title: Faecal particle size in free-ranging primates supports a 'rumination' strategy in the proboscis monkey (Nasalis larvatus).
abstract: In mammalian herbivores, faecal particle size indicates chewing efficiency. Proboscis monkeys (Nasalis larvatus) are foregut fermenters in which regurgitation and remastication (i.e. rumination) was observed in the wild, but not with the same consistency as found in ruminants and camelids. To test whether this species has exceptional chewing efficiency among primates, as ruminants have among mammals, we compared faecal particle size in free-ranging specimens with those of 12 other primate species. The discrete mean faecal particle size (dMEAN) increased with body mass (M) as dMEAN (mm) = 0.65 (95% confidence interval 0.49-0.87) M((0.33 (0.23-0.43)) in simple-stomached species. At 0.53 ± 0.09 mm, dMEAN of proboscis monkeys was particularly small for their average M (15 kg) and significantly smaller than values of two other foregut fermenting primate species. While we cannot exclude other reasons for the exceptional chewing efficiency in proboscis monkeys, this represents circumstantial evidence for regular use of rumination in this species. Thus, proboscis monkeys might be a model for convergent evolution towards rumination in a non-ungulate taxon.
authors.affiliation: Primate Research Institute, Kyoto University, Inuyama, Aichi, 484-8506, Japan, ikki.matsuda@gmail.com.
authors.forename: Ikki
authors.initials: I
authors.lastname: Matsuda
authors.forename: Augustine
authors.initials: A
authors.lastname: Tuuga
authors.forename: Chie
authors.initials: C
authors.lastname: Hashimoto
authors.forename: Henry
authors.initials: H
authors.lastname: Bernard
authors.forename: Juichi
authors.initials: J
authors.lastname: Yamagiwa
authors.forename: Julia
authors.initials: J
authors.lastname: Fritz
authors.forename: Keiko
authors.initials: K
authors.lastname: Tsubokawa
authors.forename: Masato
authors.initials: M
authors.lastname: Yayota
authors.forename: Tadahiro
authors.initials: T
authors.lastname: Murai
authors.forename: Yuji
authors.initials: Y
authors.lastname: Iwata
authors.forename: Marcus
authors.initials: M
authors.lastname: Clauss
mesh_terms: D000818:Animals; D016673:Colobinae / Q000502:physiology*; D004063:Digestion; D004064:Digestive System; D005243:Feces; D060434:Herbivory; D008409:Mastication