In ancient times the Shattered Isles used to be one huge isle. A peaceful and highly advanced civilisation prospered there. With the help of magic and breeding, they refined the very essence of all creatures on the isle. So even the animals became incredibly healthy and practically perfect beings of their species. They even acquired some intelligence that improved from generation to generation. After a catastrophe that destroyed the whole island, only a few of those animals survived. Over the years, other animals added to these special creatures, and soon only a fraction of the animals still had the attributes of their ancestors.
If someone succeeds in catching one of them, he might learn their secret of immortality along with other secrets that were thought to be lost with the destruction of the isle.
The Animal Kings
These noble animals chose one of their kind as their king and with the knowledge of their ancestors they acquired immortality. Nowadays, those animal kings still live at remote places, though some of them might have left the isles for more hospitable areas.