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SILURAN PERIOD

444-416 million years ago

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The early bony fish Psarolepis combines features associated with actinopterygians, sarcopterygians, acanthodians, and placoderms.

The fish Psarolepis is known from the Upper Siluran and Lower Devonian and is one of the earliest bony fish. It possesses traits associated with primitive sarcopterygians (its skull and lower jaw) and primitive actinopterygians (its teeth on the median rostral bone and 5 coronoid bones in the lower jaw). It also possessed a large pectoral spine in the front fin as in placoderms and acanthodians. A large spine on its back is similar to that of sharks and acanthodians. The broad size of bones in the pectoral girdle also resembles that of placoderms. Psarolepis possessed a cleithrum with a large process similar to that of placoderms. (Min, from Ahlberg, 2001). Psarolepis is either the most primitive known bony fish, predating the separation of the actinopterygian and sarcopterygian lineages or it is the most primitive sarcopterygian fish, dating from just after the split with actinopterygian lineages (Zhu, 1999).