Cannibalism in utero
Sand tiger shark embryos eat their half-sisters and -brothers while they are still in the uterus. A group of American researchers studied fifteen dead, pregnant sand tiger sharks.
The female sand tiger shark (Carcharias taurus) has two uteruses, and is often inseminated by several males. During the pregnancy, the young compete with each other. Early on, the embryos live on the yolk sac; when the embryos reach a length of approximately 10 cm, they become food for the largest (oldest) embryos. One embryo survives in each uterus. After a gestation of eight to nine months, two young are born: a metre long and completely independent.