Towards a better understanding of hominoid phylogeny

Towards a better understanding of hominoid phylogeny

Book Reviews Journal of Human Evolution (1986) 15, 219-233 TOWARDS A BETTER UNDERSTANDINGOF HOMINOID PHYLOGENY New Interpretations of Ape and Human...

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Book Reviews

Journal of Human Evolution (1986) 15, 219-233

TOWARDS A BETTER UNDERSTANDINGOF HOMINOID PHYLOGENY

New Interpretations of Ape and Human Ancestry (Advances in Primatology) Edited by Russell L. Ciochon and Robert S. Corruccini (1983). New York: Plenum Publishing Co. xxiv + 888 pp. $95.00. ISBN 0-306-41072-9. The origin of the human lineage has long been a compelling issue in palaeoanthropology. This volume aims to answer questions in this area with particular emphasis on comparative anatomical and biomolecular analyses of the living hominoids (apes and humans). In contrast to previous volumes of this kind, the focus of the present work is the origin of the Hominidae rather than relationships within the Hominidae. This broadening of interest is a welcome and beneficial change. The central theme is the Hominoidea of the Miocene with considerations of Oligocene potential hominoid ancestors and of Plio-Pleistocene potential hominoid and hominid descendants. The main themes of this volume include palaeogeography (Bernor), palaeoecology (Pickford; Andrews; and Kortlandt), descriptive analyses of new hominoid material (Dehm; yon Koenigswald; Chopra; Prasad; Fleagle & Kay; Walker & Pickford; and Morbeck); and molecular (Goodman et al.; Mai; Cronin; Sarich; and Kluge) and morphological (Ward & Pilbeam; Falk; Gantt; Fleagle; McHenry & Corruccini; Rose; Kay & Simons; de Bonis; Wolpoff; Zihlman & Lowenstein; Greenfield; Boaz; White et al.; and Ciochon) studies of hominoid relationships. From these contributions I have concentrated on four topics which I consider to be central to the questions raised concerning hominoid evolution. These are: (1) (2) (3) (4)

the influence of methodology on phylogenetic conclusions; the interpretation of ecology and function from fossils; the evolution of hominoid enamel; and the merits of morphological compared with molecular evidence in the study of hominoid phylogeny.

Finally, I have attempted to reconcile as far as possible the palaeontological and biochemical dating of cladogenic events in hominoid evolution based on the evidence presented in this volume.

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The Influence of Phylogenetic Methods on Conclusions The cladistic approach to phylogeny reconstruction was widely embraced by contributors to this volume. Cladistic methods have a great deal to offer in phylogeny reconstruction when accurate determinations of character morphocline polarity are possible. However, in spite of the fact that most contributors to the present volume used cladistic terminology (derived, primitive, etc.), few gave adequate treatment to the problems of polarity determination in general and how these relate to their data in particular. This was a notable problem with the molecular studies whose data do not appear to lend themselves to polarity determination (see below). However, polarity determination was also glossed over by the majority of morphologists. De Bonis, for example, in his discussion of the phyletic relationships of Miocene hominoids and higher primate classification used a cladistic analysis but provided few characters and no polarity analyses to support his views. This problem is common throughout the volume and tends to detract from the value of some of the contributions. It is still commonly assumed by palaeoprimatologists that the oldest fossils belonging to a group represent the primitive condition, e.g. Kay (1982b), which cannot be the case unless the fossil represents the "true" ancestor of the group. But worse than the use of fossils to determine ancestral (or primitive) character states is the use of extant species as "living ancestors". M c H e n r y & Corruccini, in their paper on the wrist of Proconsul africanus and the origin of hominoid postcranial adaptations, make the relevant point that the scala naturae concept has misled people into assuming that hominoids necessarily represent the derived condition relative to cercopithecoids and that hominines display the derived condition relative to other apes. This is not justified as an a priori assumption, and appears to be fallacious for m a n y character complexes in the light of empirical studies. Zihlman & Lowenstein's contribution on Ramapithecus and Pan paniscus, in particular, falls into this trap. They assume that a recent divergence between the human line and the African ape clade means that the common ancestor of the African ape and man clade would necessarily have resembled an African ape (p. 681). These authors proceed to produce a model for the common ancestor of the African ape and human clade based on the Bonobo (pygmy chimpanzee), which they see as a living fossil. Their study does not attempt to reconstruct the hypothetical common ancestor for the clade, against which to test their Bonobo model. They advance no evidence for the common ancestor of the African ape and human clade being equivalent to the Bonobo and appear to think that the African apes virtually ceased to evolve on diverging from the lineage leading to man! In some functional complexes (e.g. jaws and teeth, and postcranial features associated with knuckle walking) there is evidence that the African apes are derived and that humans retain the ancestral pattern, and therefore that the common ancestor of the African ape and human clade was, in fact, more human-like (see e.g. Martin, 1985). There are no good reasons to select a living example from a monophyletic group as representing the morphology of the common ancestor of that group and such studies make no useful contribution to the reconstruction of phylogeny. Despite the fact that the taxonomy of fossil hominoids is currently in a state of flux, it was not comprehensively reviewed by any contributor. Instead, Ward & Pilbeam, in their review of maxillofacial morphology of Miocene hominoids, proposed the use of the terms " r a m a m o r p h " and "dryomorph" as convenient linguistic devices to describe groups of fossil hominoids. For the Miocene apes, these broadly corresponded with the "thick-enamelled" and "thin-enamelled" hominoids respectively, as defined by Simons

