Olduvai Bed I post-cranial fossils: A reassessment

Olduvai Bed I post-cranial fossils: A reassessment

Oldwai Red I Post-cranial Fossils : A Reassessment B. A. Wood Department of Anatomy, Charing Cross Hospital Medical School, (University of London), F...

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Oldwai Red I Post-cranial Fossils : A Reassessment

B. A. Wood Department of Anatomy, Charing Cross Hospital Medical School, (University of London), F&am Palace Road, London, W6 8RF Received 27 February 1974 and accepted 27 March 1974

New fossI specimens can be interpreted as strong indications that there were two Plio-Pleistocene hominid post-cranial morphotypes. This new evidence may alter the functional interpretations placed on the important specimens, OH 8 and OH 10 from Olduvai Gorge, Tanzania. When these interpretations are critically examined there is now doubt that the OH 8 foot belongs to Homo and that the OH 10 terminal plalanx is necessarily part of a functional limb complex like that of modern Man.

Various claims and suggestions have been made in the past about hominid locomotor patterns on the basis of post-cranial fossils from Bed I at Olduvai Gorge. Using anatomical features to draw analogies with modern gait patterns is acceptable if the fossils are part of a morphological continuum and if this continuum can be traced to the extant groups with which the fossils are being compared. This type of process is distinct from the recognition of homologous features, for these though homologous in structure are not necessarily so in function. There is now, however, fossil evidence, controversial though it is, for a second hominid Post-cranial fossils from Swartkrans (Napier, 1964), and post-cranial morphotype. Olduvai (Day, 1969), were considered to be morphological distinct from modern hominids. There was until recently no indication that they represented more than a stage in the development of the modern human pattern. More recent evidence from East Rudolf (R. E. F. Leakey, 1973), suggests that this pattern was not sequential but was sympatric with material that is much closer to the modern human morphology. It is therefore apparent that assumptions which were justified before this evidence was available may not necessarily be valid now. The present relative abundance of post-cranial fossils has reduced the pressure to make locomotor predictions from material that is often less than ideal for the purpose. Those who are concerned with early hominid evolution are naturally anxious to reconstruct all aspects of behaviour. As locomotor capabilities are widely considered to have played a key role in the biological success of hominids, functional interpretation of postcranial material has been keenly pursued. However such interpretations, whether correct or not, can introduce circular reasoning into the assessment of fossil evidence. Even though they are rarely included in the diagnosis of taxa there are dangers in using criteria such as ‘striding’ and ‘propulsive’ bipedalism, even tacitly, as diagnostic criteria. For instance because of the apparent locomotor compatability of the tibia and fibula from the FLK site at Olduvai Gorge (at present OH 35) and the foot, OH 8 from FLKNN, it has been suggested that OH 35 is more likely to be associated with the second individual on the FLK floor, OH 6, than with the better known cranium OH 5 (M. D. Leakey, 1971). Similarly when the affinities of OH 10 were being considered it was stated that “a comparable type of gait has already been ascribed to the Homo habilis foot - - - -” (Day & Napier, 1966) ; this has led subsequent investigators to treat OH 10 and OH 8 as parts of the same functional foot complex (Preuschoft, 197 1). Journal of Human Euolution (1974) 3,373-378

374

B. A.

WOOD

Now that new material is available, and its study under way, the post-cranial material from Olduvai, and OH 8 and OH 10 in particular, occupy a critical position for a number of reasons. First, the functional labels that have been applied to specimens, Homo kabilis and otherwise, may influence judgements about new material. Second, material that has been atributed to Homo may in fact belong to any of the other taxa that are represented at Olduvai. Third, re-examination, with the great benefits of hindsight, may show that locomotor inferences about this material may need modification, especially if it is accepted that different hominid bipedal morphotypes may have been evolving in parallel in the Plio-Pleistocene.

