- The oldest known fossil remains of primates appeared about 60 mya.
- The Primate adaptive radiation began sixty-five to seventy million years ago in the Palaeocene epoch.
- Though the living primates could be arranged in order of increasing their anatomical and behavioural complexity, they are the end products of their own evolutionary lines.
Early Tertiary Period
The climate of the early Tertiary period (66.4 million years ago) – was warm with wide tropical and subtropical zones in both the Old and the New World. During this period, the most primitive of the primates were in existence.
Palaeocene and Eocene epochs (from 66.4 million to 36.6 mya)
Early in the Tertiary period, more advanced primates appeared. During these epochs, an explosive primate radiation took place which dwindled in the Oligocene (Oligo = small). Lemuroids, Tarsioids and Platyrrhines have been recognised in the Palaeocene and Eocene epochs of America, Europe, Egypt and Burma.
- The Lemuriformes, was the most widespread one as per the fossil record.
- The Tarsiiformes are known from one family, the Omomyidae. The characteristic tarsioid (tarsier-like) specialisation of the skull and hind limbs were already well advanced in the known fossil forms, but some had relationships with the early monkeys.
- Amphipithecus, implying both ways an ape, a platyrrhini, found in the Eocene of Burma is considered to be ancestral to the Parapithecus (Para = near) of Egypt.
- Generally speaking, there is hardly any fossil evidence of the Eocene ancestors of the Old World monkeys and apes. Thus, the Eocene epoch terminated after bout 30 million years of primate evolution with lemur-like and tarsier-like forms.
Oligocene epoch (36.6 to 23.7 million years ago)
- There came into existence primitive monkeys and exceedingly primitive anthropoid apes. Propliopithecus (Pro = before, Plio = more), the earliest anthropoid ape on record (they had small brains, long snouts, skulls resembling those of monkeys or lemurs and their teeth like those of modern apes; they lived in trees and had tails) and Parapithecus (known from some lower jaws 30 mya), a very small sized (squirrel-like) and earliest Old World Monkey on record having a generalised Tarsioid appearance.
- Gregory regarded Propliopithecus as a primitive gibbon and Parapithecus as a primitive monkey. These fossils are distinguished by traits normally necessary for adaptation to arboreal life: grasping extremities, nails instead of claws, pentadactyly, an opposable thumb and a big toe, forearm consisting of ulna and radius, reduced snout, forwardly directed eyes and orbits closed from behind, and enlarged visual centers.
- Apidium, which is also included in the family of Parapithecidae, could be the forerunner of African monkeys. The Egyptian Oligocene epoch also contributed to several primitive fossil apes including Aeolopithecus, which may be an ancestral gibbon, and Aegyptopithecus, which may be ancestral to the modern great apes. One other fossil ape from the Fayum that deserves special mention is Propliopithecus, formerly believed to be an ancestral gibbon. It has been suggested, primarily on the basis of its generalised dentition, that Propliopithecus is possibly ancestral to the hominids.
The Miocene Epoch (23-5.3 million years ago)
It was a incredible phase in primate evolution which witnessed an increase in the number of larger primates that were widely spread throughout the Old World, including Europe, Asia, and Africa. The large Miocene hominoids appear to belong to three groups, the Sivapithecus, the Dryopithecus, and the Proconsul groups.
- Asian apes formed a distinct category which diversified in Asia and Southeast Europe by fourteen million years ago (e.g., Sivapithecus, Ramapithecus, etc).
- There were other significant fossils reported from the Miocene of Europe, Egypt and Africa. The lower Miocene epoch is often referred to as the ‘Age of Apes’. Skeletal remains from Africa were classified into three major groups: Proconsul (a nonspecialised ape), Sivapithecus (a transitional form between the anthropoids and man), and Limnopithecus (an early type of gibbon).
- From Europe, the fossil material of Pliopithecus was recovered. The name means that the individual is thought out as ancestral to the modern gibbons. A small sized primitive gibbon frequented Egypt during the Miocene. This ape was slightly bigger in size than the Propliopithecus. This epoch, thus, saw the rise of the generalised apes of large size which are regarded as the offshoots of Propliopithecus of Oligocene.
- Dryopithecids and Oreopithecus were inhabiting in India and Europe during the Pliocene. Pliocene signals the decline, both in numbers and diversification, of these closely related Miocene forms and the commencement of the primitive hominids. The Dryopithecus group comprises the first specimen of the Dryopithecus fontani found in 1856 in Saint-Gaudens in France. Its molars possess five cusps and the Y-5 pattern -its fissure pattern is typical of dryopithecines.
- The Proconsul groups are known from the early Miocene period of Africa. It includes three species— Proconsul africanus, Proconsul nyanzae, and Proconsul major—as well as Rangwapithecus gordoni and several other smaller-bodied apes. The second group of Middle Miocene apes (all from East Africa) is represented by the Oreopithecidae, the large Afropithecus, and two species of Kenyapithecus.
Pliocene Epoch (5.3-2.6 million years ago)
- Hominins: The period marked significant developments in the human lineage.
- Australopithecus afarensis: One of the earliest known hominins, exemplified by the famous “Lucy” skeleton, found in East Africa.
- Paranthropus: A genus of robust hominins with specialized adaptations for heavy chewing, found in East and South Africa.
Quaternary Period (2.6 million years ago to present)
Pleistocene Epoch (2.6 million to 11,700 years ago)
- Homo Genus: This epoch witnessed the evolution and diversification of the genus Homo.
