Long-tailed vole

The long-tailed vole (Microtus longicaudus), in some areas known as the San Bernardino long-tailed vole, is a small vole found in western North America. They have short ears and a long tail. Their fur is gray brown with light gray underparts. They are around 18 cm (7.1 in) long with an 8 cm (3.1 in) tail and weigh about 50 g (1.8 oz).

The scientific name of the long-tailed vole is Microtus longicaudus. The generic name, Microtus, derives from the Greek words μικρός meaning "small" + οὖς "ear". In Latin, the species name longicaudus derives from longus meaning "long" and cauda meaning "tail". The type specimen was a female collected by Vernon Orlando Bailey in the Black Hills at an altitude around 5,500 ft (1,700 m) near Custer, South Dakota, on July 19, 1887. The description was published by C. Hart Merriam in The American Naturalist the following year. The original scientific name was Arvicola longicaudus. Certain features of the molars were noted, which distinguished the long-tailed vole from other voles known at the time. The species was formerly sometimes regarded as a member of the Old World genus Chionomys.

The Coronation Island vole, once considered to be a separate species, is now believed to be a subspecies.

The long-tailed vole is a small terrestrial mammal. They are around 18 cm (7.1 in) long with an 8 cm (3.1 in) tail. They weigh on average 50 g (1.8 oz). They have a thick body and a relatively long tail. The tail is bicolored and extends greater than one-third the animal's total length. The type specimen measured 185 mm (7.3 in), with a 65 millimetres (2.6 in) tail and a 21 millimetres (0.83 in) hind foot. The ear measured 14 millimetres (0.55 in) x 8 millimetres (0.31 in) x 13 millimetres (0.51 in).

The long-tailed vole is similar in size to the meadow vole (Microtus pennsylvanicus). However, it has a longer tail, bigger ears, and grayer coat. In addition, the skull is flatter, and the cranium is wider.

The middle upper molar lacks a posterior-internal loop or spur. Merriam also noted some "peculiarities", not otherwise specified, in the original description, which distinguish the long-tailed vole from other species known in the late 1800s. This first specimen Merriam described had large ears, with folds capable of closing the ear canal opening. Relative to the overall length of the animal, the tail was longer than any other vole described at that time. The fur is a sooty yellow-brown with some grizzled aspects. There are hints of rust coloring on the mid back. The whitish underside fur is a leaden gray towards the base. The underside fur blends seamlessly with the fur on the sides of the vole. The undersides of the tail are darker. The feet are plumbeous, a leaden gray.

The genitalia of the long-tailed vole have been described. The baculum has broad and straight proximal bone. It is similar in structure to that of the meadow vole, but with different proportions. The basal shaft is dumb-bell shaped in cross section and tapers to a blunt point at the end. The shaft is broad in dimension and connects via cartilaginous linkages to three lateral segments. The glans penis has a dorsal lobe elevated above a ventral rim. The rim has spiny fingerlike processes, but not the dorsal lobe. A rod shaped os clitoridis may be present, in front of the urethra.

Long-tailed voles can be found with unusual dentition. A female with grooved incisors was found in the Yukon. Several other voles from Oregon were found with flattened incisors and malocclusion of their incisors and molars. A specimen in New Mexico was reported with an extra tooth in the right lower jaw. An albino vole was also found in New Mexico.