Catkind

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

Physical appearance
Cats resembled the non-humanoid cats of Earth. The kittens resembled these most of all, but the adults were much taller, about the size of an average Human. (DW: Gridlock) They have retractable claws which they can use for defence. (DW: New Earth)

Life Cycle
As previously mentioned, Cat kittens looked like the kittens of non-humanoid Earth cats, while the adults were taller and humanoid. 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 50 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)