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Ceboidea (New World monkeys; order Primates, suborder Simiiformes) A superfamily that comprises the families Callitrichidae and Cebidae. Isolated, probably since the Eocene, the ceboids show certain differences from the Old World monkeys. Their noses are flat, the nostrils facing laterally (platyrrhine) due to ceboids' possession of a larger nasal apparatus than Old World forms. Facial vibrissae are present but are usually small. The tympanic bone forms a ring fused with the petrosal and the bulla is large. The second premolar tooth is retained. Social organization is elaborate. Communication is mainly vocal, in some genera (e.g. Alouatta) incorporating distinct sounds each of which has a precise meaning. All species are fully arboreal, some possessing prehensile tails with ridged tail pads used as tactile sense organs and linked to a large area in the cerebral cortex, but the thumb is not fully opposable in any species.