In an alternate timeline, a new species replaced humanity on Earth.
History
Following Ruby Sunday accidentally stepping on a butterfly in Earth's distant past, a new timeline was created in which the planet's evolutionary history was altered. A new species replaced humanity, and Ruby Sunday herself was replaced by her counterpart, Rubathon Blue. This timeline was subsequently negated following the Fifteenth Doctor's revival of the butterfly, after which he then turned on the butterfly compensation switch in the TARDIS.
The species seemed to have a culture of honour, with Rubathon taking great offence to any notion of an "incorrect accusation", even threatening the Doctor with death when she heard his shock at the butterfly being stepped on. (TV: Space Babies [+]Loading...["Space Babies (TV story)"])
Biology
Rubathon Blue's species were humanoid, with scaly skin and antennae. They also had hair, with Rubathon Blue having a hairstyle that resembled that of her original counterpart's, Ruby Sunday. They were born as hatchlings, with individuals of this species remaining associated with their hatchling group. One such hatchling group were the 57th Hemisphere Hatchlings. (TV: Space Babies [+]Loading...["Space Babies (TV story)"])