Chaoyang (Chinese: 朝阳) is a prefecture-level city of Liaoning province, People's Republic of China. With a vast land area of almost 20,000 square kilometres (7,700 sq mi), it is by area the largest prefecture-level city in Liaoning, and borders on Hebei province and the Inner Mongolia Autonomous Region to the west. The area under Chaoyang's jurisdictional control is split up into two counties (Jianping, Chaoyang), two urban districts (Longcheng, Shuangta), two county-level cities (Beipiao, Lingyuan), and the Harqin Left Wing Mongolian Autonomous County. The total regional population is 3 million, while the urban centre where the government office is located has a population of 430,000 and forms the core of Chaoyang. Known as China's 'fossil city', many important paleontological discoveries have been made in Chaoyang, and the Harqin region is the oldest currently known prehistoric site in northern China. Two of the most remarkable Early Cretaceous birds known to date were recovered in the vicinity of the Jiufotang Formation rocks and named Longipteryx chaoyangensis and Sapeornis chaoyangensis in reference to the city.