The Mesozoic labyrinthodonts were mostly aquatic with increasingly cartilaginous skeleton.
Most bony fishes - the sharks have cartilaginous skeletons - produce millions of eggs.
Their cartilaginous skeletons do not preserve well as they lack the calcification of the bony fish.
The Agnatha are ectothermic or cold blooded, with a cartilaginous skeleton, and the heart contains 2 chambers.
The ragfish body is scaleless and limp, both because of the cartilaginous skeleton, as well as its flabby muscles.
Other distinguishing characteristics include a cartilaginous, less ossified skeleton and a shorter skull.
It is revealed that instead of bones they have a cartilaginous skeleton, like a shark.
The Agnatha are exothermic, with a cartilaginous skeleton, and the heart contains 2 chambers.
The Agnatha are cold-blooded, with a cartilaginous skeleton, and the heart contains two chambers.
Sharks (superorder Selachimorpha) are a type of fish with a full cartilaginous skeleton and a highly streamlined body.