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(1976). Ward & Pilbeam characterized these groups according to facial, and especially sub-nasal, morphology; the former having the specialized Asian (orang-utan-like) morphology associated with intermediate thickness enamel and the latter having the primitive (Proconsul-like) morphology associated with thin enamel. Problems arise with the use of these terms for Plio-Pleistocene hominids and for extant taxa. Homo sapiens and fossil hominids possess thick enamel associated with the "dryomorph" facial morphology. Ward & Pilbeam clearly state that these terms are essentially gradistic rather than cladistic taxonomic categories, nevertheless, the consequent rather vague definition of species included in these grades renders their use confusing and somewhat misleading, as both are clearly not monophyletic. In the present volume, the terms seem to include different species even in the usage of single authors, and they are even more variably used by different authors. In addition, some authors have adopted these terms as taxonomic categories, going so far as to use them on cladograms (e.g. Ciochon in his concluding chapter on hominoid cladistics and the ancestry of modern apes and humans). I feel that the convenience of these terms as linguistic devices is outweighed by the misleading impressions given by their usage and would recommend other students to desist from their use. There are a number of other problems in terms of taxon definition. The first essential step in analysing fossil material is to group specimens into palaeospecies hypodigms. Kay & Simons, in their assessment of the relationship between later Miocene and subsequent hominoids, have proposed (this volume; Kay, 1982a,b) the use of coefficient of variation (CV) analyses to group morphologically homogeneous fossils into species on the basis of metrical and geographical criteria. This method has a number of problems when applied to small fossil samples and when the comparative modern samples are not constituted in the same way, in terms of both numbers of specimens and sexual composition, as the fossil sample being analysed (Martin & Andrews, 1984). A number of alternative metrical techniques have been described by Martin & Andrews (1984; Martin, 1981, 1983) which are more versatile for analysis of small samples. Having established satisfactory hypodigms for palaeospecies there is a further problem in grouping these into genera. According to cladistic principles, this should be done on the basis of shared possession of derived characters by sister species. However, some authors in this volume appear to have formed generic hypodigms on the basis of presuppositions: for example, Kay & Simons use material attributed to Dryopithecus by Martin & Andrews (1982), and apparently by Kay (1982b), to show that facial morphology is highly variable in Sivapithecus, without demonstrating that the species from the Middle Miocene locality at Rudabanya in Hungary shares any derived characters with other species of Sivapithecus. Other authors interpret these differences to mean that the Rudabanya material does not in fact belong to Sivapithecus. Authors using cladistic methods to determine relationships among genera must ensure that their groupings of species into genera are also made following cladistic principles. In general, postcranial evidence has been little used in discussions of hominoid phylogeny. Most students of hominoid postcrania have concentrated on functional aspects (see below) and have grouped fossils and living forms on the basis of total morphological similarity. The failure to distinguish between shared derived features and shared primitive features in such studies risks the confusion of functional similarity with taxonomic proximity. The postcranial evidence is potentially the most useful for catarrhine taxonomy

