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.