TAXONOMY

Order Carnivora

The order of carnivores consists of ten families with over 270 species and are found naturally everywhere, apart from Australia, New Zealand, Antarctica and many oceanic islands.

The term carnivore derives from the Latin carnis (flesh) and vorare (devour) in keeping with the fact that most species are meat eaters. However many bears are omnivo­rous and the Giant Panda is in fact a strict herbivore.

Figure 7.1 • Types of uterus found in placental mammals.

(a) Duplex (rabbit, hamster, rat)

(b) Bipartite (some carnivores and ungulates)

(c) Bicornuate (cat, dog, ferret, and ungulates)

(d) Simplex uterus (primates)

The heavy skull has a conspicuous saggital crest with well- developed temporal muscles and a large braincase (Fig. 7.2). The jaw articulation is in the dorso-ventral plane with limited transverse movement and no rotary movement. All teeth are rooted. Most species have 3/3 incisors with large conical canines and a variable amount of shearing and crush­ing premolar and molars. In most carnivores the fourth upper premolar and first lower molar are carnassial teeth that work together to provide the specialized shearing action for tear­ing at prey when feeding (Vaughan 1986a; Nowak 1999a).

Unlike lagomorphs and rodents, carnivores are typical predators and most species have excellent hearing, vision and smell for hunting. They have large auditory bullae and well-developed turbinates and olfactory epithelium.

They have 4-5 clawed digits on each limb. The first digit is not opposable and is often absent. Many, like canids and felids are digitigrade walking on their toes while Ursids, or bears, are plantigrade walking on the soles with heels touch­ing the ground.

Order Lagomorpha and Rodentia

Rodents comprise the largest mammalian order with over 1800 species (40% of all mammals) (Hurst 1999). They can be found worldwide from the Arctic to tropical and temperate regions (Nowak 1999b, 1999c). Lagomorphs

Figure 7.2 • Comparison of muscles of mastication between herbivores and carnivores. In herbivores the masseter is the main muscle of mastica­tion and the jaw articulation lies dorsal to the occlusal surfaces of the teeth.

(a) Rabbit

(b) Cat

differ from rodents in that they have four upper incisors (Vaughan 1986c) and a different jaw structure, but other­wise they share many similar behavioral and anatomical characteristics and will be included with rodents for this introductory section (Table 7.1).

Table 7.1 Classification of Lagomorphs and Rodents

Lagomorphs

Rabbits belong to the order Lagomorpha, which contains two families: the Ochotonidae, which includes the pikas (Ochotona), and the Leporidae, containing rabbits and hares (Lepus) and cottontails (Sylvilagus) (Nowak 1999c).

Lagomorphs differ from rodents in both dentition and jaw structure.

Rabbits differ from hares in having a short gestation period (28-33 days) and giving birth to altricial young in burrows underground. Hares are generally larger than rabbits, have a gestation period of 40 to 50 days, and give birth over ground to precocious young (Harkness & Wagner 1995; Nowak 1999c).

Rodents

Traditionally the order Rodentia was divided into the sub­orders Myomorpha, Sciuromorpha and the Caviomorpha (Hystricomorpha) based on skull and jaw musculature (Hurst 1999; Nowak 1999b) (Fig. 7.4). The classification of rodents is always in flux, however. More recent research on mandibular anatomy has suggested classifying rodents into just two suborders: Sciurognathi (sciuromorphs and myomorphs) and Hystricognathi (caviomorphs) (D'Erchia et al. 1996; Nowak 1999b; Vaughan 1986b).

Myomorphs

The Myomorpha, or mouse-like rodents, are the biggest suborder and include the rat, hamster, and gerbil (Fig. 7.5). They have a total of 16 teeth with no premolars, and rooted molars. Famous for their gnawing ability, a feature of this suborder is that part of the medial masseter muscles inserts not only on the lower jaw but runs through the infraorbital foramen to insert on the rostral muzzle. This unique architecture allows a more forward thrust of the jaw and more effective gnawing (King & Custance 1982; Nowak 1999b; Vaughan 1986b).

Two families from the order of Myomorpha will be fea­tured in this book: the family Muridae, which includes rats and mice, and the family Cricetidae, which includes gerbils and hamsters.

Sciuromorphs

These are the squirrel-like rodents and include the chip­munk, squirrel, and prairie dog (Fig. 7.6). They have 20-22

Figure 7.4 • Differing action of lateral and medial masseter muscles in rodents. Black = medial masseter. Red = lateral masseter.

(a) Myomorph - the medial masseter muscles insert not only on the lower jaw but run through the infraorbital foramen to insert on the rostral muzzle. This allows greater gnawing power

(b) Sciuromorph - these have the lateral masseter muscle extending cranially to aid gnawing. The medial masseter muscle is only involved in closing the jaw

(c) Caviomorph - the medial masseter muscles provide the gnawing action while the lateral masseter serves to close the jaw.

Figure 7.6 • Sciuromorph - Gray squirrel (Sciurus carolinensis).

mainly diurnal. The tail varies from short to long and is usually haired and bushy, with long hairs that project at right angles from the tail (Nowak 1999b).

Caviomorphs (Hystricomorphs)

The suborder Caviomorpha include the guinea pig and chinchilla, which eat a highly abrasive herbivorous diet (Fig. 7.7). They have 20 teeth in total and their open rooted (aradicular) molars make them especially prone to dental disease. They also produce precocious young and have a long gestation period. In contrast to the sciuromorphs, the medial masseter muscles provide the gnawing action while the lateral masseter serves to close the jaw (Hurst 1999; Nowak 1999b).