The reptile heart as transitional stage : A brief review

Abstract

The anatomical and functional significance for evolution of a lepidosaurian - and archosaurian-type of heart are discussed. In the light of cladistics the acceptance of a lepidosaurian-type of heart, as such, as ancestral to an archosaurian type, is questioned. The interventricular septum, right atrioventricular valves and conducting system of the heart of crocodilians, birds and mammals are pointed out as areas where homologies are uncertain. The evolutionary development of the heart and aortic arches of reptiles, birds and mammals is summarised in a cladogram corresponding with one based on characters derived from fossils as well as data derived from soft anatomical characters.