ORDER OF GNAWING ANIMALS 



(Rodentia, or Glires) 



'HIS is a well defined group of the smaller animals, the commonest distinguish- 

 ing character being the presence of broad chisel-like incisor teeth adapted 

 for gnawing. Such well-known animals as the Rats, Mice, Squirrels and 

 Hares belong to this order, and it is by far the largest of all in point of num- 

 bers. They are found practically all over the world. 



Rodents have other well-marked traits. The eyes are sharp and bright, 

 the ears well developed. There are no canine teeth, which leaves a gap 

 between the incisors and the molars, and the molar teeth have special adapta- 

 tions for grinding. The lower jaw is hinged with the skull in such a manner 

 that movement is possible not only up and down, but backward and forward 

 as well, and sidewise to a certain degree. This feature allows the best play 



of the opposing jaws across one another in order to secure grinding of the 

 The Rodents live very largely on vegetable food. 



of the teeth 

 vegetable fiber. 



The members of this order are fitted for every conceivable nook in nature's economy, 

 for Rodents are found in the trees, on the ground, under its surface, and in the water. One 

 species of the Squirrel family almost flies through the air. For convenience, the order is 

 divided into the sub-order Simplicidcntata (all Rodents but Hares and Pikas) and the 

 sub-order DitpUcidcntata (Hares and Pikas). These sub-orders are distinguished by the 

 difference in number of the gnawing teeth, the incisors. The Hares and Pikas have four 

 incisors in the upper jaw, a main pair of large ones with enamel extending all around the 

 tooth, and a second pair of small incisors directly behind them. The other Rodents have 

 but one pair above, and the enamel is confined to the cutting face of the tooth. 



The following table shows the division of Rodents into families and species in this 

 country : 



ORDER OF GNAWING ANIMALS (RODENTIA) 



FAMILIES 



(In North America) 



Squirrels 



{SciuridcB) 

 1 



(Typical species) 

 Gray Squirrel 

 Red Squirrel 

 Fox Squirrel 

 Tuft-eared Squirrel 

 Flying Squirrel 

 Spermophile 

 Chipmunk 

 Marmot 

 Prairie Dog 



Sewellels 



{Aplodontiidce) 



I 



(Only species) 

 Sewellel 



Porcupines 



{Erethizontidce) 



I 



(Only species) 

 Porcupine 



Conies 



{Ochotonidce) 



I 



(Only species) 

 Pika 



Beavers 



{Castoridae) 



(Only species) 

 Beaver 



Pocket Gophers 



(Geomyidce) 



I 



(Only species) 

 Pocket Gophers 



Rats and Mice 



Miiridw) 



I 



(Typical species) 

 House Rat 

 Wood Rat 

 Cotton Rat 

 Rice Rat 

 House Mouse 

 White-footed 



Mouse 

 Lemming Mouse 

 Meadow Mouse 

 Red-backed Mouse 

 Musk-Rat 



!i6i] 



Hares 



(Leporidoe) 



I 



(Typical species 

 Arctic Hare 

 Varying Hare 

 Jack Rabbit 

 Pygmy Hare 

 Cottontail 

 Swamp Rabbit 



Jumping Mice 



(Zapodidce) 



I 



(Only species) 

 Jumping Mouse 



Pocket Rats 



(Heteromyidce) 

 I 



(Typical species) 

 Pocket Mouse 

 Pocket Rat 



