Question

Lectures 6/7: The Primate Order/Functional Morphology • 6A. List the three main primate tendencies defined by Le Gros Clark. • 6B. Describe the physical adaptations that all primates share. · 6C. Characterize the variation in primate teeth and the reasons for this variation · 6D. Explain how parental investment and brain size are related in primates. · 6E. Compare and contrast the two suborders of primates, strepsirrhines and haplorhines. · 6F. Distinguish between the gradistic and cladistic taxonomic classification of living primates. • 6G. Explain the major differences between (1) New World monkeys and Old World monkeys and (2) Old World monkeys and apes (lab and Primate Features handout especially helpful) · 6H. Describe the skeletal differences between primates that are quadrupedal, vertical clinging and leaping, and suspensory.

Answer 1

6A. a.Arboreal Adaptation – enables an organism to live in trees.b.Dietary Plasticity – A diet’s flexibility in adapting to a given environment. c. Parental Investment – The time and energy parents expend for their offspring’s benefit.

6B. All primate species possess adaptations for climbing trees, as they all descended from tree-dwellers. This arboreal heritage of primates has resulted in adaptations that include, but are not limited to: 1) a rotating shoulder joint; 2) a big toe that is widely separated from the other toes and thumbs, that are widely separated from fingers (except humans), which allow for gripping branches; and 3) stereoscopic vision, two overlapping fields of vision from the eyes, which allows for the perception of depth and gauging distance. 4) Enhanced Touch – The sensitivity is due in part to the presence of dermal ridges (fingerprints and toe prints) on the inside surfaces of the hands and feet. The potto, a prosimian, has primitive dermal ridges, whereas the human, a higher primate, has more derived ridges, which provide better gripping ability. 5) Reduced Smell – Primates have a reduced sense of smell. The smaller and less projecting snouts of most primates indicate their decreased reliance on smell.6)Dietary Versatility – Primates have dietary plasticity. Part of the record primate dietary adaptation is found in the teeth. Other characteristics of primates are brains that are larger than those of most other mammals (larger brain/body ratio than similar-sized non-primates), claws that have been modified into flattened nails, typically only one offspring per pregnancy, and a trend toward holding the body upright.

6C. 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).

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.

6D. Many explanations for the evolution of large brains have been proposed. Developmental explanations- primates have large brains because their extended periods of parental investment allow them to grow large brains.