Experiments of nature: Premature unicoronal cranial synostosis in mantled howler monkeys (Alouatta palliata)

In 1960 Adolph Schultz described several cases of plagiocephaly in a collection of mantled howler monkeys (Aloutta palliata) from the forests of Central America. Since then several more specimens have been described. These individuals make up one of the largest samples of nonhuman primates that are affected by craniosynostosis. In this study, we used finite element scaling analysis (FESA) to quantify morphologic differences between adult normal (N = 19) and plagiocephalic female howler monkeys (N = 4). FESA utilizes three dimensional coordinate data to provide detailed information on size and shape differences local to biologic landmarks. The relatively large number of plagiocephalic howler monkeys provides a natural means for examining hypotheses concerning patterns of dysmorphology associated with plagiocephaly. Comparison of our results to observations from the clinical literature reveals similarities in neurocranial and facial morphology among plagiocephalic humans and howler monkeys, but the direction and magnitude of local form differences between howler monkeys and humans indicate species- specific responses to sutural constraint. Few cases of craniosynostosis in nonhuman primates are known. The number of plagiocephalic howler monkeys suggests these monkeys may be particularly susceptible to some defect that leads to premature suture closure. If this is the case, then howler monkeys may be a good model to study the cause(s) of craniosynostosis.