Stroboceras Hyatt, 1884

Korn, Dieter & Bockwinkel, Jürgen, 2022, Early Carboniferous nautiloids from the Central Sahara, southern Algeria, European Journal of Taxonomy 831, pp. 67-108 : 80-81

Genus Stroboceras Hyatt, 1884

Type species

Gyroceras Hartii Dawson, 1858 ; by original designation.

Diagnosis

Genus of the family Trigonoceratidae with discoidal, evolute conch; whorls slightly embracing, outer whorl may have lose contact with preceding whorls. Adult conch with a polygonal whorl profile; venter slightly convex, flattened, less often slightly concave, flanks almost flat or irregularly concave, dorsum slightly concave. Prominent longitudinal keels usually well developed, separated by concave zones. Suture line with small lobes and saddles reflecting keels and longitudinal grooves on the surface of the conch. Siphuncle small with subcentral position between septum centre and venter (after Shimansky 1967; emended).

Included species

Nautilus ammoneus Eichwald, 1857 , South Urals; Stroboceras anglicum Hyatt, 1893 , Yorkshire; Nautilus bicarinatus de Verneuil, 1845 , South Urals; Stroboceras evansi Ramsbottom & Moore, 1961 , Ireland; Stroboceras gordoni Niko & Mapes, 2005 , Arkansas; Gyroceras Hartii Dawson, 1858 ; Nova Scotia; Coelonautilus humerosus Schmidt, 1951 , Rhenish Mountains; Stroboceras intermedium Miller & Garner, 1953 , Michigan; Stroboceras mstense Shimansky, 1967 , Moscow Basin; Stroboceras trifer Schmidt, 1951 , Silesia; Stroboceras mane sp. nov., Algeria; Stroboceras ancilis sp. nov., Algeria.

Remarks

A systematic treatment of the morphologically diverse Stroboceras form complex is difficult and it is not clear what the relationships between the numerous species are. Turner (1954) introduced the genus Epistroboceras to separate the laterally compressed forms. These forms are supposed to differ from Stroboceras by the narrower coiling: Stroboceras should be tarphophioceraconic (i.e., with the last whorl detached), while Epistroboceras should be tarphyceraconic (i.e., with the last whorl in close contact with the preceding one).

This distinguishing criterion was also mentioned by Kummel (1964), but Gordon (1965) pointed out that only the type species S. hartii has a straightened-out whorl at maturity. However, Miller & Garner (1953) had already pointed out that the holotype of this species is “slightly crushed”. They also reported “… that the conch is coiled and is very slightly involute; though at full maturity the adoral portion of the body chamber straightens and loses contact with the preceding whorl but retains, however, the slight impressed zone.” ( Miller & Garner 1953: 134). This combination of characters is questionable; a concave whorl zone is practically always created by enclosing the preceding whorl. Therefore, it cannot be excluded that it is a preservation effect. Gordon (1965) accepted Epistroboceras only as a subgenus of Stroboceras , distinguished by the loss of longitudinal sculpture in late ontogeny.

Shimansky (1967) discussed the relationship between the two genera in detail and concluded that the relationships and boundaries of the genera Stroboceras and Epistroboceras were not entirely clear. He considered it possible that, in addition to the whorl profile, the size of the umbilical window could also serve to distinguish between the two genera.

Histon (1999) characterised the genus Epistroboceras , among other characteristics, by the strongly compressed conch, converging flanks and narrow concave venter. More recently, Niko & Mapes (2004) discussed the relationship between Stroboceras and Epistroboceras ; in distinguishing the two genera, they upheld the presumed detachment of the adult whorl in Stroboceras . As a further difference between the two genera, they mentioned that the “… lateral grooves developed in the juvenile stage become obsolescent with maturity” in Epistroboceras ( Niko & Mapes 2004: 341) .

The distinction between the two genera is an issue that cannot be solved with the material available from the Sahara Desert, it is beyond the scope of our investigations. For the time being, we follow the path suggested by Shimansky (1967) of grouping the forms with a broad venter under Stroboceras and those with a narrow venter under Epistroboceras .