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Diverse assemblages of tanaids (Crustacea) related to Albian-Cenomanian resin-producing forests in Western Europe and their paleobiological implications

Abstract : Attempts at reconstructing amber forest habitats have sometimes neglected some aspects concerning arthropod communities in the soil, particularly those related to humid terrestrial conditions with, at least, certain proximity to partially flooded areas. The improving knowledge of the Spanish and French amber-bearing localities (AlbianCenomanian) has allowed the discovery of organisms that lived close to or in aquatic environments. Among these, small crustaceans belonging to the peracaridan Order Tanaidacea are exceptionally preserved. Except for a few rare freshwater and brackish species, Recent tanaids are marine organisms which occur over the full range of depths, and they typically hide in crevices or interstices, or construct tubes or burrows. Tanaids are exceedingly sparse in the geological record, with only 13 fossil species recorded to date. These are mostly rock-impressions, and only few specimens have been found as bioinclusions in ancient resins from some deposits around the world. The history of tanaids goes back to Lower Carboniferous, with the oldest species discovered in Scotland. Paleozoic taxa are also known from the Upper Carboniferous of Illinois and Lower Permian of Germany. Various Mesozoic tanaids were described from Lower Jurassic of Germany, Middle Jurassic of Bulgaria, Germany and Switzerland, Upper Jurassic of Germany, and Lower Cretaceous of Germany, but until recently, the only fossils known as bioinclusions were three species from Lower Cretaceous amber of Spain, placed in Alavatanaidae (Suborder Tanaidomorpha). The new findings include 19 tanaids in Albian Spanish amber from Alava (Perïacerrada 1 outcrop, Burgos Province), with at least two new morphotypes. A single specimen from El Soplao amber (Cantabria Province) has been tentatively assigned to Alavatanais carabe Vonk and Schram, 2007. Furthermore, Albian-Cenomanian French amber has provided 17 tanaids among which three potential new morphotypes. These specimens were found in am ber from various localities in the Charentes region (Archingeay-Les Nouillers and La Buzinie), and in the departments of Vendée (La Garnache) and Aude (Fourtou). The new fossils ail belong to the Suborder Tanaidomorpha and are remarkably modern in appearance, which is of great interest in understanding the history of the Order and their relationships with extant families. These tanaid assemblages from palaeogeographically close Spanish and French Cretaceous amber bearing-deposits, suggest that this group was relatively common in or around the ancient resin-producing forests, and often some of them have been found together in the same amber piece. Moreover, taphonomic and palaeobiological approaches showed that Spanish tanaids were preserved together with diverse nonaquatic syninclusions originating from the litter, i.e. inorganic soil components, decayed plant debris, arthropod remains, fungal hyphae, coprolites, and body-fossils such as isopods, mites, and thysanurans. French tanaids, however, were generally preserved in a mixture of terrestrial, often litter-inhabiting arthropods and fungi, but also marine organisms like centric diatoms and sponge spicules. This provides evidence for the early adaptation of tanaids to various habitats, from edaphic conditions in moist terrestrial or freshwater habitats, as suggested by Spanish fossils, to brackish or even marine habitats, as suggested by French fossils.
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Submitted on : Friday, May 17, 2013 - 2:56:39 PM
Last modification on : Friday, April 5, 2019 - 8:17:31 PM

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Alba Sanchez-Garcia, Enrique Penalver, David Peris, Vincent Perrichot, Xavier Delclos. Diverse assemblages of tanaids (Crustacea) related to Albian-Cenomanian resin-producing forests in Western Europe and their paleobiological implications. 6th International Congress on Fossil Insects, Arthropods, and Amber, Apr 2013, Byblos, Lebanon. pp.47-48. ⟨insu-00823616⟩

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