Jaws evolved from repeating pharyngeal segments first present in chordate ancestors as respiratory structures.
Jawed vertebrates arose from non-jawed vertebrates that had a pharyngeal gill apparatus composed of gill bars and slits.
Anterior gill bars evolved into the jaw, which supports structures in vertebrates.
Then later giving rise to cartilaginous branchial baskets of jawless fishes and the bones and cartilages of the facial, upper and lower jaw, jaw support, and posterior gill or throat structures (viscero.
Tooth-like structures found on the gill arches of a primitive jawless vertebrate, suggest that teeth evolved prior to jaws and that the first jawed vertebrates were toothless.
These findings showed that teeth and jaws did not evolve together, contradicting earlier theories.
Jaws helped the vertebrates to diversify into the many kinds of fishes, amphibians, reptiles, birds and mammals, and to become one of the most successful animal groups, producing earth's largest animals (whales, elephants, dinosaurs), as well as humans.
Without this evolutionary leap, we would not be here.
Prehistoric armoured fishes called placoderms were the first fishes to have jaws.
They arose some time in the Silurian Period, about 440 million years ago, to become the most abundant and diverse fishes of their day.
The jaws and teeth of Homo sapiens have evolved, from the last common ancestor of chimpanzee and men to their current form.
Many factors such as the foods eaten and the processing of foods by fire and tools have effected this evolution course.
The 'inside-out' theory suggests that teeth originated from endoderm, with the formation of pharyngeal teeth in jawless vertebrates and moved anteriorly to the oral cavity with the evolution of jaws.
While that may be overkill for some types of soft food like ice cream or even bread, chewing, or lack thereof, may have actually contributed to the reasons human jaws became smaller and why we now have smaller numbers of teeth in those jaws.
"It's always been presumed that sometime in early Homo, we started using more advanced tools," Evans told Live Science.
"Tool use meant we didn't need as big teeth and jaws as earlier hominins.
This may then have increased evolutionary pressure to spend less energy developing teeth, making our teeth smaller."