Combined photo shows experts working during a dinosaur footprint preservation project at the Yanqing Global Geopark in Yanqing District of Beijing, capital of China, Oct. 15, 2018. Experts from China and Greece have started joint preservation work on fossilized dinosaur footprints in Yangqing to prevent them from weather damage. The footprints are believed to be left by dinosaurs some 150 million years ago. (Xinhua/Luo Xiaoguang)