Spotted hyena cubs are born with teeth already in, ready to fight their siblings

Spotted hyena clans are run by females, who outrank every male and are about a quarter larger than them. Cubs are born with their eyes open and their teeth already erupted, and same-sex littermates often fight for dominance within days of birth — fighting that kills roughly a quarter of cubs before they're a month old.

— Standard zoological accounts, Spotted hyena