Nothing except that the theory of evolution has shown to be consistent everywhere it has been tested in the zoological realm.
We have nothing but supposition to assume a particular star is held to the rest of Milky Way by gravity, other than the fact that other stars tend to obey gravitational theory. Do you think we try to prove the Gravitational Law works for every new star that's discovered?
Evolution is known to be such a ubiqitious concept that it's not a stretch to assume it generally works, as is done with any well-established theory in science.
Just because you have an idea about how the teeth came to be, that does not mean your idea is a fact. There is very little known about this fish and its history, so you are way overstating your case. That is why adding the word "presumably" is a reasonable modification.