Ascocerida
| ← Previous revision | Revision as of 19:36, 19 April 2026 | ||
| Line 1: | Line 1: | ||
{{Short description|Extinct order of molluscs}} |
{{Short description|Extinct order of molluscs}} |
||
{{Automatic taxobox |
{{Automatic taxobox |
||
| fossil_range = {{fossil range|Ordovician|Silurian}} |
| fossil_range = {{fossil range|Middle Ordovician|Late Silurian}} |
||
{{period fossil range|Paleozoic|middle Ordovician|late Silurian}} |
|||
| image = Ascoceras ontogeny.gif |
| image = Ascoceras ontogeny.gif |
||
| image_caption = The ontogeny of ''Ascoceras'', an Ascoceridian |
| image_caption = The ontogeny of ''Ascoceras'', an Ascoceridian |
||
| taxon = Ascocerida |
| taxon = Ascocerida |
||
| authority = [[Oskar Kuhn|Kuhn]], 1949 |
| authority = [[Oskar Kuhn|Kuhn]], 1949 |
||
| subdivision_ranks = Families |
|||
| subdivision = †[[Ascoceratidae]] |
|||
†[[Choanoceratidae]] |
|||
†[[Hebetoceratidae]] |
|||
}} |
}} |
||
'''Ascocerida''' (from Greek ''[[Askos (pottery vessel)|askos]]'', a vessel, and ''keras'', horn){{Cite book |last=Nicholson |first=Henry Alleyne |url=http://archive.org/details/ancientlifehist00nich |title=The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palaeontological science |date=1876 |publisher=New York, A.L. Fowle |others=Smithsonian Libraries |pages=381}} is an order of comparatively small nautiloids in the subclass [[Orthoceratoidea]], known from [[Ordovician]] and [[Silurian]] sediments in Europe and North America. They are believed to have diverged from other orthoceratoids, possibly [[Clinoceratidae|clinoceratids]], during the [[Ordovician|Middle Ordovician]], though fossils of them from this time are rare. While they suffered from the [[Late Ordovician mass extinction|Late Ordovician Mass Extinction]], they recovered in the [[Silurian]] and became extinct at the end of that period. |
|||
The '''Ascocerida''' are comparatively small [[Orthoceratoidea|orthoceratoids]] known only from [[Ordovician]] and [[Silurian]] sediments in Europe and North America, characterized by a [[deciduous]] conch consisting of a longer juvenile portion and an inflated short adult portion that separated sometime in maturity. |
|||
Members of the family are characterised by a long projection towards the rear end of their shells, known as the [[deciduous]] conch, which detached in maturity or after death. Near the shell tip, the [[Camera (cephalopod)|camerae]] (chambers) running through the shell became restricted to the upper portion. This would have provided excellent [[buoyancy]] while in a horizontal position. |
|||
==Description== |
==Description== |
||
| Line 15: | Line 20: | ||
==Taxonomy== |
==Taxonomy== |
||
Ascocerida likely branched from [[Orthoceratoidea|orthoceratoids]] in the early [[Ordovician|Middle Ordovician]], though Ordovician fossils are rare.{{Reference page|pages=|page=112}} [[Rousseau H. Flower|Rosseau H. Flower]] suggested that they derived from the family [[ |
Ascocerida likely branched from [[Orthoceratoidea|orthoceratoids]] in the early [[Ordovician|Middle Ordovician]], though Ordovician fossils are rare.{{Reference page|pages=|page=112}} [[Rousseau H. Flower|Rosseau H. Flower]] suggested that they derived from the family [[Clinoceratidae]], possibly from ''[[Clinoceras]]'' itself, through taxa such as ''[[Montyoceras]]'' and ''[[Hebetoceras]]''. The connection between these slender deciduous forms and the typically ascoceroid ''[[Probillingsites]]'' from the early Upper Ordovician can be made through ''[[Redpathoceras]]''.Rousseau H Flower; p 542, Ordovician Cephalopod Faunas and Their Role in Correlation; in The Ordovician System: proceedings of a Palaeontological Association symposium, University of Wales Press and the National Museum of Wales, Cardiff, 1976 Ascocerids appear to have undergone a major reduction in biodiversity during the [[Late Ordovician mass extinction|Late Ordovician Mass Extinction]], though recovered in the [[Silurian]], becoming abruptly extinct at its end.{{Reference page|pages=99–100, 112|page=}} |
||
=== Internal relationships === |
=== Internal relationships === |
||
