The Tancitaran dusky rattlesnake is a species of pit viper, a venomous snake with two heat sensing organs located between its eyes and nostrils. The snake is only found in west-central Mexico and grows to around 50cm in length. It is thought to inhabit pine-oak forests in areas with volcanic rock, at altitudes of 1500 metres or more.

The species has been listed as endangered by the IUCN since 2007, due to its restricted range and loss of its habitat. The size of its population is unknown and no further research into the species is underway. Given the lack of information, the Tancitaran dusky rattlesnake could very well become extinct without anyone taking notice.