OH8 This is a collection of adult left foot bones; they articulate with each other and there is no doubt that they represent a single individual. It was found in Bed I at site FLKNN in 1960 during the course of excavations. It lay on an occupation floor and evidence of erosion and scavenger activity indicates that the floor was a relatively open system (M. D. Leakey, 1971). Two proximal phalanges are catalogued under the same number. Specimens found in situ on the same occupation floor are OH 7 (L. S. B. Leakey, 1961), two metatarsals (OH 43), a clavicle (OH 48) and part of the shaft of a radius (OH 49) : other material has been found on the surface and on an erosion slope beneath the site. There is therefore evidence of at least two individuals on this floor and there is no reason to associate this adult foot with OH 7, the juvenile type specimen of Homo habilis. The left metatarsal bones (OH 43) represent a second adult individual on the floor. This horizon lies only a few feet below the level of the ‘Zinjanthropus’ floor at site FLK, some 300 yards away; the probable age for the OH 8 foot is 1.7 million years (Hay, 1971). The foot was described by Day & Napier (1964). They concluded, on the basis of many features, that the foot possessed the requirements for a “fully bipedal gait”, but added the caveat that it may not have been “precisely parallel to that of modern man”. Probably on the basis of these conclusions OH 8 was included as a paratype into Homo habilis and features of it are cited as characters of that species, (L. S. B. Leakey, Tobias & Napier, 1964). Further studies were made on the talus. Lisowski (1967) dissented from the views of Day & Napier and suggested that the foot was “far more like that of living monkeys and apes than that of man”. An anatomical examination of the talus, linked with a multivariate analysis, led Day & Wood (1968) to confirm Day and Napier’s findings and to write “while OH 8 is the foot of a biped, the striding bipedal gait of man had not been achieved”. The results of the multivariate analysis showed the Olduvai talus to be unique when compared with those Primate locomotor groups examined, but quite similar to the fossil talus from Kromdraai. A biomechanical analysis of the foot (Preuschoft, 197 1)) concluded that it was “unlikely to be a prehensile foot”, and that features such as the significant angle of dip of the neck could be interpreted as adaptations to reduce bending stresses in a bipedal gait. A comparative anatomical study of the hallucial tarso-metatarsal joint in Primates indicated that the features of that joint in the OH 8 foot are “strikingly conservative” and that the Olduvai foot” still bears some of the hallmarks of transition from arboreal to terrestrial life” (Lewis, 1972). Archibald, Lovejoy & Heiple (1972) showed that the metatarsal robusticity formula in OH 8 was unusual, but present, in a sample of modern men.

OLDUVAI

BED

1 POST-CRANlAL

FOWLS:

A REASSESSMENT

375

Thus, while there are good anatomical and biomechanical grounds for rejecting this as a prehensile foot, it is not a necessary corollary that it is therefore directly related to the modern human morphological pattern. Day & Napier (1964) wisely stated that the features they listed as the adaptations of modern Man were specific for the modern human morphotype and gait pattern. The partial or total expression of these features in a fossil foot is u posteriori no guarantee that the fossil represents a developmental stage towards the modern human morphotype or gait pattern. Equally well a fossil foot may have been bipedal and not have these, but another combination of characters. In the context of talar morphology examples of similarly misleading features are the angle of torsion and the horizontal angle of the neck. The high angle of torsion in Man (presumably because of the low values in apes) has been correlated with “the human type of gait” (Lisowski, 1967) ; in fact Colobus and other monkeys have a comparable mean Table 1

Data for modem Man and the fossils. Details of the modem human sample are given in Day 8z Wood (1968)

Variables

Mean

S.D.

Horizontal angle Dip angle Torsion angle Neck length ind. Head proj. ind. Troth. shape ind. Fib. facet proj. ind.

19.0 35.9 37.0 135.0 42.0 93.0 284.0

3.4 4.9 7.2 18.0 10.6 8.3 63.0

Modern

Man OH 8

Kromdraai

KNM-ER8

28.0 8.0 40.0 125.0 45.0 100.0 333.0

32.0 4.0 34.0 121.0 72.2 106.0 360.0

14.0 25.5 48.0 130.0 40.0 91.0 222.0

13

torsion angle. It was also accepted by some (Straus, 1963), that a wide horizontal angle went pari passu with an abducted hallux; the OH 8 foot demonstrates that this is not necessarily so. These examples indicate that unless characters have been investigated as part of a comprehensive comparative and biomechanical study their valency as special functional indicators must remain suspect. Perhaps it would be more prudent to say of such features as a low longitudinal arch, a relatively horizontal subtalar joint, an adducted hallux, the tarso-metatarsal joint and the pattern of metatarsal robustity in the Olduvai foot that, taken together, they strongly suggest a definite bipedal capability. New evidence from East Rudolf may also be relevant. A talus, KNM-ER813, found in 1971, was considered on preliminary examination to belong to Homo (R. E. F. Leakey, 1972). More detailed anatomical examination added nothing to alter this attribution (R. E. F. Leakey & Wood, 1973). Comparison with the tali from Kromdraai and Olduvai revealed many differences between them and KNM-ER8 13 ; these are summarized in the measurements given in Table 1, The results of submission of these data to the types of multivariate analysis used by Day & Wood (1968, 1969) confirm that KNM-ER813 is very similar to two groups of modern human tali (Wood, 1974); the results of the D2 distance analysis are given in Table 2. While individual features are open to misinterpretation, the several variables used in this analysis, and the nature of the multivariate technique itself, make it most likely that the degree of similarity of overall morphology as expressed in the D2 results is a valid indicator of genetic and functional affinities. Thus, broadly contemporary with OH 8, is a talus that has a better claim to belong to a Homo foot. If the present taxonomic scheme is accepted an anomaly exists as the talar

376 Table

B.

