In some species of sharks devour each other cubs in the womb Bashny.Net

Intrauterine cannibalism - a phenomenon devouring each other embryos in the uterus during pregnancy, even the mother. Often found in sharks, for example, a sand shark (Odontaspis taurus).

Pretty scary to imagine this, but intrauterine cannibalism is not evidence of cruelty these animals. In fact, it is just a means to provide seed food - within the uterus develops a greater number of embryos than a shark can give birth, it is to the weaker ones become stronger means of subsistence. Also, intrauterine cannibalism can be called self-regulation mechanism of intraspecific: shark gives birth to "My Favorites" offspring - the most powerful and aggressive animals.

via factroom.ru