| 词汇 | ammonoid |
| 释义 | ammonoid noun[ C ] uk /ˈæm.ə.nɔɪd/ us /ˈæm.ə.nɔɪd/ an ammonite菊石（见ammonite） Palaeontology & fossils ammonite biozone carbon dating fossil fossil record fossilization fossilize fossilized index fossil microfossil missing link palaeontologist palaeontology petrifaction petrify radiocarbon dating unfossiliferous ammonoid | American Dictionaryammonoid noun[ C ] us/ˈæm·əˌnɔɪd/ earth science an ammonite Examples of ammonoidammonoid The zone is 170 m thick, and ammonoids and other fossils occur as imprints in mudstones and as shell-rich layers in sandy turbidites. The diversity of the ammonoid assemblage in this zone has increased to five genera and about 15 species. Quite detailed correlations are not possible yet, but one can clearly see a westward diachronism in the first occurrence of some ammonoid genera. Abundant concretions at several levels contain well-preserved ammonoids, bivalves and occasional fish. Moreover, in the study of a highly diversified group such as the ammonoids, we believe that making too many generalizations can be risky. This zone is widely distributed, 20-150 m thick, and contains the most diverse ammonoid assemblage with seven genera. The number of ammonoid genera is greatly reduced to four, combined with a gradual shallowing-upward trend in the succession. Brachiopods, cephalopods (ammonoids and one nautiloid) and bivalves are rare. Plasticity of developmental timing as the underlying cause of high speciation rates in ammonoids. However, the preservation of the collected material is too poor and the total number of ammonoids from single beds is too scarce to allow such a revision to be undertaken. They are an extinct group of ammonoid, which are shelled cephalopods related to squids, belemnites, octopuses, and cuttlefish, and more distantly to the nautiloids. From Wikipedia This example is from Wikipedia and may be reused under a CC BY-SA license. They are an extinct group of ammonoid, which are shelled cephalopods related to squids, belemnites, octopodes, and cuttlefish, and more distantly to the nautiloids. From Wikipedia This example is from Wikipedia and may be reused under a CC BY-SA license. They are an extinct group of ammonoid, which are shelled cephalopods related to squids, belemnites, octopuses and cuttlefish, and more distantly to the nautiloids. From Wikipedia This example is from Wikipedia and may be reused under a CC BY-SA license. It is the outermost or last chamber in the shell of a nautiloid or ammonoid. From Wikipedia This example is from Wikipedia and may be reused under a CC BY-SA license. In the seas, a novel major group of ammonoid cephalopods called clymeniids appeared, underwent tremendous diversification and spread worldwide, then just as suddenly went extinct. From Wikipedia This example is from Wikipedia and may be reused under a CC BY-SA license. These examples are from corpora and from sources on the web. Any opinions in the examples do not represent the opinion of the Cambridge Dictionary editors or of Cambridge University Press or its licensors. |
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