This siltstone unit lies upon a. Their chinese name derived from patterns of suture lines on their. Ammonites were shelled cephalopods that died out about 66 million years ago.
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菊石 是 菊石亞綱 （學名： ammonoidea）物種的通稱，是一類已 滅絕 的 頭足綱 軟體動物，具有螺旋形的 貝殼 和眾多 觸手。 作為非常好的 指準化石，菊石化石往往能連結起所在地層的 地. In the new ammonite specimen, round structures interpreted as fossil remains of ovaries are well visible. Ammonite shells are used today as index fossils, meaning they can help date other fossils that are found in the same layer of marine rock.
Ammonites first appearing in the fossil record 240 million years ago, descending from straight shelled cephalopods.
The last lineages disappeared 65 million years ago at the end of the. Ammonites were marine cephalopods resembling nautilus, characterised by their spiral shells and tentacles on their heads. Most of the ammonites studied have ribs, tubercles, keels and other ornaments. Fossils of them are found all around the world, sometimes in very large concentrations.
Discover the fascinating world of ammonites — extinct marine cephalopods. Ammonites were marine animals belonging to the phylum mollusca and the class cephalopoda. They had a coiled external shell similar to that of the modern nautilus. Learn about their evolution, shell structure, fossilization, and role as key index fossils in geology.
