Diagnoza

Conodonts of the genus Siphonodella are the most common in the sample Dz-15 taken from the topmost bed of the Dzikowiec section. The sample is strongly unbalanced and the species is mostly represented by the most massive platform sp elements. There seems to be enough other elements, however, to enable apparatus study. Most fortunate for the restoration of the Siphonodella apparatus is the relative rarity of Neopolygnathus purus elements.

Their abundance in other samples containing late species of Siphonodella makes difficult separation of the symmetry transition series elements to each of the apparatuses that in this respect seem similar (note that the virtual lack of Dinodus ramiform elements in samples Dz-6 and Dz-30 is used to exclude them as possible members of the Siphonodella apparans). Although still conjectural, the apparatus of late Siphonodella is thus reconstructed here as typically polygnathid.

The most typical, and attributed there with the highest probability, are elements in the oz position. They are minute, short-bladed, and sharply denticulated. Much more problematic is the  identification of the symmetry transition series elements. There are some in the samples with sp and  z elements of the species that seem to differ from associated Neopolygnathus purus elements in their shorter processes. Such a morphology is to be expected to Siphonodella if it was really derived  from Pinacognathus. A very small adult size of the non-platform elements in the Siphonodella  pparafises would differentiate these genera if the attribution is correct. The hi elements are very similar to juveniles of associated Neopolygnathus, but seem to be separated from them, apart from short ventral processes, in a fan-like arrangement of denticles, usually with the base of the process  projecting externally. The ne elements tentatively classified here have undenticulated and  sometimes almost completely reduced ventral processes.

In the large sample of sp elements of this species different histogenetic stages are well represented. The smallest identified elements have their platform gently bent orally, resembling in morphology simple polygnathids. Because of lanceolate shape of the platform, its margins in the part of element venkal (posterior) of the cusp (identifiable only on the basis of basal pit position) reach almost vertical orientation. [n subsequent growth, a new platform margin develops at the level of the element base that grows in the same way as the initial platform until vertical position of the margin is reached. In the dorsal ('posterior') part of the element growth continues in the previous direction. This pattern is repeated several times, the largest elements found have three parallel (rostral) ridges on each side of the blade (carina). The distance between ridges is stable, approximately 120 1tm. Apparently there was a morphogenetic field along the blade and ridges inhibiting their origination in shorter distances. The ability to form ridges suddenly disappears dorsally of the cusp but during growth of the element the boundmy between ridge-bearing and ridge free areas expands somewhat dorsally which result in its obliquely angular course. At least the end of the two first originating anterior ('inner') ridges is underlined by a development of transverse junction. This is the most characteristic feature of the Dz-15 population. To be identified taxonomically, elements adult enough to have two ridges on both sides of the blade are thus required.

A few sp elements of Siphonodella found in sample Dz-15 do not show clear dorsal boundaries in the range of ridges. They do not show any apparent signs of reworking; it remains thus unknown whether they are end-members of population variability or rather came from the underlying strata.

Several populations of Siphonodella are known that show dominance of the character most typical for the latest Dzikowiec species, that is, the transverse connection between two anterior ridges in the sp element. Cooper (1939) illustrated several specimens of this morphology from the pre- Welden shale of the Arbuckle Mountains in Oklahoma, which is younger than Siphonodella obsolete in age (see Over 1992: p.297). Several new names were proposed by Cooper (1939), but to recognize their exact biological meaning a more detailed study of material from the type locality is necessary.

The type population of the species comes from the sample 9300 taken about 6 meters below the top of the Chappel Limestone at the Bamett Tfench section in Mason County, Texas (Hass 1959: pl. 48: 36). It remains unclear whether the American population has anything to do with the European one, but it seems unreasonable to separate them until more data on the population variability and vertical distribution in the type section are provided.

The same variety of element morphologies as in sample Dz-15 seems to characterise sample 438 of the Kronhafensgraben in the Camic Alps, where they have been identified as representing several species of Sriphnodella, namely S. crenulata, S. cooperi, S. obsoleta, S. isosticha, and S.  uadruplicata by Schonlaub (1969). The elements were extracted by him from the last, thin bed of the limestone sequence in the area, exactly as in Dzikowiec. Above, there are black shales with limestone concretions. Siphonodella platform elements that agree in ornamentation with those from the youngest Dzikowiec population occur also in the middle and upper part of the Limushan Formation in the Muhua section in Guizhou (Ji et al. 1989: pl. 15 l-6, 16:3-9).

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.