EFFECT OF LIFE-HISTORY ON THE SQUIRREL-MONKEY (PLATYRRHINI, SAIMIRI) CRANIUM

Among primates, squirrel monkeys uniquely possess an interorbital fene stra, in which the midline bony orbitosphenoid septum is largely absen t and the soft tissues of the orbits are separated only by a thin memb rane. Neural development may contribute to the approximation of the or bits to the midline in Saimiri, insofar as other platyrrhines with rel atively large brains also have relatively narrow interorbital spaces c ompared to their near relatives. In Saimiri the narrow spacing of the orbits is further exacerbated by intense predation pressure on infants that may select for precocial neonates. The result is a large-headed neonate that is subject to unusual parturition constraints. These part urition constraints apply to the size and dolichocephalic shape of the squirrel monkey head in general, and to the relatively large eyes and approximated orbits in particular. The unique interorbital condition in Saimiri is an example of the effects of life history on skeletal mo rphology. (C) 1995 Wiley-Liss, Inc.