On the evolution and homologies of ichthyopterygian forefins

摘要: ABSTRACT The evolution of forefins within the Ichthyopterygia is re-evaluated based on largest set data available up to present, including recently reported Early Triassic forms. Three humeral morphotypes are recognized; one plesiomorphic, and other two characterize major clades. forefin elements various ichthyopterygians identified, osteogenetic sequences topological arrangements. Both lines evidence, ontogenetic morphological, support a single conclusion that Stenopterygius, all belonging clade survived into Jurassic, lack digit I forelimb. Digits II probably absent in Shastasaurus closely related topology along primary axis digital arch conservative among examined, as expected from underlying mechanism limb development.