''Ataxioceras'' is an extinct

Ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

cephalopod genus confined to the Upper Jurassic of Europe, included in the superfamily

Perisphinctoidea Perisphinctoidea, formerly Perisphinctaceae, is a superfamily of Middle Jurassic (Bajocian) to Lower Cretaceous (Barremian) Ammonitina, ammonites, commonly with evolute shells with strong ribbing that typically divides about mid flank before cro ...

. Previously ''Ataxioceras'' was assigned to the Perisphinctidae but has now been placed in the Ataxioceratidae for which it is the type genus. These fast-moving nektonic carnivores lived during the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

period, from 155.7 to 150.8 Ma.

Description

The shell is evolute, strongly ribbed and moderately umbilicate. Primary ribs, on the order of 32 -36 per whorl, are sharp and widely spaced, originate at the umbilical shoulder. Secondary ribs form about mid flank, generally by trifurcation, but sometimes quadrifurcation (splitting into threes or sometimes fours) of the primaries. The umbilicus is about 0.4 the shell diameter.

Distribution

Fossils of species within this genus have been found in the

sediments in Germany, France, India and Romania.

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
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Jurassic ammonites Ammonites of Europe {{Ammonite-stub