The endocranial surface of the frontal bone

Only a small part of the endocranial surface of the frontal bone is present. The angle between the squama and the floor of the anterior cranial fossa is difficult to determine, because only the rostral end of the floor is present; it seems, however, to be much nearer the angle in Homo erectus pekinensis (50°) than that of modern man (about a right angle–Weidenreich, 1943, p. 32). Laterally, the posterior turn or recurvation of the squama at the postorbital constriction is clear, giving an extremely narrow frontal region. From the mid-line, the chord to the line of recurvation is only 31·0 mm. The endocranial width between the left and right lines of recurvation is 59·4 mm.

There is a thin though strong frontal crest, as in Pekin Man and other hominines. In pongids, on the other hand, it is missing or, at most, is represented ‘by a low, insignificant ridge’ (Weidenreich, 1943, p. 32). The relationship of the frontal crest to the sulcus for the superior sagittal sinus is described in Section D of this chapter (p. 63). Weidenreich regarded the internal frontal crest as part of the sagittal reinforcing system of the cranial vault of Pekin Man; he drew attention to the fact that the frontal crest fades out just where the sagittal thickening (which he unfortunately designated ‘sagittal crest’) originates on the outer surface.

On 15 August 1959 the first announcement of the discovery of a new fossil cranium from Olduvai appeared in Nature (Leakey, 1959a). A week later, on Saturday 22 August 1959, at the formal opening ceremony of the fourth Pan-African Congress on Prehistory in Léopoldville, Dr L. S. B. Leakey publicly announced to the astonished and enthusiastic delegates more details of the important new specimen (Tobias, 1960a). He reiterated his view, expressed already in Nature, that the big-toothed cranium was that of a young male, representing a new genus of the subfamily Australopithecinae. To this genus he gave the name Zinjanthropus, Zinj being ‘the ancient name for East Africa as a whole’. He enumerated twenty features in which he claimed the new specimen differed from members of either of two previously-recognised australopithecine genera, Australopithecus and Paranthropus. He went on to designate the species as Zinjanthropus boisei sp.nov., the specific name being in honour of Mr Charles Boise, whose generous financial help had made the discovery possible. Leakey's (1959a) preliminary diagnosis of its specific features reads as follows: ‘A species of Zinjanthropus in which the males are far more massive than the most massive male Paranthropus. The face is also excessively long. Males have a sagittal crest, at least posteriorly. Upper third molars smaller than the second.’

Leakey stressed the tentative nature of his generic and specific diagnosis, recognising that, if and when further material were found, ‘the diagnosis will need both enlarging and possibly modifying’.

The calvaria of Zinjanthropus is a curious blend of extraordinary robusticity in parts and unusual thinness in others. Basically a thin-walled calvaria, the brain-case is modified in parts by (a) massive ectocranial superstructures, and (b) excessive pneumatisation.

Robusticity owing to pneumatisation

One could multiply measurements apace to demonstrate the unusual thickness and robusticity of different parts of the cranium of Zinjanthropus. A good area in which to demonstrate this is the region of the parietomastoid and occipitomastoid sutures, since comparative data are available, once again provided mainly by Weidenreich (1943, p. 66).

The first thickness is that of the parietomastoid suture just in front of asterion. In Zinjanthropus, this thickness measures 22·2 mm. on the left and 24·1 mm. on the right. For comparison the values in three crania (five sides) of Homo erectus pekinensis range from 15 to 18 mm.; and in modern man from 3·5 to 7·0 mm.

The second thickness is that of the occipitomastoid suture ‘medial to the mastoid process’. As in anthropoid apes, it is extremely difficult to take this measurement in Zinjanthropus because the whole pars mastoidea (not just the mastoid process) is pneumatised. For instance, in Zinjanthropus, the parietomastoid suture just in front of asterion is not the thickest part (which it is in H. e. pekinensis); instead the thickest part is to be found just behind the right mastoid process proper, where readings of 26–29 mm. can be taken.

