The smooth-toothed pocket gophers, genus Thomomys, are so called because they are among the only pocket gophers without grooves on their incisors.[2] They are also called the western pocket gophers because they are distributed in western North America. They are considered distinct enough from other pocket gophers to be recognized as a separate subfamily or tribe.[citation needed]
Thomomys gophers are highly fossorial. They rely on their incisors for digging more than most other gophers. They feed on plants, largely from beneath the surface, but they do come above ground at night. Roots, stems, leaves, and bulbs are eaten. When not directly in an agricultural field they are a benefit to humans by enriching soil and preventing runoff.
Over one hundred subspecies have been described, but not all are currently recognized by modern authorities[according to whom?]. Like many fossorial rodents, Thomomys shows a great deal of allopatric variation.[citation needed]
Thomomys, commonly referred to as smooth-toothed pocket gophers, is a group of rodents belonging to the family Geomyidae. Members of Thomomys are unique among gophers in that they have smooth upper incisors, free of the grooves that are common in other species. All species share the trait of fur-lined, external cheek pockets that allow them to move food material to and from their underground dwellings. Size varies among species, but commonly ranges from the size of a smaller mole to a larger rat. Coloration can range from yellow, to grey, to brown, and even black. They are all full-bodied with squat legs, short hair, and small eyes and ears.[7]
Pocket gophers have special visual adaptations to match their extreme and unique subterranean lifestyle. Though the size of their eyes are typical for rodents, the lens is able to transmit light rays that fall into the ultraviolet range. They possess three different photopigments: two cone pigments specific to 367 nm and 505 nm, and a rod pigment at 495 nm. Overall, the pocket gophers have less rod density than nocturnal rodents.[8]
Members of Thomomys inhabit southwestern Canada, the western United States, and a large percentage of Mexico. They thrive in fertile land often used for agriculture, but can be found in many different localities. They prefer areas with high primary productivity and nitrogen soil concentrations.[9]