choana

The genus is notable for the position of the secondary choana within its palate.

How it evolved is not known, but it has an internal connection with the choana.

As a distinguishing feature, Olivierosuchus also has a sharp ridge near the choana, an opening in the skull palate.

Through convergent evolution, lungfishes have evolved internal nostrils similar to the tetrapods' choana.

Eusthenopteron, like other tetrapodomorph fishes, had internal nostrils, (or a choana) which are found only in land animals and sarcopterygians.

It is possible that the choana started as a natural crack between maxilla and premaxilla because of an incomplete fusion in air-breathing animals.

They define the Eryopoidea as all Euskelia in which the choana are relatively rounded and the iliac blade vertical.

However, "Fruitachampsa" can be linked to shartegosuchids on the basis of similarities in the structure of the front of the palate and the choana.

Each sinus opens into the roof of the nasal cavity via apertures on the posterior wall of the sphenoethmoidal recess directly above the choana.

Some fossil species are said to have both conventional external nostrils and a choana, but only more fossils will give a real answer to how the choanas evolved.

In the palate region of the skull, the anterior process of the vomer ventrally overlies the premaxilla at the anterior margin of the choana.

Choanal atresia is a congenital disorder where the back of the nasal passage (choana) is blocked, usually by abnormal bony or soft tissue formed during fetal development.

Kenichthys has a primitive choana, an opening on the palate that connects the nasal cavity and mouth, which would become an important adaptation for terrestrial life in later tetrapodomorphs.

Both share similarities in skull shape, as well as a short and expanded dorsal branch of the ilium and a premaxilla-maxilla suture that is anterior to the choana.

Parts of the pterygoid bones make up the rostral margin of the choana and thus separate it from the palatines, a feature also seen in the more advanced neosuchian suborder Eusuchia.

Choanal atresia (say "KOH-uh-nul uh-TREE-zhuh") is blockage by bone or tissue of the nasal passages (choana) leading from the back of the nose to the throat.

The lateral surface of this plate forms part of the pterygoid fossa, the medial surface constitutes the lateral boundary of the choana or posterior aperture of the corresponding nasal cavity.

This characteristic was once thought to be characteristic of Eusuchia, but its presence in Brillanceausuchus suggests that the trait is homoplasic, thus making the evolution of the position of the choana within crocodilians more complex than previously thought.

Recent paleontologiclal findings support homology: a 400-million-year-old fossil lobe-finned fish called Kenichthys campbelli has something between a choana and the external nostrils seen on other fish, which makes it look like it has a cleft palate or cleft lip.