2

A.

WOOD

Mabalaaobis and special

D2 distances

and probability

Comparative 1. Homo Dissecting room

Fossils

KNM-ER813

15.9

levels between

groups

cases

2. Homo Anglo

Saxon

24.2

3. Homo

Groups

4. Gorilla

5. Pan

Bushmen

12.0

47.3

48.1

(2-555y) Olduvai Kromdraai

(<@I%) morphology of the two Homo specimens is very different. To postulate such wide variability of a key structure in one lineage is to introduce unacceptable complications into hominid phylogeny; a better solution would be to place these specimens in different taxa. When these new data are added to the fact that OH 8 is similar in some ways to the Kromdraai talus, it is a reasonable suggestion to attribute OH 8 to the genus Australopithwar. OH 10 This is the distal phalanx of a right hominid hallux. It was found in Bed I at site FLKN on the occupation floor at level 5 (M. D. Leakey, 1971). No other hominids were found in situ but an isolated hominid tooth (OH 21) was found on the surface (M. D. Leakey, 1969). This phalanx is broadly contemporary with OH 8. It was reported on by Day & Napier (1966). They noted that although it most strongly resembled the bones of modern men “its morphology is not precisely matched by any of the hominoid bones or casts that have been examined”. Two features were considered to be particularly relevant. These were valgus deviation, which is most conspicuous in modern Man, and axial torsion, seen in modern Man and not in the extant African apes. The expression of these characters in OH 10 led the authors to suggest that “the Olduvai toe bone belonged to an upright bipedal hominid possessing a plantigrade propulsive gait”. In a multivariate study Day (1967) wrote of the results that they implied that “propulsive bipedalism, of the human type, was the form of gait of at least one group of early hominids evolving in East Africa at this time”; this was in reference to OH 10. The only other study to include the bone is that of Preuschoft (1971) who concluded that this form “obviously had no prehensile foot”. The claims made for the locomotor pattern of the hominid, whose hallucial phalanx this was, are definite and specific but they should nevertheless be examined critically. It was the findings of Wilkinson (1954) that prompted Barnett (1962) to investigate the valgus deviation of the terminal hallucial phalanx. He found no such deviation in 164 non-human Primates and he therefore suggested that the presence of valgus deviation in a fossil form would “provide evidence for a human type of gait”. However, just because a particular form of bipedalism is associated with a morphological feature, the presence of that feature need not imply the same pattern of locomotion; it is the classical post hoc fallacy. Barnett recognized this, for in the same paragraph he wrote “examination of many members of all the principal primate species would be necessary before this distinction

can

Barnett’s

suggestion

be regarded is

as absolute”.

correct,

It may subsequently be demonstrated that but his findings are not evidence alone, and he recognized

OLDUVAI

BED I POST-CRANIAL

FOSSILS:

377

A REASSESSMENT

this. At any event, the deviation of the OH 10 specimen apparently lies within 2 standard deviations of gorilla and outside the same range for modern Man (Day & Napier, 1966). The data on axial torsion are more impressive but, until sufficient comparative studies have been undertaken, are open to the same logical objection. The results of the multivariate analysis (Day, 1967)) might have resolved this issue. In this study, the weights of the first canonical variate acted as a successful discriminant between the hallucial terminal phalanges of modern Man and the African apes. The same weightings applied to the fossil data grouped it with the modern men. This would be most significant if the D2 distances between the fossil and the modern human groups were small and insignificant. However, Figure 2 in Day (1967) and Table 3 below, show Table 3

Fossil OH 10

Dz distances (taken from Day, between groups and OH 10

1. Modern Man (European)

2. Modern Man (East African)

Comparative Groups 3. Modern Man (Bushmen)

29.0
32.8
26.5 <0.10,;

