Fruitadens haagarorum, researchers say, is one of the smallest dinosaurs known to science.
In the Royal Society journal Proceedings B, the researchers say that the dinosaur weighed less that 1kg.
The fossils have been housed at the Natural History Museum of Los Angeles County since being discovered in Colorado in 1979.
According to the researchers, the tiny dinosaur was agile and a fast runner. It lived in the Upper Jurassic period, about 150 million years ago.
It was a member of a group of dinosaurs called the ornithischians, which were largely plant-eating creatures that included the far more imposing Triceratops and Stegosaurus.
Here is the picture of the jaw from the BBC article:
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