Based on morphological features, the Alexandrine parakeet ("Psittacula eupatria") has been proposed as the founder population for all "Psittacula" species on Indian Ocean islands, with new populations settling during the species' southwards colonisation from its native South Asia. Features of that species gradually disappear in species further away from its range. Subfossil remains of Newton's parakeet show that it differed from other Mascarene "Psittacula" species in some osteological features, but also had similarities, such as a reduced sternum, which suggests a close relationship. Skeletal features indicate an especially close relationship with the Alexandrine parakeet and the rose-ringed parakeet ("Psittacula krameri"), but the many derived features of Newton's parakeet indicates it had long been isolated on Rodrigues.