Pertucaion

Pertucaions (pronounced per-tu-kay-ons) were inter-dimensional beings that existed between dimensions. As such they would "play" with dimensions, using tissue compression to miniaturise people, animals, and objects including TARDISes and neutron stars.

They had access to all of time, were capable of manipulating the energy of the universe, and could even enter the synapsis to read minds. Using this later ability, they were able to change their form into something more comforting for whoever they encountered, though their true form, which they thought could hurt lesser species, resembled a thousand suns in stained-glass. The First Doctor believed their shapechanging and miniaturising were defensive or survival mechanisms.

The Pertucaion named "the Miniaturist" by Dodo Chaplet landed on Earth during the Permian Era to seek shelter from the dimensional noise inside the fossilised shell which formed a geological quiet spot. Here the Miniaturist created a shelter that was bigger on the inside and housed many miniaturised things she'd taken from the universe. (AUDIO: The Miniaturist)