Aiello / Dean An Introduction to Human Evolutionary Anatomy

1. Auflage 1990
ISBN: 978-0-08-057100-3
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 608 Seiten

An anthropologist and an anatomist have combined their skills in this book to provide students and research workers with the essentials of anatomy and the means to apply these to investigations into hominid form and function. Using basic principles and relevant bones, conclusions can be reached regarding the probable musculature, stance, brain size, age, weight, and sex of a particular fossil specimen. The sort of deductions which are possible are illustrated by reference back to contemporary apes and humans, and a coherent picture of the history of hominid evolution appears. Written in a clear and concise style and beautifully illustrated, An Introduction to Human Evolutionary Anatomy is a basic reference for all concerned with human evolution as well as a valuable companion to both laboratory practical sessions and new research using fossil skeletons.

Autoren/Hrsg.

Aiello, Leslie

Dean, Christopher

Weitere Mitwirkende

Cameron, Joanna

Leseproben

CHAPTER ONE AN INTRODUCTION TO CLASSIFICATION, PHYLOGENETIC RECONSTRUCTION AND THE FOSSIL RECORD Anatomy is the science of the structure of animals, and comparative anatomy provides the main basis upon which our knowledge of the course of human evolution is based. In order to interpret the fossils, to determine what hominid fossils were like in life, it is necessary to compare the structure of their fossil bones and teeth to those of humans, apes and other primates. This can help us to determine not only that they were on the human line, but also details about their function, how they moved and what they ate. Only by such analogy with modern humans and non-human primates can we have confidence in our conclusions about the nature of our evolutionary ancestors. Comparative anatomy also has further uses to the palaeoanthropologist. By understanding the ways in which bones and teeth grow and develop in humans and other primates it is becoming possible to determine the speed and the course of their individual growth and development to adulthood, their ontogeny (ontos (Gk) = really; gennan (Gk) = to produce). Comparative anatomy also provides the basis for the reconstruction of the path taken by a particular animal or group of animals during evolutionary history. Such an exercise in evolutionary inference is known as phylogenetic reconstruction, which literally means the reconstruction of the generation or development of a tribe (phylon (Gk) = a tribe; genesis (Gk) = generation). The utility of comparative anatomy does not stop here, however. It also forms the basis of our system of classification, or the naming and categorizing of fossil animals. Because it is impossible to apply the test of breeding compatibility to fossils, fossil species are defined in the first instance on the basis of their anatomy. This exercise is normally guided by the rule that fossils can be included in a single species if they vary no more from each other than do the members of an average modern species. A good working understanding of comparative anatomy is therefore essential for the palaeoanthropologist, and to this end the following chapters are primarily concerned with an introduction to and interpretation of the anatomy of humans, of apes and of the major fossils on the human evolutionary line. These chapters are oriented primarily towards the first two uses of comparative anatomy, towards the interpretation of structure and function and towards the interpretation of the ontogeny, or growth and development of the hominids. However, before embarking on this excursion into comparative anatomy a few more detailed comments about the uses of comparative anatomy in phylogenetic reconstruction and in classification will be helpful to students who are working with, or anticipating working with, fossil material. Classification and phylogenetic reconstruction
Biological classification makes no claim about evolution or evolutionary relationships. It simply involves the ordering of organisms into groups on the basis of their anatomical similarities and differences. The system that is currently in use is known as the Linnean Hierarchy and dates in its (near) present form to 1758 and the 10th edition of Linnaeus’ Systema Naturae. The Linnean Hierarchy is a pyramidal structure where each higher category includes a nest, or set, of one or more lower, or subordinate, categories. At the minimum there are seven levels to this hierarchy but in practice modern applications may include 20 or more separate hierarchical levels (Fig. 1.1). FIGURE 1.1 The Linnean Hierarchy A taxon (taxis (Gk) = arrangement) is a group of organisms at any level of the hierarchy (such as a genus or a species or a family) and taxonomy (taxis (Gk) = arrangement; nomous (Gk) = law) is literally the theoretical study of the laws, procedures and principles of the arrangement of organisms. We will shortly show that there is considerable difference of