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as the postcranial skeletons of both the cercopithecoids and hominoids appear to be derived with respect to the catarrhine ancestral morphotype (Harrison, 1982; Andrews, 1985). Morbeck provides the first description of the Hungarian (Rudabanya) hominoid postcrania and a review of Miocene hominoid posterania generally. She reports that the upper limb morphology falls into two groups among middle Miocene hominoids. Sivapithecus and Dryopithecus (from Rudabanya) resemble the extant large hominoids, while Kenyapithecus (from Fort Ternan, Kenya) and a specimen from Klein Hadersdorfin Austria are distinct. It is unclear, however, whether Kenyapithecus is distinct by virtue of unique derived characters or due to its retaining primitive features. A careful analysis of postcranial character polarity would be very rewarding in determining the affinities of Miocene hominoids. Retained primitive characters are important in functional interpretations of fossil material and it is for this reason that studies of hominoid postcrania tend to concentrate on overall morphological patterns. But in doing so, there is a tendency to allow notations concerning function to colour interpretations of phylogeny and vice versa. There is therefore a need to separate more completely the analysis of postcranial remains into two areas: phylogeny reconstruction, using derived characters; and functional studies using the total morphological pattern.

The Interpretation of Ecology and Function from Fossils In this volume, functional studies were emphasized more by scientists studying postcranial material than those studying cranio-dental morphology. The value of multidisciplinary studies was evident from the increasing emphasis on palaeoecological and palaeogeographical evidence in interpreting the adaptive niches of fossil species (e.g. Andrews, Bernor, and Pickford). Bernor provides an excellent contribution which addresses the geochronology and zoogeography of Miocene hominoids. This relates hominoids to successive mammal stages, Agenian, Orleanian etc. As an attempt to set hominoid evolution into a temporal and zoogeographical context, Bernor's paper is to be applauded and is strongly recommended reading. Pickford's paper sets the Kenyan Miocene hominoids into a temporal and environmental thmework which provides evidence of an environmental shift associated with the appearance of hominoids with thick enamel which he interprets as being related causally. Andrews reported that Sivapithecus species (and also Dryopithecusfontani, at least from Rudabanya (Martin & Andrews, 1982)) are invariably found associated with a woodland rather than a forest habitat: i.e. in ecological settings which would generally be considered marginal for living primates. This palaeoenvironmental analysis helps to define the limits of adaptations available to fossil hominoid species, but highlights the fact that it may be difficult to find modern analogues for fossil hominoids. The section of this volume on postcranial morphology opens with a chapter by Fleagle which considers the sequence of morphological change from Oligocene through Miocene hominoids. This is an excellent account which makes a real attempt to use postcranial evidence for phylogeny reconstruction as well as for functional analysis. Consequently, Fleagle's conclusions are of considerable interest as he avoids the trap of allowing functional resemblances to colour his analyses of phylogenetic position. Particularly interesting to this writer, were the findings that Proconsul africanus displays a morphology of the distal humerus from which all modern hominoids could be derived in spite of its

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apparent close resemblance to, for example, Pan troglodytes, and that PIiopithecus vindobonensis has a primitive catarrhine type of distal humerus, which accords well with the morphology of its ear region and is in contrast to its superficial resemblance to modern gibbons. In m a n y ways, Fleagle's chapter could be used as a model for combined studies of phylogeny and function in which the two are kept separate rather than one dictating the reconstruction of the other, a problem which occurs in m a n y other workers' studies. In this volume most of the interpretations of function from morphology, particularly, of the postcranial skeleton, rely on finding a matching extant morphology and then extrapolating the same functional role to the fossil species. Walker & Pickford in their description of new Proconsul material argue that one has to assume matching form with function on a one to one basis. This involves the assumption that a given morphology corresponds to a single adaptation. It might be better to start by attempting to assess, using functional parameters, the range of adaptations which a particular morphology would permit. Present day function is a complex interaction of, minimally, morphology, ecology, and behaviour. The study of the "fossil traces" of actual fimction such as dental wear studies (e.g. Kay, 1977) and microwear studies (e.g. Walker et al., 1978; Gordon, 1982) have considerable potential. However, the presumption that the actual adaptation of a fossil species can be determined by matching the pattern in a fossil species with that in an extant species may be fallacious. Palaeoecological studies are particularly important for the assessment of how likely modern morphology to provide good analogues of adaptation.