The cranium of Zinjanthropus is heavily pneumatised. All the paranasal sinuses represented show excessive development and spread into adjacent parts not regularly pneumatised in hominids. In the ninth of his twenty diagnostic criteria of Zinjanthropus, Leakey (1959a, p. 492) had commented on ‘the very great pneumatosis of the whole of the mastoid region of the temporal bones, which even invades the squamosal elements’. Each part of the cranium will be dealt with here in turn.

The maxillary sinus

Through damage to the posterior aspect of the maxillae, almost the entire volume of both maxillary sinuses is exposed from behind (pl. 18B). This excellent exposure provides an unusually good view of the antrum on each side.

The maxillary sinus is vast and partly bilocular. There are a partial septum on the right and a more complete transverse septum on the left, approximately at the level of the lower edge of the root of the zygomatic process. The partial septum cuts off a lower compartment which, inferiorly, and especially anteriorly, is largely multilocular. This lower compartment corresponds to the recessus alveolaris of the maxillary antrum in gorilla and orang (Wegner, 1956). In Zinjanthropus, the roots of M2 have broken partly through into the alveolar recess. The roots of M3 are set in the more solid bone of the maxillary tuberosity and only the mesial edge of the mesial root of M3 is set in the area thus far pneumatised.

The postcanine teeth tend to be enlarged buccolingually far more than mesiodistally. Metrical expression can be given to this tendency by the calculation of the crown shape index, in which the m.d. crown diameter is expressed as a percentage of the b.l. diameter. In Table 45, the m.d./b.l. shape indices of Zinjanthropus are compared with those of a number of other hominoids. Two distinct trends seem to characterise the hominoids listed: one is a tendency towards relative buccolingual expansion from C to the premolars, resulting in most groups in progressively lower mean indices from before backwards; the other is a similar gradient starting at M1 and decreasing through to M3.

The canine–premolar trend shows the most marked drop from C to P3; this is true in Australopithecinae (including Zinjanthropus), Homininae and Pongidae. The decrement in shape index from P3 to P4 is slight throughout these hominoids, but there are several exceptions in which P4 has a slightly higher index than P3. Zinjanthropus is one of them. Sangiran IV and Rabat are further examples, so that the overall picture in Homo erectus shows a mean shape index of P4 which is a shade higher than that of P3. The mean values for the male gorilla sample of Ashton and Zuckerman (1950) provide another instance. However, when one considers single specimens of Paranthropus and Australopithecus, in which both maxillary premolars are present and measurable on at least one side, the Zinjanthropus pattern finds a parallel in several examples of both forms.

There is no spot on earth more fascinating and more deeply significant for all of us than Olduvai Gorge. It has, to begin with, extraordinary scenic beauty. In one direction stretches the great, open Serengeti Plain, broken here and there by hills that are massifs of old, weathered rock piercing the younger sediments. In the opposite direction is the rifted Balbal depression and, beyond it, the towering slopes of the Ngorongoro Caldera. Other volcanoes, extinct and living, crenellate the long horizon. The varicoloured gorge itself displays high vertical cliffs, steep, sweeping slopes, and fantastic eroded forms. For those of us who enjoy occasional escape from our own teeming species, the gorge has an added charm: few places in the world are so free from recent works of man. It has been thousands of years since any human maintained a permanent dwelling there. The occasional visitors are all sporadic nomads: wandering tribesmen and palaeontologists.

The desert grandeur of the scene is, however, only an unexpected bonus at Olduvai. The true significance lies literally deeper, in the successive strata exposed in the walls of the gorge. The stunning dimension of the gorge is not in space but in time, not in the seemingly ageless and unchanging face of pristine Africa but in a dated sequence of major events with repercussions everywhere on earth. Here, one after another, are chapters in history ranging from sometime in the early Pleistocene to the present day.

The fauna of Olduvai is now represented by very extensive collections found in situ in Beds I and II. These are supplemented by material collected on the surface or excavated from exposures when the fossils had become visible as a result of erosion. These collections will require many years of work before the final reports can be published. This is partly because many specimens have to be sent to specialists all over the world and partly because the quantity of material in certain groups is very great indeed. In the present volume it is possible to give only a summary, but this will present a clearer picture of the fauna of Olduvai than has been possible in the past.

