Hi there,
In terms of the purpose of animals changing after sin entered the world, I think i'm right in saying a literal Bible view states this happened after the flood. [Genesis 5 Chp 2] Clearly a long time after the entrance of sin.
But the very concept of animals suddenly changing into carnivores just after the flood is a surely an erroneous one. There's a lot of people out there who would have you believe Noah took dinosaurs and sabre tooth tigers onto his ark with him. The bones of dinosaurs such as T-rex, clearly carnivores, have been reliably dated before the flood. Animals have been eating other animals pretty much since life started, and to claim otherwise doesn't make sense!
To elaborate on my previous statement about Physics changing upon the entrance of sin. Sin entered the world just after Adam, which everyone can agree was less than 2 million years ago. Assuming the universe is much, much older than that, Physics would have changed relatively recently.
Basically, Physics at present can be reduced to 2 main theories, Quantum Mechanics, which governs the very small, and General Relativity, for the really really big. The main goal of modern physics is to find a theory which unites these 2, a so called "Theory of Everything". This would mean all the phenomena we observe in Nature could eventually be boiled down and explained by a particular theory.
If this theory was "changed" [by sin for example], the ramifications would be huge. If they'd changed in the recent past, things would surely be very noticable. Indeed, our universe is set up very delicately and would probably just plain not work if anything about it's governing laws were changed!
I've probably just clouded the issue, but i think that's what i think, if you know what i mean......
P.s. Call me Nick