Sterling silver is 92.5% silver alloyed with copper for hardness: pure silver is too soft to hold a casting this detailed. The alloy is what makes the piece possible, and it is also what makes it tarnish, since the copper reacts with sulphur in the air.
The recesses here are deliberately oxidised — darkened on purpose so the mane and the claws read against the polished raised surfaces. That is a finish, not damage, but it will wear off the high points with handling. Polish with a silver cloth and store in a sealed bag.