Teleostomy

The teleostomes (Teleostomi) is a higher clade of gnathostomous vertebrates that includes the osteichthyans (the latter including the tetrapods) and the extinct acanthodian fishes, that is, all vertebrates with jaws except cartilaginous fish and placoderms.

This name is similar to that of teleosts (Teleostei), or bony fish, with which they should not be confused.

They have a single pair of gill openings covered by an operculum, characteristics that are lost in the more derived groups (tetrapods).

Origins

The origins of teleostomes are uncertain. They are traditionally assumed to be descendants of the acanthodians ("spiny sharks") of the Early Silurian period; However, more recent discoveries show that "spiny sharks" are actually a paraphyletic set leading to Chondrichthyes and placoderms such as Entelognathus are more closely related to true bony fishes. Even after acanthodians appeared at the end of the Permian, their ostiocthyan relatives flourished such that today they comprise 99% of living vertebrate species.

Physical characteristics

Teleostomes have two main adaptations that are related to aquatic respiration. The first teleostomes probably had some type of operculum. However, it was not a single piece of live fish. The development of a single respiratory opening appears to have been an important step. The second adaptation, teleostomes also evolved a primitive lung with the ability to use some atmospheric oxygen. This developed, in later species, into the lung and (later) the swim bladder, used to keep fish neutrally buoyant.

The acanthodia share with Actinopterygii the characteristic of three otoliths: the sagitta in the sacrum, the asterisk in the lagena and the lapillus in the utricle. In dipnoans there are only two otoliths and in latimeria there is only one.

However, most of the above synapomorphies can be found in various groups of cartilaginous fishes.

Phylogeny

According to molecular analyzes the phylogenetic relationships between the current groups are: