Do they also contain any flaws in their structures?

no they do not since evolution fine tunes animals over millions of years to adapt to their environment. It theoretically could happen if an animal's environment changed so quickly that the animal was unable to adapt or evolve in time to cope. This could happen if global warming continues to change the earth in such extreme ways and we continue to burn increasing amounts of fossil fuels.....or just an asteroid hitting the earth would have the same effect.