Heterodontosaurus tucki was a lightly-built and swift ornithischian dinosaur that was about 1 m (3 ft.) long.

There is only one species in the genus: H. tucki. The species was described in 1962. Its name is based on several Greek words and effectively means "different-toothed lizard".

The name reflects the dinosaur's unusual dentition: most dinosaurs had just one type of tooth, but Heterodontosaurus had three types:

• Small teeth at the front of the jaw that were most likely used for nipping vegetation.
• A pair of large canine-like tusks. Their function is unknown, but they may have been used for defensive purposes. Some scientists have suggested that only males possessed this form of tooth.
• A series of teeth at the back of the jaw that were specialized for chewing food.

Heterodontosaurus lived about 200 million years ago, during the Early Jurassic Period, in what is now South Africa.