OSTEICHTHYES

Origins: 432 million years ago (middle Silurian, Wenlock epoch, Sheinwoodian stage)

Extinction: Still extant

Osteichthyans, or bony fish, are the most diverse group of vertebrates, and are characterized for having a skeleton primarily composed of bone tissue. It is divided in the actinopterygians, or ray-finned fish, and the sarcopterygians, or lobe-finned fish, that also includes the terrestrial tetrapods.

Bony fish are characterized by a relatively stable pattern of cranial bones, rooted, medial insertion of mandibular muscle in the lower jaw. The labyrinth in the inner ear contains large otoliths. They don't have fin spines, instead supporting the fins with lepidotrichia (bone fin rays). Bony fish scales basally originate from a base of bone, with teleost scales only having one layer of bone.

Traditionally, Osteichthyes were classified as a class, recognised on the presence of a swim bladder, only three pairs of gill arches hidden behind a bony operculum, and a predominantly bony skeleton. It would traditionally exclude the tetrapods, so to make it monophyletic, tetrapods would have to be included in the Osteichthyes, making it synonymous with the Euteleostomi clade. Therefore Osteichthyes takes the role of superclass, and englobes two major clades: the Actinopterygii and the Sarcopterygii.

The phylogeny of bony fish is rather complex, understandably due to the sheer number of species that we know from this group, with coelacanths being shown as closer to tetrapods and lungfish, forming the Sarcopterygii, and the Actinopterygii forming the ray-finned fish.

Bony fish basally possessed gills, which are present in most forms of bony fish, and even in many amphibians, but not in amniotes, which rely fully on pulmonar respiration.

Bony fish range wildly in size, with the smallest ones being under a centimeter in length, while the largest can achieve lengths of tens of meters, and weigh nearly 200 tonnes.

Despite being fish, bony fish gather several differences from the cartilaginous fish, one of the most notable being, of course, the possession of a bony endoskeleton, but also the presence of a swim bladder and lungs (some bony fish later lost these features, however).

main source: Wikipedia

PHYLOGENY

Vertebrata

- Chondrichthyes

- Osteichthyes

- Actinopterygii

- Ptycholepis bollensis

- Saurorhynchus brevirostris

- Actinopteri

- Strongylosteus hindenburgi

- Dapediidae

- Dapedium pholidotum