I've got my brain in a crunch. If death, disease, pain and suffering entered the world because of the first sin, then how would one best reconcile the deaths of all the Dinosaurs and other preceding animal throughout time up until the point that God first breathed life into Man and then Mankind committed the first sin? I've been comfortable pointing to the first sin as the reason for all the death and pain in the world, but I stumped myself with this question.
The standard way of reconciling this would be to say that human death entered the world when our first parents committed original sin.
In other words, God gave man access to the tree of life that would have enabled him to live forever. He didn't give access to it (so far as we know) to dinosaurs or, in fact, any other creatures besides mankind.
Thus when the fall occurs in Genesis 3, God drives Adam and Eve from the garden so that they won't have access to the tree of life and live forever. That suggests–though it does not prove–that the tree of life represented a special offer of immortality to mankind as long as they refrained from sin.
Why? Because it apparently didn't grow anywhere except in the garden. Otherwise, Adam and Eve could have simply eaten from a tree of life growing down the road somewhere, and there would be no point in expelling them.
This suggests that the tree of life was a unique offer to man as long as he remained in spiritual harmony with God, and when he sinned, the offer was lost.
Other species, presumably, never had the offer in the first place.
One note: The Church today would likely interpret the tree of life in a symbolic rather than literal fashion as that is what it does with the other tree–the tree of the knowledge of good and evil. According to the Catechism,
How to read the account of the fall
390 The account of the fall in Genesis 3 uses figurative language, but affirms a primeval event, a deed that took place at the beginning of the history of man. Revelation gives us the certainty of faith that the whole of human history is marked by the original fault freely committed by our first parents.
396 God created man in his image and established him in his friendship. A spiritual creature, man can live this friendship only in free submission to God. the prohibition against eating "of the tree of the knowledge of good and evil" spells this out: "for in the day that you eat of it, you shall die." The "tree of the knowledge of good and evil" symbolically evokes the insurmountable limits that man, being a creature, must freely recognize and respect with trust. Man is dependent on his Creator, and subject to the laws of creation and to the moral norms that govern the use of freedom.
One is still free to interpret the two trees literally, but the common teaching of the Church, as expressed in the Catechism, would seem to take them symbolically, the one representing the opportunity for immortality in union with God and the other representing the moral limits that man must respect or fall out of harmony with God.
This moral probation was presumably unique to man, who is uniquely a moral agent in the terrestrial sphere.
310 But why did God not create a world so perfect that no evil could exist in it? With infinite power God could always create something better. But with infinite wisdom and goodness God freely willed to create a world "in a state of journeying" towards its ultimate perfection. In God's plan this process of becoming involves the appearance of certain beings and the disappearance of others, the existence of the more perfect alongside the less perfect, both constructive and destructive forces of nature. With physical good there exists also physical evil as long as creation has not reached perfection.