Domatoceratina, Korn, 2025

Suborder Domatoceratina subordo nov.

Diagnosis

Suborder of the order Nautilida , in which a ventrolateral shoulder and an umbilical margin are formed early in ontogeny. Conch usually discoidal, subinvolute to evolute. Juvenile whorl profile circular. Adult whorl profile subquadrate or inverted trapezoidal with a distinct ventrolateral shoulder and a distinct umbilical margin in the early species, showing modifications during evolution including a concave venter in some derived species. Dorsal whorl zone always present, but usually very small except for some derived species. Juvenile sculpture sometimes with radial ribs on the flank; adult sculpture is usually lacking except for elongate ventrolateral tubercles in derived species. Septa simply domed in most of the species, with septal inflexion in and corrugated septa in some lineages. Suture line usually depending on the whorl profile, usually with shallow lobes and low saddles, and with distinct lobes in one clade. Siphuncle in central or subcentral position.

Included superfamilies

Grypoceratoidea Hyatt, 1900 (Early Carboniferous to Late Triassic; 22 Palaeozoic genera, 91 Palaeozoic species).

Permoceratoidea Miller & Collinson, 1953 (Early Permian; 2 genera, 2 species).

Subclymenioidea Shimansky, 1962 (Early to Late Carboniferous; 16 genera, 108 species).

Remarks

Taxonomy

Flower & Kummel (1950) placed the Domatoceratidae in the order Centroceratida ; the family was interpreted to have descended directly from the family Centroceratidae , and the domatoceratids in turn gave rise to the family Syringonautilidae . Shimansky (1957) had a similar view. He placed the family Domatoceratidae together with the families Centroceratidae , Grypoceratidae , Thrincoceratidae , Syringonautilidae and Permoceratidae in the superfamily Centrocerataceae . The origin of the suborder Domatoceratina subordo nov. was there interpreted to be in the family Centroceratidae . In contrast, Kummel (1964) placed the family Grypoceratidae , in which he included the domatoceratids, in the superfamily Trigonocerataceae . The families Syringonautilidae and Permoceratidae should have been evolved from the Grypoceratidae .

Dzik (1984) presented a very different concept for the family Grypoceratidae ; he considered many previously accepted genera to be synonyms and included the genera Epidomatoceras , Stroboceras , Subclymenia and Permoceras in the family Grypoceratidae . On the other hand, he placed the genus Stenopoceras Hyatt, 1893 , previously placed in Domatoceratidae , in the family Phacoceratidae .

Here, the suborder Domatoceratina subordo nov. is separated to include a group of nautilids that appears to be a monophylum, which has an origin in Early Carboniferous trigonoceratids ( Dzik 1984), and, therefore, a combination with the Middle Devonian centroceratids is rejected. The suborder is characterised by a rather distinct set of characters. Most importantly, a ventrolateral shoulder and an umbilical margin are formed early in ontogeny ( Fig. 3B–C, G–H View Fig ). This character, together with flattened flanks and a flattened or concave venter, is maintained throughout the evolutionary history of the suborder. Only occasionally, these characters were regressed in side branches.

Morphology and subdivision

The species of Domatoceratina subordo nov. are usually easily recognisable as belonging to the suborder on the basis of their conch morphology and ornamentation. Apart from a few early representatives and some species in advanced side branches, all species are characterised by flattened flanks and an applanate or a more or weakly concave venter. The ventrolateral shoulder is usually subangular or angular and, in some species, skid-like reinforced. Another characteristic of Domatoceratina is the almost complete absence of coarse sculpture.

The following superfamilies are distinguished here:

Subclymenioidea . – Forms with usually quadrate whorl profile with a flattened or concave venter; sculpture absent or with inconspicuous ribs on the flank. Septa sometimes with a ventral inflexion causing a distinct external lobe.

Grypoceratoidea . – Forms with usually quadrate or inverted trapezoidal whorl profile with a more or less strongly flattened or concave venter; sculpture absent or with inconspicuous ribs on the flank.

Permoceratoidea . – Forms with inverted trapezoidal whorl profile with a more or less strongly flattened venter; sculpture absent or with inconspicuous ribs on the flank. Septa corrugated, causing distinct lobes and saddles.

Origin Dzik (1984: 168) proposed an origin of the grypoceratids from the Early Carboniferous Epidomatoceras . He saw Domatoceras , the stratigraphically oldest genus of the superfamily, as a direct descendant of

Epidomatoceras from the Viséan.

Epidomatoceras and the family Subclymeniidae are probably derived from the Thrincoceratidae via the morphologically basal genus Maccoyoceras . The formation of the umbilical margin and ventrolateral shoulder could be considered as a new feature for the evolutionary lineage to the domatoceratids.

Phylogeny

Dzik (1984: 168) published a detailed diagram of the proposed phylogenetic relationships within the domatoceratids in the broader sense. Two major lineages can be seen in this diagram. The main lineage extends from Epidomatoceras via Domatoceras to the Triassic families Grypoceratidae and Syringonautilidae ; a secondary lineage branches off from the first and extends via the Late Carboniferous Titanoceras Hyatt, 1884 and the Late Permian Pseudotitanoceras Shimansky, 1965 to the Triassic genus Germanonautilus Mojsisovics, 1902 .

Descendants

Shimansky (1957) derived the modern nautiloids (order Nautilina ) from the family Domatoceratidae Miller & Youngquist, 1949 . Kummel (1964) had a similar view and derived his superfamily Nautilaceae de Blainville, 1825 from the family Domatoceratidae via the family Syringonautilidae Mojsisovics, 1902 . Dzik (1984: 175) postulated a continuous evolutionary transition from the Triassic genus Syringonautilus

Mojsisovics, 1902 to the Jurassic genus Cenoceras Hyatt, 1884 . According to the current state of knowledge, two further suborders can be derived from the Domatoceratina subordo nov.