Solenochilina Flower, 1950

Suborder Solenochilina Flower, 1950

Diagnosis

Suborder of the order Nautilida , in which the conch form ranges from cyrtoconic, gyroconic to nearly involute with extraordinarily high coiling rate. Dorsal whorl zone missing or very small. Shell surface usually smooth. Suture line nearly straight with a small external lobe. Siphuncle in marginal ventral position.

Included superfamilies

Aipoceratoidea Hyatt, 1884 (Early Carboniferous to Early Permian; 7 genera, 54 species). Scyphoceratoidea Ruzhencev & Shimansky, 1954 (Early Carboniferous to Early Permian; 9 genera,

23 species).

Remarks

Taxonomy

The position of the solenochilids within the order Nautilida has been very unstable over the decades, with different authors expressing sometimes very different opinions. Flower & Kummel (1950) presented them as an isolated order Solenochilida , derived (with a question mark) from the family Barrandeoceratidae Foerste, 1925 .

Shimansky (1957) placed the superfamily Solenochilaceae , to which he included the families Litogyroceratidae Shimansky, 1957 , Scyphoceratidae , Dentoceratidae and Solenochilidae , in the suborder Rutoceratina . Later, Shimansky (1962, 1967) modified this scheme only in the minor detail of giving priority to the names Aipoceratidae and Aipocerataceae over the names Solenochilidae and Solenochilaceae .

Furnish & Glenister (in Kummel 1964: K440) interpreted the superfamily Aipocerataceae , to which they assigned the families Aipoceratidae , Solenochilidae and Scyphoceratidae , as an independent evolutionary lineage, which possibly derived from the superfamily Tainocerataceae ( Kummel 1964: K385).

Dzik (1984) considered the families Aipoceratidae and Solenochilidae to belong to an uncertain suborder. He suppressed the family Scyphoceratidae that was recognised by the other authors and placed the genera belonging to it in the orthoceratid family Cycloceratidae Hyatt, 1900 ( Dzik 1984: 130).

Due to the lack of new information, little can be contributed here to the two competing systematic interpretations. However, on the basis of the somewhat marginal position of the siphuncle, the family Scyphoceratidae is provisionally retained in the suborder Solenochilina .

Morphology and subdivision

The suborder Solenochilina is characterised by two main features, which are the ventrally located siphuncle and the very high coiling rate. Two superfamilies are recognised here:

Aipoceratoidea Hyatt, 1884 . – Conch cyrtoconic, gyroceraconic to subinvolute or involute, pachyconic to globular with a very mall whorl overlap zone.

Scyphoceratoidea Ruzhencev & Shimansky, 1954 . – Conch from nearly orthoconic to cyrtoconic.

Phylogeny

The origin of the suborder Solenochilina has been discussed several times in the literature and cannot yet be considered sufficiently resolved. Flower (1955: 256) interpreted all Carboniferous coiled nautiloids as derived from rutoceratids and explicitly included the solenochilids: “Probably the small Late Paleozoic order the Solenochilida has its origin also in the Rutoceratida”. This concept was supported by Shimansky

(1957, 1962, 1967), Kummel (1964) and Flower (1964: 5). Flower (1964: 12), however, stated that the solenochilids were “almost certainly” allied to the order Oncoceratida .

Dzik (1984: 156) was not sure whether the two families, Aipoceratidae and Solenochilidae , were phylogenetically related and suggested the Devonian genera Geitonoceras Zhuravleva, 1974 and Cranoceras Hyatt, 1884 as possible ancestors. According to Dzik (1984: 157), the data suggest that solenochilids “... are much more closely related to the Oncoceratidae than to the Nautilida ”. But at the same time, he suggested that “... it is more reasonable to retain the Aipocerataceae in the Nautilida until their systematic position is known”. That view is shared here.