That question has always intrigued me, and I don't know the answer. But death in animals seems to be directly linked with the fall of mankind. The Genesis account (Gen 3 14-19) appears that God cursed the entire physical universe (serpent, cattle, beast of the field, even the ground). Which brings up these questions. How smart were animals in the beginning? Did they have anything to do with mans fall?
Another scripture that bothers me is Romans 8: 19-23. Bible repeadly speaks about "creation" eagerly waits for the revealing of the sons of God. Not just human., but all creation. Now you gotta ask, are animals somehow covered under a different "covenant" with God? In the beginning somehow did animals break away from God like humans did?
In Isaiah bible speaks about the Lion lying down with the Lamb. Is this literal or just symbolic?
Just some of my thoughts and ideas, afterall I'm just an evil, crazy, apostate sinner.