Primate Evolution

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  • Topic: Primate, Lemur, New World monkey
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Primate Taxonomy

Primate Taxonomy
Introduction This first lecture is designed to introduce the primate order in terms of its classification and to familiarise you with the animals so that the rest of the course makes some sort of sense. I will cover a working definition of what makes a primate, give you a general classification scheme, describe the major features that identify the groups within the classification and discuss some of the controversial areas of the classification. I shall treat the taxonomy as a synonym for classification which seems to be its commonest current usage, although you should be aware that some people consider taxonomy to be more about the principles behind the classification than the classification itself. Definition of a primate Most primatology textbooks include a definition of a primate in their introductory chapters. This discussion comes from Martin [Martin, 1986] and is as good a starting point as any. Mivart's Definition Like many definitions, the definition of what makes a primate (as opposed to a rodent, or a carnivore etc.) is complex. There is little argument as to the core groups of animals today that are primates as I will be illustrating later, but as one goes back in the fossil record, there is more dissension. Still, a purely descriptive definition is needed as a starting point and Mivart [Mivart, 1873] provided this in figure 1. Figure 1. Mivart’s definition of a primate [Mivart, 1873] Mivart’s Primate Definition Unguiculate, claviculate, placental mammals, with orbits encircled by bone; three kinds of teeth, at least at one time of life; brain always with a posterior lobe and calcarine fissure; the innermost digit of at least one pair of extremities opposable; hallux with a flat nail or none; a well developed caecum; penis pendulous; testes scrotal; always two pectoral mammae.

Notes: Unguiculate - possessing nails, hooves or claws Claviculate - possessing a clavicle (collar bone)

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Primate Taxonomy Le Gros Clark's Definition Mivart’s definition is quite a good definition considering its age and certainly has the value of being nice and short. A rather more up to date version was produced by Le Gros Clark [Le Gros Clark, 1959] (see figure 2). Figure 2.Le Gros Clark’s definition of a primate [Le Gros Clark, 1959] Le Gros Clark’s Definition

1. Preservation of generalised limb structure with primitive pentadactyly. 2. Enhancement of free mobility of the digits, especially of the pollux and hallux (both used for grasping). 3. Replacement of sharp, compressed claws by flat nails; development of very sensitive tactile pads on the digits. 4. Progressive shortening of the snout. 5. Elaboration of the visual apparatus, with the development of varying degrees of binocular vision. Orbits ringed with bone. 6. Reduction of the olfactory apparatus. 7. Loss of certain elements of the primitive mammalian dentition. Preservation of a simple molar cusp pattern. 8. Progressive expansion and elaboration of the brain, especially of the cerebral cortex. 9. Progressive and increasingly efficient development of gestational processes. Considering each of these features in turn:

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Primate Taxonomy Preservation of generalised limb structure with primitive pentadactyly Figure 3. Diagram of the forelimb of a variety of tetrapods showing how the primate has retained the primitive pentadactyly limb (3 girdle bones; 1 upper limb bone; 2 lower limb bones; carpals/tarsals; meta-carpals/tarsals; phalanges) whereas various other mammalian orders have lost various bones (taken from Strickberger [Strickberger, 1990]).

As you can see from figure 3 the primates have retained a limb bone structure that is very similar to that of the primitive tetrapod, whereas the other mammals shown have considerably reduced bone numbers. Enhancement of free mobility of the digits, especially of the pollux and hallux (both used for grasping) Figure 3 also shows how the primate hand and...
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