Question

1.Explain the different characteristics of diet, teeth, and digestive system size among primates.

2.Contrast autonomic responses and behaviors with intentional behaviors that serve as communication.

3.Explain at least three reasons that primates spend so much time grooming each other.

4.Differentiate between absolute and relative dating techniques, giving one example of each.

5.Why do we find fossils from some places and times and not from others? Explain.

Answer 1

1.

Diet of primates :-

  The diet of primates is a factor of their ecology that, during their evolution, has clearly played an important role in their dispersion and adaptive radiation as well as in the development of the teeth, jaws, and digestive system. Diet is also closely related to locomotor pattern and to body size.

The principal food substances taken by primates may be divided into vegetable (fruits, flowers, leaves, nuts, barks, pith, seeds, grasses, stems, roots, and tubers) and animal (birds, birds’ eggs, lizards, small rodents and bats, insects, frogs, and crustacea). The flesh of larger mammals (including primates) is not listed as an important item of nonhuman primate diet, with the sole exception of chimpanzees—it is taken by baboons in special circumstances that are not yet fully understood.

While diet is selective and specific to the order in many mammalian groups, among primates it is difficult to establish any hard and fast rules. Although there are decided preferences for certain food items, catholicity is more characteristic than specificity. Generally speaking, primates are omnivorous, as the physiology of their digestive system attests. Relatively few examples of dietary specialization are to be found. The so-called leaf-eating monkeys, a sobriquet that embraces the whole of the subfamily Colobinae, including colobus monkeys and langurs, are by no means exclusively leaf eaters and according to season include flowers, fruit, and (in some cases) seeds in their diet. The howler monkeys of the New World have a similar dietary preference.

Broadly, however, certain overall dietary preferences are discernible. The leaf-eating langurs have already been mentioned. The apes (other than the mountain gorilla) are substantially fruit eaters. Many of the smaller nocturnal primitive species such as galagos, dwarf lemurs, sportive lemurs, the aye-aye, and the slender loris are substantially insectivorous; the tarsier is probably the only primate that is exclusively carnivorous, feeding on insects, lizards, and snakes. The larger diurnal lemurs (e.g., typical lemurs, the sifaka, and the indri) are more vegetarian, including fruit, seeds, and leaves. It seems apparent that size, rather than activity rhythm, governs the nature of the primate diet. The small marmosets of the South American genus Callithrix have exclusively diurnal rhythms and are insectivorous and also eat gums, while the slightly larger, but equally diurnal, tamarins (genus Saguinus) are more omnivorous. An approximate cutoff point of 500 grams (Kay’s threshold, after the primatologist Richard Kay, who first drew attention to it) has been proposed as an upper limit for species subsisting mainly on insects and a lower limit for those relying on leaves. The reason is that insects are small and hard to catch, and a large animal simply would not be able to catch enough to sustain it during its waking hours. The cellulose and hemicellulose components of leaves, on the other hand, require complex digestive processes, and a small animal would be unable to maintain a constant throughput. Fruit, as a dietary component, suffers from neither of these constraints.

Teeth of primates :-

A dentition with different kinds of teeth (heterodonty)—incisors, canines, and cheek teeth—is characteristic of all primates and indeed of mammals generally. Heterodonty is a primitive characteristic, and primates have evolved less far from the original pattern than most mammals. The principal changes are a reduction in the number of teeth and an elaboration of the cusp pattern of the molars.

The dental formula of primitive placental mammals is assumed to have been 5 . 1 . 4 . 3 / 5 . 1 . 4 . 3 = 44 teeth (the numbers being the numbers respectively of pairs of incisors, canines, premolars, and molars in the upper and lower jaws). No living primate has retained more than two incisors in the upper jaw. The incisors are subject to considerable variation in strepsirrhines. Characteristically, the upper incisors are peglike, one or the other pair often being absent; in the lower jaw, the incisors show a peculiar conformation that has been likened structurally and functionally to a comb. This dental comb is composed of the lower canines and lower incisors compressed from side to side and slanted forward; the most specialized dental combs—seen, for example, in the fork-crowned lemur (genus Phaner) and the needle-clawed galago (genus Euoticus)—are used for scraping exudates off bark, but other species use the structure for piercing fruit, for nipping off leaves, and for grooming the fur. Canines are present throughout the order but show remarkable variation in size, shape, projection, and function. Characteristically, the teeth of Old World monkeys have a function in the maintenance of social order within the group as well as an overtly offensive role; their function as organs of digestion is relatively unimportant. They are large and subject to sexual dimorphism, being larger in males than females. Great apes have smaller canines than Old World monkeys, though still sexually dimorphic; human canines are smaller still, and there is no size difference between the sexes.

The trend in the evolution of the cheek teeth has been to increase the number of cusps and reduce the number of teeth. Both molars and premolars show this tendency. No living primate has four premolars; primitive primates, tarsiers, and New World monkeys have retained three on each side of each jaw, but in the apes and Old World monkeys, there are only two premolars. The primitive premolars are uniform in shape and are unicuspid, but in primates the most posterior premolar tends to evolve either one or two extra cusps (molarization), an adaptation that extends the cheek-tooth row for a herbivorous diet. In species with large upper canines, the most anterior lower premolar assumes a peculiar shape known as sectorial, functioning as a hone for the scythelike canine. In humans, whose canines are small and unremarkable, the first and second premolars are identical in shape and two-cusped.

2.

Autonomic responses and behavior:-

  They can be modified reliably through the systematic use of antecedent (cues) and consequent (contingencies) stimuli. This means that autonomic responses, which are usually characterized as elicited reflexes, can be learned responses (viz., behaviors).

Intentional behavior:-

Everybody communicates with each other and Intentional communication means that one person is sending a message to another person in a purposeful way.

3.

Why primates spend so much time grooming each other :-

Grooming reduces tension by lowering the heart rate and releasing endorphins that are calming. It is used to reinforce male-female mate bonds as well as same sex friendship bonds. For example, the length of time macaque and capuchin females groom each other depends on their social rank.

4.

Differentiate between absolute and relative dating techniques :-

absolute dating is based on calculations of the age of rock strata based on half lives of minerals, relative dating is based on the assumed age of fossils found in the strata and the laws of super imposition.

5.

Why do we find fossils from some places and times and not from others :-

A fossil is the naturally preserved remains or traces of animals or plants that lived in the geologic past. Body fossils include the remains of organisms that were once living and trace fossils are the signs that organisms were present (i.e. footprints, tracks, trails, and burrows).

Most fossils are found in sedimentary rock. Sedimentary rock is formed by dirt (sand, silt, or clay) and debris that settles to the bottom of an ocean or lake and compresses for such a long time that it becomes hard as a rock.

So it is naturally preserved and depends on nature that where it will be deposited.

Thatswhy we find fossils from some places and times and not from others.