In this and the next two chapters, only the families, subfamilies and genera are given in some cases, since the detailed work has not yet been carried out. In other groups, such as the Bovidae and the Suidae, a more complete picture is given, with diagnoses and descriptions of new genera and species, where possible. Material which had previously been inadequately described is dealt with a little more fully and is illustrated. In a few cases the quantity of material is so great, as for example in the genera Pelorovis and Bularchus, that no attempt has been made to discuss it in detail for the time being.

In this chapter, various scientists have collaborated to present a preliminary statement, and I am most grateful to them.

The view has been expressed by a number of geologists that the magnificent fossil-bearing deposits at Olduvai can be interpreted without reference to the possibility of Pleistocene climatic changes. This does not seem to be compatible with the observed facts. The changing sequence of deposits exposed in the gorge, when taken in conjunction with their geographic setting, seems to be incapable of satisfactory explanation without reference to major fluctuations of climate during the time that they were being formed. Even if there was no other supporting evidence elsewhere in East Africa, the Olduvai sequence suggests most strongly that there were prolonged periods when the climate was wetter than it is today, and others when it was fully as dry, or even drier.

Before summarising the evidence for climatic change in Pleistocene times in East Africa, it is necessary to define clearly what we mean by the terms ‘pluvial’ and ‘interpluvial’. These two words are used to refer to major changes of climate which were comparable to the glacials and interglacials of the Pleistocene in Europe and North America. Just as the term ‘glacial’ does not imply that it snowed all day and every day, so the word ‘pluvial’ does not mean that it rained every day. In Europe the words ‘glacial period’ imply a time during which generally colder conditions than those of the same region at the present day, persisted over a prolonged period.

Fossil remains of Bovidae are exceedingly plentiful in the Olduvai deposits. There are two reasons for this. In the first place, Bovidae normally represent a high proportion of the total animal population of most African habitats other than the dense forest. Consequently, it is only to be expected that fossil remains of this group should outnumber those of any other. Secondly, the vast majority of the fossils which we find in the excavations come from livingfloors or camp-sites of prehistoric man and represent the remains of his meals. Man apparently preferred the flesh of the Bovidae to that of many other groups, as he does throughout the world today.

Some of the Bovidae described in this chapter have been named previously; others are described here for the first time. In one or two cases, species have been included which are not represented in the collections to which I have had access in London, or in Nairobi. They were specifically listed as present in the Olduvai fauna by Dr Schwarz on the basis of Professor Reek's material.

The following is a list of the subfamilies, tribes, genera and species, which are dealt with in the pages which follow.

Subfamily: BOVINAE

Tribe: Strepsicerotini

1. Strepsiceros grandis sp.nov.

2. S. maryanus sp.nov.

3. S. stromeri (Schwarz)

4. Tragelaphus cf. scriptus

Tribe: Taurotragini

1. 5. Taurotragus arkelli sp.nov.

Tribe: Bovini

1. 6. Bularchus arok Hopwood

2. 7. Gorgon olduvaiensis sp.nov.

3. 8. G. Semiticus (Reck)

Subfamily: Cephalophinae

Tribe: Cephalophini

1. 9. Philantomba cf. monticola

Subfamily: Hippotraginae

Tribe: Reduncini

1. 10. Kobus sp.indet.

2. 11. Kobus sp.indet.

3. 12. […]

BK Bell's Korongo

This site lies on the right bank of the side gorge some 2½ miles above the confluence with the main gorge and a little upstream of DC. It consists of two korongos linked by a short cliff. There are good exposures of the upper and middle part of Bed II but the base is not visible. There are also some exposures of Beds III and IV in the upper part of both the gullies included in the site. Excavations were carried out here during 1952–8 and yielded a very rich culture and many fossils, including two hominid teeth.

In the eastern part of the site, a step trench has been cut down to the floor of the gorge near to the 1953–8 camp-site. A smaller excavation in the area near this trench, also yielded many stone tools and fossils.

