The origin and evolution of primates has caused great controversy and a multitude of hypotheses since the beginning of the studies. This extensive Order of mammals, to which people belong, is one of the most threatened by humans.
In this article on our site we will learn what primates are, what characteristics define them, how they have evolved and if it is the same to talk about apes and primates. We explain everything below!
Characteristics of primates
All extant species of primates share a set of characteristics that distinguish them from other mammals. Most extant primates live in trees, so they have specific adaptations that allow them to lead this lifestyle. His feet and hands are adapted to move between branches. The big toe of the foot is very separated from the rest of the fingers (with the exception of the human being), this allows them to grasp firmly. The hands also have adaptations, but this will depend on the species, such as the opposable thumb. They do not have curved claws and nails like other mammals, they are flat and blunt.
The fingers have tactile pads with dermatoglyphs (fingerprints) that allow them to hold better to the branches, also, on the palms of the hands and fingers, there are nerve structures called Meissner's corpuscles that provide a highly developed sense of touch. The body's center of gravity is closer to the legs, which are also the dominant extremities during locomotion. On the other hand, the heel bone is longer than in other mammals.
One of the most important adaptations in primates is their eyes. First of all, they are very large compared to the body and, if we talk about nocturnal primates, they are even larger, unlike other nocturnal mammals that use other senses to live during the night. These prominent and large eyes are due to the presence of bone behind the eye, which we call the orbit.
In addition, the optic nerves (one for each eye) do not cross completely within the brain, as occurs in other species, in where information entering through the right eye is processed in the left hemisphere of the brain and information entering through the left eye is processed in the right side of the brain. This means that, in primates, information entering each eye can be processed on both sides of the brain, resulting in a much better understanding of the environment
The ear of primates is characterized by the appearance of a structure called the auditory ampulla, formed by the tympanic bone and the temporal bone, enclosing the middle and inner ear. On the other hand, the olfactory sense seems to have been reduced, and smell is no longer a striking characteristic of this group of animals.
With regard to the brain, it is important to highlight that its size is not a determining characteristic. Many primates have brains smaller than the average mammal. Dolphins, for example, have brains, compared to bodies, almost as large as any primate. What makes the primate brain different are two anatomical structures unique in the animal kingdom, the Sylvia groove and the groove of Calcarine
The jaw and teeth of primates have not undergone major changes or adaptations. They have 36 teeth, 8 incisors, 4 canines, 12 premolars and 12 molars.
Types and species of primates
Within the taxonomic classification of primates, we find two suborders: the "strepsirrhine" suborder, to which lemurs and lorisiformes, and the suborder "haplorhines", which includes tarsiers and apes.
Strepsirrhines
Strepsirrhines are known as wet-nosed primates, their sense of smell has not diminished and is still one of their senses more important. This group includes lemurs, inhabitants of the island of Madagascar. They are famous for their loud vocalizations, large eyes, and nocturnal habits. There are about 100 species of lemur, including the Lemur catta or ring-tailed lemur and the bandro or Hapalemur alaotrensis.
Another group of strepsirrhines are the lories, very similar to lemurs but inhabiting other parts of the planet. Among its species we highlight the red slender loris (Loris tardigradus), a highly endangered species from Sri Lanka, or the Bengal slow loris (Nycticebus bengalensis).
Haplorhines
Haplorhines are single-nosed primates, they have lost some olfactory ability. A very important group is the tarsiers These primates live in Indonesia and are considered diabolical animals due to their appearance. They are nocturnal, have very large eyes, very long fingers and a small body. Both the streptosyrrhine groups and the tarsiers are considered prosimians.
The second group of haplorhines are apes, and are often divided into New World monkeys, Old World monkeys, and Homonoids.
- New World Monkeys: All of these primates live in Central and South America. Their main characteristic is that they have a prehensile tail. Among these monkeys we find the howler monkeys (genus Alouatta), night monkeys (genus Aotus) and spider monkeys (genus Ateles).
- Old World Monkeys: These primates inhabit Africa and Asia. They are monkeys without a prehensile tail, also called catarrhines because their noses are down, and they also have calluses on their buttocks. This group is made up of baboons (genus Theropithecus), macaques (genus Macaca), cercopithecus (genus Cercopithecus) and colobus (genus Colobus).
- Homonoids: they are the tailless primates, also catarrhines. Human beings belong to this group that they share with gorillas (genus Gorilla), chimpanzees (genus Pan), bonobos (genus Pan) and orangutans (genus Pongo).
Evolution of Primates
The fossil most closely related to modern primates or euprimates dates from the end of the Eocene (about 55 million years ago). At the beginning of the Miocene (25 million years ago), species very similar to the current ones begin to appear. There is a group within the primates, called plesiadapiformes or archaic primates, from the Paleocene (65-55 million years) that show certain characteristics of the primates, although it is currently considered that these animals diverged before the appearance of the primates and, later, they became extinct, so they would not be related to them.
According to the fossils found, The first known euprimates are adapted to arboreal life and have many of the main characteristics that distinguish this group, such as the skull, the teeth and the skeleton in general. These fossils were found in North America, Europe, and Asia.
The first fossils from the middle Eocene were found in China and correspond to the earliest relatives of apes (Eosimians), now extinct. Fossil specimens belonging to the extinct families Adapidae and Omomyidae were later identified in Egypt.
The fossil record documents all existing groups of primates, with the exception of the Malagasy lemur, for which there are no fossils of its ancestors. On the other hand, there are fossils of its sister group, the lorisiformes. These remains were found in Kenya and are about 20 million years old, although new discoveries show that they already existed 40 million years ago. Therefore, we know that lemurs and lorisiforms diverged more than 40 million years ago and form the suborder of primates called strepsirrhines.
The other suborder of primates, the haplorhines, appeared in China in the middle Eocene, with the infraorder tarsiers. The other infraorder, the apes, appeared 30 million years ago, in the Oligocene.
The appearance of the genus Homo, to which the human being belongs, occurred 7 million years ago, in Africa. The appearance of bipedalism is still unclear. There is a Kenyan fossil of which only a few long bones remain which may suggest some ability for bipedal locomotion The most obvious fossil of bipedalism is from 3.4 million years ago years, before the famous fossil of Lucy (Australopithecus afarensis).
