Primate Taxonomy
Dr. Bill Sellers
Introduction
In the last lecture I introduced the general ideas of evolution and taxonomy. Now it's time to look at how this relates to the evolution of humans. (# slide of geological time scale) To some extent, factors shaping human evolution started back at the creation of the universe. Certainly, the origin of the earth is important, as is the first life appearing on it. From there, we have the origin of complex single celled organisms (protozoa), then multi-celled organisms (metazoa), animals with backbones (vertebrates), first land vertebrates, and even mammals. Traditionally, however, we limit the study of human evolution to the study of just our own mammalian order: that of the primates (order primata).The aim of this lecture is to discuss what a primate is, and to introduce you to the range of primates present in the world today. I will show you some pictures, but I don't expect you to remember all the names, and you certainly won't be asked to identify any of these animals in an exam, but an appreciation of the wide variation in these animals is essential for when we come on to discuss how they, and consequently how we might have evolved.
As I talk about the primates, I will attempt to map out a likely family tree, concentrating more on the animals that are most similar to ourselves. This relationship should become clearer as the course progresses.
Definition of a primate
Like many definition, 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: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. (Mivart 1873)
Unguiculate - possessing nails, hooves or claws
Claviculate - possessing a clavicle (collar bone)
This has been brought up to date with little change by Le Gros Clark 1959:
1. Preservation of generalised limb structure with primitive pentadactyly.
Describe primitive pentadactyly limb (3 girdle bones; 1 upper limb bone; 2 lower limb bones; carpals/tarsals; metas; phalanges), and how various other mammalian orders have lost various bones (especially fusing the lower limb bones).2. Enhancement of free mobility of the digits, especially of the pollux and hallux (both used for grasping).
Demonstration - and maybe get them to take off their shoes to try their feet.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.
6. Reduction of the olfactory apparatus.
These 3 are all linked and progress from prosimian through
monkeys to humans.
7. Loss of certain elements of the primitive mammalian dentition. Preservation of a simple molar cusp pattern.
Tooth formula reduction: primitive mammal 3.1.4.3/3.1.4.3; prosimians and NWMs 2.1.3.3/2.1.3.3; OWMs & apes 2.1.2.3/2.1.2.3. Note, that it is the anterior 2 premolars that we have lost.8. Progressive expansion and elaboration of the
brain, especially of the cerebral cortex.
9. Progressive and increasingly efficient
development of gestational processes.
And this has been further expanded by Napier and Napier 1967:
10. Prolongation of postnatal life periods.
11. Progressive development of truncal uprightness
leading to a facultative bipedalism.
Problems
At first view, this seems OK (apart from the dreadful language which makes the whole thing read like a life insurance document). But there are problems with this definition:Firstly, there is no unique characteristic that defines a primates. It is a list of shared characteristics and trends - most of which aren't even derived, but are retentions of ancestral features, which is definitely not good.
Secondly, many of these features are behavioural, or depend on soft tissue anatomy. They won't help us identify a fossil primate.
Fortunately, there are a number of very specific features that we can use, such as details of the bones of the foot and skull, but even so, it can be difficult, especially when dealing with very early mammals, to decide whether they are primates or not. There are even certain modern groups, such as the tree shrews (# slide of tree shrew) that some authors consider to be primates - though in general, most people classify them separately. In fact bats are sometimes now considered to be the closest relative of primates!
As I mentioned before, there are an awful lot of different ideas about the details of primate classification. I shall largely use this simplified version (# P.14 NHOTP as OHP and annotate the corrections), but if you want to see others, then you should look at appendix D at the back of Conroy's "Primate Evolution". And if you do, don't worry about it too much!
Do humans fit (# P43 PM)? Discuss...
One of the things you will have to get used to throughout this course is multiple names for very similar things. This generally results from a combination of history, and peoples desire to name things. Primate taxonomy is one such area:
Prosimians and Simians
First primate like animals appeared in the Palaeocene (70 mya), perhaps even late Cretaceous. These are described as early prosimians.But what are prosimians? (# P15 NHOTP) Give brief potted history of all I can remember about these animals...
