Pinacognathus sp. from the Tournaisian Wapnica beds of Dzikowiec.

Apparatus composition of Pinacognathus sp.

Diagnoza

This is a common species in older horizons represented by samples Dz-66 andDz-6 in Dzikowiec which can be characterised by the mode of development of its platform in sp elements. Unlike associated platform elements of other polygnathids, juveniles of P sp. Show a widely gaping basal cavity that uniformly narrows towards the dorsal ('anterior') end of the element and a relatively robust platform develops at some distance above the element base. All this gives to the sp elements of this species an appearance resembling Devonian 'Siphonodella' praesulcata,to which it seems to be, in fact, related.T he morphologyo f sp elementso f this species( Fig. 154) is more robust and less variable than in closely related populations occurring higher up in the section.

In the lower part of the Ganendorfia limestone in Dzikowiec oz elements with glossy surface, and a strong tendency to conceal denticles developed at earlier histogenetic stages, co-occur which most probably represent the same apparatus. They are very variable within each sample but most specimenshave their denticulation rather well developed @ig. 15C-D). In younger samples Dz-15 and Dz-46, sp elements are rather variable. The platform in some specimens is very low with respect to the base and remains very thin and relatively flat, which makes them transitional to associated elements classified as Polygnathus fornicatus. The only difference between transitional elements of these species thus remains the shape of the basal cavity (pit). However clearly different in typical elements, the basal cavity varies considerably both in P fornicatus and P sp. and in many cases the decision to which of the species a specimen has to be attributed remains arbitrary.

In Dzikowiec sample Dz-15 some sp elements occur closely resemble the elements from the Muhua locality identified as Polygnathus pupus Wang & Wang, 1978 (uveniles) and Polygnathus inornatus rostratusRhodes, Austin, & Druce, 1969 (mature) by Jiet al. (1989). The horizon with P dapoushanensis (Ji et a1.,1989) , where they occur, is significantly older than that in Dzikowiec and the similarity in platform element morphology may be just a result of homeomorphy. Data on the whole apparatus structure are necessary to solve the problem. The oz elements( Fig. 15L, R) that seem to be invariably associatedw ith sp elements of this kind, have a glossy surface and poorly recognisable boundaries between denticles on the element sides even at early stages of histogeny (Fig. 15R). They tend to have a rather high and robust blade, which makes them different from oz elements of older populations of Pinacognathus. The evolution in the symmetry transition and ne elements of the apparatus is not so apparent. The apparatus shows some resemblance to that of Dinodus and this refers especially to pl, hi, and ne elements, which tend to develop strong ribs along processes below their denticles (Fig. 15E-R).

Two Muhua section samples taken 0.6 and 2.3 m above the base of the Wangyou Formation contain sp elements of morphologies approaching rather P inomotus, associated with other elements of the apparatus almost identical with those co-occurring with P. sp. in sample Dz-6 of Dzikowiec. These two Muhua populations of different age seem to differ mostly in the morphology of oz elements, with a very high triangula.r profile ('P profwtdus'morphology) in the older sample and more robust and elongated in the younger, more similar to those of the typical P inornatus . Because of the derived morphology of ramiform elements some uncertainty remains regarding homology of particular element types. The most characteristic, both in Dzikowiec arrd Muhua samples, are elements with a long, undenticulated external process, possibly corresponding to the hi location. Such elements have not been found higher in the Dzikowiec section where typical P inorrntus occurs. P dapoushanensis is a succesor of P. sulcatus in the Muhua section, perhaps developing there allopatrically in respect to P sp.

The holotype of Pinacognathus nodomarginarzs (8.R. Branson, 1934),thetypelocality of which is the Hannibal of Formation of Palmyra in Missouri (Klapper 198 I : p. 379), shows the morphology of the platform much more advanced than that typical for the Dzikowiec specimens, with a tendency to develop additional ridges characterising rather P inornatus. The oz elements attributed here to the Dzikowiec species are morphologically indistinguishable from the holotype of Pinacognathus profundus (Branson & Mehl, 1934) from the Bushberg sandstone. The holotypes of Prbniodas barbatus Branson & Mehl, 1934, Palmatodella ultima Branson & Mehl, 1934, and Synprioniodina delicatula Branson & Mehl, 1934 from the same locality seem to belong to the same species but no platform element of comparable morphology to that from Dzikowiec is represented among specimens described by Branson & Mehl (1934). They may represent another species of the same genus.

Porównanie

Autekologia

Występowanie geograficzne

Zasięg czasowy

Materiały muzealne

Literatura

Dzik, J. 1997. Emergence and succession of Carboniferous conodont and ammonoid communities in the Polish part of the Variscan sea. Acta Palaeontologica Polonica 42, 57-170.