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AR103 - RN Ch#6 W2.pdf

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Jonathan Haxell

AR103 - Readings pgs. 117-151 Week 2 Notes - Sep. 20, 2011 Chapter Six: An Overview of the Primates Pages #117-154 - Chimpanzees, gorillas, and orangutans are not monkeys they’re apes - One way to understand any organism is to compare its anatomy and behaviour with that of other, closely related species. This comparative approach helps explain how and why physiological and behavioural systems evolved as adaptive responses to various selective pressures throughout the course of evolution. - Each lineage or species has come to possess unique qualities that make it better suited to a particular habitat and lifestyle. - Primates are members of the mammalian order Primates, which include lemurs, lorises, tarsiers, monkeys, apes, and humans. - Anthropoids are members of the primate infraorder Anthropoidea. Traditionally, this group includes monkeys, apes, and humans. Primate Characteristics - Primates share many characteristics with other mammals, basic mammalian traits are: - Body hair - A relatively long gestation period followed by live birth - Mammary glands, - Different types of teeth (incisors, canines, premolars, and molars) - The ability to maintain a constant internal body temperature through physiological means (endothermy) - Increased brain size - A considerable capacity for learning and behavioural flexibility - Identifying single traits that define the primate order isn’t easy because compared with most mammals, primates have remained quite generalized. Meaning that primates have retained several ancestral mammalian traits that some other mammals have lost over time. - Primatologists have drawn attention to a group of characteristics that more or less characterize the entire primate order (these are a set of general tendencies that are not all equally expressed in all primates). The characteristics in the list concern their limbs and locomotion, teeth, diet, senses, brain, and behaviour, primates reflect a common evolutionary history with adaptions to similar environmental challenges, primarily as highly social, arboreal beings. - Limbs and Locomotion - A tendency toward an erect posture [all primates show this to some degree through sitting, leaping, standing, bipedal walking] - A flexible, generalized limb structure, which allows most primates to practice various locomotor behaviours [primates aren’t restricted to one form of movement like many other mammals, they maintained a generalized locomotor anatomy, retained some bones and certain abilities] - Prehensile hands (and some feet) [primates can very skillfully manipulate things with their hands] - Retention of five digits on the hands and feet [some species show marked reduction of thumb & index] - An opposable thumb and, in most species, a divergent and partially opposable big toe. - Nails instead of claws [seen in all primates except some highly derived New World Monkeys] - Tactile pads enriched with sensory nerve fibers at the ends of digits. [enhances sense of touch] 1 AR103 - Readings pgs. 117-151 Week 2 Notes - Sep. 20, 2011 - Diet and Teeth - Lack of dietary specialization [this is typical of most primates, who tend to eat a wide assortment of food items, in general primates are omnivorous] - A generalized dentition [primate teeth aren’t specialized for processing only one type of food, a trait related to a general lack of dietary specialization] - The Senses & the Brain ({diurnal ones in particular} rely heavily on vision and less on the sense of smell, especially when compared with other mammals. This emphasis is reflected in evolutionary changes in the skull, brain, and eyes.) - Colour vision [This is characteristic of all diurnal primates. Nocturnal primates don’t have colour vision.] - Depth perception [Primates have stereoscopic vision, or the ability to perceive objects in 3 dimensions. This is made possible through a variety of mechanisms, including: - Eyes placed toward the front of the face (not the sides) [this field provides for overlapping fields, or binocular vision] - Visual information from each eye transmitted to visual centers in both hemispheres of the brain. [In primates, about 40% of the fibers remain on the same side, so that both hemispheres receive much of the same information. Whereas in nonprimate animals, most optic nerve fibers cross the opposite hemisphere through a structure at the base of the brain.] - Visual information organized into 3 dimensional images by specialized structures in the brain itself. - Decreased reliance on the sense of smell. [Correspondence with the reduction of the olfactory apparatus in the brain has increased the reliance on vision] - Expansion & increased complexity of the brain. [this is a general trend among placental mammals but especially true among primates. As primates have an evident expansion in the visual and association areas of the neocortex (portions of the brain where info from different sensory modalities is combined)] - Maturation, Learning, & Behaviour - A more efficient means of fetal nourishment, longer periods of gestation, reduced numbers of offspring (with single births the norm), delayed maturation, and extension of the entire lifespan. - A greater dependance on flexible, learned behaviour. [this trend is correlated with delayed maturation and subsequently longer periods of infant and child dependency on at least one parent.] - The tendency to live in social groups and the permanent association of adult males with the group. [Except for some nocturnal species, primates tend to associate with individuals. The permanent association of adult males with the group is uncommon in most mammals but widespread in primates.] - The tendency toward diurnal activity patterns. [this is seen in most primates] - Omnivorous is having a diet consisting of many food types, such as plant materials, meat and insects - Diurnal is active during the day - Nocturnal is active during the night - Stereoscopic Vision is the condition whereby visual images are, to varying degrees, superimposed. This provides for depth perception, or viewing the external environment in three dimensions. Stereoscopic vision is partly a function of structures in the brain. 