I'll comment on both pairings.
brekclub85 said:
ChomperxRuby
I actually think that would be more of a brother/sister relationship. Ruby is the big sister, protecting Chomper, and Chomper is the little sweet brother that doesn't get on Ruby's nerves that much.
F-14 ace said:
Littlefoot's momXTopsy
I honestly think that Little Foot's mom would be submissive. And Topsy would treat her bad because she's a longneck. If Topsy though tried to hurt Little Foot, Momma Longneck would give Topsy the beating of his life.

PteranoXSierra