teleost

phylogeny

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Phylogeny of fishes (diagram credit: evolution.berkeley.edu).

Phylogeny is the representation of evolutionary relationships, often displayed as a “tree” (i.e., branching diagram) where the most closely related organisms are connected by a node and more distantly related organisms have multiple steps back in the tree before they are connected.  Nodes are often characterized by biogeographic events and evolutionary innovations.

In fishes, jawless fishes (such as hagfish and lampreys) are the most primitive, cartilaginous, and without paired fins; sharks and rays are cartilaginous with jaws and placoid denticles; and bony fish are the most diverse and derived fishes, with scales (see cycloid and ctenoid), swim bladders, and bony skeletons.

 

 

Osteichthyes

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The Ocean Sunfish is considered to be the largest member of Osteichthyes, reaching over 2,200 lbs.

The Ocean Sunfish is considered to be the largest member of Osteichthyes, reaching over 2,200 lbs.

Osteichthyes are a taxonomic grouping of bony fishes.  This group includes ray-finned fishes (class: Actinopterygii) and lobe-finned fishes (class: Sarcopterygii).  This highly diverse group of fishes, which contains almost all fish species, is the most diverse group of vertebrates today.  Osteichthyes differ from chondrichthyes by (in most cases) possessing a bony skeleton, a swim bladder, scales (ctenoid, cycloid, or ganoid scales), and external fertilization.

Teleost

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A Slingjaw Wrasse is an extreme example of a teleost's protrusible jaw

A Slingjaw Wrasse is an extreme example of a teleost’s protrusible jaw.

Teleosts are the most diverse group of fishes (over 26,500 extant species).  Over half of all living vertebrate species are teleosts.  Teleosts are characterized by a protrusible jaw (musculature gives them the ability to move their maxilla and premaxilla) and a symmetrical tail (their spine that ends at the caudal peduncle unlike, for example, sharks).  Teleosts are estimated to have evolved during the Triassic period. By the end of the Cretaceous, the fossil record shows that teleosts dominated both freshwater and marine habitats.