Sarcopterygii Characteristics
- Muscular lobed paired fins joined to body by single bone
- Two dorsal fins with separate bases
- Has a pulmonary vein
- Phylogenetically, this clade should also include tetrapods
- Formerly treated as a subclass of the Osteichthyes (bony fishes)
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Subclass Actinistia — Coelacanths
Characteristics
- Large size (~2m)
- Distinctive caudal fin with 3 divisions
- Fins muscular, limb-like ("lobed")
- Skeleton mostly cartilagenous
- Modern species are marine, in deep water
- 2 extant species (first one discovered in 1938)
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Comorese Coelacanth, Latimeria chalumnae
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Comorese Coelacanth, Latimeria chalumnae, preserved specimen
Los Angeles Museum of Natural History
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Axelrodichthys sp., an extinct coelacanth (Cretaceous Period)
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Subclass Dipnoi — Lungfishes
Characteristics
- Elongated bodies
- Dorsal, caudal, anal fins fused into single rear fin
- Fins flipper-like or reduced to long filaments
- Paired lungs
- Live in tropical rivers or swamps prone to drying
- 6 living species
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West African Lungfish, Protopterus annectens; Order Lepidosireniformes
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Marbled African Lungfish, Protopterus aethiopicus; Order Lepidosireniformes
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Stem Tetrapodamorpha & Tetrapod Origins
Characteristics
- The following image depicts the earliest tetrapods (Acanthostega and Ichthyostega) with some closely related lobe-finned fishes
- All date from the late Devonian Period
- Osteolepiform fishes (e.g. Hyneria & Eusthenopteron) share with tetrapods various skull characteristics, internal nostrils and labyrinthodont teeth (with folded enamel)
- They also have fins with distinct humerus, ulna, radius or femur, tibia, fibula
- All of these species probably lived in fresh water (only Ichthyostega was probably partially terrestrial)
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