Solutan echinoderms from the Lower Ordovician of the Montagne Noire (France): new data and palaeobiogeographic implications

Solutans are relatively common members of echinoderm assemblages in the Saint-Chinian Formation (upper Tremadocian) of the Montagne Noire (France). The revision of all available material confirms that most specimens can be assigned to Minervaecystis vidali, which is here reconstructed for the first time. The occurrence of Plasiacystis mobilis is evidenced based on a single, well-preserved dististele. The interpretation of the small-sized individual as a putative dendrocystitid is rejected: it corresponds to a juvenile specimen of M. vidali. Early Ordovician solutans from the Montagne Noire partly fill the gap between Laurentian midâlate Cambrian syringocrinids and Avalonian-Gondwanan EarlyâMiddle Ordovician taxa

Echinoderm Lagerstätten from high-latitude Gondwana – filling the gap in the Ordovician diversification of the phylum

The phylum Echinodermata is a major component of marine ecosystems since the first appearance of echinoderms in the Cambrian. Like other metazoan phyla, echinoderms underwent two major evolutionary pulses in early Palaeozoic times: the Cambrian Explosion and the Ordovician Radiation. In the Ordovician, the exploitation of new ecological niches triggered an exponential diversification of the phylum, leading to its highest morphological disparity and class-level diversity (about 18 classes compared to only five extant classes) of the whole Phanerozoic. However, the precise spatio-temporal patterns of the Ordovician Radiation of echinoderms remain poorly known, owing to geographical and taphonomic biases. Over two centuries, the sampling effort was mostly focused on faunas from Europe and North America, providing a wealth of information on crinoid- and/or blastozoan (âcystoidâ)-dominated low-latitude assemblages from Avalonia, Baltica and Laurentia. Moreover, echinoderm Lagerstätten, bearing fully articulated skeletal elements, provide valuable snapshots of past communities but are rare in the rock record because echinoderm endoskeletons disarticulate into many calcite plates shortly after death. Recent discoveries of several new Ordovician Lagerstätten from high-latitude Gondwana, i.e., the Czech Republic (Barrandian area), France (Armorican Massif, Montagne Noire) and Morocco (Anti-Atlas, Meseta), provide a unique opportunity to fill the existing knowledge gap regarding the Ordovician diversification of the phylum. Echinoderm assemblages from high-latitude areas are dominated by asterozoans, blastozoans and stylophorans, with very few crinoids, unlike those from low-latitude regions. By comparing and combining these two sets of information, it is possible to coherently frame the early diver­sification of echinoderms in space and time

Quid novi Soluta?

International audienceSolutans are a small clade of extinct non-radiate echinoderms. Their stratigraphic range extends from the middle Cambrian (Miaolingian, Drumian) to the Lower Devonian (Emsian). Solutans are characterized by two distinct and unequal appendages inserted at opposite ends of their theca: a single free ambulacral structure (brachiole), and a longer stem-like appendage (homoiostele). Due to their unusual morphology, the taxonomic position of the class is still controversial. Solutans are considered either as a distinct class of blastozoans or as basal, preradial hemichordate-like echinoderms. This contribution aims at reviewing the major advances achieved since Caster's (1968) chapter on Soluta in the Treatise on Invertebrate Paleontology, with a special emphasis on the main results obtained since the last IEC in Nagoya (2018) and ongoing studies. The description of Pahvanticystis utahensis (Guzhangian, Utah) confirmed the probable Laurentian origin of the class (Lefebvre & Lerosey-Aubril, 2018). Work in progress lead by S. Zamora and X. Zhu will describe the earliest non-Laurentian solutan from the Guole Biota (Jiangshanian, South China). The Fezouata Biota (late Tremadocian-late Floian) yielded exceptionally preserved soft parts (gut) in a Castericystis-like solutan, as well as abundant remains of Plasiacystis mobilis (originally described in the Darriwilian of the Czech Republic) and a new taxon, morphologically intermediate between Minervaecystis and Plasiacystis (Dupichaud & Lefebvre, 2022). The revision of late Tremadocian solutans from the Montagne Noire provided the first detailed reconstruction of M. vidali and the first report of P. mobilis in that region (Dupichaud et al., in press). The very unusually-shaped Hope Shale solutan (Darriwilian, Shropshire) is still awaiting description (work in progress by K. Derstler & B. Lefebvre). The Late Ordovician genus Dendrocystites was reported for the first time in North Africa (Nohejlová & Lefebvre, 2022) and from a new echinoderm Lagerstätte in the Prague Basin (Nohejlová et al., 2019). The Neuville Formation (lower Katian, Quebec) yielded abundant remains of a new solutan, with a surprisingly plesiomorphic ('Castericystis-like') morphology (work in progress by K. Derstler). Finally, the first ever described Silurian solutan, Dehmicystis ariasi, was recently documented in the Ludlow of Spain (Zamora & Gutiérrez-Marco, in press), thus filling a long stratigraphic gap between the Late Ordovician and the Early Devonian. Another Silurian solutan from Wales is also awaiting description (Dupichaud, in progress)

Quid novi Soluta?

