Neopolygnathus communis (Branson & Mehl, 1934) from the C. quadrantinodosa Zone at Łagów, the early L. styriacus Zone at Ostrówka, the P. trachytera Zone at Kowala, the late L. styriacus and the P. jugosus Zones at Ostrówka in the Holy Cross Mountains.

Neopolygnathus communis - P₁ element.

Diagnoza

Four related species that occur in large numbers in sample Dz46 do not show any morphological transitions and thus are obviously biologically distinct: N. communis, N. purus, N. vogesi, and N. biconstrictus. Of them, N. communis shows the most generalised morphology of its sp elements. They can be distinguished from those of other species by the almost parallel and strongly bent platform margins and by the depression in the lower surface immediately dorsal (posterior) of the pit. The platform is smooth except for singular knobs constricting the central concave area of the platform from both sides.

 The species occurs commonly in the Toumaisian part of the section in Kowala, its abundant occurrence alone starting from the shale bed above the Wocklumeria limestone. In Dzikowiec it follows N. purus, being always a subordinate and rather irregularly distributed component of the fauna. Its distribution in the upper part of the Chinese Muhua section is similar (Figs 4, 5) but, unlike the European occurrences, after being replaced by N. subplanus at the beginning of the Tournaisian (sample Mu-24), it did not reappear until the latter species changes into N. purus.

The apparatus of N. communis (Fig. 23) can be reconstructed owing to sample Dz-24, where sp elements of this species dominate numerically over few elements of N. purus atd N. vogesi. The oz elements of N. communis are distinct from the related species and easily distinguishable on the basis of a cllearly separated cusp, much larger than other denticles. In this respect the species is less derived than the other two.

The type population of the species comes from the outcrop of Bushberg sandstone at Brickeys, Missouri. This is an extremely long ranging species (Klapper 1966) from which all the remaining forms of the group are derived.

Margins of the platform of P₁ elements raised adorally, with more or less distinct longitudinal crests in its ventral area; only in extreme specimens tuberculation of various kinds may develop.

Porównanie

Populations of a narrow-platform form of N. communis from the K. crepida Zone are ancestral to a clade of variously ornamented forms united only by their depressed basal pit. I am inclined rather to the alternative interpretation, that the separation of pre-platform stage from the fast growing platform marginally is rather a developmental aspect not requiring fundamental change in controlling mechanisms and thus appearing independently in unrelated lineages. This may be only an expansion of the larval stage (sinuosa larva), poorly controlled by developmental regulatory mechanisms, as suggested by great population variability in early populations. The range of variability includes forms with narrow and wide platforms, completely smooth and ornamented with transverse ridges, without any crests, bearing crests parallel to the blade or at an angle to it. This morphologic lability ceases in the latest Famennian, where a morphologic gap develops between N. communis and N. vogesi.

Autekologia

Występowanie geograficzne

Łagów, Ostrówka, Kowala, Jabłonna. 

Zasięg czasowy

C. quadrantinodosa Zone; C. marginifera Zone.   

Materiały muzealne

ZPAL:1,447 specimens.

Literatura

Dzik, J. 2006. The Famennian "Golden Age" of conodonts and ammonoids in the Polish part of the Variscan sea. Palaeontologia Polonica 63, 1-359.