Shark embryos cannibalize their littermates in the womb.

Shark embryos cannibalize their littermates in the womb, with the largest embryo eating all but one of its siblings. The researchers, who detailed their findings today (April 30) in the journal Biology Letters, analyzed shark embryos found in sand tiger sharks (Carcharias taurus) at various stages of gestation and found that the later in pregnancy, the more likely the remaining shark embryos had just one father. That finding suggests the cannibalism seen in these embryos is a competitive strategy by which males try to ensure their paternity.