The Digestive System of Vertebrates

This section summarizes the adaptations of the digestive system to the habitat, diet and other physiological characteristics of vertebrates and speculates on how these may have evolved. Speculations on the digestive system of early vertebrates are based mostly on comparisons of their skeletal remains, habitat, and environment with those of present-day species. Although our discussion has been limited to vertebrates, they represent less than 5% of the species in the Animal Kingdom. As Barnes (1987) pointed out, a taxonomist less biased than Man might have divided these animals into arthropods (over 75% of the species) and non-arthropods. Separation of the Animal kingdom into vertebrates and invertebrates is based on one characteristic of a single subphylum, and many characteristics of the vertebrate digestive system are found among the invertebrates. Therefore, a brief discussion of the invertebrate digestive systems provides some necessary perspectives.