Gastrointestinal Tract

Abstract

Prey digestion in marine mammals is as diverse as the different terrestrial lineages that gave rise to them. Pinnipeds, sea otters, and polar bears follow the typical carnivore building plan, with the exception of remarkably long small intestines. However, food passage rates are faster than for terrestrial carnivores. The cetacean digestive system reflects that of their foregut-fermenting terrestrial ancestors with a multichambered stomach. Bacterial fermentation in the forestomach breaks down chitin and wax esters. Herbivory in sirenians is unique among marine mammals, and their general building plan resembles that of terrestrial hindgut fermenters. Sirenians have exceptionally long small and large intestines that serve to break down plant material into smaller particles, while also increasing retention times. Contrary to other mammals, sirenians do not have absorptive cells in their small intestine, but instead absorb nutrients in the large intestine.