The mammal in question is commonplace, a land creature, and domesticated (although not a pet, usually).

The question is not a 'catch' question, and the answer is very simple.

The 'young' will grow up to be adults of this animal; there is no trick of the International Dateline (or any other computer dating agency...!).

It is just as possible that all traces of this creature could be lost for ten years - above or below ground, on or in water, or anywhere else. But significantly large numbers (or even just one!) could be borne after ten years, twenty years, five seconds - elapsed time is not an issue, just a red herring.

It is difficult to give many more clues without giving away the answer - but this creature shares its name with a type of footwear...

NO! It's not a kinky leather... thigh... length... boot... ooooo-er!!