Diagnoza

Morphologically, this is a rather generalized and variable species (Fig. I2A-C). It differs from associated Pinacognathzs species in the shongly concave platform of sp elements, giving them a half-cylindrical shape, ornamented with transverse ribs. P inornatus, P. sp., and P. fornicat s represent a morphocline in this respect, the occlusal surface of the platform (especially in its ventral = anterior part) ranging from a strongly convex to flat. The youngest identified juveniles from sample Dz-15 are elongated, with a thin semicylindrical appearance of the platform and relatively large and fusiform basal cavity (pit). The largest element, found in sample Dz-14, shows the first stages in development of an extended platform on both sides of the vertical ridges parallel to the blade. This is a process analogous to that so typical for Siphonodella, but the distance between parallel ridges is more than two times larger than in S iphonodella species.

Pinacognathus sp. and P inornatus co-occur sympatrically in Dzikowiec, which makes apparatus distinction difficult. Most probably, their apparatuses were very similar to each other and there is no way to say to which of the three sympatric species of the genus the best preserved specimens from sample Dz-15 belong @ig. 15F-I, l-R; an alternative attribution: Fig.24).

In the Kowala section, together with advanced Siphonodella, popdations similar to P inomatus occur that are different from those from Dzikowiec in some respects. These are usually robust but rather narrow sp elements (Fig. 12C). The extensions ofthe platform outside the ridges, so typical for large sp elements of this species, develop also in the Kowala specimens but the distance between the main row of denticles and ridges seems here significantly smaller. This parallels the differences between some populations of Siphonodella but the taxonomic value of this feature requires additional studies on more numerous and better-preserved material. The basal cavity of the Kowala populations is also more variable in size and shape than those from Dzikowiec. [n some cases (for instance sample Ko-30, 2.6 m below the top of the section) I have diffrculties with distinguishing specimens of P inornatus from those of P sp. If criteria of discrimination of P inomatus from related Polygrathus distortus Branson & Mehl, 1934 proposed by Klapper (1975) are used, at least some of Polish specimens would fall into the range of the latter species.

In the Muhua section P inomatus replaces P. dapoushanensls in the upper part of the section, having an apparatus of a similar morphology.

The type population of the species is represented by sample C 199-3 from the Hannibal Formation neat Monroe City in Missouri (Branson 1934:- pI.25:8).

Porównanie

Autekologia

Występowanie geograficzne

Zasięg czasowy

Materiały muzealne

Literatura