The Evolution of Hominoid Enamel In his concluding chapter, Ciochon states that "the degree of thickness of enamel caps on the molars of Miocene to Recent hominoids has recently become a single key character for deciphering hominoid evolution. This feature was probably discussed by more contributors than any one single issue" (p. 791). This is certainly true, although not, as Ciochon suggests, because of an expanding data base relating to enamel thickness. On the contrary, it is remarkable how much has been written about enamel thickness in the absence of any significant quantitative data. During the late 1960s and 1970s, the presence of thick enamel became the most compelling evidence for a link between "Ramapithecus" and Australopithecus and Paranthropus. When Gantt (1976, 1977) provided metrical data to support the interpretation that thick enamel was unique to hominids, he lent further support to the hypothesis that the later Miocene hominoid "Ramapithecus" belonged to the human lineage. This fossil evidence Ior the antiquity of the h u m a n lineage is at the heart of the dispute between scientists deriving cladogenic dates from biochemical data and those basing their studies on morphology. Apart from K a y & Simons (this volume; Kay, 1981) no contributor other than Gantt provides any metrical data to support their statements concerning enamel thickness. Nevertheless, a plurality of contributors accepts that the gibbons and the African apes (as well as all lower Miocene hominoids and Dryopithecus) have thin enamel, and that Homo sapiens, "Ramapithecus", Sivapithecus, Gigantopithecus, Australopithecus, and Paranthropus have thick enamel, while Pongo has enamel of intermediate thickness. Some contributors saw possession of thick enamel as overwhelming evidence for a relationship with the h u m a n lineage (Kay & Simons; de Bonis), thus pushing the date of divergence of the h u m a n clade from the African ape clade back to at least the middle Miocene. Mai recognized that the

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whole problem of the "molecular clock" versus palaeontology revolves around "Ramapithecus" and Sivapithecus. If these genera belong to the orang-utan clade (as proposed by Andrews & Cronin, 1982; Ward & Pilbeam, this volume; Lipson & Pilbeam, 1982) then the problem is diminished as palaeontological evidence for the antiquity of the human lineage is reduced. Recently, results have been published for a study of enamel thickness and rates of development in the great apes and man (Martin, 1985). According to this interpretation, the common ancestor of the Hominoidea had thin enamel which was fast formed. The developmental period for the enamel increased between this stage and the common ancestor of the great ape and human clade which had thick enamel all formed at the fast rate. This condition was primitively retained by the common ancestor of the African ape and human clade and in the exclusively hominine clade. Enamel thickness was secondarily reduced, by slowing down ameloblastic secretion, in the orang-utah clade, and to a greater extent, and by a different developmental route, in the African ape clade (Martin, 1985). In consequence, the presence of thick enamel in a fossil hominoid taxon (such as Sivapithecus or "Ramapithecus") indicates affinities with the great ape and human clade rather than with gibbons, but has no value for determining relationship within that clade. Therefore this material cannot be seen as evidence for a distinct hominine clade in the Miocene on the basis of thick enamel alone. Further, additional fossil evidence for early stages of the human line, such as specimens from Ngorora (9-12 my), Lukeino (7 my) and Lothagam (5"5-6 my) in East Africa should probably not be immediately accepted as evidence for the presence of a distinct hominid clade during the later Miocene. It will require the demonstration of other features which can be shown to be derived and which are shared with the hominids alone to argue convincingly for fossil evidence for the human lineage before about 4 my when bipedal hominids are definitely known.

Morphological versus Molecular Evidence in Hominoid Phylogerzy In many ways the argument between workers using molecular evidence and those using palaeontological evidence is an artificial one. Palaeontologists adopted the taxonomic relationships proposed by molecular workers, in particular the view that the African apes are more closely related to man than is the orang-utan relatively rapidly. It is the evidence provided by the "molecular clock" which has been the main subject of dispute. However, it seems that a rapprochement is occurring concerning the dating of branching events as fossil evidence is used to check the dates from the "molecular clock" (Andrews & Cronin, 1982). However, the value of the molecular evidence for phylogeny reconstruction has also been questioned, particularly as concerns lower order taxonomic groups, on the basis of both the problems of polarity determination and of the paucity of significant variation in molecular data among, for example, the great ape and human clade (Andrews, 1986). In the present volume, a number of workers treating material appear to begin with the molecular dates and fit fossils to a scheme based on these (e.g. Greenfield in his attempt to resolve discrepancies between phenetic and palaeontological data bearing on the question of human origins, Boaz in his consideration of relationships between Middle Miocene hominoids and late Pliocene hominids, and Zihlman & Lowenstein). This is not the correct way to proceed, particularly as fossils provide the only data with which to test (as well as to calibrate) the dates provided by the "molecular clock".

