255-262). Their conclusion was not widely accepted and it was not until 30 years later in 2003 that their earlier work was corroborated using DNA. (Clark, Moler, Possardt, Savitzky, Brown, & Bowen. 2003. Journal of Herpetology 37 (1): 145-154). With the Canebrake Rattlesnake, Crotalus horridus atricaudatus being found to be nothing more than a geographic color variation of the Timber Rattlesnake, Crotalus horridus horridus, the subspecies atricaudatus was invalidated and today both forms are collectively known as the Timber Rattlesnake, Crotalus horridus. Even so, there are still a number of herpetoculturists who still insist on refering to the population from the southeastern United States as being the Canebrake Rattlesnake, Crotalus horridus atricaudatus.

Recent studies of the Western Rattlesnake Group which has consisted of nine different subspecies of Crotalus virdis found throughout the western United States, extreme southwestern Canada and extreme northern Mexico have led to a number of taxonomic changes within that group of rattlesnakes. In 2000 Pook, Wüster, & Thorpe conducted the first phylogeographic study of this Western Rattlesnake Group and suggested that three different full species should be recognized within the group. The following year Ashton & de Queiroz formally recognized two full species within the Western rattlesnake Group. Then in 2002 Douglas, Schuett, Porras & Holycross reviewed the systematics of the Western Rattlesnake Group using a mtDNA phylogeographic approach resulting in the recognition of seven full species and two subspecies within the group. The Western Rattlesnake Group is a very complex group of snakes and as such we should expect to see further research which may result in even more taxonomic changes being proposed for this group.

Another recent (2002) taxonomic change has been the reclassification of Sistrurus ravus and its associated subspecies from Sistrurus to Crotalus.

In 2004 Alvarado-Díaz & Campbell (Herpetologica 60 (2): 281-286) described a new species of small montane rattlesnake from Cerro Tancítaro, Michoacán, México: Crotalus tancitarensis.

In 2004 Campbell & Lamar (Venomous Reptiles of the Western Hemisphere) split up the Crotalus durissus complex into three full species (durissus, simus, and totonacus). We can expect to see further taxonomic work being done with this complex in the future.

In 2007 Douglas, et al (Copia 4, 2007) elevated the Panamint Rattlesnake (Crotalus mitchellii stephensi) to species level.

In 2008 Campbell and Flores-Villela (Herpetologica 64 (2) 2008: 246-257) described a new species of Long-tailed Rattlesnake (Crotalus ericsmithi) from Guerrero, Mexico. At this time this new species remains known only from the original type specimen.

Based upon the research currently available, the below listing represents what I believe to be the currently accepted forms of Crotalus and Sistrurus. This current listing contains a total of 84 forms or subspecies representing 38 species.


