The evolution and biological iteration of the primate is one of the most fascinating aspects of the historical "timeline of life". For a non-biologist/anthropologist, primate evolution may appear quite complicated and interconnected. In this blog, I will break down this complex process into some simple milestones and explain how we arrived at the species of monkeys that currently roam our world.
The very first class of creatures to resemble a primate was the Euarchonta, an early class of mammal that appeared around 70 million years ago (mya). This half-squirrel, half-primate was tree-living with claws and forward facing eyes (located on both sides of its head). The next milestone for primate evolution occurred around 40 million years ago, during which the early proto-primates split up into two groups with distinct and emerging characteristics, the Strepsirrhini (wet-nosed) and Haplorrhini (dry-nosed) primates. The Strepsirrhini developed into lemurs and lorises, some of the smaller-bodied, rodent-like, truly tree-dwelling primates. However, the Haplorrhini as a group diverged again about 10 million years later into what we now call "New World monkeys" and "Old World monkeys".
New World and Old World monkeys spent the next 20 million or so years further evolving and defining themselves (through a process called speciation), but their key and differentiating characteristics remain the same today. New World monkeys feature a flat nose, longer prehensile tails (a functional tail used for tree-swinging), small to mid-sized bodies, and live in the tropical canopy of Central and South America. Some of these primates include the spider monkey, sakis, marmosets, and tamarins. In contrast, Old World monkeys are probably the ones you pay close attention to at your local zoo. These primates feature a downward-facing nose, mid to large-sized bodies, non-prehensile tails, anywhere from partial tree-dweller to land-dweller, and live in a range of habitats across Africa and Asia. Some of these primates include baboons, gorillas, and macaques. These primates survived quite well and developed into the human era around 7 million years ago.