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The early molecular data (Goodman, 1963) suggested that Pongo and Hylobates formed one clade, and the African apes and man a second. It was partly resistance to the idea of an Asian hominoid clade which led to suspicion about the validity of the African ape and man group. Once Hylobates had been shown to be a separate hominoid branch, and the great apes and man were recognized as a clade, morphologists accepted the evidence for the African ape and man group. It is often claimed that many morphologists have changed their interpretations in the light of molecular evidence without acknowledging this influence. A comparison of the list of authors in the present volume with those who contributed to Washburn's (1963) classic volume shows that much of the change in the views of morphological workers may also be attributable to the fact that the workers themselves are new people and are consequently presenting new ideas. With the exception of Goodman et al., who considered the bearing of molecular data on the cladogenesis and times of divergence of hominoid lineages, and of Kluge, in his discussion of cladistics, and the classification of great apes, most of the molecular workers contributing to this volume tended to ignore the evidence from palaeontology for dating divergence events, in much the same way that morphologists have done previously with regard to molecular dates.

Hominoid Phylogeny based on Molecular Evidence Goodman et al. (this volume) considered that the current evidence from combined protein analyses supports the interpretation of the Hominoidea as a monophyletic group comprising Hylobates (the gibbons), Pongo (the orang-utah), Pan (the chimpanzee and bonobo), Gorilla and Homo sapiens. They suggested that three interpretations of relationships within that clade could still not be resolved: (1) That Pongo and Hylobates are sister genera. (2) That Pongo represents the first branch, with the gibbons, African apes and man forming a clade, and (3) That Pongo is more closely related to the African apes and man than are the gibbons. Mai proposed a model of chromosome evolution and considered its bearing on hominoid ctadogenesis. He recognized the problem that the molecular approach is essentially a phenetic one, and therefore of limited value for phylogeny reconstruction in the light of Hennig (1966). He suggested that the cytogenetic data can be interpreted to produce five possible sets of relationships within the Hominoidea. In his reappraisal of apes, humans and molecular clocks, Cronin noted that, at the structural gene level, man and the African apes are ahnost identical although substantial morphological and behavioral differences exist among them. He agreed that the molecular evidence supports the interpretation that the Hominoidea are monophyletic, with the gibbons as the most ancient branch. Cronin believed that Pan, Gorilla and Homo shared unique common ancestry although he recognized that after the gibbon divergence any other branches present a problem for immunology. Like most of the molecular workers, Cronin fails to answer the question as to why the shared features among man and the African apes should be seen as derived. While arguing that the electrophoretic evidence increasingly supported a great ape and man ctade, Cronin reported that, in terms of electrophoretic mobility, Pongo is quite derived, while man and the African apes share only one derived feature. Cronin concluded that this demonstrated a close relationship between man and the African apes. However, Schwartz

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(1984) has interpreted this to show merely that the orang-utan is highly derived with respect to the common ancestor of the great ape and human clade whereas man and the African apes are primitive. Andrews (1986) has recently reviewed the molecular data for hominoid phylogeny. He pointed out that, unless character polarity can be accurately determined, the various character states found among living hominoids cannot be used to determine phylogenetic relationships. This is not to deny any possibility of future improvements in the resolution of these methods, but seems a fair statement of the current position.

The Dating of Hominoid Cladogenic Events The "Molecular Clock". Most of the molecular scientists contributing to this volume strongly supported the "molecular clock" concept, and many also defended the accuracy of dates already provided. Only Goodman et al. were prepared to accept that some of the clock dates were incorrect in the light of fossil evidence. The use of fossils to test dates provided by the "molecular clock" has been taken a stage further by Andrews &. Cronin (1982). The majority view in this book would appear to be that the cercopithecoid (Old World) monkeys diverged from the hominoid clade 20 + 2 my ago; that the gibbon clade diverged from the great ape and human clade 12 + 3 my; that the orang-utan clade diverged from the African ape and human clade 10 _+ 3 my; with the hominine/African ape split at 5 --- 1'5 my. The fossil evidence. In the present volume opinions among palaeontologists regarding the dating of hominoid cladogenic events have moved closer to that of the "molecular clock", with the exceptions of Kay & Simons, and de Bonis. Kay & Simons interpreted hominoids from the middle Miocene as belonging to a uniquely hominid clade. In his chapter on phyletic relationships of Miocene hominoids and higher primate classification, de Bonis considered Dryopithecus as the sister genus of Pan, therefore pushing the divergence between chimpanzees and gorillas to greater than 12 my! De Bonis also interpreted Proconsul as the sister group of Pan + Dryopithecus + Hispanopithecus + Gorilla, which would mean that the African ape/hominine split must predate Proconsul, i.e. go back to around 20 my. This view, as well as that of Kay & Simons, would be completely unacceptable to the advocates of the "molecular clock". A

