Sarcopterygii

Australian lungfish ( Neoceratodus forsteri )

The flesh -finned fishes ( Sarcopterygii ), including muscle -finned fishes, are one of the two classes of bony fishes ( Osteichthyes ). The scientific name of this taxon is derived from a common feature of his representative, the Sarcopterygium (Size: sarx, sarcoplasmic = Meat, pterygion, diminutive of pteryx = wing, fin), a fin-type with a fleshy stalk.

The flesh -finned fishes have their meaning primarily from the fact that under their fossil representatives of the ancestors of land vertebrates ( Tetrapoda ) can be found. Today, there are two groups, the lungfish ( Dipnoi ), with six species and the coelacanth ( Coelacanthimorpha ) with two species. In terms of cladistics but also the land vertebrates ( Tetrapoda ) belong here.

The heyday of the flesh -finned fishes, apart from the terrestrial vertebrates from already long over. Fossil leave the Sarcopterygii since the Upper Silurian 415 million years ago to prove. In Devon the originally marine meat -finned, were distributed across and populated several times independently freshwater. The Onychodontiformes that Porolepiformes (of which, however, are likely to stem from the Dipnoi ) and the Elpistostegalia died out at the end of the Devonian, the Rhizodontiformes at the end of the Carboniferous and the Osteolepiformes at the end of the Permian.

Features

Named giving characteristics of the meat is the fleshy -finned Flossenlobus the paired fins, which, however, also occurs with a completely different internal anatomy in the Flösselhechten and some fossil Strahlenflossern ( Actinopterygii ). As a common feature of the class applies to the construction of the fin skeleton that has a single, to the body running, monobasale, bony axis, which is connected to the shoulder and the pelvic girdle and are located on the side radials. This bone corresponds to the upper arm bone (humerus ) and thigh bone ( femur) at the land vertebrates to them is therefore homologous. The coelacanth fins this construction also applies to the second dorsal fin and the anal fin.

The skeleton of fossil forms was more ossified than that of today. Many even had vertebral body. The high proportion of cartilage in the skeleton of extant species is thus very probably secondary.

Also new is the caudal vena cava, the inferior vena cava, into which flows the blood of the body back toward the heart. The original cardinal veins are reduced.

Meat -finned fishes have Kosmoidschuppen. The Cosmi layer is made of enamel and dentin, and was traversed in fossil forms of pore channels. The single- melt showed also only in fossil forms, on its underside hexagonal imprints of epidermal cells.

The skull of the meat -finned corresponds to the original land vertebrates. An exception is that of the lungfish ( Dipnoi ), whose anatomy is so different that you can hardly homologized the individual bones of lungfish skull with the individual bones of other Sarcopterygierschädel. To the eye of the flesh -finned fishes have a bone ring from at least five individual bones.

Apart from the lungfish and land vertebrates have always been all meat -finned a two-part skull: a front part was towards the rear liftable front, so that better could be nabbed for prey with its mouth. The joint was behind the pituitary gland approximately at the level of the trigeminal exit across the head. The brain was usually too small to be affected. A separate pair of muscle (M. basicranialis ) was responsible for the reduction, the return to the initial position, when biting. The elevation of the front part was done indirectly through the mouth - opening, the jockstraps oppressed by her palate upwards. The Strahlenflossern like " elegant " by upward rotation (front ) of the whole skull is reached - the meat -finned avoided but by the skull - decomposition, so to speak, the " Schwindeligwerden " because the mazes of the vestibular system are located in the posterior cranial section. For active swimmers a decomposed skull (as a "bug" ), however useless, just for fish with Quetschgebiss ( lungfish ) and for land animals.

However, the ( fossilized ) joint made great interpretation difficulties. It was considered first for an artifact that is broken at a weak point, or then for a mismatch. Two years before the discovery of Latimeria stood in 1936 but by Hermann Aldinger found that these sarcopterygians had a two-part by a large articulated skull. The extent of this movement may have been different. Erik Jarvik took the view that this Cranialgelenk possession of no mobility after he reconstructed those Basicranialmuskeln at the Rhipidistier Eusthenopteron. This reconstruction is recognized, during his assumption about the lack of mobility is not shared.

System

The internal classification of meat -finned fishes is not without controversy. Genetic studies, as well as the existence of a lymphatic system in both taxa indicate that the lungfish land vertebrates are closer than the coelacanth. The fossil, leading to the terrestrial vertebrates forms are referred to as Rhipidistia.

The following cladogram shows the probable relationships (after Yu Xiaobo et al (2010) and Brian Swartz (2010). ) ( Recent taxa in bold):

Elpistostegalia → terrestrial vertebrates ( Tetrapoda )

Platycephalichthys

Tinirau

Tristichopteridae

Megalichthyidae

Medoevia

Osteolepis

Gyroptychius

Gogonasus

Canowindridae

Rhizodontidae