Belonochasma (meaning "needle mouth") is a genus of
gnathostome from the Mesozoic of Franconia , Bavaria , Germany . It was once
Kaynak: BelonochasmaThe group excludes all vertebrates with jaws, known as
gnathostome s. belong to the stem group of
gnathostomes Recent molecular data, both
Kaynak: AgnathaMyelin is considered a defining characteristic of the (
gnathostome) vertebrates , but myelin-like sheaths have also arisen by parallel
Kaynak: MyelinAgnatha comes from the Greek , and means "no jaws It excludes all vertebrates with jaws, known as
gnathostome s. Although a minor element
Kaynak: Evolution of fishIn
gnathostome fish, the first arch develops into the jaws, the second into the hyomandibular complex, with the posterior arches
Kaynak: Branchial archare more closely related to vertebrates with jaws (called
gnathostome s) than to cyclostomes Cyclostomes seem to have split off before the
Kaynak: Cyclostomatanothing is known of the rest of the body, save that it had a pair of well-developed pectoral fins, similar to osteostracans and
gnathostome fish.
Kaynak: PituriaspisInternal scales have also been recovered, some fused into plates resembling
gnathostome tooth-whorls to such a degree that some
Kaynak: Thelodonti