Crotalus aquilus  . Queretaran dusky rattlesnake"  Crotalus aquilus is a venomous pit viper species found in the highlands of central Mexico. No subspecies is currently recognized. The specific name, "aquilus", is Latin for "eagle" and refers to the high altitude at which this species is found. This species grows to a maximum reported total length of , but most adult specimens, which have been described as heavy-bodied, are less than long. They are found in the highlands of central Mexico in Guanajuato, Hidalgo, México, Michoacán, and San Luis Potosí. The type locality given is "near Alvarez, San Luis Potosí, Mexico". These snakes are found in the open grassy and generally rocky habitats north of the Transverse Volcanic Cordillera. They also occur in pine-oak forest, open karstic areas, grassy mountain meadows, and stony mesquite-grassland. This species is classified as Least Concern on the IUCN Red List (v3.1, 2001). Species are listed as such due to their wide distribution, presumed large population, or because they are unlikely to be declining fast enough to qualify for listing in a more threatened category. The population trend was down when assessed in 2007.