Once believed to be a single species for 150 years a study in 2011 concluded that the desert tortoise is actually two distinct ones divided by the Colorado River in Arizona. The Agassiz’ desert tortoise (Gopherus agassizii), pictured on top, resides west and north of the river in northern Arizona, Nevada, Utah, and California. This is the originally recognized species. The new one is Morafka’s desert tortoise (Gopherus morafkai), pictured in the middle, whose home is east and south of the river into Mexico, of which is less studied outside of the US. A map is provided above to show each tortoise’s range. Although they look indistinguishable from the untrained eye differences in life history and reproductive strategies have been observed.
“The two species have different habitat preferences,” says Kristin
Berry, a United States Geological Survey biologist who has studied
desert tortoise biology for more than 40 years and is a coauthor on the
study. “Morafka’s tortoise prefers to hide and burrow under rock
crevices on steep, rocky hillsides, while the Agassiz’s tortoise prefers
to dig burrows in valleys.”