Monkeys


In addition to the tarsiers, there are at least 145 living species of the suborder Haplorrhini (the anthropoids).  Over 90% of them are monkeys. The remaining species are apes and humans.  The anthropoids have been the most successful primates in populating the earth.  They are generally larger, more intelligent, and have more highly developed eyes than the prosimians.

There are two distinct Parvorders of anthropoids that have been evolving independent of each other for at least 30,000,000 years.  They are the Platyrrhini click this icon to hear the preceding term pronounced (New World monkeys) and the Catarrhini click this icon to hear the preceding term pronounced (Old World monkeys, apes, and humans).  These two diverse groups of species can be distinguished from each other most easily based on the form of their noses and by the number of specific types of teeth.

The platyrrhine click this icon to hear the preceding term pronounced nose (on the left below) is relatively flat with somewhat sideways projecting nostrils separated by a wide septum.  In contrast, the catarrhine click this icon to hear the preceding term pronounced nose (on the right below) has more downward projecting nostrils separated by a small septum.  If you look at your face in a mirror, you will see the typical catarrhine nose with its narrow septum.

photo of a platyrrhine nose (emperor tamarin)

 

photo of a catarrhine nose (Celebes black macaque)

Nose comparison of a New World monkey--the emperor tamarin (left)
and an Old World monkey--the Celebes black macaque (right) 

All primates have essentially the same kinds of specialized mammalian teeth adapted to eating a wide variety of foods.  Beginning at the front, each quadrant of the mouth has 2 incisors, 1 canine, and varying numbers of premolars and molars.  The incisors are used like scissors for nipping off pieces of food.  The pointed canines are for piercing and tearing.  The premolars (or bicuspids) and molars, with their multiple cusps, are used to grind and smash food.  In platyrrhine species, there are 3 premolars and 2 or 3 molars.  This results in a dental formula of 2.1.3.2 or 2.1.3.3.  In contrast, all of the catarrhines have 2 premolars and 3 molars, making a dental formula of 2.1.2.3.  The chimpanzee shown below is an Old World anthropoid species and, therefore, has a catarrhine dental formula.

photo of a common chimpanzee with its mouth open showing the catarrhine 2.1.2.3 dental formula
Catarrhine 2.1.2.3 dental formula 
(common chimpanzee)
 
photo of patas monkeys in an African grassland environment

   Patas monkeys in an African
   grassland environment        

photo of a female hamadryas baboon in estrus (note the sexual skin)

   Female hamadryas baboon in
   estrus (note the sexual skin)

All Old World monkeys, apes, and humans share this 2.1.2.3 dental formula.  This not only sets us apart from New World monkeys and prosimians, but it also reflects the evolutionary closeness of the Old World anthropoid species.  By comparison, the general placental mammal dental formula is 3.1.4.3.

In addition to these differences, New World monkeys are almost exclusively arboreal and most of them are smaller than Old World monkey species.  Some Old World monkeys and apes are semi-terrestrial.  If you see a group of monkeys casually walking around in a grassland environment (like those shown on the right), you can be sure that they are from the Old World.

Many of the larger New World monkeys have prehensile, or grasping, tails that are capable of being used as strong "third hands" for holding onto branches.  They can even hang from their tails.  None of the Old World monkeys or apes has this capability.

Many species of Old World monkeys have ischial callosities click this icon to hear the preceding term pronounced, or hairless callous pads, on their rumps which may be adaptations for long periods of sitting or sleeping on rough branches and rocks.  This trait is shared by the small apes of Southeast Asia (gibbons and siamangs).  However, New World monkeys do not have it.

In some species of Old World monkeys and apes, adult females have sexual skins or swellings, which are nearly hairless large swollen patches of skin around the genital area that become very prominent when they are in estrus click this icon to hear the preceding term pronounced.  These areas swell with fluids and turn bright pink or red due to hormonal changes that occur in preparation for ovulation.  The sexual skin also produces odors that excite males of the species. They become highly attentive to the females at this time.  In the case of olive baboons, males are most attracted to females with the largest sexual skin bulge.  Those females tend to have babies more often and subsequently pass on the genes for this impressive signal of sexual readiness.

 

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Copyright 1998-2013 by Dennis O'Neil. All rights reserved.
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