Solutans are a small clade of extinct non-radiate echinoderms. Their stratigraphic range extends from the middle Cambrian (Miaolingian, Drumian) to the Lower Devonian (Emsian). Solutans are characterized by two distinct and unequal appendages inserted at opposite ends of their theca: a single free ambulacral structure (brachiole), and a longer stem-like appendage (homoiostele). Due to their unusual morphology, the taxonomic position of the class is still controversial. Solutans are considered either as a distinct class of blastozoans or as basal, preradial hemichordate-like echinoderms. This contribution aims at reviewing the major advances achieved since Caster's (1968) chapter on Soluta in the Treatise on Invertebrate Paleontology, with a special emphasis on the main results obtained since the last IEC in Nagoya (2018) and ongoing studies. The description of Pahvanticystis utahensis (Guzhangian, Utah) confirmed the probable Laurentian origin of the class (Lefebvre & Lerosey-Aubril, 2018). Work in progress lead by S. Zamora and X. Zhu will describe the earliest non-Laurentian solutan from the Guole Biota (Jiangshanian, South China). The Fezouata Biota (late Tremadocian-late Floian) yielded exceptionally preserved soft parts (gut) in a Castericystis-like solutan, as well as abundant remains of Plasiacystis mobilis (originally described in the Darriwilian of the Czech Republic) and a new taxon, morphologically intermediate between Minervaecystis and Plasiacystis (Dupichaud & Lefebvre, 2022). The revision of late Tremadocian solutans from the Montagne Noire provided the first detailed reconstruction of M. vidali and the first report of P. mobilis in that region (Dupichaud et al., in press). The very unusually-shaped Hope Shale solutan (Darriwilian, Shropshire) is still awaiting description (work in progress by K. Derstler & B. Lefebvre). The Late Ordovician genus Dendrocystites was reported for the first time in North Africa (Nohejlová & Lefebvre, 2022) and from a new echinoderm Lagerstätte in the Prague Basin (Nohejlová et al., 2019). The Neuville Formation (lower Katian, Quebec) yielded abundant remains of a new solutan, with a surprisingly plesiomorphic ('Castericystis-like') morphology (work in progress by K. Derstler). Finally, the first ever described Silurian solutan, Dehmicystis ariasi, was recently documented in the Ludlow of Spain (Zamora & Gutiérrez-Marco, in press), thus filling a long stratigraphic gap between the Late Ordovician and the Early Devonian. Another Silurian solutan from Wales is also awaiting description (Dupichaud, in progress)

Quid novi Soluta?

Solutans are a small clade of extinct non-radiate echinoderms. Their stratigraphic range extends from the middle Cambrian (Miaolingian, Drumian) to the Lower Devonian (Emsian). Solutans are characterized by two distinct and unequal appendages inserted at opposite ends of their theca: a single free ambulacral structure (brachiole), and a longer stem-like appendage (homoiostele). Due to their unusual morphology, the taxonomic position of the class is still controversial. Solutans are considered either as a distinct class of blastozoans or as basal, preradial hemichordate-like echinoderms. This contribution aims at reviewing the major advances achieved since Caster's (1968) chapter on Soluta in the Treatise on Invertebrate Paleontology, with a special emphasis on the main results obtained since the last IEC in Nagoya (2018) and ongoing studies. The description of Pahvanticystis utahensis (Guzhangian, Utah) confirmed the probable Laurentian origin of the class (Lefebvre & Lerosey-Aubril, 2018). Work in progress lead by S. Zamora and X. Zhu will describe the earliest non-Laurentian solutan from the Guole Biota (Jiangshanian, South China). The Fezouata Biota (late Tremadocian-late Floian) yielded exceptionally preserved soft parts (gut) in a Castericystis-like solutan, as well as abundant remains of Plasiacystis mobilis (originally described in the Darriwilian of the Czech Republic) and a new taxon, morphologically intermediate between Minervaecystis and Plasiacystis (Dupichaud & Lefebvre, 2022). The revision of late Tremadocian solutans from the Montagne Noire provided the first detailed reconstruction of M. vidali and the first report of P. mobilis in that region (Dupichaud et al., in press). The very unusually-shaped Hope Shale solutan (Darriwilian, Shropshire) is still awaiting description (work in progress by K. Derstler & B. Lefebvre). The Late Ordovician genus Dendrocystites was reported for the first time in North Africa (Nohejlová & Lefebvre, 2022) and from a new echinoderm Lagerstätte in the Prague Basin (Nohejlová et al., 2019). The Neuville Formation (lower Katian, Quebec) yielded abundant remains of a new solutan, with a surprisingly plesiomorphic ('Castericystis-like') morphology (work in progress by K. Derstler). Finally, the first ever described Silurian solutan, Dehmicystis ariasi, was recently documented in the Ludlow of Spain (Zamora & Gutiérrez-Marco, in press), thus filling a long stratigraphic gap between the Late Ordovician and the Early Devonian. Another Silurian solutan from Wales is also awaiting description (Dupichaud, in progress)

