Dental Eruption Sequences in Fossil Colobines and the Evolution of Primate Life Histories

Unlike other catarrhines, colobines show early molar eruption relative to that of the anterior dentition. The pattern is variable, with Asian genera (Presbytina) showing a greater variability than the African genera (Colobina). The polarity of early relative molar eruption, as well as the degree to which it is related to phylogeny, are unclear. Schultz (1935) suggested that the trend reflects phylogeny and is primitive for catarrhines. More recently, however, researchers have proposed that life history and dietary hypotheses account for early relative molar eruption. If the colobine eruption pattern is primitive for catarrhines, it implies that cercopithecines and hominoids converged on delayed relative molar eruption. Alternatively, if the colobine condition is derived, factors such as diet and mortality patterns probably shaped colobine eruption patterns. Here we update our knowledge on eruption sequences of living colobines, and explore the evolutionary history of the colobine dental eruption pattern by examining fossil colobine taxa from Eurasia (Mesopithecus) and Africa (Kuseracolobus aramisi and Colobus sp.) and the basal cercopithecoid Victoriapithecus macinnesi. We scored specimens per Harvati (2000). The Late Miocene-Early Pliocene Mesopithecus erupts the second molar early relative to the incisors, while the Early Pliocene Kuseracolobus aramisi does not. These results demonstrate that the common colobine tendency for early molar eruption relative to the anterior dentition had appeared by the Late Miocene, and that some of the diversity observed among living colobines was already established in the Late Miocene/Early Pliocene. We discuss the implications of these results for phylogenetic, life history, and dietary hypotheses of dental development.     

How might early hominids have defended themselves against large predators and food competitors?

Judging from comparative data on mortality and survival strategies among the higher primates, the early hominids must have used weapons in order to defend themselves effectively against their Natural enemies. They were, however, too small and too weak for throwing big stones or for wielding heavy sticks in the chimpanzee manner. Did they use thorn branches?Experiments in which a bait was covered with a shield of thorn branches showed that wild-living lions are highly afraid of thorns and hardly dare to touch them with their paws. The accompanying behavioural symptoms indicated stress resulting from inhibitions.In the final experiment the bait was protected against wild-living, tame lions by an electrically operated helicopter-like rotor with four blades on which some thorn branches were attached. Every time a lion closely approached the bait the rotor was operated for a split-second, causing the nearby lions to jump wildly away. When finally a lion was struck on the nose all three lions present walked away and did not return until I had myself left.This excessive fear of suddenly moving thorn branches could perhaps indicate that the responses of carnivores which were originally adapted to porcupines, facilitated the use of thorn branches as defensive weapons among the incipient hominids. The evolution of this behaviour may have started among dryopithecines living in dry woodlands and would have promoted the emergence of regular bipedal gait.     

Nutritional geometry: gorillas prioritize non-protein energy while consuming surplus protein

It is widely assumed that terrestrial food webs are built on a nitrogen-limited base and consequently herbivores must compensate through selection of high-protein foods and efficient nitrogen retention. Like many folivorous primates, gorillas' diet selection supports this assumption, as they apparently prefer protein-rich foods. Our study of mountain gorillas (Gorilla beringei) in Uganda revealed that, in some periods, carbohydrate-rich fruits displace a large portion of protein-rich leaves in their diet. We show that non-protein energy (NPE) intake was invariant throughout the year, whereas protein intake was substantially higher when leaves were the major portion of the diet. This pattern of macronutrient intake suggests that gorillas prioritize NPE and, to achieve this when leaves are the major dietary item, they over-eat protein. The concentrations of protein consumed in relation to energy when leaves were the major portion of the diet were close to the maximum recommended for humans and similar to high-protein human weight-loss diets. By contrast, the concentrations of protein in relation to energy when gorillas ate fruit-dominated diets were similar to those recommended for humans. Our results question the generality of nitrogen limitation in terrestrial herbivores and provide a fascinating contrast with human macronutrient intake.