Wow didn't know we could upload gif.
TL;DR: the most recent revision of the PNG spec supports animated PNGs, called apng.
I read this comment years ago, and thought "huh." Fast forward to now, when I am writing my manga viewer that uses the MangaDex API. Mangadex does not serve GIFs, only PNGs (pronounced 'ping' according to the docs btw) and JPEGs. Being the stubborn idiot I was, I decided that i was going to write my own PNG decoding library in c++, instead of using the already existing library in c (libpng). In the process of developing the PNG decoder, I read the PNG specification many times over, which has lead to a lot of niche knowledge. APNGs are actually just normal PNGs, but they have extra data, and if the decoder supports it, can be used to display multiple frames in succession. For more details see
https://www.w3.org/TR/png-3