Pseudarietitinae Bartzsch & Weyer, 1987

Korn, Dieter & Weyer, Dieter, 2023, The ammonoids from the Gattendorfia Limestone of Oberrödinghausen (Early Carboniferous; Rhenish Mountains, Germany), European Journal of Taxonomy 882, pp. 1-230 : 169-171

Subfamily Pseudarietitinae Bartzsch & Weyer, 1987

[ nom. transl. Korn (1994: 75), pro Pseudarietitini Bartzsch & Weyer, 1987]

Subfamily composition

A total of 17 species of the Pseudarietitinae have been described so far; they belong to the following genera: Pseudarietites Frech, 1902 (7 species); Paralytoceras Frech, 1902 (3 species); Paprothites Bartzsch & Weyer, 1987 (7 species); Rodingites gen. nov. (2 species),

Two of the species are somewhat problematic, “ Pseudarietites serratus ” has some affinities to Paralytoceras and “ Protocanites carinatus Vöhringer, 1960 ” is difficult to interpret as only one specimen is available. The conch shape similar to “ Pseudarietites planissimus ” suggests an attribution to this genus rather than to Eocanites . For the latter two species, the new genus Rodingites is introduced here.

Morphology

The pseudarietitin ammonoids are separated from the other Early Tournaisian ammonoids by two main characters, (1) the subevolute to evolute conch (which, however, also characterises some gattendorfiins and the early prolecanitid ammonoids) and (2) the rather coarse and often sharp ribs (which are not present in the gattendorfiins and prolecanitids). An additional character of the advanced pseudarietitins ( Pseudarietites , Rodingites gen. nov., Paralytoceras ) is the raised or even attached ventral keel, which may be simple or serrate.

Ontogeny

The conch ontogeny of the species is rather simple with a more or less monophasic trajectory of the ww/ dm ratio, which is characterised by a continuous decrease. Different phases are only separable in some cases, such as Pseudarietites subtilis (see below), but they are weakly developed when compared with species of other prionoceratid subfamilies. The ventral keel of many of the genera is developed only rather late in ontogeny, at a conch diameter of about 8 mm.

Phylogeny

The origin of the subfamily Pseudarietitinae can be seen in the Gattendorfiinae , particularly in the genus Weyerella , which possibly gave rise to the morphologically simplest pseudarietin genus Paprothites . Species of both genera share a thickly discoidal, subevolute conch; the two genera differ mainly in the presence of ribs in Paprothites . These ribs, however, can be rather variable in Paprothites ; P. raricostatus and P. beckeri sp. nov., for instance, possess very faint ribs and in this character are rather close to Weyerella .

Within the Pseudarietitinae , an evolution from the non-keeled Paprothites to the other two genera with keeled forms is obvious; it can also be observed in the stratigraphic succession with non-keeled Paprothites below the first occurrence of keeled Pseudarietites . The formation of the keel starts with the presence of incipient paired ventral grooves (which can be seen in Paprothites ruzhencevi ), which in the genus Pseudarietites are then much more pronounced and allow a midventral keel to be developed. The keel is simple in the typical species of Pseudarietites (e.g., P. silesiacus and P. westfalicus ) but serrated in the advanced P. serratus .

Stratigraphic occurrence

The genera of the subfamily Pseudarietitinae do not occur at the base of the Hangenberg Limestone or its time equivalents. In the Oberrödinghausen railway cutting, the first occurrence of Paprothites dorsoplanus is in bed 4 (according to Vöhringer 1960) and the first occurrence of Pseudarietites westfalicus is in bed 3c; the highest diversity of the subfamily occurs in beds 3c and 3b. These two species were selected by Vöhringer (1960) as index fossil for the middle two subzones of his Gattendorfia Stufe.

It has to be noted that the stratigraphic succession of the species of the subfamily does not perfectly reflect the proposed phylogenetic succession. The proposed phylogenetically simplest form Paprothites raricostatus was found only above the obviously more derived P.dorsoplanus .Furthermore, Paralytoceras sp. was collected in bed 3d, which means that the genus occurs slightly below the stratigraphic range of Pseudarietites .

Geographic occurrence

The Pseudarietitinae is a subfamily that is largely known from only three regions worldwide, Lower Silesia with the single locality Dzikowiec (e.g., Tietze 1870; Frech 1902; Weyer 1965; Dzik 1997), the Rhenish Mountains with a number of localities such as Hasselbachtal, Oese, Oberrödinghausen and Drewer (e.g., Schmidt 1924; Vöhringer 1960; Korn 1994; Korn et al. 1994; Korn & Weyer 2003) as well as Guizhou with the localities Wangyou ( Sun & Shen 1965; Ruan 1981) and Dapoushang ( Sheng 1989). There exists only one illustrated report of Pseudarietites from Thuringia ( Bartzsch & Weyer 1982, 1986) and one report on Paprothites from Pomerania ( Korejwo 1979). Other regions with considerably diverse Early Tournaisian ammonoid records are the Montagne Noire of France ( Korn 1993; Korn & Feist 2007), the Carnic Alps of Austria and Italy ( Korn 1992b; Schönlaub et al. 1992), the Anti-Atlas of Morocco ( Bockwinkel & Ebbighausen 2006; Ebbighausen & Bockwinkel 2007) and the Gourara region of Algeria ( Ebbighausen et al. 2004), however these regions did not provide material of the Pseudarietitinae .

The four genera occur, in the three regions, in different frequencies. Only Paprothites and Pseudarietites occur rather regularly in the middle part of the Hangenberg Limestone of the northern Rhenish Mountains. By contrast, specimens of Rodingites gen. nov. and Paralytoceras belong to the rarest Early Tournaisian ammonoids and are known from only few places (Lower Silesia, Rhenish Mountains, Guizhou). In all sites they occur in extremely low numbers. In the Rhenish Mountains, for instance, Rodingites is known by only one specimen of each of the two species. The genus is also very rare at Dzikowiec ( Weyer 1965; Dzik 1997).

Only two specimens of Paralytoceras crispum are known from the type locality at Dzikowiec in Lower Silesia and only two fragmentary specimens are preserved from the Oberrödinghausen railway cutting. One of these was shown by Weyer (1965, pl. 6, fig. 4) and the second was found in the unpublished parts of the Vöhringer collection. During intensive field collections by DW in 1993 and 1994, only a few further specimens of Paralytoceras species was collected.

Palaeogeography

The distribution patterns of the species of the subfamily are not fully investigated. According to current knowledge, the Central European occurrences in the Rhenish Mountains and Lower Silesia are rather similar and largely composed of the same species but they differ markedly from the assemblages known from Guizhou. The reports on the species Pseudarietites serratus and Paralytoceras crispum from Guizhou ( Ruan 1981) cannot be confirmed. The specimen of “ P. serratus ” is strongly corroded and does not clearly show a serrate keel and the specimen of “ P. crispum ” is a poorly preserved fragment difficult to identify.