1967) and probability

4. Gorilla

62.9
levels

5. Pan

66.7
that though the fossil is further from the apes than from the men it is still a significant distance from the men. Oxnard (1972) has pointed out recently how this situation can give rise to misleading canonical analysis results; a reanalysis of data from Miocene tali (Wood, 1973), has revealed a similar case. Unless it can be demonstrated that this toe bone analysis was not subject to the same potential error the results must be reinterpreted as being no more than equivocal about the specifically human bipedal capabilities of this phalanx. These comments may perhaps be justly criticised for being pedantic and ignoring the practical difficulties of dealing with an inadequate fossil sample. Indeed most of the locomotor inferences were only suggestions, but even suggestions have a way of becoming incorporated into hominid ‘folk-lore’ in the guise of proven facts. When more data are available these locomotor predictions may be vindicated, but meanwhile the evidence for them is equivocal. While this is so, it is important that specific functional epithets should not be attached to Homo hub&. For, not only may they be incorrect, but the specimens on which they were based may not even belong to the genus Homo. I thank Dr Mary Leakey and Professors T. W. Glenister and J. R. Napier for reading and commenting on this manuscript; the responsibility for its contents, however, remains my own. References Archibald, J. D., Lovejoy, C. 0. & Heiple, K. G. (1972). Implications of relative robusticity in the Olduvai metatarsus. American Journal of Physical Anthropology 37, 93-95. Barnett, C. H. (1962). Valgus deviation ofthe distal phalanx of the great toe. Journal of Anatomy 96,171-l 77. Day, M. H. (1967). Olduvai Hominid 10: a multivariate analysis. Nature 215,323-324. Day, M. H. (1969). Femoral fragment of a robust australopithecine from Olduvai Gorge, Tanzania. Nature 2!21,230-233. Day, M. H. & Napier, J. R. (1964). Hominid fossils from Bed I, Olduvai Gorge, Tanganyika: Fossil foot bones. Nature 201, 968-970. Day, M. H. & Napier, J. R. (1966). A hominid toe bone from Bed I, Olduvai Gorge, Tanzania. Nature 211,929-930.

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WOOD

Day, M. H. & Wood, B. A. (1968). Functional affinities of the Olduvai Hominid 8 talus. A&n 3 (3), 440-455. Day, M. H. & Wood, B. A. (1969). Hominoid tali from East Africa. Nature 222, 591-592. Hay, R. L. (1971). Geologic Background of Beds Z and ZZ. Stratigraphic Summary in Olduuai Gorge, Volume 3, pp. 9-18. Cambridge: Cambridge University Press. Leakey, L. S. B. (1961). New finds at Olduvai Gorge. Nature 189,649-650. Leakey, L. S. B. (1961). The juvenile mandible from Olduvai. Nature 191, 417-418. Leakey, L. S. B., Tobias, P. V. & Napier, J. R. (1964). A new species of the genus Homo from Olduvai Gorge. Nature 202, 7-9. Leakey, M. D. (1969). Recent discoveries of hominid remains at Olduvai Gorge, Tanzania. Nature 223, 754-756. Leakey, M. D. (1971). Olduvui Gorge, Volume 3, pp. I-306. Cambridge: Cambridge University Press. Leakey, R. E. F. (1972). Further evidence of Lower Pleistocene Hominids from East Rudolf, North Kenya, 1971. Nature 237, 264-269. Leakey, R. E. F. & Wood, B. A. (1973). New evidence of the genus Homo from East Rudolf, Kenya. II. American Journal of Physical Anthropology 39, 355-368. Lewis, 0. J. (1972). The evolution of the hallucial tarso-metatarsal joint in the Anthropoidea. American Journal of Physical Anthropology 37, 13-33. Lisowski, F. P. (1967). Angular growth changes and comparisons in the primate taIus. Foliu Primafologica 7, 81-97. Napier, J. R. (1964). The evolution of bipedal walking in the hominids. Archives de Biologic (Liege) 75 (Suppl.), 673-708. Oxnard, C. E. (1972). Some African Fossil foot bones; a note on the interpolation of fossils into a matrix of extant species. American Journal of Physical Anthropology 37, 3-12. Preuschoft, H. (1971). Body posture and mode of locomotion in Early Pleistocene hominids. Folia PrimatoIogica 14, 209-240. Straus, W. L. (1963). The classification of Oreopithecus. In (S. L. Washburn, Ed.), ClassiJication and Human Evolution, pp. 146-177. Chicago: Aldine. Wilkinson, J. L. (1954). The terminal phalanx of the great toe. Journal of Anatomy 88,537-541. Wood, B. A. (1973). Locomotor affinities of hominoid tali from Kenya. Nature 246,45-46. Wood, B. A. (1974). A Homo talus from East Rudolf, Kenya, Journal of Anatomy 117,203-204. Wood, B. A, (1974). Evidence about the locomotor pattern of Homo from the early Pleistocene of Kenya. Nature, in press.