Plotopteridae they became extinct. That they became extinct at the same time as the giant penguins of the Southern Hemisphere, which also coincided with the radiation of the seals and dolphins, has led to speculation that the expansion of marine mammals was responsible for the extinction of the Plotopteridae, though this has not been formally tested. Plotopteridae Plotopteridae is the name of an extinct family of flightless seabirds from the order Suliformes. Related to the gannets and boobies, they exhibited remarkable convergent evolution with the penguins, particularly with the now extinct giant penguins. That they lived in the North Pacific, the
Ratite as a whole probably had an origin in the northern hemisphere. Early Cenozoic northern hemisphere paleognaths such as "Lithornis", "Pseudocrypturus", "Paracathartes" and "Palaeotis" appear to be the most basal members of the clade. The various ratite lineages were probably descended from flying ancestors that colonised the south in multiple waves, probably initially in South America, and then evolved gigantism. Loss of flight allows birds to eliminate the energetic cost of maintaining flight-enabling pectoral muscle mass. The basal metabolic rate of volant species is much higher than that of flightless terrestrial birds. But energetic efficiency can only help explain the loss