화석명 : 암모나이트(Ammonite)
학명 : Douvilleiceras mammilatum
시대 : 백악기(Upper Early Cretaceous, Albian Stage)
산지 : 마다가스카르 (Mahajanga Province, Madagascar)
크기 : 90x60mm

도우빌리세라스는 백악기 초에 살았던 암모나이트로서 개방나선형을 하고 있다. 늑골 구조의 요철이 깊고 투박하며 늑골 위에는 여러 개의 결절이 있어서 마치 군용 트럭의 바퀴를 보는 듯하다. 이런 형태는 열악한 서식 지역에서 자신을 보호하기 위해 발전된 구조로 보인다. 아프리카에서 발굴된 것들은 일반적으로 거칠고 보존 상태가 나쁜 반면 유럽 지역에서 발굴된 것들은 늑골 구조가 보다 뚜렸하며 보존 상태가 좋은 것들이 많다.

This fine ammonite is Douveilliceras mammilatum from Madagascar which has had the original shell removed, allowing you to see how the ammonite’s shell was reinforced with small impact upon its weight, and important factor for an animal which needed to move freely within the water column in pursuit of prey The interior shell is preserved as a cream and green colored Calcite, with the sutures in fine relief. Notice the tubercles present on this example. Members of the genus are found with spines, tubercles, or knobs, and they are thought to be indicative of a hostile environment in which such structures were necessary as a defense. Additionally, you can see the dark line running along the center of the shell. This is the siphuncule, which is what was used by the ammonite to adjust its depth in the water column, much like a submarine. See my other listing for examples of another species.