Harvesting apparatus

Physically, the harvesting apparatus is housed within an elongated and bluntly pointed skull and is an important structure within the ruminants' body. The jaws are the housing to which the teeth and muscles are attached. The upper jawbone, often called the "maxilla," is fused to the skull, and the lower jawbone, termed the "mandible," is hinged at each side to the bones of the temple by ligaments. Common incisiform canines

Incisors-

Incisors-

Mandible

Pre-molar and molar teeth

FIGURE 5.1 Harvesting apparatus of a sheep, illustrating the maxilla and mandible.

Mandible

Pre-molar and molar teeth

FIGURE 5.1 Harvesting apparatus of a sheep, illustrating the maxilla and mandible.

to all ruminants are the four-paired anterior teeth consisting of true incisors and incisiform canines set on the lower jaw, believed to have evolved for harvesting of plant material. On the upper jawbone, above the incisors, a thick pad of connective tissue (the dental pad) is present. Unlike odd-toed ungulates (the equids, e.g., horses, asses, zebras, and rhinos), ruminants do not possess incisors on the upper jawbone. Toward the back of the mouth, ruminants have sets of molars and premolars (Figure 5.1) that are flat and lined with sharp ridges of enamel. Because tooth shape governs functionality, these posterior teeth generally do not make contact with the bulk of the grasped forage during prehension, and their pivotal role lies in chewing the severed bite contents.

Jarman [8] recognized the functional interrelationships between the size and dispersion of food items in the environment and animal species' body size. Smaller animals have a smaller harvesting apparatus in absolute terms and can remove smaller bites, but relative to body mass, smaller animals require a diet of higher nutritional quality compared with larger animals to meet the higher metabolic requirements per unit of body weight (W075). It is believed that small animals have, therefore, evolved a jaw configuration that is narrower relative to larger-bodied animals and additionally supported by prehensile and mobile lips that permit the selection of leaves, which in the extreme scenario may come from thorny browse species. By contrast, larger-bodied animals have a wide jaw configuration, and irrespective of whether these species can perceptually discriminate between leaf and stem, they are constrained by the inability to selectively remove leaf from stem because of the constraints of the wide muzzle. A long prehensile tongue that primarily serves to sweep forage toward the center of the bite, increasing the effective bite area, aids larger-bodied species.

The harvesting apparatus and body mass of animals accounts for much of the variation that exists in selection strategies between species. There is, however, extensive overlap in body mass between species within the three feeding types, as documented by Gordon and Illius [9] who presented an excellent examination of the jaw configuration of 34 species of grazers, 27 species of intermediate feeders, and 19 species of browsers, varying in body mass from 3 to 1200 kg. Their results provided compelling evidence that large-bodied grazers have a broad and flat incisor arcade, where incisor arcade is defined as the distance between the outer edges of the incisiform canines on the right and left ramus, compared to large-bodied browsers of a similar body mass who have a more narrow and pointed arcade. Similar patterns are evident between small-bodied grazers and browsers of a similar body mass.

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