Bos K Bos Korongo

This site lies on the right bank of the main gorge, slightly upstream of ‘Hand-axe Cliff’ and about 1 mile below the fifth fault. Extensive exposures of Bed IV have yielded some implements and also a crushed, rather incomplete bos skull, which was found during 1962.

CK Camp Korongo

This is a long gully on the left bank of the gorge between the second and third faults and adjacent to the 1931 camp. Beds IV, III, II and I are all exposed. It was at this site that the first hand axes ever recognised at Olduvai were discovered by L. S. B. Leakey in Bed IV, shortly after the arrival of the 1931 Expedition.

AGE OF BED I, OLDUVAI GORGE, TANGANYIKA

Olduvai Gorge is justly famous because of its unique geological sequence of Pleistocene deposits, which are exceedingly rich in fossil fauna, as well as a long sequence of stages of evolution of the earlier Stone Age cultures.

In the monograph published in 1951 the view was expressed that, although Bed I differed from Bed II in faunal content, both belonged to the lower part of the Middle Pleistocene. This view was revised by one of us in 1959 as a result of reviewing the fauna collected in the series of detailed excavations during the period 1952–9 inclusive.

Leakey claimed that it was now apparent that the time-interval between Bed I and Bed II was greater than had been previously supposed, and he reverted to the view which he had published in 1935 that Bed I was of Lower Pleistocene age. In view of the extraordinary wealth of fossil and cultural material in the Olduvai deposits, it was not surprising when in 1959 a most important fossil hominid skull—Zinjanthropus boisei—was found in Bed I, at site FLK I, in association with faunal remains and Stone Age Culture material of the Olduwan Culture. In 1960, thanks to the Research Committee of the National Geographic Society, the Wenner Gren Foundation and the Wilkie Trust, very extensive further work was carried out, resulting in the discovery of pre-Zinjanthropus fossil hominid material at a lower geological level in Bed I.

In my report on Olduvai, which was published in 1951, a brief chapter was included which had been written by the late Professor Hans Reck. In it he summarised the geological evidence which was then available as the result of his own 1913 expedition and of his work with us during 1931. This preliminary chapter had, in fact, been written at a time when he had not yet worked through all his field notes. He had planned to prepare a much more detailed report, accompanied by drawings of selected sections of the geological deposits, after his return from his expedition to Portuguese East Africa. Owing to his sudden death on that expedition, this full report was never written, and after the end of the war in 1945 it proved impossible for his widow to trace his many books of field notes. Thus, all that was available for me to use in the 1951 volume was the original preliminary note prepared before the war.

Dr P. E. Kent was a member of my 1935 expedition to Olduvai and he subsequently published a brief general note on the geology of a small part of the exposures which he had examined.

In 1961 Dr R. Pickering, a member of the Tanganyika Geological Survey, spent some four and a half months with us at Olduvai, by kind permission of the Director. He concentrated, mainly, upon making a detailed map of the FLK region where Zinjanthropus had been found in 1959.

INTRODUCTION

In chapter n the faunal evidence which was available in 1951 was reviewed. It was pointed out that many of the conclusions drawn at that time were no longer tenable. This was due, in part, to the relative lack of in situ specimens and, in part, to faulty identifications of material that was often very fragmentary.

In chapters III, IV and V the present state of our knowledge has been set out. Very many new specimens have been collected, and the faunal list has, in consequence, been considerably extended. But the position is still far from satisfactory. Only a small part of the available fauna has been studied in any detail. There is now so much material in many of the groups that it will take many years for the various specialists to complete their reports. The position is further complicated by the fact that field work is still continuing, so that every year species new to the collections are found, together with further and often more complete specimens of species already known. Since so many of the reports on the faunal material are only of a preliminary character, this review of the fossil evidence must, itself, be regarded as wholly tentative.

In 1951 it was possible to list only 51 mammals as probably present in the Olduvai deposits. Another 20 were known to occur in similar formations at Laetolil, some twenty miles to the south.