''Asymptoceras'' is a genus of
aipoceratids (
Nautiloidea
Nautiloids are a group of cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and species rich, with over 2,500 recorded species. Th ...
) similar to ''
Aipoceras
''Aipoceras'' is a genus of loosely coiled aipoceratid nautiloids with laterally compressed whorls; shells expanding moderately to fairly rapidly with a tendency to uncoil at maturity. Juvenile forms are somewhat cyrtoconic. The apical end forms ...
'' but tightly coiled and with only part of the body chamber divergent from the previous
whorl
A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs).
In nature
File:Photograph and axial plane floral diagra ...
. Shell
evolute
In the differential geometry of curves, the evolute of a curve is the locus (mathematics), locus of all its Center of curvature, centers of curvature. That is to say that when the center of curvature of each point on a curve is drawn, the result ...
, expanding fairly rapidly;
umbilicus open,
perforate
A perforation is a small hole in a thin material or web. There is usually more than one perforation in an organized fashion, where all of the holes collectively are called a ''perforation''. The process of creating perforations is called perfor ...
; whorl section ovoid to
subquadrate.
''Asymptoceras'' is known from
Mississippian (Lower Carboniferous) sediments in
Europe
Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
and
North America
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
.
References
* Bernard Kummel, 1964. Nautiloidea - Nautilida; Treatise on Invertebrate Paleontology, Part K. Geological Society of America.
''Asymptoceras''i
Fossilworks
Prehistoric nautiloid genera
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