ACTINOPTERYGII- infraclasses Chondrostei, Holostei and Teleostei

RHIPIDISTIA

The rhipidistians are a mixed group of lobe-finned fishes that form outgroups ('ancestors') to the two main living groups, the Actinistia and the Dipnoi. Rhipistians also include ancestors of the tetrapods. These fish groups - such as the porolepiform Holoptychius and the osteolepiform Eusthenopteron, were restricted in time mainly to the Devonian, with a few survivors into the Carboniferous.

The tristichopterid 'rhipidistian' Eusthenopteron

Rhipidistian characters that ally them with tetrapods are seen in the arrangement of the bones in the skull and in their lobe fins - many details of the skeleton of the pectoral and pelvic fins match fairly closely the bones in the forelimb and hindlimb of tetrapods.

ACTINISTIA

The coelacanths arose in the Devonian. They are characterized by their three-lobed tail: the tail is symmetrical, with a curved upper and lower section, and a longer, projecting, rather lobed middle portion. Famously, the coelacanths were thought to have gone extinct in the Cretaceous, when the laast fossils are found. But then in 1938, a living (or recently dead) specimen of a 2-metre-long coelacanth was fished up in the Indian Ocean, off East Africa. Since 1938, as many as 200 specimens of the living coelacanth, Latimeria, have been found, some of them now off Indonesia.

A specimen of the living coelacanth Latimeria

DIPNOI

A fossil and a living lungfish

The lungfishes also arose in the Devonian, when forms such as Dipterus were important predators. Since the Devonian, lungfishes evolved specialized tooth plates, and other characters, so they had most of their modern features by the Permian. Today there are three species of lungfishes, living in Australia, souther Africa, and South America. Lungfishes do indeed have lungs, as do all the other sacropterygians. Indeed, lungs were probably present in most basal osteichthyans, and they have simply been lost subsequently in the actinopterygians.


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