Carry On, Jeeves
Evolution is like a really good butler or valet, who's already standing there with a favorite beverage for you just at the moment you realize you're thirsty. Whether you are a vertebrate that goes by land or by sea, in getting your food it helps a lot to have jaws and teeth. The most primitive fishes lacked jaws, so how did they get them? A report in Nature documents the curious brain structure of a jawless fish that swam in Chinese and Vietnamese seas 435-370 million years ago.
As the research team found using an impressive high energy X-ray technique that allowed them to see into the cranial cavity without breaking up a precious fossil, galeaspids had a brain similar to a shark, rather than to that of modern jawless fish, hagfishes or lampreys. The cranial anatomy emerged in this evolutionary form before the jaw that would ultimately go with it. Had it not, the embryological development of the jaw would be impossible.
A co-author of the study, Philip Donoghue at the University of Bristol, explained to Science Daily: "In the embryology of living vertebrates, jaws develop from stem cells that migrate forwards from the hindbrain, and down between the developing nostrils. This does not and cannot happen in living jawless vertebrates because they have a single nasal organ that simply gets in the way."
Evolution again seems to have anticipated the needs of creatures that it has shaped long before those needs actually came into existence. How obliging of it to do so.