Crotalus viridis is a widespread species of rattlesnake, occupying an ecologically, physiographically and climatically complex range in the western USA, southwestern Canada and northern Mexico. It shows considerable variation in both morphology and venom composition. This makes it an excellent model for studies of the causes of geographic variation, particularly in venom composition, a subject of great topical interest. Rattlesnake Phylogeny, and Relationships among Populations of the Montane Rattlesnakes in the Sky-Islands of Arizona and New Mexico. Rattlesnakes are considered to be a highly evolved group of pit vipers.
Rattlesnakes only occur in the New World, and currently about thirty species are recognized.
Unfortunately, very few researchers have examined relationships between rattlesnakes. Through examining the DNA from living snakes, researchers can begin to make better decisions regarding the evolutionary relationships between these animals. This may have direct effects on management of populations of these species, and in some cases, lower taxonomic groupings. Rattlesnake Relocation at the Arizona-Sonora Desert Museum. ASDM removes and relocates rattlesnakes found on grounds to prevent snakebite to visitors, staff and volunteers.