Diagnoza

The sp elements with a triangular platform developed along the posterior margin of the inner process (at least in adult specimens).

Synonims:

 Prioniodus variabilis sp. n.; BERGSTROM,1962; Prioniodus variabilis BERGSTROM; BERGSTROM, 1971; Keislognathus gracilis RHODES; BEDNARCZYK, 1971; Prioniodus variabilis BERGSTROM; DZIK, Text-fig. 24h- 1.
1981. Prioniodus variabilis BERGSTROM; NOWLAN, 1976; Baltoniodus variabilis (BERGSTROM); CHEN and ZHANG, 1984; Baltoniodus variabilis (BERGSTROM); BERGSTROMet al. , 1985; Baltoniodus variabi lis (BERGSTROM); BERGSTROMand ORCHARD, 1985.

Porównanie

An apparatus reinterpretation of the species was given by BERGSTROM ( 1971), all its elements were also illustrated by DZIK ( 1976). The shape of the platform in the sp elements of this species is subject to great population variability, which practically precludes its taxonomic identification unless adult robu st specimens are preserved in a sample. Juveniles do not have any platform; they exhibit a more or less low triangular shape of the posterior margin of the process. Mature specimens usually show a shelf-like margin of this triangular are a which has a distinctly triangular outline, but some specimens can always be found that depart from the mode. The thickened margin (platform) is actually the only feature that allows the distinction of the species from its predecessor, P. prevariabilis. Unfortunately, in older samples this feature can be detected only in large, adult specimens. Probably the modification took place somewhere at the level of 0.2 m above the bentonite (samples MA-70 and 71). Adult specimens present in both of these samples seem to differ slightly in this respect (with the platform already developed in some elements in the sample MA-70) enabling the recognition of the evolutionary change. This demarcation of the boundary between the se two chronospecies has to be taken with some caution , however, because of rather small sample size .Contributions of elements lacking a platform decrease slowly upwards, and the evolutionary process
seem s to be connected with an ontogenetic acceleration. Even much higher in the section juveniles may still lack a platform. As most specimens in the samples from MA-72 to MA-85 are small this does not make them especially useful in time correlation. A rudimentary platform develops also in large oz elements. Other elem ent type s do not seem to differ from related species within the lineage. I am also unable to trace any discontinuity in the population variability of the hi-ke elements. They are virtually identical and if there are any differences between these element in the apparatus, they are completely obscured by the variability.

Autekologia

Występowanie geograficzne

Mójcza

Zasięg czasowy

Populations occurring higher than 0.2 m above the bentonite in Mójcza are,
somewhat arbitrarily, assigned to the species . It is widely distributed in the North Atlantic province(BERGSTROM 1971). B ERGSTROM et al. (1987 ) give the lower range of the species well within the P.anserinus Zone, thus much below that chosen here. Without thorough biometrical studies of the sp elements this app arent discrepancy cannot be resolved.

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.