When some scientists at the University of Auckland "analysed mitochondrial DNA sequences from 650 to 8000-year-old tuatara remains and compared them with those of living tuatara, they found that the reptile is evolving almost 10 times as fast as the average animal. It is accumulating an average of 1.37 substitutions per base pair every million years compared with an average of 0.2 (Trends in Genetics, DOI: 10.1016/j.tig.2007.12.002)."
Aside from its powers of speedy evolution, the tuatara is also unique in nature in that it has two rows of upper teeth which overlap one row of lower teeth, and has a parietal "third eye", whose specific function scientists are still trying to figure out (it's connected to the brain but covered in opaque scales and appears to have evolved from a working eye -- one possible theory is that it acts as a light sensor and assists in basking). They can hear without having any external ear present, and the males are penis-less. The tuatara also retains a number of unique skeletal characteristics, possibly as a remnant of its evolution from fish.
Probably the only reason they have not yet evolved into our terrifying lizard overlords (besides the fact that they were endangered for many years) is because they reproduce so slowly, taking 15 years to reach sexual maturity, with females producing eggs only every two to four years.
Still, they are badass. The Maori revere the tuatara as a god-form, specifically a messenger of Whiro, the god of death and destruction. Maori women are forbidden to eat them, and the tuatara's presence is said to mark the boundaries between the mundane and the sacred.
All hail the tuatara!