Question

Essay Question 1) Describe the 5 major adaptive radiations of primates.Mention what primates evolved and what features make them different from their predecessors.Mention geographic regions and environments that may have contributed to their evolution.

2) Describe the development of bipedalism.Talk about physical attributes that bipedal apes have, and what affects bipedalism can have on their biology, as well as their behavior in the environment. What are the benefits of bipedalism and what evolutionary explanations do we have for the origin of Bipedal apes?

Answer 1

1)

5 major adaptive radiations in primates are:

- Appearance of Strepsirrhines (lemurs, lorisoids and extinct Adapiforms)

- Appearance of Haplorrhine – Tarsiiforms (tarsiers)

- Appearance of Haplorrhine – Simiiforms (catarrhines and platyrrhines).

- Radiation of Catarrhines – Appearance of great apes (Hominoidae) and Old World monkeys (Cercopithecidae).

- Radiation of Platyrrhines (New World Monkeys) – Appearance of several families: Callitrichidae, Cebidae, Aotidae, Pitheciidae, Atelidae.

This is a scheme that illustrates this phylogenetic radiation:

Evolutive trends of all primates are:

· Enlarged cranial box.

· Rotation of the orbits towards the frontal plane.

· Appearance of a complete bone ring that forms the orbit, the back wall that closes it.

· Reduction of the oral and nasal region.

· Retraction of the face to a position under the skull, not in front.

· Displacement of the foramen magnum from the back to below the skull, and central.

· Retention of pentadactyl extremities.

· Conservation of generalized structure of the members associated with great mobility.

· Progressive visual power in proportion to a reduction in olfactory.

· Conservation of a simple type of molars.

· And especially development of a large and complex brain, which results in:

· Elaboration and differentiation of the crust.

· Complexity of the brain and cerebellum through folds and fissures that delimit functional areas: motor, general sensory, visual sensory, associative ...

Specific evolutive traits in each group are:

· Strepsirrhines. They are the smallest primates.

All lemurs evolved in Madagascar, due to the isolation that occurred when this island was detached from Africa. Thus, the diversity of lemurids was greatly increased. Characteristics:

- Eyes in frontal plane, bulging of the skull.

- Very pointed muzzle. They still retain great importance of the sense of smell. Scent glands in the hands.

- Long and ringed tail, which impregnate odoriferous secretion and wave to emit olfactory signals.

· Haplorrhines.

- Tarsiiformes. Very big eyes adapted to nocturn vision.

- Simiiformes.

ú Catarrhines.

They are present in Europe, Africa and Asia, except in Madagascar. There are many species, which are mostly adapted to the arboreal environment.

The hominid line appeared in East Africa. 16 - 20 million years ago the fate of our species was on the move: climatic fluctuations opened large gaps in areas of tropical forest, an ecological niche occupied by cercopithecids and hominids. In these spaces, adaptations are not necessary to move around the trees, and the tendency to bipedism prevails, which in turn entails the liberation of the upper extremities. The behavior evolved makes the appearance of well-organized social structures, since the group has greater protection advantages in open spaces than the individual. These societies become more complex and the position of each individual is organized hierarchically.

ú Platyrrhines.

New World Monkeys that evolved due to their isolation after separation of Africa from America.

They have particular adaptations: the nose area is flattened, and the nostrils open on the side. Most are daytime and have only one calf at a time. Just a nocturnal species that can have more than one calf.

They have specialized adaptations to food, such as resin. Red hair coloring is also common as an adaptive advantage.

The brain appears more and more evident in relation to the type of nutrition; the more diverse, the more volume, since you have to make more effort to choose what to eat, how to find it and get it. Eg: spider monkeys.

2)

Hominization did not occur, as previously thought, in the savanna, but in the open forest.

Hominid physical adaptations

- Reduction of the anterior dentition (incisors, canines), and increase of the molars. Thick enamel.

- Material culture: manufacture and use of tools, using elements of nature.

- Brain development, increased cranial capacity. This is characteristic of hominids. The limit is 600 cm3, although some have less and others more.

- Erect gait, biped. This is currently thought to be the key to considering a hominid species. From here all the other characters come.

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Bipedalism: origin, Hypothesis and benefits

The upright march would serve to see them above the tall grass, which would give them the ability to defend themselves and survey prey. This is no longer clear, since it is known that they did not develop in savanna but in open forest. Several hypotheses have been formulated:

- Hunter man hypothesis. Bipedalism would serve them to travel long distances chasing prey, organize ambushes ... However, it has been shown that this hypothesis is not valid: man can no longer be presented as a great dominant hunter, since he was relatively small, he did not dominate the rest of animals. Their physical morphology made it impossible to be great hunters, and they had not yet developed their hunting tools. Proponents argue that they would use tools from perishable organic materials, such as bamboo. The little contribution of meat they got was by carrion, by opportunism.

- Gathering man hypothesis. It also advocates the use of tools. The biped march would be useful to move behind the herds and take advantage of the dead individuals; they would get meat out of opportunism. However, meat intake has not been found useful or clear; This was not their main food.

- Hypothesis of the collecting woman. Eating meat is not their main food, the most important are the seeds, the fruits ... The women would be the ones who traveled the land to collect and forage vegetables. For this they need to have their hands free, both to collect and to carry the young.

- Provisioning man hypothesis. The men are the ones who stock up on food, especially vegetables, and take him to the base camp, where his wives and children await them. Introduces the concept of monogamous family.

- Solar radiation hypothesis. In a warm and dry environment, an upright individual receives less sunlight. When standing, by sweating it expels more heat, if it were a quadruped it would condense under the body.