Prionoceratinae Hyatt, 1884

Korn, Dieter & Weyer, Dieter, 2023, The ammonoids from the Gattendorfia Limestone of Gattendorf (Devonian-Carboniferous boundary; Upper Franconia, Germany), European Journal of Taxonomy 883, pp. 1-61 : 6-7

Subfamily Prionoceratinae Hyatt, 1884

[nom. transl. Bartzsch & Weyer (1988a: 136), pro Prionocerae Hyatt, 1884]

Diagnosis

Subfamily of the family Prionoceratidae with the sutural formula E A L U I, adventive lobe V-shaped or lanceolate, pointed. Conch in the juvenile stage usually subinvolute, rarely subevolute; adult stage involute or subinvolute. Coiling rate usually very low or low (WER=1.40–1.75). Shell ornament with fine to coarse growth lines, without ribs.

Included genera

Prionoceras Hyatt, 1884 ; Haugiceras Cossmann 1900 [synonym of Prionoceras ]; Postprolobites Wedekind, 1913 [synonym of Prionoceras ]; Paragattendorfia Schindewolf, 1924 ; Cunitoceras Weyer, 1972 [problematic genus]; Mimimitoceras Korn, 1988 ; Globimitoceras Korn, 1993 ; Rectimitoceras Becker 1996 [synonym of Mimimitoceras ]; Kornia Ebbighausen & Bockwinkel, 2007 .

Morphology

Species of the subfamily Prionoceratinae are characterised by a simple conch geometry; the conch is discoidal and more often pachyconic to globular with a nearly closed or closed umbilicus and almost always a very low or low coiling rate. This morphology is shared by the two main genera Prionoceras and Mimimitoceras (e.g., Korn et al. 2014, 2015). Another common feature of the two genera are the shell constrictions, which are present in all species at least in the early stage of ontogeny. Almost all species have a shell ornament consisting only of growth lines; these almost always have a convex course on the flank and form a broad, shallow ventral sinus.

The suture line also shows little variation. It consists of the basic elements E A L U I; the shape of the external and adventive lobe varies between species. Usually, species with a discoidal conch show a narrower, sometimes lanceolate external lobe, while in globular species it is often broader and V-shaped. A deviation from this rule, however, is Globimitoceras with a globular conch but with a very narrow external lobe.

Ontogeny

The species of the subfamily underwent a comparatively simple ontogenetic development; this means that the morphology of juveniles and adults does not differ markedly. Conch allometry is usually weakly developed; the ontogenetic trajectories ( Korn 2012) are often monophasic with a simple decrease of the ww/dm ratio, for example. These simple ontogenetic trajectories are mainly caused by the small width of the umbilicus in the juvenile stage. Therefore, the whorl profiles are rather similar at all growth stages and range from C-shaped to horseshoe-shaped. Only the trend towards more slender conchs that is present in most Palaeozoic ammonoids is evident.

Phylogeny

The Prionoceratinae are the ancestral subfamily of the family Prionoceratidae and thus of all post Devonian ammonoids. While the prionoceratids of the Famennian formed only one previously known side branch, the subfamily Balviinae with its paedomorphic conchs ( Korn 1992a, 1995a, 1995b) is distinguished by divergent morphologies. Several side branches formed in the earliest Carboniferous. The most successful of these is the subfamily Acutimitoceratinae , described in more detail below. Less successful side branches are the genera Globimitoceras , Kornia and Paragattendorfia , all of them restricted to the Early and Middle Tournaisian, but apparently extinct without descendants.

Stratigraphic occurrence

The Prionoceratinae have its acme in the middle and late Famennian, where several taxa are used as index species ( Korn et al. 2014, 2015) that complement the clymeniid-based zonation. According to current knowledge, the Prionoceratinae are one of the few ammonoid lineages that survived the Hangenberg Event at the Devonian–Carboniferous boundary ( Korn 1986, 1993, 2000; Becker 1993; Kullmann 2000). In contrast to the “failed survivors”, the cymaclymeniids, which survived the biocrisis with a few forms but became extinct shortly afterwards ( Korn 1990; Korn et al. 2004), the evolution of the prionoceratids is, in contrast to the cymaclymeniids, not a “dead clade walking” ( Jablonski 2002), but the evolution of a group with a very successful radiation in the Early Carboniferous. However, this successful radiation was caused by flourishing of the subfamily Acutimitoceratinae , while the genera of the Prionoceratinae have only a short stratigraphic range, apparently restricted to the early and middle Tournaisian. The late Tournaisian record of the problematic species Cunitoceras schindewolfi Weyer, 1972 in the Harz Mountains requires confirmation.

Geographic occurrence

The Prionoceratinae are a subfamily with an almost global distribution in the Middle and Late Famennian; in the Early and Middle Tournaisian the distribution is significantly restricted. The most important occurrences in Europe are in the Rhenish Mountains ( Vöhringer 1960; Korn 1994; Korn & Weyer 2003), Franconia ( Schindewolf 1923; Korn 1994), Thuringia ( Weyer 1977), questionably the Harz Mountains ( Schindewolf 1951), Silesia ( Dzik 1997), the Carnic Alps ( Korn 1992b) and the Montagne Noire ( Becker & Weyer 2004; Korn & Feist 2007). Early Carboniferous species are also known from the Anti-Atlas ( Bockwinkel & Ebbighausen 2006), the South Urals ( Popov 1975), Guizhou ( Ruan 1981), Karaganda ( Librovitch 1940) and possibly Michigan ( Winchell 1862; Miller & Garner 1955).