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| Titel: |
Endocochliate embryo model in the Mesozoic Ammonitida |
| Auteur: |
Tanabe, Kazushige |
| Verschenen in: |
Historical biology |
| Paginering: | Jaargang 2 (1989) nr. 3 pagina's 183-196 |
| Jaar: |
1989-08 |
| Inhoud: |
An endocochliate embryo model for the Mesozoic Ammonitida is proposed based on scanning electron microscopy of the ammonitella (= embryonic shell) stage of well-preserved Japanese Cretaceous specimens belonging to nine species of five superfamilies. As in other specimens described previously, the ammonitella wall succeeding from the initial chamber ("protoconch") in the species examined consists of the inner prismatic, middle subprismatic and outer prismatic layers, with minute tubercles resting on the outer. Developmental patterns of these structures and their comparison with primary shell formation in modern Nautilus and Spirula suggest that the outer thin prismatic layer with microtubercles was secreted by the exterior epithelium after the completion of the main ammonitella wall by the interior shell gland. Thus, the early ammonite embryo might have had an endocochliate structural plan as in coleoids, and at the time of hatching the overlying mantle epithelium had shifted anteriorly to become an ectocochliate condition. |
| Uitgever: |
Taylor & Francis |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
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