Rapprochement? The disagreement between the molecular evidence and the palaeontological evidence concerning the dating of hominoid cladogenic events has revolved around the position of"Ramapithecus". This position has been determined with considerable emphasis on varying interpretations of the evolution of enamel thickness as part of a powerful jaw complex. The finding that thick enamel is primitive for the great ape and human clade (Martin, 1985) removes a major component of the evidence supporting the interpretation of Sivapithecus (including "Ramapithecus") as an early hominid. This is particularly the case in the light of the shared possession of derived facial morphology between Sivapithecus and the orang utan (Andrews & Tekkaya, 1980; Andrews & Cronin, 1982; Ward & Pilbeam, this volume). This enamel thickness interpretation also weakens the evidence for the hominid lineage in the late Miocene and early Pliocene from the few fragmentary fossils of this age from East Africa.

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There is at present no known fossil material which can be shown definitely to belong to the hominid clade prior to the afarensis specimens from Laetoli, Tanzania dated at about 4 my. Fossil material pertaining to the ancestry of the African apes, or to the common ancestry of the African apes and man is completely unknowr~. There is fossil evidence (disputed-by some, e.g. Kay & Simons, this volume) for a separate orang-utan clade in the late Miocene (Andrews & Tekkaya, 1980; Pilbeam, 1982; Ward & Pilbeam, this volume). The evidence for a separate orang-utah clade during the middle Miocene is less clear, although specimens from Chinji, Pakistan, dated at about 11 my appear to share derived characters with this clade (Raza et al., 1983). Fossil hominoids from Pa~alar, Turkey, may also share derived characters with the orang-utan clade at about 13-14 my (Martin, 1983). Therefore fossil evidence exists to suggest that the divergence between the African ape and human clade and the orang-utah clade occurred prior to 12 my ago. While there is still no convincing fossil evidence for the Hylobates clade, there is clear evidence for the great ape and human clade during the middle Miocene. This includes the presence of thick enamelled species of Sivapithecus at Pa~alar at about 13 my (which may in fact belong to the orang-utan clade) and of Kenyapithecus in Kenya at about 12-15 my. In addition, a new hominoid genus from Saudi Arabia (Andrews & Martin, in press) dated at about t6-17 my can be shown to share derived characters with the great ape and human clade which were not present in the common ancestor of the Hominoidea. This means that the gibbon clade must have diverged from the great ape and human clade prior to 16 my ago. The position of Proconsul from the lower Miocene of East Africa is currently the subject of debate. Harrison (1982) has argued that it cannot be shown to be more closely related to the hominoids than are the Old World monkeys. Other workers, myself included, would interpret Proconsul as being the sister group of the extant hominoids (Andrews, 1985). Still others regard Proconsul as the sister group of the great ape and human clade. In either of the last two cases this would mean that the Hominoidea had diverged from the Cercopithecoidea (Old World monkeys) prior to 18 my ago. The fossil evidence therefore suggests that the minimum divergence dates for hominoid cladogenic events are as follows: (1) (2) (3) (4) (5)

African ape/hominid divergence > 4 my. Gorilla/chimpanzee divergence--no data. Orang-utan/African ape and man divergence >12 my. Gibbon/great ape and man divergence > 16 my. Hominoid/cercopithecoid divergence >18 my.

None of these minimum divergence dates derived from analysis of fossil hominoid material contradicts the dates provided by the "molecular clock". However, they do mean that the ranges of dates provided by the '"molecular clock" can be reduced slightly so as to be compatible with the fossil evidence.

