xxSilverPhinxx

This^ I think so too (layperson opinion, so maybe I'm confusing things here). Also, as for the reverse gravity example, isn't it looking a bit like the grandfather paradox? I'm assuming you're not talking about anti gravity here...

I don't know, if the tiger is anything like a slightly weaker version of a lion, who can kill a lioness with one swip of their paw, then the Great Danes might run into some problems. However, I know that Brazilian mastiffs, which are roughly the size of a bull mastiff were used to hunt jaguars (and catch run away slaves, but that's besides the point). One on one I think the tiger would win, though.

The classification or organisms is taxonomy, and as for ecology, the wiki link explains it well. It's basically the study of ecosystems.

*** As for the question: I don't think it would be an example of reverse evolution, or "de evolution", but a new molding of a limb they already have if there were selective pressures that favour the remolding.

Dolphins have the fish, reptilian and higher mammalian (like us) parts in their brains.

I think the brains of marine mammals such as whales and dolphins are interesting because though they're separated from our lineage by a few million years, they've evolved a similar brain cortex.

Evaporating water takes more heat away from the surface of our skin than a fan removing heated air from the proximity of a dog's body, but the principal is the same. It's just not as effective for them but it happens.