2 AR103 - Readings pgs. 117-151 Week 2 Notes - Sep. 20, 2011 - Binocular Vision is vision characterized by overlapping visual fields provided by forward- facing eyes. Binocular vision is essential to depth perception. - Hemispheres is the two halves of the cerebrum that are connected by a dense mass of fibers. (The cerebrum is the large rounded outer portion of the brain.) - Olfaction is the sense of smell - Neocortex is the more recently evolved portion of the brain that is involved in higher mental functions and composed of areas that integrate incoming information from different sensory organs. - Sensory Modalities is different forms of sensation (e.g. touch, pain, pressure, heat, cold, vision, taste, hearing, and smell) Primate Adaptions - Environmental Circumstances refers to interrelated variables; climate, diet, habitat, predation. Evolutionary Factors - The group of characteristics shared by primates has traditionally been explained as the result of adaption to arboreal living - Arboreal is tree-living: adapted to life in trees. - Other mammals were adapting to various ground-dwelling lifestyles and marine environments, the primates found their adaptive niche. Other mammals were adapting to arboreal living but nested in trees and searched for food on the ground. But eventually throughout evolution, primates increasingly found food in trees such as; leaves, fruits, nuts, seeds, insects, and small mammals. - Adaptive niche is an organism’s entire way of life, what it eats, how it gets food, how it avoids predators, and so on. - This adaptive process is also reflected in how heavily primates rely on vision. - In complex, 3-dimensional environments with uncertain footholds, acute colour vision with depth perception is extremely beneficial - Grasping hands and feet also reflect an adaption to living in trees - Cartmill proposed an alternative to the traditional arboreal hypothesis, called the visual predation hypothesis - He pointed out that while some animals don’t have forward-facing eyes, visual predators like cats and owls do, and this fact may suggest additional factor that could have shaped primate evolution. - Sussman suggested that the basic primate traits developed in conjunction with another major evolutionary occurrence, the appearance and diversification of flowering plants that began around 140 million years ago. - These hypotheses aren’t mutually exclusive. The complex of primate characteristics might well have originated in non-arboreal settings and certainly could have been stimulated by the new econiches provided by evolving angiosperms. Geographical Distribution and Habitats - With a few exceptions, nonhuman primates are found in tropical or semitropical areas of the New and Old Worlds. - New World areas include southern Mexico, Central America, and parts of South America - Old World primates are found in Africa, India, Southeast Asia, and Japan - Even though most nonhuman primates are arboreal and live in forest or woodland habitats, some Old World monkeys spend much of the day on the ground in places where trees are sparsely distributed, same goes for the African apes 3 AR103 - Readings pgs. 117-151 Week 2 Notes - Sep. 20, 2011 - None the less no nonhuman primate is adapted fully to terrestrial lifestyle, so they all spend some time in the trees. Diet & Teeth - Majority of primates mostly eat a combination of fruit, nuts, seeds, leaves, other plant materials, and insects. - Many also get protein from birds and amphibians - Some occasionally kill and eat small mammals, including other primates - Others have become more specialized and only eat leaves - Almost all primates, like other mammals, have 4 kinds of teeth\ - Incisors & Canines (for biting and cutting), and Premolars & Molars (chewing and grinding) - Biologists use what’s called a dental formula to describe the number of each type of tooth that typifies a species - Dental formula is a numerical device that indicates the number of each type of tooth in each side of the upper and lower jaws. - Indicates the number of each tooth type in each quadrant of the mouth - (upper) ▯ (lower) - Primates have fewer teeth than the ancestral pattern of, because of a general evolutionary trend toward fewer teeth in many mammal groups - The overall lack of dietary specialization in primates is reflected in the lack of specialization in the size and shape of our teeth, because tooth shape and size are directly related to diet - Most primates have premolars and molars with low, rounded cusps, a pattern that enables them to process most types of foods. - Cusps are the bumps on the chewing surface of premolars and molars Locomotion - Almost all primates are to some degree, quadrupedal. But at the same time, most primates use more than one form of locomotion, and they’re able to do this because of their generalized anatomy. - Quadrupedal is using all four limbs to support the body during locomotion; the basic mammalian (and primate) form of locomotion. - Vertical clinging and leaping, another form of locomotion, is common in some lemurs and tarsiers. They can support themselves vertically by grasping onto trunks of trees by other large plants while their knees and ankles are tightly flexed. By forcefully extending their long hind limbs, they can spring powerfully away either forward or backward. - Brachiation is arm swinging, a form of locomotion used by some primates. Brachiation involves hanging from a branch and moving by alternatively swinging from one arm to the other. - Another form of locomotion - The body moves by being suspended