Ceteacean Gastrointestinal Tract

      Cetaceans such as killer whales and dolphins evolved from their terrestrial, herbivorous ancestors millions of years ago. Many ancestral features like limbs and hair that are required on land, were lost during their transition to the carnivorous aquatic mammals they are today. However, cetaceans do have a chambered stomach, which is likely a derivative of their ruminating ancestors, although having quite contrasting functions now. (Wang et al., 2016)

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      The gastrointestinal tract (GIT) of all cetaceans is quite similar, and we can compare the Atlantic whiteside dolphin (Lagenorhynchus acutus) (Fig. 1) to the GIT of killer whales. There are three chambers in the cetacean stomach: the forestomach, glandular fundic, and pyloric. Food initially enters the forestomach (Fig. 1-A), which is responsible for mechanical digestion and has muscular walls that can expand to fit prey that was swallowed whole. The digested food then passes into the glandular fundic (Fig. 1-B) where proteases and lipases begin chemical digestion. The last chamber food reaches is the pyloric (Fig. 1-C), which functions as a site of further chemical digestion. Finally, after passing through the pyloric sphincter, the unspecialized hindgut begins with the small intestine followed by the large intestine (Fig. 1-D). The small intestine and large intestines of cetaceans have similar functions of nutrient absorption and are relatively uniform in size throughout the GIT. (Wang et al., 2016; Battaglia et al., 2020)