In a really astounding discovery, it was confirmed that a 2001 birth by a female Hammerhead shark was achieved in the complete absence of males, in a process called parthenogenesis. While at first it was believed that the female shark mated before being captured, and stored the sperm for three years (ew), testing on the resulting offspring showed that their DNA only matched the mother and showed no evidence of a father. This phenomenon, while seen in some other vertebrates like birds and amphibians, has never been demonstrated in such a major vertebrate line as sharks. Mammals are now the only major vertebrate group that has yet to show evidence of parthenogenesis.