I have referenced a few Russian lesson pages, but I have not come up with an answer for why the ending changes in this particular manner. Could somebody explain this to me? I had thought that the change was from “е” to “я”
Животное is a nominalised adjective. These retain their adjectival declension in Russian but are otherwise treated as nouns for all intents and purposes. So for example there's столовая the adjective, meaning "table" (as in "table spoon"), and there's столовая the noun, meaning "canteen".
However, it's worth noting that животное and other taxonomical terms were (I think) 18th-century scholarly coinages calqued (with some liberties) from Latin and given a Church Slavonic-esque sound:
— and with the exception of the latter, they were these nominalised adjectives right from the start, and hadn't really had a prior history as adjectives.
Where животный does get used as an adjective in modern Russian (as in животная притягательность "animal magnetism"), it's actually a back-transition into an adjective meaning "of or pertaining to animals", from the noun "animal", from a theoretical Church Slavonic adjective meaning "endowed with life".