Fossil Hand Bones from Olduvai Gorge

Abstract

IN Nature of December 17, 1960, Dr. L. S. B. Leakey reported on the discovery of a number of fossil bones of the hand and the foot on a living floor some 20 ft. below the uppermost limit of Bed I, Olduvai. Later (Nature of February 25, 1961), Dr. Leakey reported the discovery of a mandible and two parietal fragments of a juvenile from the same site and associated with a well-defined living floor of an Oldowan culture. Fifteen of the hand bones pertaining to at least two individuals, an adult and a juvenile, have been identified and examined, and are described here. Their allocation is given in Table 1. The middle phalanges (Fig. 1, second row) from the juvenile hand, lacking only their epiphyses, constitute a series II-V from the right hand. They are robust bones, rather more so than phalanges of comparable length of juvenile Gorilla and adult Homo sapiens. They are strongly curved and, palmad, bear well-defined grooves which are situated in the distal half of the bone for the insertion of flexor digitorum superficialis. The adult proximal phalanges (Fig. 1, third row) are also more robust than bones of comparable length in modern man; they are strongly curved both longitudinally and transversely, fusiform in shape and deeply hollowed out on the palmar aspect; sharply defined fibrous flexor sheath ridges extend from the base of the bones to their necks. The terminal phalanges (Fig. 1, top row) which are juvenile, having incompletely fused epiphyses, are characteristically sapiens in form. The terminal phalanx of the thumb is of particular interest; it is stout and broad and bears a deep impression for the insertion of flexor pollicis longus. The carpal bones (Fig. 1, 4th row) are all damaged, but sufficient of their original form remains to determine their structural and functional affinities. The lunate surface of the scaphoid has a rectangular outline; and the tubercle, which is broken off at its root, was probably somewhat elongated, though not as long as in the anthropoid apes. The trapezium has a well-defined saddlesurface but the evidence provided by the other articular surfaces indicates that its 'set' in the carpus was unlike that found in modern man and similar to the condition in Gorilla. The capitate, though badly eroded, is generally more sapiens than apelike. Morphologically, the Olduvai hand bones cannot be closely matched with any known hominoid species living to-day. They bear, however, a greater similarity to juvenile Gorilla and adult H.s. sapiens than to adult Gorilla, Pan or Pongo. This is due largely to the absence in the fossil bones of any features peculiarly characteristic of brachiators. The adult gorilla hand has a number of specializations that are presumably related to its secondarily terrestrial mode of life and its great body-weight; these features, again, are absent from the fossil bone. The juvenile gorilla hand lacks the secondary specializations of the adult, and it is possibly for this reason alone that its bones have affinities with those of the fossil. The fossil bones differ from those of modern man in a number of features: (1) robustness; (2) dorsal curvature of the shafts of the phalanges; (3) distal insertion of the flexor digitorum superficialis; (4) strength of fibrotendinous markings; (5) 'set' of trapezium in the carpus; (6) the form of the scaphoid; (7) the depth of the carpal tunnel. The fossil bones resemble modern man in the following features: (1) presence of broad, stout terminal phalanges on fingers and thumb; (2) form of the distal articular surface of the capitate; (3) ellipsoidal form of metacarpo-phalangeal joint surfaces. TABLE 1