Connection between dragons & demons

Hey all, it feels like I haven't posted a thread asking for advice in ages. I've run into a worldbuilding problem while integrating what used to be two different constructed worlds into one. Basically, there used to be dragons in the world but they went extinct a few hundred years before the present day. Among human populations of the world there are demons--people born with draconic traits such as horns, a tail, and a greater capacity for magic.

I know dragons and the phenomenon of demons are connected, but I'm not sure how. At first I had the demons be the result of magical experiments to hybridize humans and dragons, but that felt a little cliche and didn't fit with the tone of the world. I'm at a loss and I'd appreciate it if a couple brains other than mine threw some ideas at this.

 

Thanks for the suggestions, guys! The world's magic system is based on souls, so I was thinking some kind of soul energy gets transferred from dragons to humans at some point in history. I'm just having trouble coming up with an event that would allow that to happen (some kind of cataclysm or giant shift in the world's magic, I guess). Souls are generally pretty hard to displace from their original owner, unless forced to merge with another soul by magic.