by one arm or the other. - Brachiation is seen in species characterized by arms longer than legs, a short, stable lower back, long curved fingers, and reduced thumbs. - Some New World monkeys, such as the spider monkey, are called semibrachiators, since they practice a combination of leaping with some arm swinging. - Some New World monkeys enhance arm swinging by using a prehensile tail, which in effect serves as a grasping fifth hand. No Old World monkeys have prehensile tails 4 AR103 - Readings pgs. 117-151 Week 2 Notes - Sep. 20, 2011 - All apes have arms longer than their legs, and some practice a special form of quadrupedalism called knuckle walking. Because their arms are so long relative to their legs instead of walking with the palms of their hands flat on the ground like some monkeys do, they support the weight of their upper body on the back surfaces of their bent fingers. Primate Classification - The taxonomy living primates are categorized into is based on the system originally established by Linnaeus. - Primates are broken down into 2 categories at suborder; Strepsirhini & Haplorhini. - Strepsirhini is the primate suborder that includes tarsiers, monkeys, apes, and humans. - Haplorhini is the primate suborder that includes tarsiers, monkeys, apes, and humans. - The traditional system was based on physical similarities between species and lineages, but it wasn’t foolproof do to some species being grouped together do to looks and in fact were very distinct from each other. By looking only at physical characteristics, it’s possible to overlook the unknown effects of separate evolutionary history. - The rapidly growing number of species whose genomes have been sequenced, geneticists can now make direct comparisons between the genes, and indeed the entire genetic makeup, of different species. This analysis is called comparative genomics. Providing more accurate picture of evolutionary and biological relationships between species than was possible before the 1990’s. - Comparisons of the genomes of different species are important because they reveal such differences in DNA as the number of nucleotide substitutions and/ore deletions that have occurred since related species last shared a common ancestor. - Geneticists estimate the rate at which genes change, and then they combine this information with the amount of difference they observe to estimate when related species last shared a common ancestor. A Survey of the Living Primates Lemurs & Lorises - The suborder Strepsirhini includes the lemurs and lorises, the most primitive living primates. Meaning that they are more similar anatomically to the earlier mammalian ancestors than are the other primates. - Their greater olfactory capabilities (compared to other primates) are reflected in the presence of a moist, fleshy pad, or rhinarium, at the end of the nose and a relatively long snout. - Rhinarium is the moist, hairless pad at the end of the nose seen in most mammalian species. The rhinarium enhances an animal’s ability to smell. - Lemurs and lorises mark their territories with scent, something not seen in most primates. - Other characteristics distinguishing lemurs and lorises from other primates are; - Eyes placed more to the side of the face, differences in reproductive physiology, and shorter gestation and maturation periods. And a unique derived trait called a “dental comb” formed by forward-projecting lower incisors and canines (used in both grooming and feeding). ▯ Lemurs - Only found on the island of Madagascar and adjacent islands off the east coast of Africa. The only nonhuman primates in Madagascar, and diversified into numerous ecological niches without competition from monkeys and apes. - There is a great deal of behavioural variation among lemur species ▯ Lorises 5 AR103 - Readings pgs. 117-151 Week 2 Notes - Sep. 20, 2011 - Are able to survive in mainland areas by becoming nocturnal. They were and are able to avoid competition with more recently evolved primates (the diurnal monkeys). - At least 8 kinds of species, all of which are found in tropical forest and woodland habitats of India, Sri Lanka, Southeast Asia, and Africa. - Locomotion in some lorises is a slow, cautious, climbing form of quadrupedalism. - Females leave young infants behind in nests while they search for food, a behaviour not seen in most primate species. Tarsiers - 5 recognized tarsier species, which are restricted to islands of Southeast Asia, where they inhabit a wide range of habitats, from tropical forest to backyard gardens. - Are nocturnal insectivores that leap from lower branches to shrubs onto small prey - They appear to form stable pair bonds, and the basic tarsier social unit is a mated pair and their young offspring. - They are highly specialized animals and have several unique characteristics, presenting a complex blend of characteristics not seen in any other primate. - They can rotate their heads 180 degrees to compensate for their inability to move their eyes, also they have enormous eyes dominating most of their face which are immobile within their sockets. Anthropoids: Monkeys, Apes, and Humans - The distinguishing characteristics between lemurs & lorises and anthropoids are; - A larger average body size - Larger brain in absolute terms and relative to body weight - Reduced reliance on the sense of smell, as indicated by the absence of a rhinarium and other structures. - Increased reliance on vision, with forward-facing eyes placed more to the front of the face - Greater degree of colour vision - Back of eye socket protected by a bony plate - Blood supply to the brain different from that of lemurs and lorises - Fusion of the 2 sides of the mandible at the midline to form one bone (in lemurs & lorises, they’re 2 distinct bones joined by cartilage at the middle of the chin) - More generalized dentition, as seen in the absence of a dental comb
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