- You may be looking for their mammalian predecessors.
The reptilian Betrushians were the second race to evolve on Betrushia.
The Betrushians were tall and thin humanoids. They were covered in greyish green scales and had crests along their cheeks and on their head. They had large blue or yellow eyes with slitted pupils. Their fingers and toes had sharp claws and they had small pearly teeth. They had rows of bony groves parallel to their spines. Betrushians produced milky white sweat when agitated. They reproduce using leathery, brown eggs, which needed to be kept warm to survive. They had purple hearts and dark, thick blood. Some Betrushians were described as having grey hair.
The Betrushians were split into two known countries, the Ismetch and Cutch. The main differences between the two societies was their religion. The Cutch were polytheistic, while the Ismetch had one God. The Ismetch believed that the Cutch were a degraded race and needed to be exterminated to protect the Ismetch blood-line. Despite their differences, both groups believed in the Keth and its second coming.
In 2133, the Ismetch declared war on the Cutch in order to exterminate them to maintain racial purity. Millions were killed in the conflicts and very little progress was made. In 2148, the Ismetch attempted to broker a peace. The Seventh Doctor and Bernice happened to have landed on the planet at this point and were captured as spies.
Unfortunately, at this point in time the Chapter of Saint Anthony were moving towards Betrushia, destroying the ring system in the process. This awoke the Keth, which started to kill off the Betrushians. The Chapter also started to destroy major Betrushian cities, leading to a communication blackout. The Cutch took advantage of the chaos and attacked the remaining Ismetch soldiers, but they were forced to band together when the Chapter finally landed and took them prisoner. The surviving Betrushians were eventually able to take over the Chapter's ships and with the help of the Doctor, were able to trap the Keth on Betrushia, which had become unstable during the attack. The Betrushians were able to rescue several hundred survivors before the planet destroyed itself and the refugees moved to Massatoris. (PROSE: St Anthony's Fire)