COMPARISON OF HYPOTHESES ON THE RELATIONSHIPS OF SARCOPTERYGIANS

Seven contrasting hypotheses of relationships of sarcopterygian groups are compared. The sister-group relationship of tetrapods to different fossil and Recent sarcopterygians is presented in the various hypotheses. Three possible sister-group relationships of tetrapods (to the Recent sarcopterygians, the Dipnoi, and Actinistia) are found among the seven hypotheses. The analyses presented here support all three possibilities to different degrees. Analysis of the complete data set drawn from studies that supported all seven hypotheses indicates that fossil taxa are more closely related to tetrapods than are Recent taxa. The Panderichthyida is the sister group of tetrapods, and both groups, together with Osteolepiformes, form the Choanata (the only osteichthyans with a true choana and one external nasal opening). The differences among the seven hypotheses are based on differences in selection of characters, as well as differences in hypotheses of homology. A test for congruence (synapomorphy) supports the initial homologizations. A careful analysis of each character for similarity and congruence is required before we may gain a higher level of reconciliation among the proposed hypotheses.