Remember that Madagascar was probably colonized by a chance rafting of an early prosimian in the Eocene (50 mya), which then adapted to fill the available niches in a similar fashion to the Galapagos finches. (In fact, it seems likely that Madagascar was colonised by a small number of events - probably 2).
Features
Tooth comb from incisorsLocomotor specializations: vertical clinging and leaping, slow quadrupedalism
Wet noses
Dog-like faces
Nocturnal (well, often)
Orbital bar
Ectotympanic ring
Epitheliochorial placenta
Tapetum
Tarsiiformes
As you saw from the diagram, there is a big split between the prosimians on the one hand and the anthropoids on the other, with tarsiers somewhere in the middle. The position of the tarsiers is still a major question in primatology. However, it has been largely resolved by a change of nomenclature. Prosimians becoming strepsirhini and anthropoids becominghaplorhini. By this definition, tarsiers become haplorhines, and the problem neatly goes away. Taxonomists don't like trichotomous branches. (Oddly enough, lots of these branches have the word "rhine" in them. This is from the Greek rhis, rhinos meaning nose, and generally refers to specific nasal anatomy that can be used to distinguish these groups. Strepsirhines have dog-like, wet noses, whereas the rest of the primates have dry noses.)First haplorhines (single noses), appeared in the Eocene. This group may be ancestral to the rest of the anthropoids.
And these infamous tarsiers? (#P17 NHOTP) Give brief potted history of all I can remember about these animals...
Features
VCLEctotympanic tube
Orbital closure
Extremely large eyes
Haemochorial placenta
New World Monkeys
Here our geography and our classification meet. The infraorders of platyrrhines (flat noses) and catarrhine (down facing noses) coincides neatly with the animals found in South America (the "New World") and with those found in Africa and Asia (the "Old World"), so the terms are almost synonymous. New World Monkeys are all platyrrhines, but catarrhines include apes as well as OWMs.South America was isolated from the rest of the world in the Eocene and Oligocene. It seems to have been colonised by early anthropoids, either from Africa or North America via some sort of land bridge, of floating vegetation raft about 40 mya (end of Miocene). Thenceforth, these monkeys have developed independently in quite a distinct pattern. New World monkeys are every bit as advanced as Old World monkeys with some very impressive adaptations that the OWMs lack such as prehensile tails. Interestingly, there are no prosimians in the New World. Their nocturnal insectivorous niche is taken up by other mammals such as opossums (South American marsupials), though there is also one nocturnal NWM, Aotus, the owl monkey (# P115 NHOTP).
And draw up the NWM bit of the tree.
There are no extant primates in North America even though it is where some of the oldest primate fossils have been found. There isn't a good explanation for this.
Features
Poorly developed thumb & finger gripLarger, more convoluted brain
Diurnal
Well developed tail - prehensile in some groups
Outward facing nostrils
Catarrhines
This group includes the rest of the monkeys and apes including humans. Very widespread. 2 major groups: hominoidea (apes) and cercopithecoidea (monkeys).Features
Better thumb & finger gripShorter (or no) tail
2 premolars
down facing nostrils
Cercopithecoidea
Cercopithecines
Mixed diets. Macaques (note Barbary macaque), Baboons, Guenons.Colobines
Leaf eaters. Colobus (Africa) and Langurs (Asia).Hominoids
Late Oligocene (25 mya). Two extant families: hominidae and hylobatidae. (Some authors have 3 families, with only humans as hominids, and a separate family, pongidae, for great apes).Gibbons (hylobatids) are unique in habitually travelling by brachiation - swinging through the trees suspended by their arms. They are found in South East Asia
Features
Larger brainsNo tails
Arms and shoulder girdle for suspension
Y-5 shaped pattern on molar teeth
Hominids
Or great apes (& humans). Orang-Utans of Borneo and Sumatra; Gorillas of central Africa; Chimpanzees - central Africa but more widespread; and Humans - almost everywhere. Early hominids/pongids appeared in the Miocene (20 mya).Features
Still larger brainsLarger
Mostly terrestrial
Hominins
The real human group. Dates back to around 5 mya. Lots more about this later.Geographical Distribution
These animals are grouped not only on their appearance but also on their geographical distribution (#P9 NHOTP). It's important to remember just how important geography is to classification.This page is maintained by Steve Paxton