opinion over the manner in which taxa (= plural of taxon) should be grouped in the hierarchical system. However, there is no possibility for difference of opinion over how various taxa are defined and named. Nomenclature (nomenclatos (L) = listing of names), the application of names to the taxa in the hierarchy, is strictly governed by the International Code of Zoological Nomenclature. This code is based on the concept of name-bearing types, which are particular specimens or taxa that provide an objective standard of reference against which other specimens or taxa must be compared before they are included in the rank of interest. For example, each family or subfamily has a type genus, each genus a type species and each species a type specimen. The code stipulates that a family or subfamily name is formed by adding to the stem of the name of the type genus the latinized suffix ‘–idae’ for a family name and ‘–inae’ for a subfamily name. Moreover, it recommends that the suffix ‘–oidea’ be added to the stem for the name of a superfamily and ‘–ini’ for the name of a tribe. For example, in the classification of the human species, the genus Homo gives its name to the tribe Hominini to the subfamily Homininae to the family Hominidae and to the superfamily Hominoidea (see Figs. 1.6 and 1.7). FIGURE 1.6 A clade-based classification of humans and apes. (a) The classification; (b) the relationship between the classification and the cladogram. FIGURE 1.7 A grade-based classification of humans and apes after Simpson (1963). (a) The classification; (b) the relationship between the classification and the cladogram. The family Pongidae and the subfamily Ponginae are paraphyletic taxa. The code also specifies that all species (and only species) should be referred to by two names, their genus name and their species name. Such a double name is known as a binomen and is the reason why this naming system is known as the system of Binominal Nomenclature. The genus name always begins with an upper-case letter and the species name with a lower-case one as, for example, Homo sapiens, the binomen for modern humans. Frequently with fossil material it may not be possible to assign a particular specimen to a particular species, but it may be possible to assign it to the next highest taxonomic level, the genus. In this case the binomen for that specimen would be, for example, Homo sp. indet. which identifies the particular specimen as a member of the genus Homo but of an indeterminate species. Sometimes the term ‘cf.’ (= confer) may also be included in a binomen as, for example, Homo cf. erectus. This indicates that there is some doubt about the formal referral of the particular specimen to the species erectus. A species name might also be qualified as, for example, Homo habilis s.s. (= sensu stricto) or Homo habilis s.l. (= sensu lato). The use of these terms is not governed by the International Code. However sensu stricto is generally used in the sense of the type of the species, referring specifically to those fossil specimens that are formally included in the type series of the taxon (see below). Likewise, sensu lato refers to the broader (and perhaps more variable) group of specimens that might have been referred to the species subsequent to its formal establishment. Such a group of referred specimens is known as the hypodigm. As a last general word about the International Code of Zoological Nomenclature it is also common to see various fossil specimens referred to as holotypes or para-types. A new species must have a designated specimen or series of specimens as the name-bearing type(s) for that species. These terms refer to particular categories of name-bearing type that are important in the definition of a new species. The holotype is the single specimen designated as the name-bearing type of a species or subspecies when it was established. Each specimen of a type series other than the holotype is known as a paratype. A type series consists of all the specimens eligible to be name-bearing types included in the original description of a new species. The International Code of Zoological Nomenclature lays out specific rules for both the establishment and the naming of taxa, but other areas of classification engender potential controversy and deserve further discussion. These areas are: (1) the definition of and recognition of species; (2) the grouping of taxa into an hierarchical system; and (3) the assignment of taxa to their proper levels in the Linnean Hierarchy. The definition and recognition of species
Species are the lowest level in the Linnean Hierarchy. However, this definition of species is not of much use to the practical palaeontologist or palaeoanthropologist who is trying to define species or to assign particular fossil specimens to one or another species. A number of other definitions of the species are more useful for this purpose. Perhaps the most common definition of species is the biospecies definition of Mayr (1940: 254). Here biospecies are defined as groups of actually or potentially interbreeding...