Orthocephalization in the postweaning squirrel monkey.

Twenty male squirrel monkeys (Saimiri sciureus boliviensis) raised in captivity were allotted to one of the following groups: weanling control (C6) sampled at 6 months of age; young control (C24) fed ad libitum on a control diet and killed at 24 months of age; and malnourished (M24) fed ad libitum on a low-protein diet and sampled at 24 months of age. Cranial points and the lateral semicircular canals were marked. On each skull, a strict lateral teleradiograph was taken, and the lengths of the midsagittal chords and their angles with respect to the vestibular line were measured. Age changed the lengths in about 70% of the chords and more than 50% of the angles. Malnutrition arrested about 50% of the lengths, but the angles were practically not affected. It is concluded that the postweaning Saimiri sciureus undergoes orthocephalization according to a general pattern already observed in rodents and suggested for pongids. Postweaning malnutrition affected growth in size but not shape changes related to the orthocephalization of the Saimiri skull.