First, it should be noted that the idea of animal death coming before the
fall of humans is not a product of modern scientific discoveries, but
rather had been proposed based on Genesis 1-2 by Augustine, if not earlier.
Three possibilities I know of:
One that you seemed to hint at: "Seems to me there is another "agent"
involved in the way this universe works ...and he is very worried about
self-preservation."
Satan was fallen before we were. At what point and to what extent he began
meddling with creation is not specified. Such a scenario is present in C.
S. Lewis's space trilogy and Tolkien's Silmarillien.
Another possibility is that our fall had consequences chronologically
before it happened. Spiritual effects do not have to occur after their
causes, e.g., the effectiveness of faith in the OT.
Thirdly, the death of animals is not clearly a moral issue. Certainly, in
our role as stewards, we should be concerned for them, but whether
immortality for them would be the unfallen state is not clear.
What is certain is that God is sovereign and that He knows what He is doing.
David C.