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
Hesperornithes to that in Neognathae, are today considered to be due to convergent evolution. In 2015, a species-level phylogenetic analysis found the following relationships among hesperornithiforms. Hesperornithes Hesperornithes is an extinct and highly specialized group of aquatic avialans closely related to the ancestors of modern birds. They inhabited both marine and freshwater habitats in the Northern Hemisphere, and include genera such as "Hesperornis", "Parahesperornis", "Baptornis", "Enaliornis", and "Potamornis", all strong-swimming, predatory divers. Many of the species most specialized for swimming were completely flightless. The largest known hesperornithean, "Canadaga arctica", may have reached a maximum adult length of over . Hesperornitheans were