Revisiting brachyuran crabs (Malacostraca: Decapoda) from Oligocene and Miocene fish beds of Europe

Year, pages: 2022, 579 - 597

The fossil records of decapod crustaceans (Malacostraca) from Oligocene and Miocene fish beds (i.e. laminated deposits with exceptional fish preservation and high organic content) of Europe have lacked a uniform taxonomic approach, prohibiting assessments of their diversity and distribution. Therefore, we revisited the systematics of brachyuran crabs from these deposits preserved in the Great Caucasian Basin, the Outer Carpathian Basin, and the Pannonian Basin. The revised material originates from the Lower Oligocene of Hungary (Tard Clay Formation), Poland (Menilite Formation), Romania (Dysodilic Shale Formation), and Ukraine (Menilite Formation); Upper Oligocene of Poland (Menilite Formation); and the Lower Miocene of Azerbaijan (Maikopian Series), the Czech Republic (Ždánice–Hustopeče Formation), and Russia (Maikopian Series). Previously unreported material includes decapod specimens from the Lower Oligocene of Abadzekhskaya, Russia. In total, three crab species were distinguished, including Platymaia lethaea (Smirnov, 1929), Liocarcinus oligocenicus (Paucă, 1929), and Necronectes sp. Among them, L. oligocenicus occurs at all studied localities and is the most widespread taxon. Although earlier records of this species were often recognized as separate taxa, we propose that Portunus musceli Paucă, 1929; Portunus lancetidactylus Smirnov, 1929; Portunus arcuatus var. priscus Smirnov, 1929; Nautilograpsus prior Smirnov, 1929; and Portunus atropatanus Aslanova & Dzhafarova, 1975, are junior subjective synonyms of Liocarcinus oligocenicus. Although decapod specimens preserved in Oligocene and Miocene fish beds are often represented by complete or near-complete articulated bodies, their extreme flattening distorts the outline of exoskeleton elements and obscures diagnostic characters on the dorsal carapaces, such as the development of grooves, regions, and cuticular ornamentation, posing a major problem in taxonomic evaluation of these decapods. Other traits commonly not preserved in the fossil record, such as eyes, antennae, and even gonopods can be observed, although their comparison with modern counterparts is limited.

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Hyžný, M., Kovalchuk, O., Świdnicka, E., Barkaszi, Z., Berezovsky, A., Dumitriu, S., Grădianu, I., Stefaniak, K. 2022. Revisiting brachyuran crabs (Malacostraca: Decapoda) from Oligocene and Miocene fish beds of Europe. In Geologica Carpathica, vol. 73, no.6, pp. 579-597. 1335-0552. DOI: https://doi.org/10.31577/GeolCarp.73.6.3

Hyžný, M., Kovalchuk, O., Świdnicka, E., Barkaszi, Z., Berezovsky, A., Dumitriu, S., Grădianu, I., Stefaniak, K. (2022). Revisiting brachyuran crabs (Malacostraca: Decapoda) from Oligocene and Miocene fish beds of Europe. Geologica Carpathica, 73(6), 579-597. 1335-0552. DOI: https://doi.org/10.31577/GeolCarp.73.6.3