Heart structure and the phylogeny of the amphibia

Abstract

The amphibian heart is studied on a broad comparative basis in the major taxa of Amphibia, deriving primitive and advanced criteria from the heart of species in closely related classes, namely two lungfishes and one reptile. The results of these studies indicate that the heart has deviated more and more from the lungfish model (the primitive type), becoming progressively more reptilian-like (the advanced type). These changes do not appear to be radical in nature as indicated by the numerous similarities between distantly related forms or by the few differences between closely related ones. As a result, it is proposed that the heart in the Amphibia is a good tool for determining relationships among major taxa. In addition to these general phylogenetic conclusions, the more specific ones are discussed using the amphibian taxa to exemplify the various levels of change in the organ. To clarify and summarize these conclusions, the historical changes in each part of the heart are listed and shown in a series of phylogenetic trees. The changes are in the: (1) orientation of the heart's long axis, (2) orientation of the heart's chambers, (3) orientation of the heart's apertures, (4) posterior vena cava, (5) ducts of Cuvier, (6) anterior vena cavae, (7) common pulmonary vein, (8) shape of the ventricle, (9) ventricular trabeculae, (10) septation in the atria, (11) septation in the ventricle, (12) conus arteriosus, (13) spiral valve, (14) pylangial and synangial pocket valves, (15) truncus arteriosus, (16) common pulmonary vein in Anura, (17) sinus venosal partition in Anura, (18) ventricular basal angles in Anura, (19) conus arteriosus in Anura, (20) conus arteriosus in Urodela..