The rattlesnake is a common predacious reptile that is found within North American ecosystems such as the Sonora, Chihuahuan, and Mojave Deserts. There are two distinctive groups of rattlesnakes that are found in these deserts. The most primitive rattlesnake belongs to the genus Sisturas group, while the more advanced forms of rattlesnakes belong to the genus Crotalus. Rattlesnakes are a distinctive species that can easily be identified based on their appearance. However, intraspecific recognition becomes very difficult due to the many variations in color and skin patterns that this species has. The rattlesnakes have a relatively robust body, with a diamond-shaped head, famous rattle tail, and hidden fangs which makes them easily identifiable as one of the most dangerous reptiles in the world. The species varies in ground color from gray, olive, greenish gray, greenish brown, brown, yellowish brown, tan, salmon, and black (O’Shea, 2008). The dorsal body pattern found on them consists of a series of twenty to fifty hexagonal or circular blotches, which may become more like cross bands towards the end of their body near the tail. This paper will focus on where these rattlesnakes evolved from, their biology and reproduction, survival adaptations, what they prey on, as well as who their predators are. It will also examine how certain variables help in the determination of the rattlesnake population growth and whether there is an an increase or decreases in population size, relative to the environment in which they live in.

Background History Rattlesnakes belong to the pit viper family named Crotalidae, which possess visible loreal pits, also known as lateral heat sensory organs. These organs are located between the snakes eye and nostril on both sides of their head (Phillips, 2009). Rattlesnakes occur only in North and South America and range from sea level to approximately 11,000 feet (over 3,000 m) in California and 14,000 feet (4,000 m) in Mexico (Klauber, 1997). The name Sisturus is a Latinized term derived from the Greek word “tail rattler” (Wright, 1957). Rattlesnakes that belong to this genus include the Massasauga and Pigmy rattlesnakes. The name Crotalus, for the second group of rattlesnakes, is derived from the Greek word Krotalon which means “rattle” or “castanet” (Klauber, 1997). Some well known rattlesnakes that belong to the genus Crotalus group include: the Eastern Diamondback, the Speckled Rattlesnake, the Western Diamondback, the Red Diamond, the Mohave Rattlesnake, the Sidewinder, and the Timber Rattlesnake.
Rattlesnake’s reside in high desert or lower mountain slopes and are often found near scrub brush such as mesquite and creosote and may also reside in lowland areas of sparse vegetation such as cacti, Joshua tree forests, or grassy plains (Campbell and Lamar, 2004). The species tend to avoid densely vegetated and rocky areas, preferring open, arid habitats. On a broader perspective, it is important to note that snakes essentially evolved from lizards and therefore are part of the reptile order of Squamata. The Squamata, which are classified as scaled reptiles, are the largest recent order of reptiles. This order has over nine thousand species and is the second-largest order of vertebrates after the Perciformes (Evans, 2008).
The oldest rattlesnake fossil dates back to the Pliocene era which is said to be from approximately four to five million years ago (Price, 2009). During the Pleistocene, which came after the Pliocene, the Laurentide Ice Sheet rearranged and diversified biotic distributions in eastern North America. However, this had minimal physical impact in western North America where lineage diversification was the result from climatic changes (Douglas et al, 2006). In a recent study at the university of Colorado State, Douglas suggests that the evolution of rattlesnakes within the warm deserts of western North America is shaped by Neogene vicariance and quaternary climate change