#prosimian

Humans and Monkeys (Part 1 of 3): Prosimians and Simians Back early in our education if you remember, we were taught that humans evolved from monkeys or apes and that they were our closest ancestors. Yet, that was about all we were taught, but really there’s a lot more to it! In this series of 3 posts, we’re going to explore in detail just how this happened. First came the lower primates, which are known as the Prosimians. The Prosimians can be divided into two groups, the Strepsirrhines and the Haplorrhines. The Strepsirrhines are named due to their ‘curly’ nostrils on their straight snouts. Strepsirrhines have wet noses as they are connected to their upper lip and gum. Examples today of Strepsirrhines include Lemurs (picture 1) and Bush Babies. The Haplorrhines, however, have dry noses as they are not connected to their gums. Haplorrhine eye sockets are also slightly different to strepsirrhines’ as bones completely enclose their eye socket. An example of a Haplorrhine is the Tarsier which evolved in 58 million years ago.

The next major group of primates are the Simians. Between these two groups, a transitional form is needed to link the pair. In the modern day there are no living examples of such a creature, however in 1994 Eosimias (known as the dawn monkey) was discovered in China (dated to 40 million years ago). Eosimias was tiny, it weighed only 100g and could have fit in the hand of a human.

Finally, there are the simians, which can be divided into New World Monkeys and Old World Monkeys, which separated from each other 40 million years ago. The New World Monkeys are Platyrrhines (they have a flat nose with sideways pointing nostrils). They are small to mid-sized (ranging from the Pygmy Marmoset up to the Southern Muriqui as seen in picture 2) and are thus mostly arboreal (live in trees). Unlike Old World Monkeys they tend to lack trichromatic vision (seeing in colour as humans do) and opposable thumbs (can be placed opposite fingers on the same hand which is essential for holding tools for example). Despite this, New World Monkeys have a prehensile tail which can grasp and hold objects, which suits their arboreal lifestyle.

Old World Monkeys differ in several ways to New World Monkeys. This difference can be attributed to the fact that they live in differing environments and thus are adapted in other ways. Old World Monkeys are medium to large in general with the smallest being the Talapoin Monkey and the largest the male Mandril. These monkeys can be arboreal such as the Colobus Monkey (picture 3) or terrestrial (live on the ground) such as the Baboon. We are far more closely related to this group than any discussed above due to their opposable thumbs, which have been essential for human evolution. ~SA