''Newmarracarroceras'' is an

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 ...

from the early middle

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. ...

with a ribbed subinvolute shell with a keel running along the venter, or outer rim. The umbilicus is moderately wide, exposing the inner whorls exposed in part. ''Newmarracarroceras'' has a fairly wide geographic range and includes species previously described under '' Fontannesia''. Related genera include ''

Asthenoceras ''Asthenoceras'' is a genus of ammonoid from the Middle Jurassic (Lower Bajocian) with dwarfish, evolute, smooth, compressed, discoidal, strongly keeled shell. ''Asthenoceras'' belongs to the Sonniniidae and may be a subgenus of the Lower Jurassi ...

'', ''Fontannesia'', '' Guhsania'', and '' Witchellia''.

References

* Ammonitida genera Sonniniidae Ammonites of Australia Jurassic ammonites Ammonites of Europe {{ammonitina-stub