Primates are a diverse order of mammals that includes humans and our closest relatives. They are classified into several major groups based on their evolutionary history and shared characteristics. The three main primate groups are:
1. Strepsirrhines (Wet-Nosed Primates):
- Strepsirrhines include lemurs, lorises, and galagos.
- They are characterized by a moist nose, a grooming claw on the second toe, and a relatively simple brain structure.
- Lemurs are found primarily in Madagascar, while lorises and galagos are found in Africa and Southeast Asia.
2. Haplorhines (Dry-Nosed Primates):
- Haplorhines include monkeys, apes, and humans.
- They are characterized by a dry nose, a lack of a grooming claw, and a more complex brain structure compared to strepsirrhines.
- Haplorhines are further divided into two sub-groups:
- Anthropoids: This group includes monkeys, apes, and humans. They have opposable thumbs, advanced cognitive abilities, and reduced sense of smell.
- Tarsiiformes: This group includes tarsiers, small primates found in Southeast Asia. They have specialized eyes for enhanced night vision and long hind limbs for leaping.
3. Platyrrhines (New World Monkeys):
- Platyrrhines are monkeys found in Central and South America.
- They have a flat nose, three-cusp lower molars, and a prehensile tail (in some species).
- Platyrrhines include several families, such as marmosets, tamarins, capuchins, and howler monkeys.
Phylogenetic Relationships:
The phylogenetic relationships among these primate groups are supported by evidence from molecular studies, comparative anatomy, and fossil records:
- Strepsirrhines: Strepsirrhines are considered the most basal or primitive group of primates. They diverged from the other primates around 60-80 million years ago.
- Haplorhines: Haplorhines are a monophyletic group that diverged from strepsirrhines around 55-60 million years ago. They are further divided into anthropoids and tarsiiformes.
- Anthropoids: Anthropoids are a monophyletic group that diverged from tarsiiformes around 40-45 million years ago. They include monkeys, apes, and humans.
- Catarrhines: Catarrhines are a monophyletic group within anthropoids that diverged from platyrrhines around 25-30 million years ago. They include Old World monkeys, apes, and humans.
- Platyrrhines: Platyrrhines diverged from catarrhines around 35-40 million years ago. They are found exclusively in the Americas.
Within each of these groups, there are further sub-groups and species that have evolved over millions of years, giving rise to the diversity of primates we see today.