Book Review

Function, Phylogeny, and Fossils: Miocene Hominoid Evolution and Adaptations

Edited by David R. Begun, Carol V. Ward, and Michael D. Rose, Plenum Press, New York and London, 1997, xii + 424 pp.

Homo and four other genera are all that remain of the superfamily Hominoidea that once flourished in great diversity. During the Miocene (23 to 5 m.y.) we know of at least 30 genera and these took all kinds of different forms. Unlike today's impoverished sample, apes of the past adapted to a wide variety of niches. There were frugivores, folivores, and some with large rooted canines and procumbent incisors for seed predation similar to that in the bearded saki of South America. There were tiny ones like Micropithecus who tipped the sales at 3.5 g and one Pleistocene form, Gigantopithecus, that may have weighed 300 kg.

One might expect from such diversity that the 22 specialists who wrote the 18 chapters of this volume would have widely different opinions about the adaptations and phylogenetic relationships of the Miocene hominoids. That was certainly true two decades ago when some lumped almost all of the large-bodied Miocene apes into two genera, Dryopithecus and Ramapithecus, and others split the superfamily into many genera. But there is remarkable consensus in this book. Of course, there are important differences of opinion, but the editors were able to draw together some very important points of agreement in the last chapter.

The editors describe the purpose and scope of the volume in the first chapter noting the importance of integrating functional studies with phylogenetic analyses. The results of such integration show the nature and extent of parallel and convergent evolution resulting in the occurrence of homoplasy. D. Pilbeam reviews the history of Miocene hominoid studies in the next chapter. Few are better suited for this task since he has been a key player for three decades and it was his expedition that found the Sivapithecus face that led to the reevaluation of the hominid status of Ramapithecus. He entered the field before the precise weapons of cladism were widely applied in primatology and had to rearm in midcareer like many of us of an earlier generation. His reflections on these and other changes are invaluable lessons.

The senior author of the next chapter, P. Andrews, is another survivor from the pre-cladistic era who became an early convert and effective advocate of Hennig's systematics. Here the reader is treated to an analysis of the relationships between the paleoenvironments of the Miocene hominoids and their functional anatomy. The unusual forelimb and trunk morphology of all modern members of Hominoidea that makes possible forelimb suspensory behavior is not directly related to closed tropical forests but appears in seasonal subtropical forests as well.

R. Kay and P. Ungar analyze the molar shearing crests found in 14 species of Miocene hominoids and their relationship to diet. Among other things they note a remarkable shift towards increased molar shearing that occurred through time in several different clades independently. B. Brown takes on the difficult task of examining the functional and phylogenetic inferences that can be gleaned from the abundant mandibular sample. J. Kelley focuses on life-history variables inferred from dental development in Sivapithecus and other hominoids and explores the evolutionary emergence of the protracted life histories characteristic of Hominoidea.

There are three chapters that apply phylogenetic analyses to specific regions of the body. T. Rae uses 12 facial characters to develop a cladogram placing Micropithecus as sister to all other Hominoidea, Hylobates as sister to Proconsul nyanzae and other early Miocene genera, and Afropithecus, Kalepithecus and Simiolus as a branch before the divergence of the living great apes. The study excludes the best preserved Early Miocene face, Proconsul heseloni and other specimens "because none of these taxa possess derived features of the face that would unequivocally place them with any catarrhine clades without severely diminishing the revolution of the consensus tree" (p. 69). M. Rose presents a beautiful exposition of the forelimb functional anatomy that makes it clear how unusual the modern species of Hominoidea are. Genera often placed in this superfamily (e.g. Pliopithecus, Dendropithecus, Simiolus) are closer to platyrrhines, Aegyptopithecus and Cercopithecoidea than to Proconsul and other later hominoids. C. Ward presents a more formal cladistic analysis of the hindlimb and finds somewhat similar results although her analysis does not include Cercopithecoidea and Ceboidea. Both of these postcranial studies reveal the close relationship of Oreopithecus to extant large-bodied apes.

The placement of Oreopithecus had been hotly debated for decades, but in this book there is remarkable agreement among the different authors. T. Harrison and L. Rook address this issue most thoroughly and find overwhelming evidence in its postcrania of a close relationship to the living great apes and Dryopithecus. They note that the East African genus, Nyanzapithecus was probably not its ancestor but rather a form that evolved dental resemblances to Oreopithecus independently. New material from Maboko Island of Nyanzathecus reported by B. Benefit and M. McCrossin at the 1997 meeting of the American Association of Physical Anthropologists, however, lead them to emphasize that there is a close relationship between it and Oreopithecus.

New discoveries at Maboko Island also affect the status of Kenyapithecus. Two decades ago this East African Middle Miocene hominoid was championed as a direct ancestor of the human lineage by some, but the vastly expanded sample excavated by the Benefit-McCrossin expedition lead them to conclude in Chapter 12 that ". . . the middle Miocene radiation of large-bodied apes . . . can be considered as broadly ancestral to, but not true members of, the clade to which extant hominoids and fossil hominids belong" (p. 259). Kenyapithecus has dental specializations for sclerocarp foraging similar to Chiropotes and Cacajao and a semiterrestrial digitigrade mode of locomotion lacking the key feature of all modern member of Hominoidea. However, M. McCrossin reported at the 1997 AAPA meeting the discovery of a straight-shafted humerus and other postcrania that have lead him to the view that Kenyapithecus is part of the African clade.

The better known genera of Miocene hominoids are each treated to detailed descriptions and analyses in separate chapters. A. Walker presents a definitive piece on Proconsul including its taxonomy, body and brain size, locomotion, sexual dimorphism and social system, and phylogeny. M. Leakey and he do the same for Afropithecus and note, among other things, that this genus had Proconsul-like postcrania lacking most of the modern hominoid specializations and an anterior dentition adapted to sclerocarp feeding similar to Kenyapithecus. S. Ward reviews what is known about Sivapithecus and concludes that this Asian Middle Miocene form shares a close relationship to Pongo despite the fact that it had quadrupedally adapted limbs. D. Begun and L. Kordos do a formal cladistic analysis of the craniodental and postcranial remains of Dryopithecus compared to Griphopithecus + Kenyapithecus, Sivapithecus, Ouranopithecus, Australopithecus, and Proconsul, and modern great apes. The results put Dryopithecus and Ouranopithecus on the African clade. L. De Bonis and G. Koufos present evidence that Ouranopithecus is on the hominine clade with Australopithecus and Homo. J. Schwartz incorporates an ontogenetic perspective to effectively analyze 11 key characters of Lufengpithecus and finds that it should be included on the Asian clade with Sivapithecus and Pongo.

The last chapter is a wonderful synthesis of our current understanding of the Miocene Hominoidea written by the three editors of this volume. Here is a 240-characters analysis of the eight best-known genera. The most parsimonious cladogram contains the branching sequence Proconsul - Afropithecus - Kenyapithecus - Hylobates - Oreopithecus - Lufengpithecus - (Sivapithecus - Pongo) + Ouranopithecus - Dryopithecus - Gorilla - (Australopithecus + Pan). Other cladograms are tested but are less parsimonious. The implications of this phylogenetic hypothesis are many. One is that homoplasy is common and is lowest in the postcrania.

This is a superbly written and skillfully edited volume that addresses some of the most interesting issues in the evolutionary biology of our superfamily. Beyond that it is a useful guide to the current methods of phylogenetic analysis and to the broader issues in evolutionary biology, particularly the patterns of parallel and convergent evolution.

Henry M. McHenry
Department of Anthropology
University of California, Davis
Davis, CA 95616