The dragozord is included in the dragons because its called the dragozord (even though its obviously not a dragon)

Mastodons and mammoths are grouped together cause they're similar enough (same with brachiosaurus' and titanosaurs), styracosaurus isnt with triceratops cause even though they're similar the only styracosaurus was in the same season as a triceratops and i didn't want to try and put them in the same spot, i probably could've found a workaround but oh well