Evolutionary patterns of Perissodactyla and Artiodactyla (Mammalia) with different types of digestion

Abstract

Described and discussed are the comparative and functional anatomy of the digestive tract in ungulates, as well as the retention of digesta in the total digestive tract and in its compartments. Additionally, the history of distribution of ungulates under special consideration of the connections between continents and the development of different biomes is discussed. The last 40 million years are considered. During the Caenozoic the forestomach-fermenting Artiodactyla were strongly radiating, which is in contrast to conditions in hindgut-fermenting Artiodactyla (Suidae) and Perissodactyla (Equidae, Rhinocerotidae, Tapiridae). The Pecora have been especially successful forestomach-fer-menters because they are able to reduce particle size of digesta through the process of rumination and thus increase digesta passage. This is advantageous because not only the metabolic products (mainly volatile fatty acids) of microbial activity are made available to the mammal, but also a higher percentage of those nutrients that can be autoenzymatically digested by the ungulate.