Diagnoza

Samples Dz-6 andDz-66 have yielded a small number of elements of this species (Fig. 14E-G; the former sample was taken from a breccia and both may have actually originated from the same bed).

Small sizes of available samples make apparatus reconstruction difficult and it can only be considered as tentative. In sample Dz-6, a few elements of the Dinodus symmetry transition series have been found but the set of elements attributed to this genus shows no correlation with Siphonodella sp elements in its distribution in Dzikowiec and in Muhua. Perhaps the symmetry transition series of S. duplicata is represented by rare elements of morphologies similar to associated elements of Neopolygnathus purus bttt more gracile and with shorter processes in the lo and pl elements. The minute oz elements that may be potentially attributed to S. duplicata in this and other samples grade morphologically into juvenile oz elements of N. purus or N. vogesi. They seem to differ in a triangular gaping of the basal cavity. If their attribution to S. duplicala is correct, the non-platform part of the apparatus in this species would be very gracile and small-sized. This resembles in some respects the apparatus of Vogelgnathas (see Purnell & Bitter 1992); perhaps in both cases a primitive appearance is related to small element size.

Yet another possibility of restoring the apparatus of S. duplicate is suggested by the material from a sample taken from 2.3 m above the base of the Wangyou Formation in Muhua. Some sp elements of morphology typical for this species co-occur there with oz elements showing a characteristically oblique profile of the external margin of the base (resembling in shape short Mehlina sp elements) and symmetry transition series elements with very robust processes and reclined cusps. This Muhua population represents an unusually late return of the species, after being for a long time replaced by much more advanced members of the lineage. Virtually identical elements occur in the sample Dz-6 associated there with typical S. duplicata and robust asymmetrical sp elements identified here as S. sp. [aff. S. crenulata (Cooper, 1939)]. Only because of the robust appearances hared by these sp and symmetry transition series elements I place them in the same apparatus. The outcome of this decision is that the Chinese second S. duplicata represents the same lineage.

The lectotype of Siphonognathus duplicata Branson & Mehl, 1934, as chosen by Klapper (1975), was collected from the Bushberg sandstone at the same locality as the type series of S. lobata, S. quadruplicata, and S. sexplicata. This is not a natural co-occurrence of these species as usually understood and the lectotype is hardly conspecific with what is now considered Siphonodella duplicata. Unless it is reworked from older strata, it corresponds rather to the Chinese return of the S. duplicata morphology or even to an aberrant specimen of a more advanced Slphonodella. Perhaps the name S. duplicata, as applied to the eartest species of Siphonodella s.s., should rather be abandoned in favour of Polygnathus planaHuddle, 1934, with its type population coming from the upper New Albany shale of Indiana and undoubtedly conspecific with the early Tournaisian  populations under discussion.

Porównanie

Autekologia

Występowanie geograficzne

Zasięg czasowy

Materiały muzealne

Literatura