Wikipedia
Delphyodontos
Delphyodontos dacriformes is a prehistoric holocephalid fish from the early Carboniferous-aged Bear Gulch Limestone Lagerstätte, in Montana. The adult form is unknown, as the only fossil specimens are of aborted fetuses or recently born young. Sharp teeth and fecal matter in the fossils suggests that Delphyodontos practiced intrauterine cannibalism, like some modern sharks, such as gray reef sharks.