It is from God's self-disclosure in Scripture alone that we gain the understanding of His salvific purposes and plan which His natural revelation, the created universe, cannot give. In the Bible the living God of unfathomably rich redeeming love and perfect righteousness makes known that only through Jesus the Son of God is there a way of salvation from God's just wrath, and why that wrath is due to us all in the first place.
Although the science of theology must never impute its formulae into Scripture, our Scripturally accurate understanding of God MUST inform our hypotheses and theories as we investigate God's universe; this great theatre of His glory. Hence the saying "theology is the queen of sciences." Like all human pursuits, scientific ones must be done righteously.
When it comes to the branch of science known as *cosmogony, are we doing justice to the Bible and a Biblical understanding of God's being and nature if we believe that death for animals existed even before the Fall of Man into sin?
The Bible says it was that tragic Fall, the most surpassingly tragic event in history (real history, not the evolutionary re-write) which brought death into God's once perfect world (Romans 5:12). Can we reasonably limit that to human death?
How so, considering that God sent every kind of animal to Noah for the deliverance from extinction by the Great Flood?
How so, if we are mindful of the divine Lawgiver Who ordained a sabbath rest for man and beast (Exodus 20:10,11)?
How so, remembering that the God of all mercies expressed to the prophet Jonah His concern for even the cattle of the city of Nineveh (Jonah 4:11)?
How so, if the Creator Who says of His image-bearer that righteousness involves tender concern for the lives of animals (cf. Proverbs 12:10)?
How so, if the prophet Isaiah (chapter 11) foresaw peaceful co-existence where the predator and prey relationship exists now?
Yes, at 1 Corinthians 9:9 we read "For it is written in the law of Moses, 'You shall not muzzle an ox while it treads out the grain; is it oxen God is concerned about?"
However, the rhetorical question does not deny God's concern for an ox, it makes an application to laborers who are more important than oxen. "The LORD is good to all, and His tender mercies are over all His works." — Psalm 145:9
No kind of death, decay, corruption, or futility inhered anywhere in God's very good creation (Genesis 1:31) at the beginning. Christ's apostle summarizes why those things exist now, as well as the hope which the Bible believer has regarding their ultimate and eternal demise:
"For the creation was subjected to futility, not willingly, but because of Him who subjected it in hope; because the creation itself also will be delivered from the bondage of corruption into the glorious liberty of the children of God. For we know that the whole creation groans and labors with birth pangs together until now." (Romans 8:20-22)
Perhaps you're remembering Nathan's parable to guilty David about the cruel rich man who killed a poor man's pet lamb for food (2 Samuel 12:1ff). And you ask "What of my pet animal?"
Martin Luther apparently believed that his dog would be resurrected! But though venerable, dear Martin is not infallible. So let us not go beyond what is written in the infallible Scriptures, and be satisfied knowing that there will be no sorrow or disappointment whatsoever in the heavenly life to to come.
*cosmoGONY is concerned specifically with the origin of the cosmos - the universe. CosmoLOGY is a more broadly concerned with its nature and structure.