This is probably going to end up as a "Work In Progress" or even "Under Construction", but I think it's better to announce these ideas, finished or not.
(Fresh/Hatchling) Lizmon-0.8+ ft. tall/ 2 ft. long
(In-Training) Carnimon-2-3 ft. tall/ nearly 2 meters long (about 5.6 ft. long)
(Rookie) Dinamon-2.4 meters tall (8 ft.)/ 3.7-4 meters long (13.5-16 ft. long)
(Champion) Spinasaumon-7 meters tall (22.9 ft. tall)/ 13.1-13.7 meters long (43-45 ft. long)
(Ultimate) Ark Spinasaumon-15 meters tall (50 ft. tall)/ 26.5 meters long (up to 87 ft. long)
(Mega) Apex Spinasaumon-20-27 meters tall (65.6-88.5 ft. tall)/
Nearly/Over 40 meters long (124.6-154.1 ft. long)