While I was previously content with the pegasus tag being aliased to pterippus, reversing this decision seems to go against what e621's tagging rules would suggest.
While the mythical horse's name is used to refer to pterippi as a whole these days, this modern usage does not erase the historically recorded name for the species nor the fact that using pegasus to refer to pterippi is only colloquial in nature.
This informal and casual use of pegasus as a species name is in complete opposition to the usually very accurate method of species tagging that I see on this site, and it stands to reason that if one were to go out of their way to make tagging as accurate as possible for existing species then we should do the same with mythological species, at least as much as research will allow.
Furthermore, the use of pterippus as the official tag is an opportunity to educate those who do not know of the term, once again this would be in line with what e621 is supposed to stand for - to familiarise people with terms and species they may not be familiar with and by using a casual and informal term e621 is going against that, seemingly just for simplicity's sake. These obscure terms should not have to be, pardon my language, dumbed down just because modern usage has clouded them.
I know the debate between these terms is a touchy one, but I'd expect e621 to prioritise accuracy here like it does in the rest of its tagging program.
Updated by Millcore