Evolutionary History

There exist 17 genera and over 70 species of Platyrrhines(new world monkeys of South and Central America) nowadays. Up to a few years ago, there was a big box covering all monkeys from the Caribbean and South America, but in this time, more information has been found in regards of the evolutionary history of these monkeys.

According to the fossil record there are four main groups (on the basis of age and geography) that conform the Platyrrhines: the earliest from the Oligocene locality in Bolivia; some genera from the early and middle Miocene of Southern Argentina and Chile; a group of modern genera from the late Miocene from Colombia; and a group of species from the Pleistocene in the Caribbean and Brazil.

Ancestors of the spider monkey fall into the last mentioned group. Some fossil primates were found in Cuba,  such as the “Montanea anthropomorphus”, which appears to be an ancestor of the spider monkey brought to the island by native people.

Shared Derived Traits

One characteristic that defines the New World Monkeys from the Old World Monkeys (from Africa) is the presence of a prehensile tail. A prehensile tail is characterized by having a patch of skin at the tip of the tail enabling the animal to use it like a fifth hand (allows them to grip and pick up objects).

Also, the presence of a central eye area is characteristic of this group. It can be seen in the phylogenetic tree as a characteristic that differentiates the spider monkeys from the lemurs.

Shared Ancestral Traits

• A shortened snout and forward facing eye orbits reflect the primates increased reliance on vision rather than smell
• The diversity of teeth types allows primates to have a varied diet.
• The presence of clavicles (collarbones) allows primates to have a bony link between the trunk of the body and the arms
• Having two separate bones in the limbs allow for more precise movements
• The diversity of teeth types allows primates to have a varied diet
• Primates tend to have longer periods of infancy and childhood, which allow more time for learning and brain growth
• Increased thumb mobility allows primates to manipulate objects (spider monkeys have lost some of this mobility due to habitat requirements)

Figure 1. Phylogenetic tree of the Vertebrates  

Figure 3. Phylogenetic Tree of select Primates showing synapomorphies.

Sources

http://tolweb.org/treehouses/?treehouse_id=3029

Kinzey, W.G. (1997). New World Primates, Ecology, Evolution and Behavior. New York: Aldine de Gruyter.

http://www.honoluluzoo.org/spider_monkey.htm