Order Lagomorpha

Family Ochotonidae

Genus Ochotona – pikas

Note the typical lagomorph characteristics (2/1 incisors), and

partial fenestration of the rostrum (not pronounced). Also typical of

lagomorphs is the posterior flange on the zygomatic arch (it’s broken

off on the left side of this specimen).

What is the common distribution and lifestyle of pikas?

Order Lagomorpha

Family Leporidae

Cottontail rabbits belong to the genus Sylvilagus. Note the differences

between the eastern cottontail (S. floridanus) and the western cottontail

(S. auduboni).

Order Lagomorpha

Family Leporidae

Genus Oryctolagus

Old world rabbits were domesticated in Eurasia early in human history.

They have been introduced to every part of the world, and remain a

very important economic commodity in many parts of the world.

Family Leporidae

Genus Lepus

The jackrabbits of this genus are the most highly modified of all the

rabbits for cursorial locomotion. Most live in open ground situations

either in a hot, desert environment or in the open plains of North

America. Note the long feet and ears of this black-tailed jackrabbit

from Texas. What are these adaptations for?

Please be sure to look at Walker’s Mammals of the World,

to get a feeling for the vast numbers and diversity of Rodents!

Order Rodentia

Suborder Sciurognathi

Family Aplodontidae

This family is represented by a single living species - the

mountain beaver, Aplodontia rufa. Today they are found only

in the Pacific NW, but formerly occurred throughout the US and

Eurasia. Primarily because of their primitive zygomasseteric

structure (protrogomorphic), they are considered to be the most

primitive living rodent. They live in social groups in riparian

woodlands. They excavate burrows and feed on a great variety

of leaves, grasses, twigs and bark.

Suborder Sciurognathi

Family Sciuridae

Tree squirrels

Note the arched skull and sciuromorphic characters of

Sciurus carolinensis (Eastern gray squirrel). Sciurus are all tree

squirrels. Other genera of tree squirrels include Tamiasciurus

(our example is T. hudsonicus, the Eastern red squirrel) and

Glaucomys = New World flying squirrels (G. volans is the

Eastern flying squirrel). Why are all flying squirrels tree squirrels?

Note the strong, sharp claws of the tree squirrels. These are the

ones who can rotate their hindfeet 180^o to cling to the bark.

Suborder Sciurognathi

Family Sciuridae

Ground squirrels

Again note the arched skull and sciuromorphic structure

typical of all sciurids. Many species of ground squirrel abound

throughout the US. The most common genus is Spermophilus

(seed-loving). Examples include:

Spermophilus spilosoma = spotted ground squirrel

S. richardsoni = Richardson’s ground squirrel

S. tridecemlineatus = 13-lined ground squirrel

Chipmunks are also typical of No American ground squirrels.

The Eastern type is the single species of its genus, Tamias striatus.

In the West, we find several species of the genus Eutamias =

Western chipmunks.

Suborder Sciurognathi

Family Sciuridae

Genus Marmota

Sciurids also include the marmot (= woodchuck = groundhog),

a large fossorial rodent. Note the strong claws and teeth, and the

sciuromorphic zygomasseteric structure.

Suborder Sciurognathi

Family Sciuridae

Genus Cynomys

The prairie of the Western US is home to the infamous, prairie

dog, a large burrowing ground squirrel. What is their lifestyle like?

Suborder Sciurognathi

Family Castoridae

There are only two living species of beavers: Castor canadensis

is the No American form, and Castor fiber is found in boreal forests of

Eurasia. Both have a very similar lifestyle (be able to describe it!).

Castor is often used as the best example of sciuromorphic zygomasseteric

structure.

Suborder Sciurognathi

Family Geomyidae

These are the pocket gophers. Note the light fur on the cheeks of

the Western gopher, Thomomys bottae, indicating the cheek pouches.

Note the large humerus and powerful femur of this fossorial animal.

Geomys bursarius is the larger Eastern variety of gopher. What

adaptations of the skull indicate that he is a powerful digger?

Suborder Sciurognathi

Family Heteromyidae

The most common genera of this family are Dipodomys

(kangaroo rats) and Perognathus (pocket mice). Compare the skulls

and skins of these 2 genera. What similarities are there? Differences?

Examine the skeleton of Dipodomys ordii. What features indicate

a saltatorial lifestyle?

Suborder Sciurognathi

Family Muridae - Old World and New World mice, rats, etc.

This is the largest family of rodents, comprising the greatest numbers

and diversity of species. Most are relatively mouse-like. You should

be able to recognize the different subfamilies displayed.

The family has evolved the unique zygomasseteric structure know as

the myomorphic type. Please note wherever skulls are displayed.

