Shrews and Moles Study Guide

ORDER SORICOMORPHA - SHREWS, MOLES, ETC. (formerly a subset of Insectivora) Members of Soricomorpha are small mammals with elongated pointed snouts, small eyes, and reduced ear pinnae. There are five toes on each foot. The genitalia and anus are in close proximity, resembling a cloaca (also found in monotremes). The fur is usually soft and silky. As their previous ordinal name implies, these animals prey primarily on small invertebrates; consequently, Soricomorphs have jaws lined with sharp teeth. The canines are present, but are no more prominent than the other teeth. The zygomatic arches are either absent or weakly constructed and the auditory bullae are likewise underdeveloped. Similar Species: The insectivore specimens are most likely to be confused only with the rodents from which they can be easily separated by the presence of 5 toes on each foot (as opposed to only four conspicuous toes on the front feet of most rodents). The teeth easily separate the skull from the rodents as there is no gap between the incisors and cheek teeth as in the rodents (1A). Bat skulls may be similar, but have a gap separating the upper incisors on each side of the skull (2A) and always have zygomatic arches and auditory bullae. In small carnivores such as the least weasel, the canines are enlarged (1B) whereas it is the first pair of upper incisors that are enlarged in the insectivores (1C). Insectivore Skull Insectivore Skull Rodent Skull Carnivore Skull Bat Skull 1A 2A 1B 1C Family Talpidae - Moles Moles are familiar mouse to rat-sized animals renowned for their burrowing abilities. The forearms are greatly enlarged (larger than the hind limbs) and are equipped with long, thick, blunt claws for digging. The snout is long and narrow. The eyes are tiny and often inconspicuous; the ear pinnae are absent. Similar Species: Moles can be distinguished from shrews (and most other small mammals) by the distinct front feet which are larger than the hind feet. Voles are often confused with moles because of their short tails and small ears and eyes, but voles lack enlarged forefeet and have only four toes on each front foot. The pocket gopher has a small fifth toe on its front foot (not as developed as in the moles), has longer and sharper claws that vary in length on different toes (more equal in length and blunt in the mole), lacks the long narrow snout, and has external cheek pouches. Skull The skull is about the size of that of a large mouse or small rat. The braincase is rounded and the rostrum elongated. Thin zygomatic arches are present. The teeth are mostly sharp and pointed. The front incisors usually jut forward such that they form the anteriormost part of the skull. The auditory bullae are incomplete, but present. Similar Species: Shrews lack zygomatic arches (1A) which are present in the moles (1B); the shrews also have dark enamel tips on their teeth, and have tympanic rings (2A) instead of auditory bullae (2B). Pocket Gopher (Rodent) Mole Prairie Mole, Scalopus aquaticus Specimen A large mole about the size of a rat. The fur is grayish to brownish black, often with a silvery sheen. The forearms and claws are especially enormous (1A). The snout is long but narrow (rather carrot-shaped) (1B), contrasting with the plump head and body. The tail is short and so scantily haired that it appears as if it is naked (1C). The feet are similarly naked. Similar Species: The star-nosed mole has a much longer tail, smaller front feet and claws, and the distinctive tentacled nose. 1A 2A 1B 2B Mole Skull Shrew Skull 1B 1A 1C Skull The skull is roughly triangular in shape with a strong constriction in the interorbital area (1A) that widens again anteriorly toward the rostrum. The nostrils open forward on the skull (1B). The zygomatic arches are thin. Dental Formula: I: 3/3 C: 1/0 P: 3/3 M: 3/3 = 42 Similar Species: The skull of the star-nosed mole is smaller without a constriction in the interorbital area. The zygomatic arches are also much thinner and the nostrils open upward. Star-nosed Mole, Condylura cristata Specimen A smaller mole about the size of a vole. The fur is dark brown or nearly black with tail and feet of the same color. The front feet are enlarged, but less so than in the prairie mole. The snout is not as elongated as in the prairie mole, but terminates with 22 tentacles (1A). The tentacles are diagnostic, but are not as conspicuous on dried specimens. The tail is long (about the length of the body minus the head), sparsely haired, and fleshy (1B). 