Crotalus pusillus

Crotalus pusillus, or the Tancitaran Dusky Rattlesnake, is a venomous pit viper species found in west-central Mexico. No subspecies are currently recognized.

Description
Adult males may grow to more than 50 cm in length, while females are smaller. The largest recorded length for a specimen was 68.2 cm.

Behavior
Campbell and Lamar (2004) found this species only to be active during the day. Within its range, night temperatures are low and seem to restrict its activity.

Geographic range
It is found in west-central Mexico in the Sierra de Coalcomán of southwestern Michoacán, the Transverse Volcanic Cordillera of west-central Michoacán, and in adjacent Jalisco. It is probably also found in northeastern Colima. Its type locality is reported as "Tancítaro, Michoacán, Mexico, altitude 5,000 ft" (5,000 ft = 1,524 m). It occurs at elevations between 1525 and 2380 m.

Conservation status
This species is classified as Endangered on the IUCN Red List of Threatened Species. The population trend was unknown when assessed in 2007.