- Homo habilis: Known as the “handy man” for its association with early stone tools, found in East Africa.
- Homo erectus: Exhibited a larger brain and more advanced tools, with fossils found in Africa, Asia, and Europe.
- Neanderthals (Homo neanderthalensis): Adapted to cold climates and coexisted with early modern humans, found in Europe and Western Asia.
- Homo sapiens: Anatomically modern humans that eventually spread globally, with early fossils found in Africa (e.g., Omo Kibish).
Holocene Epoch (11,700 years ago to present)
- Continued Evolution of Homo sapiens: Modern humans continued to develop complex societies, technologies, and cultures.
Evolutionary Trends
There is a group of evolutionary trends (Clark, 1971) which, to a greater or lesser degree, characterize the entire order. Keeping in mind, these are set of general tendencies and are not synonyms with progress. In evolutionary terms, we are using “trend” only to reflect a series of shared common characteristics (i.e., general homologies).
A common evolutionary history with similar adaptations to common environment challenges is reflected in the limbs and locomotion, teeth and diet and in the sense, brain and art behaviour of the animals that make up order. Following is a list of those evolutionary trends that tend to set the primates apart from other mammals.
1. Limbs and Locomotion
- Retention of five digits in the hands and feet-pentadactyle.
- Nails instead of claws.
- Flexible hands and feet with a good deal of prehensility (grasping ability).
- A tendency toward erectness (particularly in the upper body).
- Retention of the clavicle (collar bone).
2.Teeth and Diet
- A generalized dental pattern, particularly in the back teeth (molars).
- A lack of specialization in diet. This attribute is usually correlated with change in pattern of teeth.
3.Senses, Brain and Behaviour
- A reduction of the snout and the proportionate reduction of the smell (olfactory) areas of the brain.
- An increased emphasis on vision with elaboration of visual areas of the brain. A trend related to the decreased dependence on smell. Except for some specialized nocturnal forms, colour vision is most likely present in all primates.
- Expansion and increasing complexity in the brain.
- A more efficient means of foetal nourishment, as well as longer period of gestation (with single births the norm), infancy and extension of the whole life span.
- A greater dependency on highly flexible learned behaviour is correlated with longer periods of infant and child dependency. As a result of both these trends, parental investment in each offspring is increased so that although fewer young are born, they receive more efficient rearing.
- Adult males often associate permanently with the group.
MORPHOLOGICALAND ANATOMICAL FEATURES OF APES
Apes are a group of anthropoid primates native to Africa and Southeast Asia. In traditional use, apes are excluded from humans and are differentiated from other primates in terms of locomotion. Apes are divided into two extant branches or super families: Hominoidea (gibbons or lesser apes) and Hominids (great apes).
The Apes: Characteristics of the Apes: General
- They have no tail.
- Only apes (and humans) have five cusps on their teeth, known as Y-5 pattern. Monkeys have four cusps to their teeth.
- Locomotion is by several means, in the trees and knuckle-walking on the ground (Quadrupedal).
- The arms are long in comparison with their hind limbs.
- Their rib cages are flattened from front to back.
- Their brains are larger than those of monkeys, which allow them to learn quite complex behaviour patterns.
- The upper lip is free of the gums. This allows the apes to have mobile and expressive faces, so they use facial expression for communication.
Gibbons
- These are the smallest of the apes, the largest being no more than 10.5 kg.
- They live in the dense tropical forests of Southeast Asia.
- They are acrobatic brachiators 75 per cent of the time, the rest is spent quadrupedally or bipedally.
- They show no sexual dimorphism. (Apes vs Humans & Skeletal Differences, n. d.)
- Face and Ischial callosities are devoid of hair covering.
- Digital formula: 3>2>4>5>1.
- Digits except thumb are provided with nails.
Orangutan
- They live in thick tropical rain forests in Sumatra and Borneo.
- They are fruit eater.
- They have reddish hair coating on the body.
- They brachiate and often hang by their arms, which are very long. They have long curved hands.
- They tend to be too heavy to swing from one tree to another, so they have to come down on to the ground where they knuckle – walk to the next tree.
- Live in small group of 2-4 members.
- Each night they make a new nest to sleep in.
- Digital formula: 3>4>2>5>1.
- Their thumb is short and other fingers are long bear flat nails.
Chimpanzee
- Found in forest fringe and open woodland habitats in Africa.
- They are knuckle walkers on the ground and in the trees and they brachiate and can walk on two legs.
- Their main diet is fruit, supplemented by insects such as termites. They do not eat meat very often but it is greatly relished when they do.
- Their visual sense is highly developed; each animal looks different and is recognized by facial features.
- They live in troops of about 20 animals; children remain with their mothers for 4 or 5 years. During this time they learn from their mothers many complicated behaviors, including how to raise young babies.
- These are highly intelligent animals, able to fashion tools out of a piece of stick, throw stones when frightened, or pickup sticks to defend themselves.
Gorillas
- They are found in Africa
- These are the forest dwellers and spend most of their lives on the forest floor.
- They forage for food, mostly eating a type of celery and many leaves and shoots rather than fruit.
- They are nomadic, travelling daily to new feeding areas in groups of about 12-20 animals.
- They show sexual dimorphism; the males are bigger and have large canine teeth.
- They make nests each night.
- Fore limbs are considerably longer than hind limb (Apes vs Humans & Skeletal Differences, n.d.).