David Pilbeam

New hominoid primates from the Siwaliks of Pakistan and their bearing on hominoid evolution.

Siwalik deposits in the Punjab have yielded a rich collection of hominoidprimate remains. Together with other recent finds they indicate the need for some changes in hominoid classification.

Of mice and men: Fossil-based divergence dates and molecular “clocks”

Abstract The magnitude of immunological differences between species has been used to estimate the time of divergence of lineages, especially among primates. Calibration of “clocks” based on immunological differences has relied heavily on data from Pakistan suggest that the lineages leading to Mus and Rattus diverged between 14 and 8 million years ago rather than 30 or more million years ago as suggested by techniques invoking constant rates of molecular evolution. Molecular analyses of pairs of mammal species which appear well documented paleontologically should be undertaken in order to expand our understanding of the tempo and mode of molecular evolution.

The Miocene fossil beds of Maboko Island, Kenya: Geology, age, taphonomy and palaeontology

The results of excavations in Miocene deposits at Maboko Island, Western Kenya, in 1973 are described. An account is given of the geology, and it is concluded that the deposits form part of a sequence of floodplain overbank deposits. These consist mainly of diagenetically altered sediments laid down in wet conditions and they differ from the more dry conditions indicated by the pedogenetically altered sediments, with the development of calcretes, to the north of Majiwa and Kaloma. The Maboko fauna contains abundant aquatic elements whereas the Majiwa and Kaloma faunas have greater terrestrial affinities, although the differences between the faunas is small. Faunal analysis and radiometric data reported here suggest that the age of the Maboko fauna is about 15 Ma.

A gorilla-sized ape from the miocene of India.

A large ape existed in India at the close of the Miocene or the beginning of the Pliocene epochs; this ape shows a complex of anatomical structures at the opposite pole from its contemporary, Ramapithecus. Although found in the same beds, the two seldom occur at the same exact sites and levels. Considering the thickness of these beds, recovery close to Haritalyangar does not, of itself, prove sympatry of these two different kinds of Hominoidea. However, both are definitely present at one recently located site representing, most probably, a death assemblage. Observations by the authors on scores of chimpanzees suggest that, at least in this ape, wear gradients on molar crowns exist, but that the wear differential between adjacent molars is almost never raised to the degree seen in most Ramapithecus. Dryopithecus itdicus and D. fontani (from southern France), in contrast, show almost no wear gradient at all; that is, whether an individual is dentally young or old, wear on all three molars and the two premolars has proceeded to about the same degree. It is of considerable importance in understanding hominid phylogeny to be able to stress that an ape known to be contemporary with Ramapithecus shows far less differential wear than does the hominid. This, in turn, strongly suggests that the molar eruption sequence of D. indicus was rapid, while that of the hominid was delayed. The implication is that, as far back as the late Miocene, the hominid maturation period was lengthened, relative to that of apes. A further fact which emerges is that the rate of interstitial wear was faster in the Haritalyangar ape than in the hominid contemporary with it. This, together with its large size, flatness of unworn tooth crowns, and other associated characters, suggests that D. indicus is in, or close to, the ancestry of Gigantopithecus. From this emerges yet another object lesson, emphasizing the caution one has to observe in the manner and method by which ancient and modern apes are compared and contrasted. None of the species of Hominoidea dealt with here, whether pongid (D. indicus and Pan troglodytes) or hominid (R. punjabicus), accumulates either interstitial or crown wear at the same rate or in the same manner.