Primitive and derived patterns of relative growth among species of iorisidae

Abstract

Evolutionary lineages may be described as series of successively modified ontogenies ( Gould, 1977 ). Because of this important link between evolutionary change and ontogenetic modification, insight into phylogenetic relationships may be gained through comparing patterns of growth among species. Here, patterns of relative growth among the species of Lorisidae (Nycticebus coucang, Nycticebus pygmaeus, Loris tardigradus, Perodicticus potto and Arctocebus calabarensis) are described and compared. External postcranial measurements were taken on captive N. coucang, L. tardigradus, N. pygmaeus and P. potto throughout growth, and comparable skeletal measurements were obtained for adult A. calabaraensis. Scaling trends were analysed with standard bivariate regression techniques and principal components analysis. Nycticebus coucang, N. pygmaeus and P. potto generally have coinciding growth trajectories, while those for L. tardigradus are consistently steeper than those for the other lorisids. Ontogenetic data for N. coucang, N. pygmaeus and P. potto, as well as adult data for A. calabarensis, were clearly separated from data for L. tardigradus along the second component in the principal components analysis. Postcranial growth patterns for L. tardigradus are most likely derived among the species of Lorisidae, while Nycticebus, Perodicticus, and perhaps Arctocebus have mainly retained primitive patterns of relative growth.