1A 1B Similar Species: see prairie mole Skull The skull is similar to that of the prairie mole, but is smaller and more slender. The zygomatic arches are extremely thin and thread-like. The skull is widest at the braincase and tapers to the rostrum without the interorbital constriction (1A) seen in the prairie mole. The openings for the nostrils face upward (1B) (although they face forward on the live animal). The star-nosed mole is also the only Wisconsin mammal with 44 teeth. Dental Formula: I: 3/3 C: 1/1 P: 4/4 M: 3/3 = 44 Similar Species: see prairie mole 1A 1B 1A 1B Family Soricidae - Shrews Shrews include some of the smallest of our mammal species. At first glance, they are often mistaken for rodents. The body is roughly cylindrical with short legs and small feet. The hind feet are larger than the forefeet. The tail is short to moderate in length and is covered with hair. The snout is long and pointed. The ear pinnae are usually present, but are underdeveloped and often hidden by the fur so that the animal looks earless. Similar Species: see the account for the mole family. Skull The shrew skull looks decidedly bird-like when viewed from above with its greatly inflated braincase and narrow tapering rostrum. The zygomatic arches are absent and the auditory bullae reduced to ring-like structures (1A). At least some of the tips of the teeth are covered in black or brown enamel (1B). 1B 1A In shrews it is convenient to divide the teeth of the upper jaw as follows: 1 pair of incisors (I), 4 or 5 pairs of unicuspids (U), and 4 pairs of "molars" (M). The unicuspids represent incisors, canines, and some premolars that all appear rather uniform in shape. The "molars" which are larger than the unicuspids actually contains one premolar tooth. Similar Species: The lack of zygomata and ring-like auditory bullae easily separate the shrew skull from that of the moles. Genus Sorex - Long-tailed Shrews Members of this genus and the closely related Microsorex have a long tail that is roughly the same length as the body. The skulls are difficult to separate without the aid of magnification; separation is based primarily on the size of particular unicuspid teeth. All members of this group have 5 pairs unicuspid teeth. Dental Formula: I: 3/1 C: 1/1 P: 3/1 M: 3/3 = 32 Masked Shrew, Sorex cinereus Specimen The second smallest mammal in the state. Despite the name, there is no obvious mask. The color is brownish-gray or dark brown with paler underparts, creating a two-toned effect. The tail is about the length of the body (not including the head). I U M Similar Species: The pygmy shrew is impossible to differentiate from the masked shrew without viewing the skull. The arctic shrew is larger and has a tricolor effect in its coat pattern. The water shrew is much larger with a fringe of hairs on the border of the hind feet and a tail that is as long as the entire body (including the head). Skull The skull is as described for the genus. The unicuspids are tiny. The 5th (last) upper unicuspid is peg- like, but all of the unicuspid teeth are similar in size and easily visible under magnification. Similar Species: The small size and tooth pattern separates the skull from the arctic and water shrews (arctic shrew has larger unicuspids and the water shrew has the 3rd upper unicuspid smaller than the 4th). In the pygmy shrew, only 3 pairs of upper unicuspids are easily visible because the unicuspids are not uniform in size. 5th Arctic Shrew, Sorex arcticus Specimen A medium-sized Sorex similar in general appearance to the masked shrew, but with a distinct tricolor pattern. The fur is black dorsally, brown on the sides, and finally grading to a paler grayish brown on the belly. The difference in color from the back to the sides is usually quite obvious with a more or less distinct line separating the colors (1A). The color change from the sides to the belly is gradual. It is best to independently compare the fur color on different sections of the animal rather than to look for sharply defined transition zones. Similar Species: The arctic shrew is larger than the masked and pygmy shrews, and smaller than the water shrew. The tricolored pattern is unique to this species. Skull The most conspicuous difference between the skull of the arctic shrew and that of the other Sorex is that the unicuspids are relatively larger. Similar Species: The skull of the arctic shrew is larger than that of the masked and pygmy shrews and the unicuspids are much larger. All 5 pairs of upper unicuspids are visible compared to the 3 that are visible in the pygmy shrew. The water shrew skull is a little larger with the 3rd unicuspid being smaller than the 4th (3rd is larger than the 4th in arctic shrew - see picture above). 