The walrooster (Marepsittacus occinerator) is the largest sea parrot species being 4 meters long, and weighing about as much as the (much sleeker and longer) imperial seaguin. This is partly because of their rather heavy and robust bones, which help them dive (walroosters are also known to swallow stones for the same purpose).

These massive divers live in the arctic sea, feeding mostly on bottom-dwelling mollusks such as shellfishes, which they detach from rocks using their hooked beaks, and crush the shells with their impressive battery of teeth. They also occasionally catch crabs, but hardly ever even try chasing ammonites like their smaller and swifter ancestors. There have also been reported cases of walroosters scavenging. It seems that with their powerful jaws and teeth they can crack the bones to get to the marrow, inaccessible to most predators.

Walroosters can often be seen in large numbers resting on arctic rocky beaches or ice floats. The males have a very loud and recongizable voice, used during the mating season and related social disputes.