Sarcopterygii is a subclass of bony fishes. The axial skeleton is in the form of a chord. The jaw arch is attached to the skull (amphistylia) or merged with it - in bipedal fish (autostylia). Scales cosmoidal. There are internal nostrils - choanae. Paired fins biserial type. Caudal fin diphycercal. The heart retains an arternal cone, the intestine has a spiral valve, and there is a cloaca. The subclass has two infraclasses (superorder): the keysteppers - Crossopterygii and the dipterans - Dipnoi.
Most Sarcopterygii (including the most primitive representatives of the class) had well-developed fleshy lobes in the paired fins, characterized by a dismembered internal skeleton and the presence of complex musculature (hence the names "lapastepterygii", "fleshy-lobed"). In modern bipedal limbs have acquired lanceolate or flagellate form. In ancient Sarcopterygii the body was covered with thick rhombic cosmoidal scales, and the cavities between the teeth of the cosmoidal layer and the pores that opened outward, cavities contained, apparently, electroreceptors. In the course of evolution there was a reduction of the cosmine layer, which completely disappeared in modern representatives of Sarcopterygii. Ancient shovelnosefishes (unlike most rayfishes) had two dorsal fins (this feature is also characteristic of modern latimeria). Elpistostegalia have lost their dorsal fins. The caudal fin of Sarcopterygii was initially heterocercal, later becoming dificercal.
Musculoskeletal apparatus: the movement of double-breathers is made with the help of lateral bends of the body. They can use their fins to crawl along the bottom and crawl to another body of water.
Respiration: gills and lungs. Mechanism of ventilation: oropharyngeal and by means of gill covers. In most Sarcopterygii (except for coelacanths) paired external nostrils were connected by nasal passages with choanas (internal nostrils). Paleontologists believe that the original purpose of the choanas was the forced washing of the olfactory epithelium with a through stream. Bivalves breathe gills or lungs - modified swim bladder, connected to the esophagus. There are the base of the paired fins - fleshy, which allows the fins to rest on the ground.
Circulatory system: since there are lungs, there is a second (pulmonary, small) circle of blood circulation.
Digestion: a variety of ways of eating.
There are 3 orifices: genital, anal, excretory.
Reproduction: internal fertilization, a small number of eggs may develop in the mother's body.
Nervous system: forebrain is well developed, choans (internal nostrils) appear.