The Light Bite: Red-Nosed Cuxiu (Chiropotes albinasus, Primates) Exploit Differential Penetrability of Hard Fruit Husks When Selecting Dental Puncture Sites

The Amazonian primate Chiropotes albinasus (red-nosed cuxiu) is a specialist on seeds of hard-husked unripe fruit. These are accessed with specialized processing behavior, involving highly modified canines and incisors. This is energetically demanding and carries a high dental damage risk. Hypothesizing that red-nosed cuxiu process foods in ways that minimize both energetic
expenditure and maximize dental safety, we predicted that individuals would selectively bite fruit husks at locations that were easiest to penetrate. Sutures were the easiest area to penetrate for all the 11 analyzed red-nosed cuxiu diet species with functioning (non-fused) sutures. Quantification of bite mark locations on these fruits showed significant clustering along the lower penetrability areas (sutures) in 8 of 11 species (72.7%). This pattern did not exist for another 10 species that lacked sutures; bites did not cluster on the thinnest (and most easily penetrated) parts of the husk for 9 of these 10 species (90%). For four species that were functionally indehiscent due to fused or thick sutures, penetrability was lowest at the face (2 species) and suture (2 species).
Thus, despite robust crania, mandibles, and dentition that appear highly suited for resisting forces generated by powerful biting action, red-nosed cuxiu deploy a more refined technique and often select the weakest areas of fruits for their seed-accessing bite sites, especially when the fruits are dehiscent with unfused sutures.