Subfamily Prolecanitinae Hyatt, 1884

Diagnosis

Subfamily of the Prolecanitidae with a lanceolate or pouched external lobe.

Subfamily composition

Prolecanites Mojsisovics, 1882; Paraprolecanites Karpinsky, 1889 [synonym of Prolecanites Mojsisovics, 1882]; Metacanites Schindewolf, 1922; Rhipaeocanites Ruzhencev, 1949 [synonym of Prolecanites Mojsisovics, 1882]; Dombarocanites Ruzhencev, 1949; Eocanites Librovitch, 1957; Michiganites Ruzhencev, 1962; Katacanites Kullmann, 1963; Asioclymenia Sun & Shen, 1965 [synonym of Eocanites Librovitch, 1957]; Becanites Korn, 1997; Kahlacanites Ebbighausen, Bockwinkel, Korn & Weyer, 2004; Nomismocanites gen. nov.

Morphology

Most of the representatives of the Prolecanitinae share the “standard prolecanitid morphology”, meaning that they have an evolute conch with a compressed oval whorl profile and a very small whorl overlap zone. Most of the species possess a weak ornament consisting only of fine growth lines. It appears that the highest morphological diversity in the shape of the conch appears at the beginning of their evolutionary history, the earliest prolecanitid genus Eocanites shows a rather wide range of whorl profiles including compressed oval, circular, subquadratic shapes with rounded, flat and concave venter. The ornament ranges from delicate to coarse with lateral folds and weak riblets.

Ontogeny

Most of the representatives of the subfamily Prolecanitinae have a simple conch ontogeny, simply because the juvenile conchs usually do not differ markedly from the adults. Like many other Palaeozoic ammonoids, the conch of the prolecanitids tend to be more slender during ontogeny.

Eocanites has, like most of the other early prolecanitid ammonoids, an ontogeny with nearly monophasic trajectories of the cardinal conch parameters.As seen in specimen GPIT-PV-63981 (E. delicatus sp. nov.), the ww/dm trajectory decreases from about 0.65 at 1.2 mm diameter to 0.28 at 12 mm diameter. The uw/ dm trajectory shows an initial increase to 0.57 at 3 mm diameter and then stays at this value. The whorl expansion rate fluctuates between 1.60 and 1.70 in the growth interval between 2 and 12 mm diameter.

Phylogeny

It is up to now not clear from where the genus Eocanites and with this the entire order Prolecanitida derives. An origin from Devonian ammonoids of the order Agoniatitida, as proposed by Schindewolf (1929) because of the putative different suture ontogeny (“U type ontogeny”) and accepted by Ruzhencev (1960) does not have to be discussed any longer. Already Vöhringer (1960) suggested an origin of the prolecanitid ammonoids from prionoceratids with wide umbilicus in the juvenile stage (such as Stockumites intermedius). Korn et al. (2003b) provides rather firm evidence that the suture ontogeny of the prolecanitids shows the A-mode and hence does not differ from the goniatitids, hence an origin from prionoceratids at the Devonian–Carboniferous boundary is most likely.

Eocanites appears suddenly with the rather distinct species E. ruani and this cannot be connected with any other ammonoid species so far. Among the genera with open umbilicus in a rather late growth interval, only Gattendorfia is known to occur at the same stratigraphic level. However, G. subinvoluta and G. rhenana sp. nov. possess inner whorls with a very characteristic trapezoidal profile, while these in Eocanites are circular or depressed oval. A tendency towards trapezoidal whorl profiles can also be seen in Stockumites, such as S. hilarus from the Devonian–Carboniferous boundary beds of the Anti-Atlas in Morocco (Korn et al. 2004, 2007). This may exclude a direct phylogenetic connection.

Stratigraphic occurrence

Representatives of the subfamily Prolecanitinae are known from near the base of the Carboniferous throughout to the Serpukhovian; particularly in the latest Viséan to early Serpukhovian strata of the South Urals they are diverse and very common (Ruzhencev & Bogoslovskaya 1971).

Eocanites is obviously restricted to the Hangenberg Limestone and its time equivalents in other regions. Detailed bed-by-bed collections are only available from the Rhenish Mountains and it is particularly the Oberrödinghausen railway cutting that yielded numerous specimens from a number of horizons. At this place, the genus has not been recorded from the lowermost limestone bed (bed 6) but enters with E. ruani in bed 5. Only somewhat higher, the other species occur successively, e.g., E. nodosus in bed 4, E. brevis and E. spiratissimus in bed 3d, E. tener in bed 3c, E. supradevonicus in bed 3b, E. delicatus sp. nov. in bed 2 and E. planus in bed 1.

Geographic occurrence

Many of the Early Tournaisian ammonoid occurrences contain specimens of Eocanites and hence the genus shows a wide geographic distribution. The genus is reported from Alberta (questionable; Schindewolf 1959), south Portugal (Korn 1997), the Montagne Noire (Becker & Weyer 2004; Korn & Feist 2007), the Rhenish Mountains (Schmidt 1924; Schindewolf 1926b; Vöhringer 1960; Korn 1994; Korn & Weyer 2003), the Thuringian Mountains (Bartzsch et al. 2003), Lower Silesia (Frech 1902; Dzik 1997) the Carnic Alps of Austria and Italy (Korn 1992b; Schönlaub et al. 1992), Guizhou (Sun & Shen 1965; Ruan & He 1974; Ruan 1981) and the Anti-Atlas of Morocco (Bockwinkel & Ebbighausen 2006; Ebbighausen & Bockwinkel 2007).