Catkind

Cats were a race of humanoid felines living on New Earth during the 5,000,000th millennium.

Physical appearance
Cats resembled the non-humanoid cats of Earth, though closer to the size of a Human. They had cat-like faces and fur of a variety of lengths and colours, including brown, black and striped (DW: Gridlock). They had retractable claws which they can use for defence. (DW: New Earth)



Life Cycle
Cat kittens looked like the kittens of non-humanoid Earth cats. Cats reproduced in their teenage years, and often had litters of several kittens. They could also reproduce with Humans, with the kittens still having the feline appearance. (DW: Gridlock)

Cats could apparently live for at least 80 years, as Novice Hame, a member of the Sisters of Plenitude, was young in the year 5,000,000,023 at the time of the order's dissolution, and lived beyond the Face of Boe's death in 5,000,000,053. (DW: New Earth, Gridlock)

History
The Cats had been involved in several important events on New Earth.


 * Based on the comments by Novice Hame, the Cats may have been the original inhabitants of New Earth. The Sisters of Plenitude, at least, were on the planet before the Humans arrived.

The Sisters of Plenitude ran a hospital called Pleasure Gardens near New New York on New Earth. They had cures for nearly every known ailment and were able to heal their patients with a remarkable success rate. Unfortunately, these amazing skills were gained by using thousands and thousands of grown Human clones. They were infected with every known disease and culled in the rare cases of them starting to show signs of thought. These disease carriers were released by Lady Cassandra and eventually cured by the Doctor, producing the New Humans. The Sisters were later arrested by the NNYPD for their actions. (DW: New Earth)

After the loss of the New Earth Senate to a deadly mood virus, several Cats were trapped in the Motorway, including Thomas Brannigan. (DW: Gridlock)


 * Presumably, all of the Cats in the upper levels of New New York were wiped out by this virus.