Subfamily Neotominae
deer mice, woodrats, and relatives

Neotominae is a large New World subfamily of rat-like or mouse-like cricetid rodents. This group includes the packrats and woodrats, as well as the familiar deer and white-footed mice. There are 124 neotomine species in 16 genera, distributed among four tribes. (Musser and Carleton, 2005)

Neotomines are distributed throughout North America, from Panama to Alaska and northern Canada. (Nowak, 1999)

These rodents occupy a wide variety of habitats, including prairies, savannahs, mountains, deserts, marshes, agricultural fields, suburban human dwellings, forest edges, scrub forests, rainforest, coniferous forest, and temperate and tropical deciduous forest. (Nowak, 1999)

Traditionally, neotomines were classified as part of a broadly-defined Cricetinae, which included New World muroid rodents as well as Palearctic hamsters (Miller and Gidley 1918, Ellerman 1941, Simpson 1945). Alternatively, the New World group was separated and given the subfamily name Hesperomyinae (Tullberg 1899, Chaline et al. 1977). Hooper and Musser (1964) broke the New World group down even further, recognizing that North American taxa and South American taxa had different penis morphologies. The North American, or "neotomine-peromyscine" group, later became formally known as the subfamily Neotominae, whereas the South American group became the Sigmodontinae (Reig 1980). Still, some authors were reluctant to recognize two subfamilies based on penis morphology alone, and thus retained neotomines within a broadly-defined Sigmodontinae (Carleton and Musser 1984). Molecular data supports the separation of sigmodontines and neotomines into different subfamilies, and also supports the monophyly of each group (Michaux et al. 2001, Jansa and Weksler 2004, Steppan et al. 2004). Steppan et al. (2004) date the divergence between the North American Neotominae and the mostly South American tylomyine-sigmodontine clade at 16.8 to 18.1 million years ago. (Carleton and Musser, 1984; Chaline, Mein, and Petter, 1977; Ellerman, 1941; Hooper and Musser, 1964; Jansa and Weksler, 2004; Michaux, Reyes, and Catzeflis, 2001; Miller and Gidley, 1918; Reig, 1980; Simpson, 1945; Steppan, Adkins, and Anderson, 2004; Tullberg, 1899)

Neotomines are mouse-like or rat-like in overall appearance, with long tails and prominent ears. Their head and body length ranges from 50 to 351 mm, and their tails range from 35 to 240 mm. They weigh 6 to 450 grams. In some species, males weigh more, and are sometimes longer than females (Schulte-Hostedde et al. 2001). Male neotomines often have prominant ventral sebaceous glands, but they usually lack rump, hip, and flank glands. The pelage is usually dense, ranges from short to long, and can be either coarse or soft. Neotomines range in color from pale to very dark, and they are yellowish, reddish, brown, or gray on their dorsal surface and buffy, grayish, reddish, or white below. Some populations consist of more than one color morph (Smith 1972). The tail is sparsely haired or bushy with a tufted tip and ranges from long and skinny to short and fat. The large ears are usually sparsely haired.

The neotomine dental formula is 1/1, 0/0, 0/0, 3/3 = 16. The incisors are usually orthodont or opisthodont, and the molars are rooted and have a biserial cusp arrangement (in contrast to the triserial cusp arrangement of most murines). Each molar has a longitudinal enamel crest (mure or murid). The molars range from brachydont to hypsodont, and the third molars are usually smaller than the second molars. Neotomine skulls have flat or slightly recessed pterygoid fossae, and small to medium-sized auditory bullae. In addition, the mastoid bullae are not hypertrophied, and an accessory tympanum is always present. The malleus is of parallel construction. Other neotomine skull characteristics vary widely. A skeletal characteristic shared by most neotomines is the presence of a prominant neural spine on the second thoracic vertebra. Finally, neotomines have one- or two-chambered stomachs, and the tongue bears a single circumvallate papilla. (Carleton and Musser, 1984; Nowak, 1999; Schulte-Hostedde, Millar, and Hickling, 2001; Smith, 1972)

Most neotomines do not live more than a year in the wild. The record lifespan in captivity is eight years, five months. (Nowak, 1999)

Neotomines are terrestrial, arboreal, or semiarboreal rodents. Their feet are modified for running or for climbing. Those that are terrestrial often build runways through ground vegetation or through leaf litter that they follow as they go about their daily business. Neotomines can be nocturnal, diurnal, or crepuscular. They are active year round, though some experience bouts of torpor during cold weather. Some species dig burrows or use those made by other animals, others build elaborate nests on the ground or in trees, and some simply shelter in natural crevices. Some neotomine species are solitary, territorial, and aggressive, while others are fairly social and may even share nests with several conspecifics. (Nowak, 1999)

Neotomines have acute senses of smell, touch, hearing, and vision. They communicate with a variety of calls, chirps, and even miniature "wolf" howls. Some neotomines communicate with ultrasounds (Smith 1972), and they occasionally drum their front feet rapidly on the ground when alarmed. Chemical signaling with pheromones and scent marks is an extremely important aspect of communication in this group, as these odors can quickly send a signal about the identity and status of an individual (Ma et al. 1999). (Ma, Wiesler, and Novotny, 1999; Nowak, 1999; Smith, 1972)

Neotomines range from herbivorous to carnivorous in their eating habits. Foods consumed include seeds, roots, stems, cacti, pine needles, leaves, nuts, fungi, insects, scorpions, other rodents, and carrion. Many store food inside of their burrows for later consumption. (Nowak, 1999)

These rodents are preyed upon by a variety of other animals, including hawks, owls, snakes, and carnivorous mammals. Neotomines may avoid predation by decreasing their activity level on bright, moonlit nights (Topping et al. 1999), and by having fur that matches their background (Kaufman 1974). Additionally, some neotomine species have tails that break off easily when grabbed, allowing escape. (Carleton and Musser, 1984; Kaufman, 1974; Nowak, 1999; Topping, Millar, and Goddard, 1999)

Neotomines are primary and higher-level consumers, and they are a staple food source for various predators. Also, they impact forest regeneration by consuming seeds and tree seedlings (Cote et al. 2003) and they may be important dispersers of mycorrhizal fungi (Mangan and Adler 2000). Finally, neotomines are parasitized by ticks and mites, fleas, lice, bot flies, nematodes, and flukes (Kinsella 1991). (Cote, Ferron, and Gagnon, 2003; Kinsella, 1991; Mangan and Adler, 2000; Nowak, 1999)

Some neotomines are vectors of human diseases, including hantavirus and lyme disease. Also, they are considered nuisance animals when they enter homes, raid food stores, gnaw on household goods, and build nests in unwelcome places. (Nowak, 1999)

Neotomines are bred in captivity and used as lab animals for genetic and physiological research. (Nowak, 1999)

The IUCN lists 15 neotomine species as lower risk, 9 species as vulnerable, 13 species as endangered (6 Neotoma species, 5 Peromyscus species, Jico deer mice, Habromys simulatus, and Cozumel harvest mice, Reithrodontomys spectabilis), and 2 species as critically endangered (Slevin's mice, Peromyscus slevini, and false canyon mice, Peromyscus pseudocrinitus, both of Mexico). In addition, one species has gone extinct recently (Pemberton's deer mice, Peromyscus pembertoni, from San Pedro Nolasco Island in Mexico). Many neotomine species have small, restricted ranges, narrow habitat requirements, and are threatened by encroaching human development. (IUCN, 2004)