Thank you for the suggestion!
Although I’m not really sure if Tumblr offers the option to separate posts by content type (someone tell me if you know how!), what I can do is tag posts to help you sort it all out.
For my future posts:
Photos will be tagged “photo”
Animated GIFs will be tagged “GIF”
Videos will be tagged “video”
You’ll be able to sort them like you can the current content tags. Hope that helps!
I’ve gone back and added tags to a few older posts (and will likely do more in the future), but don’t expect this to be retroactive for all my posts (as I don’t have quite that much time to devote to this Tumblr).