This study investigates the skeletal architecture of the anteroproximal surface of the anterior pectoral basals in squaliform sharks, which presents distinctions at the insertion of one of the components of the depressor pectoralis muscle. Some squalomorph and galeomorph sharks studied have a different orientation of the propterygium or anteroproximal portion of the composite pectoral basal, as these project dorsally to form a distinct anterolateral plan for the insertion of the depressor pectoralis muscle. An exclusive condition of the anterior articular surface was observed in Centrophoridae, Dalatiidae, Oxynotidae, and Somniosidae, which have a hook-like process on the flattened and widened surface of the anteroproximal margin of the single or composite anterior pectoral basal. This distinct pectoral fin skeletal condition may represent evidence of a closer relationship among these taxa, whereas a dorsally projected anteriormost pectoral basal may represent the generalized condition among sharks.
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Vol. 103 • No. 4