Holostei

Holostei Temporal range: Late Triassic–Recent PreЄ Є O S D C P T J K Pg N
Spotted gar, Lepisosteus oculatus
Bowfin, Amia calva
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Subclass:	Neopterygii
Infraclass:	Holostei
Orders
Amiiformes Lepisosteiformes †Pachycormiformes

Holostei are bony fish that retain basal characteristics inherited from an early time in their evolution. There are eight species divided among two orders, the Amiiformes represented by a single living species, the Bowfin (Amia calva), and the Lepisosteiformes, represented by seven living species in two genera, the gars. Further species are to be found in the fossil record and the group is often regarded as paraphyletic. Holosteians are closer to teleosts than are the chondrosteans, the other group intermediate between teleosts and cartilaginous fish. The spiracles are reduced to vestigial remnants and the bones are lightly ossified. The thick ganoid scales of the gars are more primitive than those of the bowfin.

Characteristics

Holostei share with other non-teleost ray-finned fish a mixture of characteristics of teleosts and sharks. In comparison with the other group of non-teleost ray-finned fish, the chondrosteans, the Holostei are closer to the teleosts and further from sharks: the pair of spiracles found in sharks and chondrosteans is reduced in holosteans to a remnant structure: in gars, the spiracles do not even open to the outside; the skeleton is lightly ossified: a thin layer of bone covers a mostly cartilaginous skeleton in the bowfins. In gars, the tail is still heterocercal but less so than in the chondrosteans. Bowfins have many-rayed dorsal fins and can breathe air like the bichirs.

The gars have thick ganoid scales typical of sturgeons whereas the bowfin has thin bony scales like the teleosts. The gars are therefore in this regard considered more primitive than the bowfin.

The name Holostei derives from the Greek, holos meaning whole and osteon meaning bone: a reference to their bony skeletons.

Phylogeny

File:Cipactlichthys scutatus holotype.png

Cipactlichthys scutatus holotype fossil, from the Lower Cretaceous Tlayua Formation of Mexico

The cladogram shows the relationship of the Holostei to other bony fish, the great majority of which are Teleosts, and to the terrestrial vertebrates (tetrapods) that evolved from a related group of fish. Approximate dates are from Near et al., 2012.

Osteichthyes	Actinopterygii 400 mya part of "Chondrostei" Polypteridae (bichirs) part of "Chondrostei" Acipenseriformes (sturgeons, paddlefish) Neopterygii 360 mya Holostei (bowfins, gars) 275 mya Teleostei 310 mya Sarcopterygii Actinistia (Coelacanths) Dipnoi (Lungfish) Tetrapods Amphibians Amniota Mammals Sauropsids (reptiles, birds)

External links

• Holostei on The University of Liverpool website