Haplorhines

Tarsiers; New World and Old World biogeography; diversity; anatomy; behaviour; classification.

General Anatomy

Here are some general anatomical features that distinguish haplorhines:

* Short snout

* Unsplit nostrils

* Undifferentiated skin around nose

* Haemo-chorial placentation

* Post orbital closure

* Diurnal

* No tapetum

* Ectotympanic tube (catarrhines)

* Fused metopic suture

* Fused mandibular symphysis

* Central sulcus (no coronolateral sulcus)

* Internal carotid artery

Major Groups

Tarsiiformes

Tarsiidae

The tarsiers are small, nocturnal, insectivorous primates living in the jungles of Indonesia. They weigh approximately 100g and their most noticeable feature is the huge size of their eyes. They have a dental formula of 2.1.3.3/1.1.3.3, and although they used to be classified in the sub-order Prosimii are clearly haplorhine with a typical dry nose as well as the other haplorhine features. A unique feature of these animals is that the tibia and fibula are fused down the lower third of their length. In addition, they have elongated tarsal bones, and these seem to be adaptations for leaping. They lack the tooth comb commonly seen in strepsirhines. They can also rotate their heads through 180deg..

Platyrrhini

The platyrrhines are also known as New World Monkeys because their present day distribution is restricted to South and Central America. This distribution is interesting because in the Oligocene (35mya) when NWM's first appear in the fossil record, South America as an island continent (continental drift). In the same way as Madagascar, it is assumed that the continent was colonised by primates rafting or island hoping either from North America or across from Africa. NWM's have then evolved their own unique sets of features (adaptive radiation) in a similar fashion.

Platyrrhines do not have an ectotympanic tube, like the catarrhines, but retain the ancestral ectotympanic ring. The general dental formula is 2.1.3.3/2.1.3.3 like the strepsirhines too. The zygomatic bone extends backwards to articulate with the parietal bone. Their nostrils are widely separated and open to the sides.

The main families are as follows:

Callitrichidae

Marmosets or Tamarins. Small primates (100 to 1000g), eating mostly insects and gum with some fruit as expected from this size range. Tail not prehensile, thumb not opposable, all digits except hallux (great toe) have pointed nails (almost claws) rather than the normal, primate-like flat nails. Males have a bacculum and females have one pair of mammae. Dental formula is 2.1.3.2/2.1.3.2 except for Callimico which has 3 molars. They have a wide range of brightly coloured pelages, and are very agile at leaping and quadrupedal running and climbing.

They have an unusual social system, with one female mating with several males, with the other females in the group reproductively suppressed. The litter size is usually 2 and the males help in infant care. Another interesting feature is that these animals often form stable, mixed species groups. This may be due to the physiological group size due to reproductive suppression being less than the ecologically optimal group size.

Cebidae

These are much larger monkeys than the callitrichids, ranging from about 1 to 10kg. Thus, they are mainly frugivors, with some of the larger animals eating leaves. They include the only nocturnal haplorhine (Aotus, the owl monkey), and spider, woolly and howler monkeys (sometimes put in their own family, the Atelidae) have fully prehensile tails complete with dermatoglyphs to aid grip on the ventral side of the distal end. The squirrel and capuchin monkeys can be described as having semi-prehensile tails: they wrap their tails round branches for support, but they do not have the complete independence of movement found in the fully prehensile tails. The howler monkey (Alouatta) has a greatly enlarged hyoid bone which enables the animal to produce an extremely loud call.

They have a dental formula of 2.1.3.3/2.1.3.3. The males usually have a bacculum (except Aotus, Ateles and Lagothrix) and the thumb is not opposable.

Catarrhini

This group include the old world monkeys (Cercopithecoidea) and apes (Hominoidea). Catarrhines have an ectotympanic tube and a general dental formula of 2.1.2.3/2.1.2.3. The zygomatic bone does not articulate with the parietal bone. Their nostrils are set close together and open to the front. No catarrhines have prehensile tails, and unlike the platyrrhines, some are terrestrial. The hominoids will be the subject of a later lecture, so I will only talk about the cercopithecoids today. There is only one family:

Cercopithecidae

Their geographical range is Africa, south-central and south-east Asia, Japan and the East Indies as far as Sulawesi and Timor. They are large monkeys, with sizes from 3 to 50kg. They tend to have naked faces, hands and feet. They have so called bilophodont molars (2 crests connecting transverse pairs of cusps). There are two distinct sub-families:

Cercopithecinae

These are the cheek pouched monkeys including macaques, baboons and guenons. Some of these (especially baboons) are largely or completely terrestrial. They have closely set eyes, shallow jaws, and rounded, low cusps on their molar teeth. Their cheek pouches are used for storing food and they have arms and legs of similar lengths to aid quadrupedalism.

Colobinae

These are the leaf eating specialists including colobus and langurs. They are all arboreal. They have specialised guts containing a micro flora to aid in leaf digestion and a multi-chambered stomach convergently similar to ruminants. They have more widely set eyes, deeper jaws (stronger chewing), sharp, pointed cusps on their teeth, very long tails and hind-limbs to aid leaping. Their thumbs are short or absent.

Teeth

Mammalian teeth are extremely important taxonomically. They are the most common fossils found and the exact pattern of cusps is thought to be more to do with ancestry than function. They have their own nomenclature (Conroy 379) based on the supposed primitive eutherian dentition.

* buccal/lingual

* mesial/distal

* trigone: paracone, metacone, protocone

* talon: hypocone

* trigonid: paraconid, metaconid, protoconid

* talonid: hypoconid, hypoconulid, entoconulid

There is an overall pattern in tooth shapes and numbers among the primates (Conroy 380, CEHE 57).

Bibliography

Library

 AUTHOR(S)       :Clark, Sir Wilfrid Edward Le Gros 1895-1971
 TITLE           :The antecedents of man : an introduction to the evolution of
                  the primates
 EDITION         :3rd ed.
 IMPRINT         :Edinburgh : University Press, 1971
 SERIES          :Edinburgh University publications. Science and mathematics
                  texts ; 2

 AUTHOR(S)       :Nowak, Ronald M.
 TITLE           :Walker's Mammals of the world
 EDITION         :5th ed. / Ronald M. Nowak
 IMPRINT         :Baltimore London : Johns Hopkins University Press, 1991

 AUTHOR(S)       :JONES, Steve  et al.,
 TITLE           :The Cambridge encyclopedia of human evolution / edited by
                  Steve Jones, Robert Martin and David Pilbeam / executive
                  editor Sarah Bunney
 IMPRINT         :Cambridge : Cambridge University Press, 1994.
      

Other

Conroy, G. C., 1990. Primate Evolution, Norton, London.

Napier J. R., Napier P. H., 1985. The natural history of the primates, British Museum (Natural History), London.