The fatlip islesnapper split from its ancestor. Fatlip islesnappers still hunt in packs while on land, but only occasionally hunt in groups while diving. Fatlip islesnappers are still able to glide in emergencies, but far less effectively than their ancestors. However, they are excellent swimmers and rival the island skysnapper in swimming ability. They use their wings to paddle through the water, and use their tail help propel them forward. They still use their wings for communication when on land, but have to rely on more subtle physical cues of the tail when in water, because of this their eyesight has gotten better. They have a small pouch in their mouth, which they use to catch and store food, that is able to expand slightly. This pouch can also be engorged as a warning or when the creature is threatened, though this method of communication is rarely used between members of the same species.
They are warm-blooded and have oily outer feathers with softer, dry down-like feathers beneath them.