Family Muridae

Subfamily Murinae - Old World mice and rats

This is the most diverse subfamily containing species widely

adapted for fossorial, terrestrial and arboreal lifestyles. Some are

even semiaquatic! The most common genera of murines are Mus

and Rattus. Mus musculus is the common field mouse. Rattus

rattus (the black rat) and Rattus norvegicus (Norway rat) are both

common pests of human occupation, and have been introduced

all over the world. These are the rats that most often carry the

organisms that cause bubonic plague, typhus, rabies, etc. Note

the myomorphic zygomasseteric structure.

Family Muridae

Subfamily Sigmodontinae - New World mice and rats

These comprise the second largest subfamily of murids. The

most common genera in this group are Peromyscus (deer mice),

Sigmodon (cotton rats) and Neotoma (wood rats).

Examples shown are:

Peromyscus truei = big-earred cliff mouse

P. maniculatus = common deer mouse

P. leucopus = white-footed mouse

Sigmodon hispidus = hispid cotton rat

Neotoma albigula - Western wood rat (not labeled)

Note the zygomasseteric structure of the Neotoma skull.

Family Muridae

Subfamily Gerbillinae - gerbils

The gerbils are semifossorial, living in arid desert environments.

They are also good bipedal saltators. What adaptations for

saltation would you expect to find? How about for arid habitats?

What other groups of rodents have these adaptations?

Describe the process of parallel evolution.

Family Muridae

Subfamily Arvicolinae - voles, lemmings, muskrat

This family contains forms that occur only in the Northern

hemisphere of the Old and New Worlds. They are all relatively

short-tailed, with chunky bodies and short legs - why?

The only exception is the muskrat - what does he use his tail

for? Microtus are the meadow voles or meadow mice.

Pitymys are pine voles. Cleitheromys is the Southern red-backed

vole (note its longer tail).

Note the zygomasseteric structure in Ondatra, the muskrat. This

skull also shows the complex, prismatic cusp pattern on the cheek

teeth that is typical of arvicolines (compare with beaver, gopher

and porcupine). What do you think this is adaptive for?

Suborder Hystricognathi

Family Erethizontidae - New World porcupine

This is the single species of porcupine found in North America

(Erethizon dorsatum). Several others occupy Mexico and South

America. Note the typical features of the skin. What kind of

lifestyle does he have? What is the zygomasseteric structure?

Suborder Hystricognathi

Family Octodontidae - octodonts

This small family of South American rodents are the only

New World hystricognaths to have developed highly fossorial

lifestyles. This particular species, the degu, is not very fossorial,

but lives among the rocks and crevaces in the foothills of the Andes.

Unfortunately, he is a poor specimen. These guys have extremely

enlarged infraorbital foramina, typical of hystricomorphic rodents.

The enamel ridges on their cheek teeth are figure-8 shaped, giving

this family its name (not shown).

Suborder Hystricognathi

Family Dasyproctidae - agoutis

Family Hydrochoeridae - capybaras

These families are found entirely in tropical and subtropical regions of

So America. Both are adapted for running, and are among the best at this

for rodents. They have relatively long legs and compact feet.

The agoutis live in the forest and burrow, often using natural crevices at the

base of giant fig trees. This model skull is from the largest agouti, the paca.

The most highly modified runner among rodents is also the biggest

living rodent, the capybara (Hydrochoeridae=water-pig). Its name reflects

the fact that it spends most of its time in the water, foraging on plants in or

near rivers and ponds. When it does venture into meadow and forest, it

keeps a constant eye out for predators (it is a favorite meal for the jaguar).

If threatened, it follows well-worn foraging paths back to the nearest water.

Read more about their lifestyles, foraging habits and predator avoidance.

Suborder Hystricognathi

Family Myocastoridae - nutria

These are large, semiaquatic rodents that look and behave much like

the North American muskrats. They are native to South America, but

have been introduced into Eurasia and No America. As you’d expect of

a well-adapted semiaquatic form, they have very thick wooly fur, and as

beavers declined, nutria were introduced to take their place in the fur

trade. Unfortunately, as with many human experiments, something went

wrong, some of them escaped, and they now occupy regions of at least

15 states. As with other exotics, they have spread unchecked where they

have gotten a foothold and now threaten native species. Fortunately, they

are considered pests by farmers and their numbers are kept down in areas

where they coexist with people.

Note the marked hystricomorphic zygomasseteric structure.

Two sciurognath families we don’t have specimens of are the springhares

(Family Pedetidae) and the jerboas (Family Dipodidae). Look them up in

the old edition of Walker’s Mammals of the World (pp. 755-758 & 992-1003).

There are three hystricognath families that we also lack specimens of. You’ll

find them in Walker, pp. 1071-1077 (Bathyergidae), pp. 1004-1009 (Hystricidae)

and pp. 1015-1020 (Caviidae).

We actually do have this skull of a caviid - a large relative of the guinea pig.

What single feature would you look at first to ID it as to Suborder?