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Juracyclus posidoniae n. gen. and sp., the first cycloid arthropod from the Jurassic
- Günter Schweigert
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- Journal:
- Journal of Paleontology / Volume 81 / Issue 1 / January 2007
- Published online by Cambridge University Press:
- 14 July 2015, pp. 213-215
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- Article
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The cycloids represent an enigmatic arthropod group of probably crustacean affinity, occurring mostly in the younger Paleozoic, from the early Carboniferous up to the Late Triassic (Schram et al., 1997). Superficially, cycloids strikingly resemble crabs and were thought to have had a similar lifestyle, becoming extinct when crabs started to radiate. Recently, the existence of a Late Cretaceous cycloid, Maastrichtiocaris rostratus Fraaije et al., 2003, from the Maastrichtian of the Netherlands, proved that cycloids did not go extinct at the end of the Triassic as believed for a long time, but survived much longer, co-occurring with crabs. Due to obvious collecting bias and the incompleteness of the fossil record of arthropods with relatively delicate carapaces in general, neither Jurassic nor Early Cretaceous representatives have been reported hitherto. However, from the Lower Jurassic Posidonienschiefer (‘Posidonia Shale’) of southwestern Germany—famous for its excellent fossil preservation, not only of marine vertebrates and large crinoids living on driftwood, but also many other invertebrate groups (Riegraf et al., 1984; Urlichs et al., 1994)—now a single specimen of a cycloid is recorded and described herein. Although this record helps link the bias between the Triassic and the Late Cretaceous occurrences, the characters of the specimen differ strongly from those of other cycloids, thus requiring the erection of a new genus and species.
10 - Crustacea of the Crato Formation
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- By Günter Schweigert, Staatliches Museum für Naturkunde, Abteilung Paläontologie, Rosenstein 1, D-70191 Stuttgart, Germany, David M. Martill, Reader in Palaeobiology in the School of Earth and Environmental Sciences University of Portsmouth, Mark Williams, Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK
- David M. Martill, University of Portsmouth, Günter Bechly, Robert F. Loveridge, University of Portsmouth
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- Book:
- The Crato Fossil Beds of Brazil
- Published online:
- 22 August 2009
- Print publication:
- 13 December 2007, pp 133-141
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Summary
Although crustaceans are often abundant and diverse in fossil Konservat Lagerstätten, their remains are remarkably rare in the Nova Olinda Member and, indeed, they are only abundant at a few localized horizons in the Crato Formation as a whole. Reasons for this rarity compared with other fossil Lagerstätten are unclear, but are probably related to salinity levels and substrate chemistry. By far the most abundant crustaceans are ostracods, which occur in rock-forming quantities in shales and fissile laminated muddy limestones at the transition between the Rio da Batateiras Formation and the Crato Formation at Cascata, near Crato. In these same deposits conchostracans occur with the ostracods at Cascata, although they are not as abundant, and in dark-coloured silty shales beneath a series of laminated limestones at Estiva, near Araporanga. Here they occur without ostracods, but in a sequence that is similar to, though slightly younger than, that at Cascata. Decapod crustaceans have only been reported from the laminites of the Nova Olinda Member in the Crato Formation.
Decapoda: Beurlenia, the ‘sole’ shrimp from the Crato Formation
The Crato Formation yields only a single species of decapod crustacean: Beurlenia araripensis. Originally described as a palaemonid shrimp by Martins-Neto and Mezzalira (1991), Maisey and Carvalho (1995) cast doubt on its palaemonid affinities, referring it to? Palaemonidae. Palaemonids are a family within Caridea that are scarcely recorded from the fossil record. We here concur with Maisey and Carvalho (1995) and transfer B. araripensis to Familia incertae sedis within Caridea.