Ataxioceras
Encyclopedia
Ataxioceras is an extinct Ammonite
cephalopod genus confined to the Upper Jurassic of Europe, included in the superfamily Perisphinctaceae.
The shell is evolute , strongly ribbed and miderately umbilicate. Primary ribs, on the order of 32 -36 per whorl, are sharp and widely spaced, originate at the unbilical shoulder. Secondary ribs form about mid flank, generally by trifurcation, but sometimes quadrafurcation (splitting into threes or sometimes fours) of the primaries. The umbilicus is about 0.4 the shell diameter.
Previously Ataxioceras was assigned to the Perisphinctidae but has now been placed in the Ataxioceratidae for which it is the type genus.
Ammonitida
The Ammonitida is an order of more highly evolved ammonoid cephalopods from the Jurassic and Cretaceous time periods, commonly with intricate ammonitic sutures....
cephalopod genus confined to the Upper Jurassic of Europe, included in the superfamily Perisphinctaceae.
The shell is evolute , strongly ribbed and miderately umbilicate. Primary ribs, on the order of 32 -36 per whorl, are sharp and widely spaced, originate at the unbilical shoulder. Secondary ribs form about mid flank, generally by trifurcation, but sometimes quadrafurcation (splitting into threes or sometimes fours) of the primaries. The umbilicus is about 0.4 the shell diameter.
Previously Ataxioceras was assigned to the Perisphinctidae but has now been placed in the Ataxioceratidae for which it is the type genus.
References
- D.T. Donovan et al. Classification of the Jurassic Ammonitina, in The Ammonoidea, M.R. House and J.R. Senior (eds); Academic Press 1981. Systematics Association Special Volume. 18. http://rogov.zwz.ru/Donovan,%20Callomon,%201981_J%20Ammon.PDF