Baby Shark Cannibals: The Ultimate Sibling Rivalry

For sand tiger sharks, survival of the fittest begins long before birth. Even in the womb, siblings battle it out, devouring each other until only the strongest survive.

Recent research by Field Museum scientist Dr. Kevin Feldheim and his collaborators has revealed even more to the unusually gory story of sand tiger reproduction.

The embryos of sand tigers feed not only on one another, but also on any unfertilized eggs inside the mother. The extra protein ensures that the winning combatant is born typically measuring a whopping three feet long, with well-developed eyes and teeth—not a meal many predators would attempt!

While a female sand tiger carries eggs fertilized by several males in her two wombs, paternity tests performed in The Field Museum’s DNA Pritzker Laboratory have determined who’s the ultimate shark daddy—“Jerry-Springer” style. It’s likely the male who arrived first to the party. His offspring hatch earliest, giving them the chance to gobble up their competitors before birth.

In the end, only one pup emerges from each womb. Sometimes these two surviving victors are only half-siblings, sired by different early-bird dads. But often, they’re full-blooded brothers or sisters whose father managed to fend off other suitors long enough for his offspring to get a developmental head start.

Discover more about the DNA work happening in the Pritzker DNA Lab.