Scientific Name：Placenticeras meeki

Category：Fossil

Year：Cretaceous Period (about 99 million years ago)

Size:Length:44 x Width:55 (cm)

Weight:31.97kg

Introduction：Ammonites were an extinct group of mollusks in the Cephalopoda. The earliest ammonites appeared during the Devonian around 400 million years ago, which was 170 million years earlier than the dinosaurs. They thrived during the Mesozoic Era and were distributed throughout the world's oceans, therefore ammonites are excellent index fossils for the Mesozoic.

The early ammonites descended from strait-shelled bactrites. During the Devonian Period, the outer shells of the ammonites gradually coiled tighter, which probably reduced the speed of movement, but it also increased their sensitivity and ability to turn.

Ammonites come in various kinds and forms, ranging from 1 cm to 200 cm in diameter. Inside the shells of ammonites are siphuncle, chambers, as well as thin walls (septa) that help to control water flow and pressure. The chambers are linked by a siphuncle that siphon and pump air to squirt jets of water. This may be a major characteristic that helps the ammonites to scoot from dangers.

Ammonite shells are found in the process of animal fossilization. Canada is famous for its vividly colorful ammonites. Ammonites were buried in volcanic ash that contained rich minerals, and later during Glacial Ages, were trapped in ice layers that compressed heavy pressure. The calcium carbonate on the surface of the ammonite was subsequently fossilized to calcite and aragonite. The iridescent color of the ammonite came from diffraction of lights inside the aragonite's fine and ordered structure, enhancing the colors on the outer shell and forming the bright, vivid colors of these ammonites.

Accession Number:0003677