Lenodus variabilis (Sergeeva, 1963) from the Mójcza Limestone.

Apparatus of Lenodus variabilis (Sergeeva, 1963).

Diagnoza

The anterior process of the sp elements with a short bifurcation appearing relatively late in the ontogeny, the oz elements with processes widely flaring and with thick and prominently ornamented platform . Strongly asymmetric ne elements weakly denticulated with posterior rib without
denticles .

Synonims:

Amorphognathus variabilis sp. n.; SERGEEVA, 1963; Eoplacognathus variabilis (SERGEEVA); TIPNIS et al.,1978; Prioniodus prevariabilis FAHRJEUS, 1979; Lenodus clams SERGEEVA,1979; cf. ?Amorphognathus? sp. A; STOUGE, 1984; Eoplacognathus suecicus BERGSTROM; HUNICKEN and ORTEGA, 1987;
Eoplacognathus suecicus BERGSTROM; WATSON, 1988; Eoplacognathus foliaceus ? (FAHRJEUS); WATSON, 1988.

Porównanie

Large platform elements of the species (especially oz ) show tuberculation , which makes them remotely similar to cooccurring elements of Polonodus. Whether this is a feature of phylogenetic significance or not , remains on open question.
The oz elements do not form a mirror-im age pair but the difference is not profound. The anterior and inner processes in the dextral element are linearly arranged while in the sinistral element the anterior process is strongly curved, the remaining processes forming a line. No apparent asymmetry was identified in the sp pair.

Autekologia

Występowanie geograficzne

Zasięg czasowy

Volkhovian populations of Lenodus are still inadequately known but it seems that the lack of bifurcation of the anterior process in the sp elements as well as the presence of an inner-posterior rib in the ne elements (the feature diagnostic of L. falodiformis SERGEEVA), reported in few known, poorly preserved specimens from the latest Volkhovian, is typical for them. The exact level of transition between L. falodiformis and L variabilis has not been identified yet. Although it
was hypothetized that in the Halludden section, bland , this took place somewhere close to the boundary between the Volkhovian and Kundan (DZIK 1983) the data of STOUGE and BAGNOLl (1991)
from the Hagudden section suggests that it was well within the Early Kundan. In the Lesieniec I borehole, in the Polish part of the East European platform, Lenodus occurs even earlier. together with typical Baltoniodus navis and aroistodus originalis, and this may be the ancestral species of the lineage. The upper range of L. variabilis has not been precisely traced , either. In Mójcza it is replaced 0.5 m below the discontinuity surface (between samples MA-125 and MA-I27) with Eoplacognathus
zgierzensis and Sagittodontina kielcensis. Both these species are probable successors of Lenodus but
the available material is too incomplete to show the transition. A direct connection between L.variabilis and E. zgierzensis seems very probable. These two species differ almost exclusively in the degree of elongation of the anterior process in the sp element. S. kielcensis is more derived and may represent an immigrant lineage.with

Materiały muzealne

Literatura

Dzik, J. 1994a Conodonts of the Mójcza Limestone. In: J. Dzik, E. Olempska, & A. Pisera. Ordovician carbonate platform of the Holy Cross Mountains. Palaeontologia Polonica 53, 43-128.