Temnocheilidae Mojsisovics, 1902

Family Temnocheilidae Mojsisovics, 1902

Fig. 10 View Fig

Diagnosis

Family of the superfamily Trigonoceratoidea with subinvolute or subevolute conch; coiling rate usually very high. Whorl overlap small if present. Adult whorl profile commonly ranging from triangular to trapezoidal with weakly embracing whorls; juvenile whorl profile broadly oval or bicarinate. Ornament with longitudinal ridges or lines in the juvenile stage, adult conch with ventrolateral nodes, spiral ridges or smooth, sometimes with spiral ornament. Position of the siphuncle between centre and venter. Suture line with broadly rounded external and lateral lobes; internal lobe broadly V-shaped; sometimes with an annular process.

Included genera

Temnocheilus M‘Coy, 1844 (Viséan to Kasimovian; 10 species).

Endolobus Meek & Worthen, 1865 (Viséan to? Roadian; 14 species).

Knightoceras Miller & Owen, 1934 (Viséan to Artinskian; 9 species).

Tylodiscoceras Miller & Collinson, 1950 (Serpukhovian; 2 species).

Valhallites Shimansky, 1954 (Viséan to? Artinskian; 8 species).

Nikenautilus Shimansky, 1962 (Serpukhovian; 2 species).

Kummeloceras Shimansky, 1967 (Artinskian; 1 species).

Temnocheiloides Shimansky, 1967 (Bashkirian to Moscovian; 2 species).

Latitemnocheilus Sturgeon, Windle, Mapes & Hoare, 1982 (Serpukhovian to Asselian; 9 species). Paravalhallites Shimansky, 1990 (Bashkirian; 1 species).

Alexoceras Leonova & Shchedukhin, 2020 (Asselian or Sakmarian; 1 species).

Remarks

The Temnocheilidae is a family that has been defined in various ways over the years. Originally, it was placed by Mojsisovics (1902: 230) as the fourth family within his higher taxon “ Nautilidae ” and contained a number of morphologically very different genera such as Temnocheilus M‘Coy, 1844 , Metacoceras Hyatt 1883 , Tainoceras Hyatt 1883 , Foordiceras Hyatt, 1893 , Pleuronautilus Hyatt, 1900 and Germanonautilus Mojsisovics, 1902 . It should be noted that the concept of the family had a different meaning at that time than it does today. Later the family Temnocheilidae was largely ignored and Temnocheilus was usually placed in the family Tainoceratidae . Turner (1954) then redefined the family, pointing out the close relationship between Temnocheilus and the newly described genus Subvestinautilus .

Kummel (1964) did not accept the validity of the family and considered it a synonym of the Koninckioceratidae Hyatt, 1900 . This family contained a rather heterogeneous list of genera; Temnocheilus stood next to Millkoninckioceras Kummel, 1963 , Endolobus Meek & Worthen, 1865 , Planetoceras Hyatt, 1893 , Foordiceras Hyatt, 1893 and Tylodiscoceras Miller & Collinson, 1950 . In contrast, Shimansky (1967, 1979) distinguished the families Temnocheilidae and Koninckioceratidae ; he even considered both groups to be independent superfamilies, each containing only one family. Dzik (1984) placed Temnocheilus and related genera in the family Trigonoceratidae and Histon (1999) followed Kummel (1964) in placing Temnocheilus in the family Koninckioceratidae .

The typical early representatives of the Temnocheilidae are known from Tournaisian and Viséan strata ( Fig. 10 View Fig ), and it is not certain that stratigraphically younger genera really belong to the same group. This is particularly true for the records of Temnocheilus -like genera from Late Carboniferous strata of North America, which have usually been placed in the genera Temnocheilus and Latitemnocheilus . This is also true for T. annulonodosus Sturgeon, Windle, Mapes & Hoare, 1982 , in which Sturgeon et al. (1982)

found the internal lobe to be broadly rounded and shallow with a small annular lobe. However, in Viséan representatives of Temnocheilus the internal lobe is broadly V-shaped ( Korn & Klug 2023).

It seems worth discussing whether the supposed Late Carboniferous temnocheilids are in fact derived from Early Carboniferous species, or whether they have arisen independently, e.g., by regression of a previously present umbilical margin. Since this cannot be resolved here, these species are provisionally and cautiously placed in the family Temnocheilidae .

Both Turner (1954) and Dzik (1984) suggested that Temnocheilus was derived from Vestinautilus . The main argument for this was the similar conch geometry; the longitudinal ridges were said to have been transformed into a ventrolateral row of nodes. For this reason, the genera Vestinautilus and Subvestinautilus are considered here to be the ancestors of the family Temnocheilidae . The material now available allows the reconstruction of a very plausible evolutionary lineage, leading from species of the Trigonoceratidae with conchs completely ornamented with longitudinal lines or ridges (e.g., Rineceras ) with an increasing reduction of the number of these spiral elements to almost unornamented conchs (e.g., Knightoceras ).

The position of the genus Endolobus has not yet been fully resolved. While Kummel (1964) placed it in the family Koninckioceratidae, Shimansky (1967 , 1979) placed it in the family Temnocheilidae . Dzik (1984) saw Endolobus as derived from Vestinautilus in a parallel evolutionary lineage to Temnocheilus . Indeed, the rather narrow and deep internal lobe in Endolobus can be seen as a good indicator for a placement within the Temnocheilidae .