00:01
Jaws first evolved in an ancient group of fish approximately 460 million years ago.
00:23
Fossil evidence shows that the early fish that were jawless had these flexible cartilaginous bars supporting their gills.
00:31
And the understanding between many different groups that have different theories over why this occurred, the understanding is that one of these flexible cartilaginous gill supports, likely moved forward to become a primitive jaw.
00:52
Now, one camp on why this occurred is called the neoclassical theory.
00:57
And basically, this comes from comparing the morphology in embryos and adult fishes, comparative and functional morphology of those jaw parts.
01:09
And this hypothesis explains that the jaw first evolved for better improved ventilation and then eventually became used for new methods of grasping prey.
01:20
So the emphasis is on this jaw structure first primarily being for ventilation.
01:27
The heterotropic hypothesis is not as conservative.
01:31
It basically states based on developmental study in lampraes and amniocanathostomes like chicken and mouse models.
01:40
The upper jaw, according to this theory, is basically an evolutionary nymphostom.
01:45
Novelty...