Pikaia, the earliest known chordate fossil
Amphioxus (sea lancet)
SUBPHYLUM VERTEBRATA
Class AGNATHA (Jawless fishes)
Lamprey, a modern cyclostome
ORIGIN OF JAWS
Jaws probably evoloved from gill arch supports.
Dunkleosteus, also known as Dinichthys, a large fish up to 15 meters (50 feet) long
Class CHONDRICHTHYES
Class OSTEICHTHYES
Anatomy of a bony fish.
Notice the swim bladder, a lung that has been transformed
into a hydrostatic organ capable of controlling buoyancy (and thus the depth at which the fish swims)
Latimeria, the only living member of the Crossopterygii
Class AMPHIBIA
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A moose (class Mammalia) showing a diagonal walking gait. | 
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