 The teeth are tusk-like, but are only visible in males, which are presumed to use these teeth in combat for females for reproductive rights.In females, the teeth do not develop and remain hidden in the gum tissues.In December 2008, researchers from the Marine Mammal Institute at Oregon State University completed a DNA tree of 13 of 15 known species of "Mesoplodon" beaked whales (excluding spade-toothed whale, which was then only known from a skeletal and a few stranded specimens).