Tainoceras is an extinct coiled cephalopod that live during the later part of the Paleozoic

Paleozoic

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

 and Triassic

Triassic

The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

, that belongs to the nautiloid family Tainoceratidae.

Tainoceras has an evolude shell with a subquadrate whorl section that bears a double row of nodes on either side of its broad outer rim (venter). Metacoceras

Metacoceras

Metacoceras is a nautilitoid cephalopod from the Upper Carboniferous and Permian, the shell of which is moderately evolute with a subquadrate whorl section, bearing nodes on the ventral or umbilical shoulders or both, but otherwise smooth. The siphuncle is small, subcentral and orthochoanitic...

is similar except for lacking the double rows of nodes. Tainionautilus

Tainionautilus

Tainonautilus is an extinct coiled cephalopod that lived during the Permian and Early Triassic which is included in the nautiloid family Tainoceratidae....

is similar, except that instead of nodes it has thick slanting lateral ribs

References

• Kummel 1964, Nautiloidea—Nautilida. Treatise on Invertebrate Paleontology Part K Mollusca 3. Geol Soc of America and Univ Kansas Press Teichert and Moore (eds)