Protognathus

Protognathosaurus is known only from a single piece of lower jaw, called a dentary, which had about 18 tooth positions.1

Its name was first Protognathus, but that name was already used for a beetle, so in 1991 it was changed to Protognathosaurus.1

The jaw shows sharp replacement teeth still growing in, which is why the species name oxyodon means 'sharp tooth'.1

It lived about 168 to 161 million years ago, during the Middle Jurassic.1

The fossil was found in the Lower Shaximiao Formation, which is made of sandstone and mudstone from an ancient lake.2

Scientists think it was a medium-sized primitive sauropod, with a thick and heavy lower jaw.2