Standard 2D animation solutions?

Hi guys! First time poster, but long time lurker. My question is about what standard solutions are used for animation in the world of 2d Java game programming.

The obvious first answer (I assume…?) is frame-based animation via sprite sheets. I’m sure you guys know all about this without me having to say much more - flip through the different images to create the animation: run1.png, run2.png, etc.

Now I don’t think this solution is appropriate for my project, unfortunately. My friend (artist) and I (programmer) are creating a 2D game with hopefully more complex images and animations. The images are sized in the range of 500 to 1000ish pixels in each dimension. We want this to provide high resolution graphics and the ability to do things like zoom in & out. In addition, our animations have like 60-80 frames in them sometimes. Loading each image separately is taking way too long (like 15+ seconds for what will probably be like 1/1000 of all the images in the game). We’ve tried making spritesheets, but this seems pointless since we sometimes can only fit a few images in each dimension with a maximum texture size of only a couple thousand pixels in each dimension.

So I was thinking there must be more scalable, standardized solutions that games with a bit higher graphics must be using? I mean the spritesheets I assumed worked great for games like Super Mario Brothers, but are games these days only still using that? If it helps, my artist uses After Effects to create the animations. Another important consideration is ease of implementing with a Java game engine. We started with Slick, but are currently trying to migrate over to LibGDX because it seems a little bit more full-blown and powerful. But I’m willing to try out whatever you guys think would suit us best.

Thanks in advance.