The earliest historian was probably the legendary Cangjie during the reign of Huangdi, more than 4,000 years ago. According to various legends, Cangjie was a gifted person with great intelligence and physical features. There is a type of medicinal ingredient in traditional Chinese medicine called 'dragon bones', which are the fossils of animal bones. There have been discoveries of even earlier symbols on potsherds and animal bones in many ancient archaeological sites, dating between 4500 and 8000 years BP. Some of these symbols resemble those in the oracle bone script. The oracle bone script is characterized by sharp and square lines and by shapes that bear a certain degree of resemblance to objects, with some simplification. In the Shuo Wen Jie zi, Chinese characters are further classified into six different types: pictograms, indications, ideogrammic compounds, rebus, phono-semantic compounds and derivative cognates.