Symmetrical reduction of M3 and hypoconulid loss in M. mulatta

Abstract

An adult male rhesus macaque from Morgan Island was found to have reduced third upper molars and to have lost the hypoconulid on the lower third molar. The pattern of reduction was symmetrical, with hypocone, metacone, and eleven of thirteen upper cheek tooth measurements markedly diminished in size. Mandibular cheek teeth were less affected. The pattern of size reduction yields a specimen whose individual teeth resemble in size those of Cercopithecus aethiops in particular and the Cercopithecini in general in its 'derived features of M3 reduction, hypoconulid loss, and reduced cheek tooth size.Reduction of the distal moiety of the third upper molar together with loss of the hypoconulid on the third mandibular molar is considered a diagnostic and derived feature of members of the tribe Cercopithecini (Delson, 1973(Delson, , 1975. Among the papionini, the hypoconulid is almost invariably present, reportedly lacking only in rare Papio and Cercocebus albigena individuals (Delson ,1975;Leutenegger, 1971). Despite the conventional wisdom that M3 is usually longer than M2 in papionins, the size relations between the upper molars in general show a varying relationship between M2 and M3. Swindler (1976) shows that Papio harnadryas cynocephalus and Theropithecus gelada have larger mean values for M3 than M2; however, the 95% confidence limits overlap. This is also the case for Ethiopian P. h. anubis and P. h. hamadryas, (Phillips-Conroy, 1978), for other 'savannah' baboons (Jolly, 1963), and is likely true for a number of macaque species as well. Szalay and Delson (1979) have recently commented that among the macaques "hypoconulid loss occurs only in some individuals of small species," a revision of Delson's earlier contention that ". . . in small macaque species it

New macaque fossil remains from Morocco

“…The hypoconulid has been lost in cercopithecins and is reduced in smaller Asian colobines (Swindler, 1983(Swindler, , 2002Szalay and Delson, 1979) but is almost invariably present in papionins, where it shows some degree of intraspecific variation (Swindler, 1983). It is only rarely missing in some Papio, Cercocebus and Macaca individuals (Delson, 1973(Delson, , 1975Szalay and Delson, 1979;Phillips-Conroy, 1982), resulting in the reduction of the hypoconulid lobe (Phillips-Conroy, 1982).…”