The Sibro was a species which came from a Sibro tree. This tree could hatch up to 100 Sibro as most of their young didn't survive. The Sibro had ten arms and five eyes. It could stop its enemies from talking, just by uttering one word: "Quiet". The Doctor met the Sibro when adventuring after stealing the type 40 TARDIS from Gallifrey.
The Sibro were very small in numbers. There were only thirty of them, born from the same tree they never repopulated. The Doctor, in his first incarnation, saved half of them when their planet was impacted by a meteorite and was slowly moving towards the solar system's star. The Doctor didn't know what happened to the Sibro species, only that fifteen of them might still be alive.
The Sibro were also suspected to be able to live up to 250 years. (COMIC: Chime Time)