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Jurassic Forum » JURASSIC references & paper reviews » Jurassic of Russia and former USSR » Mitta V. V. (2010) (Late Volgian Kachpurites of the Russian Platform)
Mitta V. V. (2010)
mhornДата: Sunday, 16.01.2011, 11:07 | Сообщение # 1
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Mitta V. V. (2010) Late Volgian Kachpurites Spath (Craspeditidae, Ammonoidea) of the Russian Platform // Paleontological Journal, Vol. 44, No.6, P.622–631.

Pdf: http://rogov.zwz.ru/Mitta,2010_Kachpurites_en.pdf

Ammonites of the genus Kachpurites are characteristic of the lower part of the Upper Volgian Substage of the Russian Platform. K. fulgens fulgens (Trautschold), K. fulgens tscheremkhensis Mitta et al., K. subfulgens (Nikitin) are established in the Fulgens zone. The genus Kachpurites in opinion by Mitta also includes ammonites previously described as Anivanovia mola Kiselev (and its microconch Volgidiscus singularis), which earlier accepted as index-taxa of the uppermost levels of the Volgian Stage in the Russian Platform, “Volgidiscus singularis Beds”. Mitta also suggested position of the “Beds with Kachpurites mola” are in the basal part of the Upper Volgian Subditus Zone. Genus Kachpurites is also briefly described, micro- and macroconchs are established. But both new interpretation of previous records of Anivanovia and Volgidiscus as well as [M]/[m] recognition in Kachpurites are very questionable. Mitta presented only two weak evidences for new interpretation of Anivanovia and Volgidiscus records – in his opinion Anivanovia resembles suggested Kachpurites macroconchs and unfigured “Kachpurites mola” from the ? Subditus Zone of the lost locality Kamenik are present in the collection by Prigorovsky. Anivanovia and suggested macroconchs of Kachpurites are really close to each other by their mature shells, but strictly differ by character of the inner whorls, which are well-ribbed in Anivanovia and always lacking ribbing in Kachpurites. Collection by Prigorovsky, partially described and figured earlier (Prigorovsky, 1906), mainly includes ammonites from the Fulgens Zone (Craspedites, Garniericeras and Kachpurites). Mitta suggested proximity of lithology in ammonites from Prigorovsky collection with those of the Volgidiscus-Anivanovia ammonites from Seltso-Voskresenskoe locality as additional evidence for the age of the latter assemblage. But this is strange evidence, because as well as in the many other Upper Volgian sites of the Jaroslavl region, these fossils are preserved as brown sandstone moulds. Some paratypes of the Volgidiscus singularis species Mitta considered as Craspedites krylovi, but ribbing of these ammonites is quite different and this opinion cannot be accepted. C. krylovi characterized by slightly prorsiradiate mainly biplicate ribs and weakening of the ribbing in the middle parts of the lateral sides, while secondaries has the same thickness as primaries. V. singularis characterized by much higher rib ratio, stronger primaries and weaker slightly rursiradiate secondaries – the ribbing pattern, typical for true Volgidiscus. Assigning of other paratypes of V. singularis to Kachpurites is even more questionable. Ribbing of these ammonites and kind of its development through ontogeny are very different. Evolution of the Kachpurites lineage showing strong reduction of ribbing in the inner whorls: dense weak ribbing is present in the oldest Middle Volgian still undescribed species of this genus only. Appearance of the strong ribbing in the inner whorls of the suggested youngest member of the lineage was not explained by Mitta (and even not mentioned!). Suggested dimorphism in Kachpurites is possible, but again evidences are very simple and descriptive – Mitta don't provides any data on ontogeny of the suggested counterparts or their measurements. As other Boreal perisphinctoid ammonites craspeditids lacking any remarkable mature modification of the mouth.


Middle Jurassic - Lower Cretaceous ammonites & aptychi
 
Jurassic Forum » JURASSIC references & paper reviews » Jurassic of Russia and former USSR » Mitta V. V. (2010) (Late Volgian Kachpurites of the Russian Platform)
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