Vastra is a Silurian, one of a quasi-matriarchal species of warlike intelligent dinosaurs which are in suspended animation under the earth until such time as the planet warms up again and the naked apes die out. Every now and then a few get thawed out for Reasons and A) try to take over the world, or in Vastra's case, B) fall in love with a human woman in Victorian England and solve crimes together. It's a Doctor Who thing.