Not sure if it was technically a movie, or instead perhaps a short film one-off. I think it was something we rented from the local video store; time frame would be late 80s or very early 90s. It was animated -- I recall the style being not traditionally "cartoony" -- and about prehistoric humans in some way. Memory insists that the main characters were a couple of children, possibly a brother and sister. I don't remember much else, aside from the setting being "rocky", the mood being weirdly desolate (like these kids were probably all on their own), and the ending being kind of weird ("transformative" in some way?; possibly a depiction of death, but I'm not really sure).
It's possible this doesn't actually exist, or that my brain is smashing together multiple pieces of media I once saw, but if anyone has any leads, I'd love to know something!
