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CARABELLI'S TRAIT EXPRESSION IN AGILE MANGABEYS (CERCOCEBUS AGILIS), ANGOLAN COLOBUS MONKEYS (COLOBUS ANGOLENSIS) AND OLIVE BABOONS (PAPIO ANUBIS): THE ROLE OF SIZE AND PHYLOGENY

Abstract

Carabelli’s trait is an extension of the cingulum at the base of the lingual surface of the protocone on the maxillary molars. This trait can range from a small pit to a large cusp with a free apex. Since the expression of Carabelli’s trait is neutral with respect to selection, its presence or absence serves to approximate relatedness. Carabelli’s trait is commonly found in humans, apes and baboons, and understanding its varying expression can aid in reconstructing the diversification of fossil primates during the Miocene, 23-5 million years ago. In addition to phylogeny, tooth size may also influence trait expression with larger molars tending to exhibit morphological traits that are not present in smaller counterparts. To examine the extent to which size and phylogeny influence the expression of Carabelli’s cusp in catarrhine monkeys, we examined three taxa, including agile mangabeys (Cercocebus agilis, n = 45) and Angolan colobus monkeys (Colobus angolensis, n = 24), which are similar in size but distantly related, and olive baboons (Papio anubis, n = 21) which are much larger than the other two but more closely related to mangabeys. Individuals were compared using the Great Ape Dental Scoring System in which Carabelli’s trait is categorized as exhibiting four discrete morphological stages of expression. We anticipated Papio to exhibit the greatest degree of expression of Carabelli’s trait given its larger size and complex dental morphology, followed by Cercocebus due to phylogeny. The results indicate that larger primates (Papio) do indeed present a greater frequency of Carabelli’s trait. Papio often exhibits a larger Carabelli’s trait compared to the other taxa which are restricted to a minimal expression. Cercocebus yields a slightly greater frequency than Colobus. Although its expression is limited, this is likely to be the first reported incidence of Carabelli’s trait in Cercocebus and Colobus.

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