Psittacosaur.

Here is an unfinished pencil-on-illustration board sketch from 2009.

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This dinosaur is the prototypical psittacosaurid, called Psittacosaurus mongoliensis. P. mongoliensis is known from China, Mongolia, and Siberia. Fossils of P. mongoliensis are so abundant, nearly a full skeletal ontogeny is known for the species. At least one species of Psittacosaurus (and there are many) exibited a patch of long, moderately-flexible and hollow bristles along the dorsal surface of its tail.