Crotalus adamanteus, Eastern Diamondback Rattlesnake

Crotalus aquilus, Queretaran Blotched Rattlesnake

Crotalus atrox, Western Diamondback Rattlesnake

Crotalus basiliscus, Mexican West Coast Rattlesnake

Crotalus catalinensis, Santa Catalina Island Rattlesnake

Crotalus cerastes, Sidewinder

Crotalus cerastes cerastes, Mojave Desert Sidewinder

Crotalus cerastes cercobombus, Sonoran Desert Sidewinder

Crotalus cerastes laterorepens, Colorado Desert Sidewinder

Crotalus cerberus, Arizona Black Rattlesnake

Crotalus durissus, South American Rattlesnake

Crotalus durissus cascavella, Northeastern Brazilian Rattlesnake

Crotalus durissus collilineatus, Central Brazilian Rattlesnake

Crotalus durissus cumanensis, Venezuelan Rattlesnake

Crotalus durissus durissus, Guianian Rattlesnake

Crotalus durissus marajoensis, Marajoan Rattlesnake

Crotalus durissus ruruima, Mt. Roriama Rattlesnake

Crotalus durissus terrificus, South American Rattlesnake

Crotalus durissus trigonicus, Rupunini Rattlesnake

Crotalus enyo, Baja California Rattlesnake

Crotalus enyo cerralvensis, Cerralvo Island Rattlesnake

Crotalus enyo enyo, Baja California Rattlesnake

Crotalus enyo furvus, Rosario Rattlesnake

Crotalus ericsmithi, Guerreran Long-tailed Rattlesnake

Crotalus horridus, Timber Rattlesnake

Crotalus intermedius, Mexican Small-headed Rattlesnake

Crotalus intermedius gloydi, Oaxacan Small-headed Rattlesnake

Crotalus intermedius intermedius, Totalcan Small-headed Rattlesnake

Crotalus intermedius omiltemanus, Omilteman Small-headed Rattlesnake

Crotalus lannomi, Autlan Long-tailed Rattlesnake

Crotalus lepidus, Rock Rattlesnake

Crotalus lepidus castenaeus, Neuvo Leon Rock Rattlesnake

Crotalus lepidus klauberi, Banded Rock Rattlesnake

Crotalus lepidus lepidus, Mottled Rock Rattlesnake

Crotalus lepidus maculosus, Durango Rock Rattlesnake

Crotalus lepidus morulus, Tamaulipan Rock Rattlesnake

Crotalus mitchellii, Speckled Rattlesnake

Crotalus mitchellii angelensis, Angel de la Guarda Island Speckled Rattlesnake

Crotalus mitchellii mitchellii, San Lucan Speckled Rattlesnake

Crotalus mitchellii muertensis, El Muerto Island Rattlesnake

Crotalus mitchellii pyrrhus, Southwestern Speckled Rattlesnake

Crotalus molossus, Blacktail Rattlesnake

Crotalus molossus estebanensis, San Esteban Island Blacktail Rattlesnake

Crotalus molossus molossus, Northern Blacktail Rattlesnake

Crotalus molossus nigrescens, Mexican Blacktail Rattlesnake

Crotalus molossus oaxacus, Oaxacan Blacktail Rattlesnake

Crotalus oreganus, Western Rattlesnake

Crotalus oreganus abyssus, Grand Canyon Rattlesnake

Crotalus oreganus caliginis, Coronado Island Rattlesnake

Crotalus oreganus concolor, Midget Faded Rattlesnake

Crotalus oreganus helleri, Southern Pacific Rattlesnake

Crotalus oreganus lutosus, Great Basin Rattlesnake

Crotalus oreganus oreganus, Northern Pacific Rattlesnake

Crotalus polystictus, Mexican Lance-headed Rattlesnake

Crotalus pricei, Twin-spotted Rattlesnake

Crotalus pricei miquihuanus, Eastern Twin-spotted Rattlesnake

Crotalus pricei pricei, Western Twin-spotted Rattlesnake

Crotalus pusillus, Tancitaran Dusky Rattlesnake

Crotalus ravus, Mexican Pigmy Rattlesnake

Crotalus ravus brunneus, Oaxacan Pigmy Rattlesnake

Crotalus ravus exiguus, Guerreran Pigmy Rattlesnake

Crotalus ravus ravus, Central Plateau Pigmy Rattlesnake

Crotalus ruber, Red Diamond Rattlesnake

Crotalus ruber exsul, Cedros Island Diamond Rattlesnake

Crotalus ruber lorenzoensis, San Lorenzo Island Diamond Rattlesnake

Crotalus ruber lucansensis, San Lucan Island Diamond Rattlesnake

Crotalus ruber ruber, Red Diamond Rattlesnake

Crotalus scutulatus, Mohave Rattlesnake

Crotalus scutulatus salvini, Humantlan Rattlesnake

Crotalus scutulatus scutulatus, Mohave Rattlesnake

