Beneath the surface The Promise and Problems of the Laetoli Site. Review of Laetoli A Pliocene Site in Northern Tanzania edited by M. D. Leakey and J. M. Harris. Oxford Clarendon Press 1987 584 pp. $150код для вставкиСкачать
American Jou r n a l of Primatology 20:57-62 (1990) BOOK REVIEW Beneath the Surface: The Promise and Problems of the Laetoli Site Review of Laetoli: A Pliocene Site in Northern Tanzania, edited by M.D. Leakey and J.M. Harris. Oxford, Clarendon Press, 1987, 584 pp., $150.00. INTRODUCTION Primates, especially hominids, are usually a minor component of the fauna recovered from a n East African Pliocene fossil site. They are equally scarce in this volume, and even thorough digging will yield only a small amount of data on these rare mammals. This book follows the tradition of paleoanthropolgy in that it presents a wide range of data from a single hominid fossil locality. It departs from this tradition in giving only scant attention to the hominid fossils themselves, with less than 11% of the book devoted to primate and hominid fossils and footprints. This review will focus only on the parts of the volume of immediate concern to primatologists and paleoanthropologists, and many important chapters dealing with other faunal groups will not be discussed. The book succeeds a t its stated purpose, which is, according to M.D. Leakey (p. 2) “. . . to place the previously described Laetoli hominids in their correct chronological and paleoenvironmental context.” In this endeavor the authors set a new milestone in the application of the multidisciplinary approach to hominid fossil sites. Laetoli is extraordinarily important, being a unique East African Pliocene record of a habitat without a significant water source. With the publication of this book it becomes one of the best understood Pliocene sites and will further our understanding of the adaptations of hominids and other animals in what must have been a common environmental setting. The unique nature of Laetoli is demonstrated by the fact that more than 25 new species have been defined a t least partly from fossils recovered a t this site, including two primate species, Australopithecus afarensis [Johanson et al., 19781 and Galago sadimanensis (chapter by A.C. Walker). A third primate species, Parapapio ado was reorganized out of preexisting taxa, its distinctiveness apparent only upon analysis of the Laetoli collection (chapter by Leakey and Delson). The status of this volume has been grist for the rumor mills of paleoanthropology for years. Whether it was worth the wait can only be answered on a n individual basis, but for me it was not. The papers were written during the early 1980s, and, not surprisingly, most of the material of relevance to paleoanthropologists has already appeared elsewhere. In the Introduction, Leakey makes it plain that there will be no discussion of the phylogenetic relationships of the Laetoli hominids, because she considers the status of the probably conspecific Hadar specimens to be uncertain. At this time, however, the taxonomic and phylogenetic status of the Hadar remains is about a s well resolved as that of most other collections of early hominids. Most paleoan0 1990 Wiley-Liss, Inc. 58 / Skelton thropologists accept the hypothesis that both the Hadar and Laetoli remains belong to one variable species, A. afarensis [see White, 1985, for a convincing demonstration]. A. afarensis is the oldest and most primitive hominid species yet discovered, and there is near unanimity in considering it to be the stem ancestor from which all later hominids trace their ancestry in some fashion [see Delson, 19871. One is hampered in a search for the significance of most of this material by the lack of any overall conclusions or synthesis of the mass of data presented. Krishtalka [19871 also notes this in his review of this volume. The editors have done little to fulfill their responsibility to extract and present the important information present in this large body of data, thereby making the task of understanding easier for those of us to whom the meanings of bone element counts and such are not self-evident. Even the summary, by J.M. Harris, fails to address any of the broader issues that the data imply. Apparently, the missing conclusions were published elsewhere [Harris, 19851. GEOLOGY AND PALEOENVIRONMENT The chapter titled “Geology of the Laetoli Area” by R.L. Hay and the subchapter titled “K-Ar Geochronology of the Laetoli Fossil Localities” by R. Drake and G.H. Curtis are straightforward presentations of the geology and dating of the beds and localities within the Laetoli area. The materials described in this volume date to between 3.46 and 3.76 MY. The results of the many chapters presenting data about the paleoenvironment at Laetoli cry out for synthesis and reconciliation. Characterizations of the paleoenvironment range from “an open savannah” (R. Bonnefille and G. Riollet, p. 