The late Middle Jurassic lagerstätte at La Voulte-sur-Rhône, in the Ardèche region of southwestern France, offers paleontologists an outstanding view of an undisturbed paleoecosystem that was preserved in fine detail as organisms died at the site and settled to the bottom of a shallow epicontinental sea, with a folded floor that in places exceeded 200 m at this site. The site preserves a marine system of the Lower Callovian stage, a little over 160 mya. The sequence is exposed in a series of quarries at La Boissine, west of the village of La Voulte-sur-Rhône. Iron pyrites in the silty shale are symptoms of an anoxic environment. The site was recognized among French paleontologists from the mid-nineteenth century for its finely detailed fossils.
Preservation
Some soft parts of organisms are preserved as phosphatised concretions, in exceptional cases down to cellular details, e.g. retinal structures in the eyes of conchyliocarid crustacea. Apart from Beecher's Trilobite Bed and the Hunsrück Slate, La Voulte-sur-Rhône is the only other locality where extensive pyritization of soft parts occurs. see page 41 However, pyritisation is not the only preservation pathway; several stages of mineralization (originally phosphate followed by calcite or gypsum, then pyrite and finally galena) are seen, each successive mineralization event degrades the detail preserved, with only gross morphological features preserved in the most advanced stages. "La Voulte-sur-Rhone" by Sarah Joomun, Dept. of Earth Science, Bristol University
Fauna and flora The fauna preserved can be broadly divided into the allochthonous fauna (consisting of soft-bodied organisms which lived on the sea floor (benthic) or swam freely just above it (nektobenthic)) and the in-situ mortality horizon.
The allochthonous fauna contains rare and well-preserved organisms. Fossils of pycnogonids ("sea-spiders"), the first find in Mesozoic strata in an admittedly very patchy fossil record, were identified in 2007. A coleoid cephalopod (a single specimen of a small octopus) was described from La Voulte-sur-Rhône in 1982. The marine crocodile Metriorhynchus, fish, decapod, mysid crustaceans, thylacocephalans, crinoids, and ophiuroids (most commonly Ophiopinna elegans) are also to be found.
The in situ mortality horizon consists of abundant pavements of the bivalve Bositra buchi and trace fossils of suspected worm burrows.
Two specimens of plants suggest that a shoreline was not far distant, represented today by France's Massif Central.
Paleobiota
InvertebratesGenusSpeciesHigher taxonNotesImagesVampyronassaV. rhodanicaVampyroteuthidaeRelatively similar to modern vampire squid, but an active predator instead of a detritivore VampyrofugiensV. atramentumVampyromorphidaHas both ink and bioluminescent organsProteroctopusP. ribetiVampyropodaOriginally interpreted as a basal octopus, hence the nameRhomboteuthisR. lehmaniPlesioteuthididaeHas a preserved ink sacRomaniteuthisR. gevreyiPlesioteuthididaeRelatively similar to PlesioteuthisGramadellaG. piveteauiMyopsidaOne of the oldest "true" squid knownMastigophoraM. brevipennisLoligosepiina (Vampyromorpha)May bear a pair of elongate tentacles, however these may be from associated Belemnotheutis fossils?IubarenicolaI. fischeriCapitellidaUnclear familyPaleoaphroditeP. gallica, P. briggsiana, P. adeliaeAphroditidaeOne of the earliest scaleworm fossils knownProtopholoeP. rhodanitisAphroditoideaUncertain familyRhondeletiaR. scutataSipunculaOne of the only Mesozoic sipunculan fossilsMegaderaionM. callovianumEnteropneustaAlso known from OstenoRhodanicarisR. deperetiPenaeidaeAegerA. brevirostrisAegeridaeOne of the most common crustaceans from La VoulteMandocarisM. polyphagaAcanthephyridaeArcheosolenoceraA. straeleniSolenoceridaeSynonymous with Antrimpos secretaniaeStenochirusS. vahldiekiStenochiridaeThe oldest record of the genusGlypheopsisG. voultensisGlypheidaeErymaE. ventrosum, E. cumonti, E. mandelslohiErymidaeExcellent preservation has shown almost all of its internal organsVoulteryonV. parvulusEryonidaeMay have been transported from shallow waters as evidenced by its eye structureEryonE. ellipticusEryonidaeFormerly used for all polychelid fossilsCycleryonC. romaniEryonidaeVery similar to Eryon itselfProeryonP. giganteus, P. charbonnieriColeiidaeFormerly placed in CycleryonWillemoesiocarisW. ovalisColeiidaeHellerocarisH. fallotiPolychelidaeClosely related to modern polychelidsAdamanteryonA. fournetiPolychelidaUncertain familyEucopiaE. praecursorEucopiidaeOne of the earliest lophogastrid fossils knownLophogasterL. voultensisLophogastridaeOne of the earliest lophogastrid fossils knownPalaeocumaP. hessiCumaceaEarliest crown-cumacean fossil knownSiriellaS. antiqua, S. carinataMysidaeExtant genusUdoraU. gevreyi, U. minutaProcaridideaPalaeopycnogonidesP. gracilisPalaeopycnogonididae (Pycnogonida)Has a relatively unusual arrangement of head appendagesColossopantopusC. boissinensisColossendeidaeA large pycnogonid with a very long proboscisPalaeoendeisP. elmiiEndeidae (Pycnogonida)Vaguely similar to Haliestes?OstenocarisO. ribetiThylacocephalaFormerly classified as Clausocaris ribeti, much smaller than the type species of OstenocarisMayrocarisM. spThylacocephalaPreviously known from SolnhofenDollocarisD. ingensThylacocephalaOne of the largest thylacocephalansParaosteniaP. voultensisThylacocephalaAlso known from the TriassicAustriocarisA. secretanaeThylacocephalaFormerly classified under DollocarisKilianicarisK. lericheiThylacocephalaParaclausocarisP. harpiThylacocephalaRelatively similar to Clausocaris itself except for the carapace marginTerminasterT. cancriformisForcipulataceaKnown from other localities across EuropeDecacuminasterD. solarisValvatidaName translates to "pollarded star", as the top seems to have been "cut off" like a pollarded treeRhodanometraR. lorioliPterocomidae (Comatulida)One of the few complete crinoids known from La Voulte
References