Crotalus simus, Neotropical Rattlesnake

Crotalus simus culminatus, Northwestern Neotropical Rattlesnake

Crotalus simus simus, Central American Neotropical Rattlesnake

Crotalus simus tzabcan, Yucatan Neotropical Rattlesnake

Crotalus stejnegeri, Sinaloan Long-tailed Rattlesnake

Crotalus stephensi, Panamint Rattlesnake

Crotalus tancitarensis, Tancitaran Rattlesnake

Crotalus tigris, Tiger Rattlesnake

Crotalus tortugensis, Tortuga Island Diamond Rattlesnake

Crotalus totonacus, Totonacan Rattlesnake

Crotalus transversus, Cross-banded Mountain Rattlesnake

Crotalus triseratus, Mexican Dusky Rattlesnake

Crotalus triseratus armstrongi, Mexican Dusky Rattlesnake

Crotalus triseratus triseratus, Central Plateau Dusky Rattlesnake

Crotalus unicolor, Aruba Island Rattlesnake

Crotalus vegrandis, Uracoan Rattlesnake

Crotalus viridis, Prairie Rattlesnake

Crotalus willardi, Ridgenose Rattlesnake

Crotalus willardi amabilis, Del Nido Ridgenose Rattlesnake

Crotalus willardi meridionalis, Southern Ridgenose Rattlesnake

Crotalus willardi obscurus, New Mexico Ridgenose Rattlesnake

Crotalus willardi silus, Western Chihuahuan Ridgenose Rattlesnake

Crotalus willardi willardi, Arizona Ridgenose Rattlesnake


Sistrurus catenatus, Massasauga

Sistrurus catenatus catenatus, Eastern Massasauga

Sistrurus catenatus edwardsii, Desert Massasauga

Sistrurus catenatus tergerminus, Western Massasauga

Sistrurus miliarius, Dusky Pigmy Rattlesnake

Sistrurus miliarius barbouri, Dusky Pigmy Rattlesnake

Sistrurus miliarius miliarius, Carolina Pigmy Rattlesnake

Sistrurus miliarius streckeri, Western Pigmy Rattlesnake


Alvarado-Díaz, J. & J.A. Campbell. 2004. A new montane rattlesnake (Viperidae) from Michoacán, Mexico. Herpetologica 60(2): 281-286.

Ashton, K. G. & de Queiroz, A. 2001. Molecular Systematics of the western rattlesnake Crotalus viridis (Viperidae) with comments on the utility of the D-Loop in phylogenetic studies of snakes. Molecular Phylogenetics and Evolution 21(2): 176-189.

Campbell, Jonathan A. & Flores-Villeta. 2008. A New Long-Tailed Rattlesnake (Viperidae) from Guerrero, Mexico. Herpetologica 64 (2): 246-257.

Campbell, Jonathan A. & Lamar, William W. 2004. The Venomous Reptiles of the Western Hemisphere. Comstock Publishing, Ithaca & London.

Clark, A. M., Moler, P. E., Possardt, E.E., Savitzky, A. H., Brown, W. S., & Bowen, B. W. 2003. Phylogeography of the Timber Rattlesnake (Crotalus horridus) Based on mtDNA Sequences. Journal of Herpetology 37 (1): 145-154.

Douglas, Michael E., Marlis R. Douglas, Gordan W. Schuett, Louis W. Porras and Blake L. Thomason. 2007. Genealogical concordance between mitochondrial and nuclear DNAs supports species recognition of the Panamint rattlesnake, Crotalus mitchellii stephensi. Copeia. 2007 (4): 920-932.

Douglas, Schuett, Porras, & Holycross. 2002. Phylogeography of the Western Rattlesnake (Crotalus viridis) Complex, With Emphasis on the Colorado Plateau. Pp. 11-50, Biology of the Vipers. Eagle Mountain Publishing, Eagle Mountain, Utah.

Klauber, Laurence M. 1972. Rattlesnakes: Their Habits, Life Histories, and Influence on Mankind, 2nd edition. University of California Press, Berkeley & Los Angeles.

Pisani, G. R., Collins, J. T., & Edwards, S. R. 1972. A re-evaluation of the subspecies of Crotalus horridus. Transactions of the Kansas Academy of Science, 75:255-263.

Pook, C. E., W. Wûster & R. S. Thorpe. 2000. Historical biogeography of the western rattlesnake (Serpentes: viperidae: Crotalus viridis), inferred from mitochondrial DNA sequence information. Molecular Phylogenetics and Evolution, 15: 269-282.

Rubio, Manny. 1998. Rattlesnake: Portrait of a Predator. Smithsonian Press, Washington & London.

Date submitted 02/28/07
Last updated and revised 07/22/08

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