Summary Interpretations of hominoid evolution are changing so rapidly that one volume cannot hope to stand as the definitive work for long. This volume provides important papers on the interpretation of the hominoid fossil record from the points of view of palaeogeography, palaeoecology, functional morphology and phylogeny. It is a worthy successor, twenty years later, to the classic volume on hominoid evolution Classification and Human Evolution (Washburn, 1963). It contains descriptions of important new fossil material, and the

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are to be especially c o n g r a t u l a t e d for a r r a n g i n g for the p u b l i c a t i o n o f some m a t e r i a l which has been u n d e s c r i b e d for m a n y years. However, m a n y of the p r o b l e m s in h o m i n o i d p h y l o g e n y have a c t u a l l y been resolved by better analysis a n d k n o w l e d g e of the extant hominoids, p a r t i c u l a r l y o f their e n a m e l structures, postcrania, a n d b i o c h e m i s t r y r a t h e r than as the result o f the discovery o f new fossils. A consensus is e m e r g i n g concerning the r a p p r o c h e m e n t b e t w e e n the formerly irreconcilable b i o m o l e c u l a r view of h u m a n origins and the p a l a e o n t o l o g i c a l view as the result of a m o r e liberal view of the m o l e c u l a r clock a n d the fact that no k n o w n M i o c e n e h o m i n o i d , including "Ramapithecus", can be considered to be an exclusively h o m i n i d ancestor. New Interpretations of Ape and Human Ancestry is well edited with a useful a u t h o r citation index a n d t a x o n o m i c index. T h e s p e c i m e n index is helpful a l t h o u g h the failure to distinguish clearly, e.g. b y typeface distinctions, between the specimen n u m b e r s a n d page n u m b e r s r e n d e r s this index s o m e w h a t less accessible to the uninitiated. T h e subject index is excellent as are the tables of c h a r a c t e r s used by all contributors which a r e compiled by Ciochon in his c o n c l u d i n g chapter. T h e v o l u m e is well p r i n t e d (with the exception of at least one missing line from the i n t r o d u c t i o n to the final p a r a g r a p h on p. 789) and beautifully p r e s e n t e d . This book will be r e q u i r e d r e a d i n g for all students of p r i m a t e evolution a n d will be of considerable interest to m a n y palaeobiologists, and as such will be essential in all libraries of schools d e a l i n g with p a l a e o b i o l o g y , a n a t o m y , a n t h r o p o l o g y , a n d v e r t e b r a t e zoology. N o serious s t u d e n t of h o m i n o i d evolution will be able to m a n a g e w i t h o u t a p e r s o n a l copy of this book as it certainly represents the state of the science to the end of 1982. LAWRENCE MARTIN Department o f Anthropology, State University of New York, Stony Brook, N Y 11794, U.S.A.

References Andrews, P. (1985). Family group systematics and evolution among catarrhine primates. In (E. Delson, Ed.) Ancestors: The Hard Evidence. New York: Alan R. Liss. Andrews, P. (1986). The molecular evidence for catarrhine evolution. In (B. Wood, L. Martin & P. Andrews, Eds) Major Topics in Primateand Human Evolution. Cambridge: Cambridge University Press. Andrews, P. & Cronin, J. E. (1982). The relationship of Sivapithecusand Ramapithevusand the evolution of the orang-utan. Nature 297, 541-546. Andrews, P. & Martin, L. (in press). The phyletic position of the Ab Dabtiyah hominoid. Bull. Br. Mus. nat. Hist. (Ceol.). Andrews, P. & Tekkaya, I. (1980). A revision of the Turkish Miocene hominoid Sivapithecusmeteai.Palaeontology 23, 85-95. Gantt, D. G. (1976). Enamel thickness: Its significance and possible phylctic implications. Am. J. phys. Anthrop. 44, 179-180. Abstract. Gantt, D. G. (1977). Enamel of primate teeth: Its thickness and structure with reference to functional and phyletic implications. Ph.D. thesis. Washington University. Goodman, M. (1963). Man's place in the phylogeny of the primates as reflected in serum proteins. In (S. L. Washburn, Ed.) Classificationand Human Evolutionpp. 204-234. Chicago: Aldine. Gordon, K. (1982) i A study ofmicrowear on chimpanzee molars: implications for dental microwear analysis. Am. J. phys. Anthrop. 59, 195 215. Harrison, T. (1982). Small-bodied apes from the Miocene of East Africa. Ph.D. thesis, University of London. Hennig, W. (1966). PhylogeneticSystematics. Urbana: University of Illinois. Kay, R. F. (1977). Diets of early Miocene African hominoids. Nature268, 628-630.

