Metacoceras is a nautilitoid

Nautilitoidea

The Nautilitoidea is a superoder within the subclass Nautiloidea, comprizing the phylogenetically related Nautilida, Oncocerida, and Tarphycerida....

 cephalopod from the Upper Carboniferous

Carboniferous

The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 (Pennsylvanian

Pennsylvanian

The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...

) and Permian

Permian

The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "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

Siphuncle

The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula...

 is small, subcentral and orthochoanitic. The suture has shallow ventral and lateral lobes but no dorsal or annular lobe.

Matacoceras, named by Hyatt, 1883, is a genus in the nautilid

Nautilida

The Nautilida constitute a large and diverse order of generally coiled nautiloid cephalopods that began in the mid Paleozoic and continues to the present with a single family, the Nautilidae which includes two genera, Nautilus and Allonautilus, with six species...

 superfamily Tainocerataceae

Tainocerataceae

The Tainocerataceae is a superfamily in the cephalopod order Nautilida characterized by straight to loosely coiled shells, generally with a degressed, such that the width is greater than the height, to quadrate whorl section. Many bore spines, ribs, frills, wings, or nodes...

. Its distribution is cosmopolitan.

Aulametacoceras, also a tainoceratid genus, is like Metacoceras except for having several longitudinal ridges and grooves along the venter. It is also a later genus with a more limited distribution, found in the Lower Permian and Upper Triassic in North America (U.S.A) and Europe (Alps).

Mojvaroceras is a tainoderatid genus, like Metacoceras and its direct evolutionary descentant, differing in being slightly more involute and having a lobe on the inner, dorsal, side. It is known from Triassic sediments in Eurasia and western North America.

References

• Bernhard Kummel, 1964. Nautiloidea-Nautilida. Treatise on Invertebrate Paleontology, Part K. Geological Soc. of America and University of Kansas press. Teichert and Moore (eds)
• Metacoceras -Paleodb 11/07/10