A new echinoderm Lagerstätte from the Pliensbachian (Early Jurassic) of the French Ardennes

Abstract

A succession of clays with thin shell beds from the French Ardennes, dated to the late Early Pliensbachian Davoei Zone and yielding abundant well-preserved remains of all five extant classes of echinoderms, is described here as a new Lagerstätte. The echinoderms occur in the form of isolated ossicles, semi-articulated plate aggregates and abundant intact skeletons with even the most delicate appendices preserved in place and the finest skeletal structures hardly blurred by recrystallisation. The outstandingly good preservation of the echinoderm specimens allows for a morphological assessment of the represented taxa in detail only rarely achievable by fossil material. The material described herein thus significantly contributes to a better understanding of the systematic position and phylogenetic background of many Early Jurassic echinoderm taxa. The echinoderms are considered to have been buried as an autochthonous or at least parautochthonous assemblage among clumps and beds of Modiolus bivalves. The depositional setting most likely represented a relatively shallow, near-shore soft-bottom environment in which conditions repeatedly favoured the settlement and subsequent effective burial of bivalve-echinoderm assemblages, leading to the formation of the thin highly fossiliferous shell beds intercalating the otherwise nearly sterile clays. The new Lagerstätte opens a unique window into the palaeoecology of an extinct shallow-water soft-bottom community closely comparable to recent analogues.

First glimpse into Lower Jurassic deep-sea biodiversity: in situ diversification and resilience against extinction

“…To assess the origin, resilience and bathymetric range shifts of the deep-sea fauna, we classified the families/superfamilies of the Glasenbach assemblage as well as coeval shelf (less than 200 m palaeo-depth) faunas [20,21,[23][24][25][26][27][28][29][30][31][32][33][34][35][36] as extinct, or extant and, according to their present-day bathymetric distribution, typically deep, typically shallow, or without depth preference (eurybathic) (figure 3; electronic supplementary material, table 1). Our bathymetric classification was based on the averaged mean depth distribution of the extant species of the families/superfamilies (calculated by averaging the upper and lower distribution boundaries for each species and by computing the arithmetic mean of the obtained values for each family/superfamily): typically deep-averaged mean depth greater than 500 m; typically shallow-averaged mean depth shallower than 200 m; eurybathic-averaged mean depth between 200 and 500 m. The upper boundary of the deep sea is commonly set between 200 and 500 m, in line with the fading of seasonal variations in physical parameters (e.g.…”

Brittle stars from the British Oxford Clay: unexpected ophiuroid diversity on Jurassic sublittoral mud bottoms

“…The material nevertheless stands out as it almost entirely consists of articulated skeletons and thus provides unpreceded insights into the morphology of the concerned taxa. They are among the very few cases in which exceptionally preserved ophiuroid fossils represent more than single-taxa occurrences (e.g., Thuy et al, 2011).…”

New fossils of Jurassic ophiurid brittle stars (Ophiuroidea; Ophiurida) provide evidence for early clade evolution in the deep sea

“…1), dated to the late Early Pliensbachian (Davoei chronozone, Early Jurassic), and deposited in a shallow, sublittoral, near-coastal setting. A detailed description of the locality, including its stratigraphy, depositional setting and echinoderm fossil content was provided by Thuy et al (13). Dissociated lateral arm plates described below as Ophioduplantiera noctiluca gen. et sp.…”