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The Sarcopterygii are one of two subclasses of bony fish (Osteichthyes), the other being the Actinopterygii. The name Sarcopterygii means 'lobe-fins' and reflects their main feature that distinguishes them from the Actinopterygii or the 'ray-fins'. The fins of sarcopterygians are thick and fleshy, are supported by a single bone and have muscles that modify the posture of the fin. The actinopterygians, on the other hand, have fins that are supported by many, narrow bony rods called radials. The bones in sarcopterygian fins can be matched directly to bones in the tetrapod limb. Therefore it seems clear that the tetrapods are derived sarcopterygians.
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Early sarcopterygians could also be distinguished from early actinopterygians by their massive jaw muscles and special skull characteristics. They have been further described as having very similar body shapes and sizes (20-70 cm), two dorsal fins, an epichordal (upper) lobe on the heterocercal (asymmetrical) caudal fin and paired fins that were fleshy, scaled, and had a bony central axis. Their body was also covered with a layer of cosmine, a dentinelike material that might have been periodically reabsorbed and reprocessed. These features are retained in some modern forms as well as the unique materials in their teeth like enameloid which is related to enamel.
The different groups
of both extinct and living sarcopterygians all have distinguishing
morphological features that are described further on their representing
sites.
Author: Snorri Sigurdsson (Email: ss4460@bristol.ac.uk)
Last updated: 14 November 2004
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