Allometric Scaling in Platyrrhine Molars and Relationships between Their Relative Size and Loss of the Third Molar in the Callitrichinae

Abstract

There is the hypothesis (Ford, 1980) that the callitrichines, which are rapidly dwarfed, should have relatively large postcanine teeth in comparison with other platyrrhines (non-callitrichines) and the loss of the third molars is probably the result of crowding from the disproportional enlarged molar teeth. In the present study, to test this hypothesis, the allometric relationships between body weight and molar area were analyzed on the basis of species arrangements of recent platyrrhine taxonomy (16 genera and 84 species). The abscissa variable was body weight and ordinate variables were sum of the first and second molar areas and total molar areas in each jaw. After logarithmic transformation of these variables, allometric equations were computed among the callitrichine species (4 genera and 25 species) and among the non-callitrichine platyrrhine species (12 genera and 29 species), respectively. The slopes for the regression lines did not differ between callitrichines and non-callitrichines in each type of molar area. The intercepts were not statistically different between callitrichines and non-callitrichines in sum of the first and second molars, whereas callitrichines were significantly smaller in intercepts for total molar area than non-callitrichines. These results reveal that callitrichines have smaller total molar area relative to body weight than non-callitrichines due to the loss of the third molar. Thus the present study does not support the above-mentioned hypothesis.