Subclass SARCOPTERYGII
The Sarcopterygii includes the Crossopterygii (coelacanths
plus four other groups of primitive fishes known only from
fossils) and the lungfishes (Dipnoi). The lungfishes (3
families occurring in freshwaters of South America, tropical
Africa and Australia, plus several fossil forms) are thought
to be the nearest relatives of the amphibians (Rosen et al.,
1981), or the sister-group of the crossopterygian ancestor of
the amphibians (Wiley, 1979), or even a branch from the
chondrichthyan stem (Jarvik, 1980).
Superorder CROSSOPTERYGII
Bony fishes with two dorsal fins, lobelike paired fins, 2
external nostrils and skull with an intracranial joint between
the anterior and posterior parts of the cranium, allowing the
front part to be elevated during feeding. Numerous genera
and species are represented in the fossil record from the
Lower Devonian (400 million years ago) to the end of the
Cretaceous (70-80 million years) ago, when they were
thought to have become extinct along with the dinosaurs
and many other fossil groups. One group, the coelacanths
(Actinistia) has evidently survived the Cretaceous Period to
leave a living relic of this ancient group.
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