Nielsenoceras is a Paraceltitid

Paraceltitidae

Paraceltitidae is a family of Middle and Upper Permian cephalopods, that comprise the earliest of the Ceratitida. Paraceltitidids have variably ribbed, discoidaly evolute shells with compressed elliptical whorl sections and simple suture lines. Their origin is most likely in the Daraelitidae of...

 genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of from the lower Upper Permian, known from sediments in west Texas. The genus is distinguished by exceptionally broad prongs of the ventral lobe and by the presence of a shallow groove on the outer flanks.

Paraceltitids (family Paraceltitidae

Paraceltitidae

Paraceltitidae is a family of Middle and Upper Permian cephalopods, that comprise the earliest of the Ceratitida. Paraceltitidids have variably ribbed, discoidaly evolute shells with compressed elliptical whorl sections and simple suture lines. Their origin is most likely in the Daraelitidae of...

) are ceratitid

Ceratitida

The Ceratitida is an order that contains almost all ammonoid cephalopod genera from the Triassic as well as ancestral forms from the Upper Permian, the exception being the phylloceratids which gave rise to the great diversity of post Triassic ammonites....

 ammonoid cephalopods that lived during the Late Permian, near the end of the Paleozoic

Paleozoic

The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...

.