Osteichthyes The Bony Fishes

The bony fishes are divided into two clades, the Actinopterygii and Sarcopterygii, both of which appeared in the latest Silurian, and radiated through the Devonian. These are distinguished readily by their fins (Figure 3.18) —actinopterygians have 'ray fins'that are supported by a series of narrow cartilaginous or bony rods called radials, whereas sarcopterygians have fleshy 'lobe fins' supported by a single basal bone and with muscles that can modify the posture of the fin. These distinctions were not clear among the first oste-ichthyans, and a new fossil fish from China sheds some light on the phylogeny of the group (see Box 3.5).

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