Allometry and Sexual Dimorphism in the Snail-eating Turtle Malayemys macrocephala from the Chao Phraya River Basin of Central Thailand

– Allometric growth and sexual dimorphism of the shell is evident in Malayemys macrocephala from the Chao Phraya River Basin of central Thailand. Differences in allometric growth between males and females produce sexually dimorphic adults. Adult females exhibit larger sizes and have relatively wider and higher shells and longer plastra than males. Brophy (2004) recently reviewed the systematics of the genus Malayemys (Testudines: Geoemydidae [Bataguridae]) and argued for the presence of two taxonomically distinct species. Analyses of head-stripe and shell characters revealed a clear pattern of geographic variation that was consistent with the topography of Southeast Asia and the poor dispersal abilities of these turtles. Turtles from the Mekong River Basin retained the name M. subtrijuga (Schlegel and Müller 1844), whereas those from the Chao NOTES AND FIELD REPORTS 159