Everything about Gnathostomata totally explained
Gnathostomata is the group of
vertebrates with
jaws.
The group is traditionally a
superclass, including the familiar classes of
fish,
birds,
mammals,
reptiles, and
amphibians, and a sister group of the jawless vertebrates
Agnatha. However, recent genetic studies are causing a reassessment of Gnathostomata as a grouping.
New fossil founds suggests
thelodonts as the closest relatives of the Gnathostomata.
It is believed that the jaws evolved from anterior
gill support arches that had acquired a new role, being modified to pump water over the gills by opening and closing the mouth more effectively - the
buccal pump mechanism. The mouth could then grow bigger and wider, making it possible to capture larger prey. This close and open mechanism would with time become stronger and tougher, being transformed into real jaws.
Placoderms used sharp bony plates as teeth instead, and newer research indicates the jaws in placoderms evolved independently of the rest of the remaining gnathostomates.
Other distinguishing characteristics of living gnathostomates are the
myelin sheathes of
neurons, and an adaptive
immune system.
The Gnathostomata first appeared in the Ordovician period and became common in the Devonian period.
Taxonomy and phylogeny
Subphylum
Vertebrata
├─(unranked)
Gnathostomatomorpha
└─
Infraphylum Gnathostomata
├─Class
Placodermi -
extinct (armored gnathostomes)
└Microphylum
Eugnathostomata (true jawed vertebrates)
├─Class
Chondrichthyes (cartilaginous fish)
└─(unranked)
Teleostomi (Acanthodii & Osteichthyes)
├─Class
Acanthodii -
extinct ("spiny sharks")
├Superclass
Osteichthyes (bony fish)
│ ├─Class
Actinopterygii (ray-finned fish)
│ └─Class
Sarcopterygii (lobe-finned fish)
└Superclass
Tetrapoda
├─Class
Amphibia (
amphibians)
└(unranked)
Amniota (amniotic egg)
├─Class
Sauropsida (reptiles or sauropsids)
│ └─Class
Aves (birds)
└─Class
Synapsida
└─Class
Mammalia (mammals)
Note: lines show evolutionary relationships.
Further Information
Get more info on 'Gnathostomata'.
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