Evolution

Auteryx evolved from sharp-witted raptor-like dinosaurs (specifically, archaeopteryx) that got stuck on an island that drifted off of the mainland. Having been isolated and stuck in a novel environment, Auteryx evolved from such raptors over millenia, losing their nimble frame, quick running skills, and agility for traits such as swimming ability, blubber, and more.

Auteryx have different subspecies, as can be seen here, but they have such small differences that it is not really necessary to distinguish them in terms of speciation!

The detailed evolution of Auteryx can be depicted below through this visual; there are 2 distinct stages of proto-auteryx that can be classified as "transitional species". Furthermore, the current timeline of birds' evolutions are also depicted, acting as a good comparion for Auteryx. Due to this tree, the closest living relative of Auteryx in our current world are birds!