Simian

The simians, also called anthropoids or higher primates, are a group of primates known as the infraorder Simiiformes. This large family includes all animals we commonly call monkeys and apes. Within this group are two main branches: the Platyrrhini, known as New World monkeys, and the Catarrhini, which includes Old World monkeys and apes, the latter of which includes humans.

Simians are closely related to tarsiers, and together they make up a group called haplorhines. These animals began to diversify about 60 million years ago during the Cenozoic era. Around 40 million years ago, some simians traveled to South America and evolved into the New World monkeys. The other simians, known as catarrhines, later split into two groups: the Cercopithecidae family and the apes, which include humans.

These fascinating creatures have played an important role in understanding evolution and human origins. By studying simians, scientists can learn more about how humans and other primates are connected and how life has changed over millions of years.

Taxonomy

Simians, also known as anthropoids, include monkeys and apes. They are part of a group called haplorhines, which also includes tarsiers. Earlier classifications grouped simians under Anthropoidea, but modern science places them alongside tarsiers in the suborder Haplorhini.

The terms Simiiformes and Anthropoidea are both used to describe simians, with some scientists preferring Simiiformes because it follows the naming rules for infraorders better. There are also extinct simian species that lived millions of years ago, adding to our understanding of these primates.

Main article: Anthropoidea
Main articles: Primatology, Paleoanthropology

Evolution

Scientists believe that anthropoid primates, which include monkeys and apes, likely first appeared in Africa. However, some think they may have started in Asia and traveled to Africa on natural rafts during the Eocene period. Early fossils of these primates have been found in northern Africa, in places like Algeria, Libya, and Egypt.

Around 40 million years ago, New World monkeys separated from the rest of the simian line. This left the Old World monkeys and apes to continue evolving together. About 25 million years ago, the Old World monkeys split from the apes, showing they share a closer relation to apes than to New World monkeys.

Main articles: Cercopithecidae

Classification

The simians are a group of primates that include all monkeys and apes. They belong to the infraorder Simiiformes, which is part of the suborder Haplorhini. This group includes tarsiers and monkeys, with simians being closely related to tarsiers.

Simians are divided into two main groups: the parvorder Platyrrhini, which are New World monkeys, and the parvorder Catarrhini, which includes Old World monkeys and apes. New World monkeys are found in South and Central America and include families like marmosets, capuchins, and spider monkeys. Old World monkeys and apes are primarily found in Africa and Asia and include gibbons and great apes, such as chimpanzees, gorillas, and humans.

Biological key-features

Simians, also known as anthropoids, share several important biological features. They have large brains, forward-facing eyes for better vision, and acute color vision suited for daytime living. These primates also have fused jawbones, binocular vision, and their females typically have a single uterus.

One key difference between New World simians and Old World simians is their nose shape and teeth. New World simians have broader noses with nostrils that face forward and more teeth, while Old World simians have narrower noses with downward-facing nostrils and fewer teeth.