60) to “thicker vegetation cover” (R. Hay, p. 331, to “trees . . . nearby” (A. C. Walker, p. 90). This pattern of seemingly inconsistent results is repeated in the paleoenvironmental analyses of the various vertebrate and invertebrate fossils. A synthetic overview of this material could probably reconcile these diverse results using notions of environmental change through time and across space. GALAGINES The chapter titled “Fossil Galaginae From Laetoli” by A.C. Walker presents exciting new information. Using about four pages, Walker compares the Laetoli galagines to galagines recovered elsewhere, describes the specimens, describes the new species Galago sadimanensis, concludes based on solid interpretations of primitive and derived character states that G. sadimanensis is not ancestral to living galagos, presents a testable functional hypothesis for the difference between G . sadimanensis and living galagines, and points out the paleoenvironmental implications of having recovered galagines from the site. Related material not discussed includes the Fayum lorisid [Simons et al., 19861, which is possibly the oldest identifiable lorisid yet recovered, and other important lorisid fossils from outside Africa [Jacobs, 19811. CERCOPITHECOIDS Laetoli yielded a large, although fragmentary, collection of Pliocene cercopithecoids. In the chapter titled “Fossil Cercopithecidae From the Laetolil Beds,” M.G. Leakey and E. Delson identify four species of cercopithecoid: 1)Parapapio ado, a papionin roughly the size of Papio cynocephalus; 2) Paracolobus sp., a medium sized colobine; 3) Colobinae gen. et sp. indet.; and 4) Papio sp., a species about the size of the large extinct Theropithecus oswaldi. Leakey and Delson use this evidence to place the timing of the African colobine and papionin [sensu Delson Laetoli Site / 59 and Szalay, 19791 radiations prior to the time span represented a t Laetoli. They also remind us that Purupupio is possibly a stem ancestor for the African papionins. HOMINID FOSSILS The chapter concerning the hominid remains, written by M.D. Leakey, consists of fewer than nine pages of text, photographs (apparently identical to those published previously by White [1977,1980, 19811),and data. As one who chauvinistically believes that the hominid fossils were the most important items recovered a t Laetoli, I was disappointed by this brevity. Leakey makes plain her feeling that the lack of material in this chapter is a result of T.D. White’s recalcitrance. Doubtless, White has his own story, and a search for fault here would be unprofitable. For descriptions of the Laetoli hominids, Leakey refers the reader to those of White [1977, 1980, 19811. Since this chapter was written, Peuch et al.  and Peuch  have reconstructed the Garusi Hominid I palate, which was recovered from Laetoli by Kohl-Larsen in 1939. This chapter would have been made more useful by the inclusion of some form of synthesis or critique of White’s descriptions. Those of us who admire Leakey and her unparalleled contribution to paleoanthropology would like to hear what she has to say about the hominid fossils. At this time, however, she chooses to let White’s work speak for her. HOMINID FOOTPRINTS, STATURE, AND WALKING SPEED The chapters titled “Hominid Footprints From Site G ’ by the late L.M. Robbins and “Kinesiological Inferences and Evolutionary Implications From Laetoli Bipedal Trails G-1, G-213, and A” by R.H. Tuttle are mostly complimentary analyses of the footprints and footprint trails. The footprints provide evidence that there were three individuals present. Robbins considers the tallest individual (G-2, 5 feet 9 inches) to be a male, the medium-sized individual (G-3,slightly under 5 feet) to be a female, and the shortest individual (G-1, slightly under 4 feet) to be a child. These attributions of gender and age to these size categories assume that the pattern of sexual dimorphism in early hominids was similar to that of modern humans. We have recently begun to suspect, however, that A. afarensis had a level of sexual dimorphism in body size about like that of Gorilla or Pongo [McHenry, 1986a,b]. Given this, an equally plausible interpretation is that G-1 was a n adult female and that G-2 and G-3 were males, G-3 possibly a subadult. Both Robbins and Tuttle estimate statures for the individuals who made the footprints. Although their methodologies differ in detail, their results are similar. One problem with both analyses is that the authors assume the relationship between foot length and stature in the Laetoli hominids to be similar to that in modern humans. Recently, Jungers [19881 has determined that the foot length of the Lucy (A.L.288-1)A. afurensis specimen from Hadar is longer in proportion to stature than is true of modern humans, making the probable statures of the makers of the Laetoli footprints shorter than the estimates made by Robbins and Tuttle. Using the data from Jungers, the stature estimate for G-1 is 3 feet 6 inches, a result very similar to the estimated statures of other female early hominids such as Lucy, the STS-14 A. ufricunus specimen [Jungers, 19881, and the 0.H.62 Homo hubilis specimen [Johanson, et al., 1987; Lewin, 19871. The recalculated stature for G-2 is 5 feet 4 inches, and the recalculated stature for G-3 is 4 feet 3.5 inches. These statures fall within the range of statures of other Plio-Pleistocene hominids [Feldesman and Lundy, 19881. 