Abstract
An osteological study of two species of the family Trichonotidae reveals numerous differences with members of the family Creediidae. Distinguishing characters include the following: trichonotids possess a flat pelvis base (not bowl-shaped) with oblique lateral flanges, a rodlike ectopterygoid that lacks a fanlike base, a dentary shelf that is notched anteriorly, a welldeveloped postmaxillary process, six infraorbitals, pleural ribs that arise from larger epipleural ribs, a hypurapophysis, and a large predorsal bone. Available evidence supports the view that these two families are monophyletic taxa with a marked gap in morphological characters between them. However, similarities in such bones as the ectopterygoid and mesopterygoid suggests that these two families are relatively closely related.
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