(From Greek: adelphos=brother + phagos=eating)
Adelphophagy, which literally means "eating one's brother", refers to the act of pre-birth cannibalism. In other words, it's the killing and devouring of broodmates while the cannibal and victim(s) are still in their mother's womb.
Talk about your sibling rivalry.
This type of cannibalism, which is also known as "embryophagy", is common in many species of deep sea sharks that give birth to live young (see below). It was first discovered in 1948 when a marine biologist who was poking about in the uterus of a pregnant sand tiger shark got a nasty vagina dentata surprise: one of the unborn sharks chomped his hand.
Adelphophagy has also been seen in other fish, and it's suspected in coelacanths (Latimeria chalumnae).
Other aquatic and marine species engage in a less-gruesome form of adelphophagy: oophagy. These fetal organisms eat unfertilized eggs that their mother releases into her womb to supplement the nutrition they get from their yolk sacs. Scientists first documented oophagy in mackerel sharks in 1907. Since then, it's been identified in a wide range organisms: mollusks, crustaceans, echinoderms, polychaete worms, and kynorynchs.
Evolutionarily, any form of adelphophagy is about producing bigger and stronger offspring that are ready to compete in a brutal world the moment they're born.
Known Adelphophagic Shark Species