gnathostomata

The Gnathostomata are a superorder of sea urchins, including the familiar sand dollars.

Placoderms were among the first jawed fish, the Gnathostomata.

New fossil finds suggests thelodonts as the closest relatives of the Gnathostomata.

The very first Gnathostomata (jawed fish]) appeared in the Upper Ordovician.

Infraphylum Gnathostomata (vertebrates with jaws)

Superclass Gnathostomata (jawed vertebrates)

They are more commonly known as the Branch Gnathostomata, and are described as having double nasal chambers, or nostrils, and jaws.

Vertebrates were subsequently divided into two major sister-groups; Agnatha and Gnathostomata (jawed vertebrates).

Placoderms used sharp bony plates as teeth instead, and newer research indicates the jaws in placoderms evolved independently of those in the other Gnathostomata.

Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates, the extant members of which all fall into Teleostomi.

Late Ordovician-aged microfossils of what have been identified as scales of either acanthodians or "shark-like fishes," may mark Gnathostomata's first appearance in the fossil record.

The Gnathostomata first appeared in the Ordovician period and became diverse in the Devonian period, the 'Age of Fishes'.

Instead of vertically articulating jaws like Gnathostomata (vertebrates with jaws), they have a pair of horizontally moving structures with tooth-like projections for pulling off food.

Phylogenetic research in 1998 and 1999 supported the idea that the hagfish and the lampreys form a natural group, the Cyclostomata, that is a sister group of the Gnathostomata.

Currently, characters of organogenesis are described for Vertebrata, Gnathostomata, Tetrapoda, Amniota, Sauropsida, Squamata, Mammalia, and Monotremata.

While there is no fossil evidence directly to support this theory, it makes sense in light of the numbers of pharyngeal arches that are visible in extant jawed (the Gnathostomata), which have seven arches, and primitive jawless vertebrates (the Agnatha), which have nine.

However, the validity of the taxon "Craniata" was recently examined by Delarbre et al. (2002) using mtDNA sequence data, concluding that Myxini is more closely related to Hyperoartia than to Gnathostomata - i.e., that modern jawless fishes form a clade called Cyclostomata.