Among all these fossils of ancient extinct life, fossils of ammonite were the most ancient. Ammonite was an oceanic invertebrate mollusk living 200 million years ago. Being a kind of invertebrate and semi-natatory mollusk, they generally dwelled in the seabed 50 m to 80 m under the surface. There are more than 200 pieces of ammonite fossils excavated in Heyuan Ammonite oryctocoenose, ranking first in amount and varieties and scale in the country. Heyuan Ammonite oryctocoenose is reputed as the "King of Ammonite in Southland". Among the ammonite fossils, the biggest one has a diameter of 42 cm while the smallest has the same size as the fingernail surface. Geoscience specialist considers that, the discovery of Heyuan ammonite fossil community is of great significance to the research of ancient geography, geologic climate and environment as well as tourism development in South China.

The ammonite fossil has a semi-revolute shell, with flat and shrunken sides and a furrow in the center of the belly. The shell surface is thickly dotted strips of fine and slightly crooked cross ribs, which slantwise extends from umbilical wall to the front of shell and forms an obvious tubercle around the belly. With perfect preservation and odd appearance and texturing, these fossils look like chrysanthemum embedded in stone with lovely shape. They are also precious ornamental stones.