Freshwater Hesperornitheans

Brodavis by Scott Reid, a taxon that occurs in freshwater environments.

Hesperornithes are some of the most iconic extinct birds. Or rather, the larger, marine members of this group like Hesperornis or Canadaga are; little discussion is there to be made of the myriad membrs of this group that not only were smaller, but lived in freshwater.

Typically, when such animals are brought up, they’re considered “primitive” members of the group, still capable of flight. But not only did the invasion of freshwater habitats began late in the evolution of these birds, they were equally as flightless as their marine cousins. This is quite extraordinary, a group of marine flightless seabirds having invaded freshwater biomes, some as far inland as Mongolia!

Now, the invasion of freshwater bodies by marine tetrapods is not new. Freshwater seals, dolphins and manatees co-exist with us today, and in the past various lineages of plesiosaurs invaded freshwater. Likewise, flightless diving birds occur in freshwater, in the form of some highly endangered grebes. But flightless seabirds invaded deep into continental waterways is unprecedented, occuring in ecosystems not only dominated by terrestrial (and freshwater) predators but also far inland. Most freshwater diving birds today are of the flying variety, not only to evade predators but to cover distances as freshwater environments are seldomly permanent.

Seeing as hesperornitheans were functionally similar to cormorants and ducks it makes one wonder if cormorants would have gone flightless in a world without predatory mammals. Again, these birds rely on flight for migration and seeking new territories, something these freshwater hesperornitheans didn’t have access to, but were successful enough to expand far and wide.

More studies should be conducted on their biology, as these freshwater birds are quite unlike any aquatic tetrapods alive today.