60 I Skelton Both Tuttle and Robbins conclude that the makers of the Laetoli footprints had a foot anatomy very similar to that of living humans. Tuttle makes i t clear here and in a previous work [Tuttle, 19851 that he does not believe that the A . afarensis foot bones from Hadar are consistent with the morphology of the Laetoli footprints. Tuttle’s is a minority opinion within the paleoanthropological community [Lewin, 19831. Stern and Susman [19831and Susman et al.  advocate the view that both the Laetoli footprints and the Hadar feet represent a hominid with a foot morphology transitional between that of nonbipeds and modern humans. White and Suwa  argue that A. afarensis a s represented by the Lucy foot is the best candidate for the maker of the Laetoli hominid footprints and hypothesize that both the footprints and the foot are morphologically fairly modern. Tuttle’s view is supported, however, by the recent analysis of a metatarsal of A. (Paranthropus) robustus by Susman and Brain [19881, which suggests that Australopithecus did not have the same type of toe-off mechanism as that of Homo. The walking speeds of the footprint makers have been the subject of much reanalysis. The Tuttle chapter, Charteris e t al. [1981, 19821, and Alexander [19841 have each presented slightly different estimates of walking speed, all of which are between 1 and 2 miles per hour. CERCOPITHECOID AND OTHER NONHUMAN FOOTPRINTS The chapter titled “Animal Prints and Trails” by M.D. Leakey, with contributions from several other scientists, emphasizes the diversity of animals represented at Laetoli by their footprints. Of special interest are the 25 cercopithecoid prints. Although these prints have been described previously [Leakey and Hay, 19791, a few new insights are added here. Leakey characterizes the footprints from site C as being “. . . within the size range of living baboons” (p. 4551, and the analysis of Michael E. Bird, presented in a n appendix, makes it clear that these prints are very similar to those of living Papio cynocephalus. Could these be the footprints of Parapapio ado? This possibility is not explored, but the implication is clear given that P. ado is the only papionin in that size range present in the fossil collection. This is important evidence that Parapapio had a baboon-like form of locomotion, a n inference with significance for our understanding of papionin evolution. There also seems to be a set of colobine footprints present a t site D. Although the taxonomic assignment is not given, Leakey and Hay  observe that one set of tracks was probably made by a cercopithecoid with a foot anatomy and foot/hand placement pattern different from those represented at site C. In her description of these prints, Leakey notes that the “thumb of the hand seems short. . .” (p. 463). Given that short thumbs are characteristic of colobines [AnkelSimons, 19831, a n inference could be made that these prints were made by the larger of the two colobines present, Paracolobus sp. This idea has significance for our understanding of colobine evolution, implying that Paracolobus may have been terrestrial like most early colobines rather than primarily arboreal a s previously suspected [Delson and Szalay, 19791. CONCLUSIONS In conclusion, I cannot recommend this book. Its importance is unquestionable, yet primatologists will find little that they can really use. Without any sort of preprocessing on the part of those who know the material best, other than to put it between two elegant covers, it becomes like a sandwich stacked so high with tasty ingredients that it is impossible to sink your teeth into. I am afraid that, like Laetoli Site / 61 such a sandwich, it will be cut up i n t o smaller parts by those w h o are expected t o c o n s u m e it. M a n y people will simply Xerox the portions of interest to them and avoid buying the book. By including a synthesis of the d a t a , the a u t h o r s could have made the book b o t h i m p o r t a n t and useful. As it stands, it is merely important. Randall R. Skelton Department of Anthropology Emory University Atlanta, Georgia REFERENCES Alexander, R.McN. Stride length and speed for adults, children, and fossil hominids. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 63:23-27, 1984. Ankel-Simons, F. A SURVEY O F LIVING PRIMATES AND THEIR ANATOMY. New York, Macmillan, 1983. 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