It was a question. A simple question. One not yet recognized for its importance as all great discoveries tend to start.
Before the Discourse Era, around the period of Unification and Equestria's founding, before the reign of the Royal Sisters and during the rule of Platinum's bloodline, ponies had limited exposure to many species of Terrae. Many factors contributed to this: The Three Tribes themselves were still working out their differences
and as a prey species ponies had an instinct in the herd to avoid straying far from the rest-- at best the interactions most known before Discord were with the Dragons, Griffons, Bison, and Saddle Arabians. All creatures that shared the same proximity with the Equestrians and so ultimately wasn't much of a stretch in terms of exposure, and more of a inevitable result of acquiring new land.
Say what you will but Discord's appearance in the world itself would mark not just a change for the world but an introduction to various species unknown that would start a future beginning for the Royal Sisters.
Star Swirl, a pony whose name appears randomly throughout multiple centuries, was the only pony to ask the one question no one wanted to ask years following Discord's defeat and it was a simple question: "Where were all the draconequui?"
There was no answer to this question. No one had wanted an answer. And there was no easy way to have it solved during that time.
And so, he set out to find one. And find one he did...a few centuries later.
An entry in the Chaosverse