1A U U S. arcticus; note the large unicuspids (U) Typical Sorex skull; note the small unicuspids (U) relative to S. arcticus 3rd 4th Water Shrew, Sorex palustris Specimen The largest of our Sorex and also the species with the longest tail (roughly half of the total length). The color is slate gray to nearly black above and silvery to brownish-gray below. The hind foot is relatively large and is equipped with a fringe of stiff hairs along the edges of the toes and foot (1A), a feature that is visible even in preserved specimens. Similar Species: No other long-tailed shrew is as large, has such a long tail, or has the fringe of hairs on the hind feet. The coat pattern is bicolored, not tricolored as in the arctic shrew. 1A Skull The skull of the water shrew is larger than that of the arctic shrew and has relatively smaller unicuspids. The 3rd pair of upper unicuspids is slightly smaller than the 4th. Pygmy Shrew, Microsorex hoyi Specimen The smallest of all Wisconsin mammals. It is so similar in size and appearance to the masked shrew that the two species cannot be accurately differentiated without observing the skull. Similar Species: see account for masked shrew on ways to distinguish it from other Sorex. Skull The skull of Microsorex is similar to that of Sorex. It is best identified by observing the upper unicuspids. In the pygmy shrew, the 3rd and 5th unicuspids are extremely tiny and disc-like (see below), being wedged between the other teeth; the overall effect is that only 3 pairs of upper unicuspids are easily visible. The dental formula is the same as in Sorex. 3rd 4th 3rd 5th Short-tailed Shrew, Blarina brevicauda Specimen This is our largest (about the size of a small vole) and most abundant shrew. The fur is slate or lead-gray to nearly black above and slightly lighter on the underparts. The tail is short (about 1/5 the total length). Similar Species: The short tail separates it from all other shrews except the least shrew which is distinguished by its much smaller size. Skull The skull is more heavily built than that of other shrews and the braincase flatter and less bulbous. There is a ridge running along the center of the cranium (1A) similar to a sagittal crest and two other ridges paralleling it (1B). There is a prominent thorn-like lateral process (1C) that, together with the thorn-like appendage pointing rearward on the posterior edge of the rostrum, gives the appearance that a zygomatic arch was present, but had been broken off. The 5th pair of upper unicuspids is very tiny and may not be easily seen. Dental Formula: I: 3/1 C: 1/1 P: 3/1 M: 3/3 = 32 Similar Species: Size alone can usually separate the Blarina skull from the other shrews. If you are unsure, look for the two ridges paralleling the sagittal crest, which are absent in our other shrews (the other shrews may have a single small ridge running down the center of the braincase) or for the thorn-like lateral processes on the sides of the braincase (where you would expect the ear opening to be). 1A 1B 1C 5th Least Shrew, Cryptotis parva Specimen A tiny shrew that is only slightly bigger than a large bumblebee. It closely resembles the masked shrew except that the tail is short as in Blarina (never more than twice the length of the hind foot). The fur is brownish-gray above and whitish or grayish below. Similar Species: This species is too small to be confused with Blarina and usually is more brownish in color. The short tail distinguishes it from the other species of Wisconsin shrews. Skull The skull is small and easily confused with that of the long-tailed shrews. The rostrum is rather broad so that the skull is less bird-like. This is the only shrew with 30 teeth, the upper unicuspids reduced to 4 pairs instead of the 5 seen in all other shrews. The last upper unicuspid is minute and wedged between the 3rd unicuspid and 1st molar so that only 3 pairs of unicuspids may be visible at first glance. Dental Formula: I: 3/1 C: 1/1 P: 2/1 M: 3/3 = 30 1st 2nd 3rd 4th Similar Species: The dental formula and presence of only 4 pairs of upper unicuspids distinguishes it from all other shrews. However, only 3 of the unicuspids may be noticeable, a pattern also seen in the pygmy shrew. The broader rostrum may also aid in the differentiation. Relative and Actual Size of the Wisconsin Shrews. From left to right: Sorex cinereus, Sorex arcticus, Sorex palustris, Microsorex hoyi, Blarina brevicauda, Cryptotis parva. Jeff