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Kay, R. F. (1981). The Nut-Crackers-A new theory of the adaptations of the Ramapithecinae. Am. J. phys. Anthrop. 55, 141-152. Kay, R. F. (1982a). Sexual dimorphism in the Ramapithecinae. Proc. Natl. Bead. Sci. USA 79, 209-212. Kay, R. F. (1982b). Sivapithecus simonsi, a new species of Miocene hominoid, with comments in the phylogenetic status of the Ramapitheeinae. Int. J. Primat. 3, 113-173. Lipson, S. & Pitbeam, D. (1982). Ramapithecus and hominoid evolution. J. hum. Evol. 11,545 548. Martin, L. (1981). New specimens of Proconsul from Koru, Kenya. J. hum. Evol. 10, 139-150. Martin, L. B. (1983). The relationships of the later Miocene Hominoidea. Ph.D. thesis. Univ. of London. Martin, L. (1985). Significance of enamel thickness in hominoid evolution. Nature 314, 26(~263. Martin, L. & Andrews, P. (1982). New ideas on the relationships of the Miocene hominoids. Primate Eye 18, 4-7. Martin, L. & Andrews, P. (t984). The phyletic position ofGraecopithecusjreybergi KOENIGSWALD. Cour. Forsch. Senckenberg 69, 25-40. Pilbeam, D. (I982). New hominoid skull material fi'om the Miocene of Pakistan. Nature 295, 232-234. Raza, S. M., Barry, J. C., Pilbeam, D., Rose, M. D., Shah, S. M. I. & Ward, S. (1983). New hominoid primates from the middle Miocene Chinji Formation, Potwar Plateau, Pakistan. Nature 306, 52-54. Schwartz, J. H. (1984). The evolutionary relationships of man and orang-utan. Nature 308, 501-505. Simons, E. L. (1976). The nature of the transition in the dental mechanism from pongids to [email protected] hum. Evol. 5, 511-528. Walker, A., Hoeck, H. N. & Perez, L. (1978). Microwear of mammalian teeth as an indicator of diet. Science 201, 908-910. Washburn, S. L. (Ed.). (1963). Classification and Human Evolution. Chicago: Aldine.

Functional Morphology of the Miocene Hominoid Foot By J. H. L a n g d o n (1986). Contributions to Primatology, Vol. 22. New York: K a r g e r . x + 226 pp., 69 figs, 22 tabs, 1 a p p e n d i x . Cloth cover. $41.75. I S B N 3-8055-4258-5 I n - d e p t h a n a t o m i c a l a n d m o r p h o m e t r i c studies of p r i m a t e p o s t c r a n i a are often s t i m u l a t e d by the recovery o f fossil parts. T h u s , Paleogene remains have p r o v i d e d the i m p e t u s for generations of students to e x a m i n e " p r o s i m i a n " skeletons (Gregory, 1920; Szalay & Decker, 1974; Dagosto, 1986) a n d m o d e r n a n t h r o p o i d genera are similarly s t u d i e d to i n t e r p r e t O l i g o c e n c and M i o c e n e finds (Fleagle, 1983). L a n g d o n ' s Ph.D. dissertation, p u b l i s h e d in the m o n o g r a p h i c series Contributions to Primatology, is o f this genre. T h e p u r p o s e of his work is to u n r a v e l the functional m o r p h o l o g y of the foot in M i o c e n e h o m i n o i d s . L a n g d o n c o m b i n e s a d e s c r i p t i v e - a n a t o m i c a l a p p r o a c h with m o r p h o m e t r i c s to describe the foot of m o d e r n l a r g e r - b o d i e d a n t h r o p o i d s and the M i o c e n e fossils. F o r the functional i m p l i c a t i o n s of his d a t a he relies on analogies d r a w n from p u b l i s h e d accounts of the positional b e h a v i o r of living animals. T h e r e are five sections to this book. T h e first sets the stage with a review of previous studies on M i o c e n e h o m i n o i d postcrania. Fossil catarrhines and the localities yielding the M i o c e n e m a t e r i a l are also p r e s e n t e d in this section. L a n g d o n ' s discussion is informative b u t I would have found it easier to follow if a classification h a d been p r e s e n t e d or referenced. I s y m p a t h i z e with his r e l u c t a n c e to formally recognize super-generic a s s e m b l a g e s for the Miocene t a x a known p r i m a r i l y by dentitions, since it is an a n a t o m i c a l region he did not h i m s e l f study. Nevertheless, he never defines the term " c e b i d s " which can refer to several g r o u p i n g s of the b e t t e r - k n o w n genera (Hershkovitz, 1977; Rosenberger, 1979; F o r d , 1980) a n d his inclusion of P a r a p i t h e c i d a e with Oligocene h o m i n o i d s (p. 11)