The oldest African echinoderms (Morocco): Morphology and implications for the diversification of blastozoans in the early Cambrian

Since their first appearance in the fossil record (Cambrian Stage 3, ~520 Ma ago), echinoderms were already relatively diverse (classes Edrioasteroidea, Eocrinoidea, Helicoplacoidea, and Lepidocystoidea) and cosmopolitan. This suggests a possible earlier origin of the phylum, although no evidence for this has been found due to the absence of Lagerstätten able to preserve non-mineralized ancestral forms. The major diversification of echinoderms during the Cambrian and Ordovician (about twenty classes, so four times the number of extant classes) renders particularly difficult the identification of homologous structures and the construction of a phylogeny encompassing the whole phylum. The goal of this study is to clarify whether feeding appendages of blastozoans (brachioles) and crinoids (arms) are homologous (or not) and thus if those two groups belong (or not) to a same clade Pelmatozoa. In this context, the gogiid genus Alanisicystis -the oldest echinoderm known so far from the African continent, situated in Western Gondwana- is of particular interest. Its morphology was analyzed based on abundant and remarkably preserved specimens from the Issafen Formation (Cambrian Series 2, Stage 3; Morocco). This eocrinoid has a short stem composed of small, irregularly arranged circular plates. The theca is made of a mosaic of irregularly polygonal plates, ornamented with a fine granulation and numerous respiratory structures (epispires). Its aboral end consists of a single basal plate. The brachioles consist of two series of alternating flooring plates and two series of alternating cover plates. Those long appendages branch from the adoral end of the theca, at the edges of the oral fram

The oldest African echinoderms (Morocco): Morphology and implications for the diversification of blastozoans in the early Cambrian

International audienceSince their first appearance in the fossil record (Cambrian Stage 3, ~520 Ma ago), echinoderms were already relatively diverse (classes Edrioasteroidea, Eocrinoidea, Helicoplacoidea, and Lepidocystoidea) and cosmopolitan. This suggests a possible earlier origin of the phylum, although no evidence for this has been found due to the absence of Lagerstätten able to preserve non-mineralized ancestral forms. The major diversification of echinoderms during the Cambrian and Ordovician (about twenty classes, so four times the number of extant classes) renders particularly difficult the identification of homologous structures and the construction of a phylogeny encompassing the whole phylum. The goal of this study is to clarify whether feeding appendages of blastozoans (brachioles) and crinoids (arms) are homologous (or not) and thus if those two groups belong (or not) to a same clade Pelmatozoa. In this context, the gogiid genus Alanisicystis -the oldest echinoderm known so far from the African continent, situated in Western Gondwana- is of particular interest. Its morphology was analyzed based on abundant and remarkably preserved specimens from the Issafen Formation (Cambrian Series 2, Stage 3; Morocco). This eocrinoid has a short stem composed of small, irregularly arranged circular plates. The theca is made of a mosaic of irregularly polygonal plates, ornamented with a fine granulation and numerous respiratory structures (epispires). Its aboral end consists of a single basal plate. The brachioles consist of two series of alternating flooring plates and two series of alternating cover plates. Those long appendages branch from the adoral end of the theca, at the edges of the oral fram

The oldest African echinoderms (Morocco): Morphology and implications for the diversification of blastozoans in the early Cambrian

Since their first appearance in the fossil record (Cambrian Stage 3, ~520 Ma ago), echinoderms were already relatively diverse (classes Edrioasteroidea, Eocrinoidea, Helicoplacoidea, and Lepidocystoidea) and cosmopolitan. This suggests a possible earlier origin of the phylum, although no evidence for this has been found due to the absence of Lagerstätten able to preserve non-mineralized ancestral forms. The major diversification of echinoderms during the Cambrian and Ordovician (about twenty classes, so four times the number of extant classes) renders particularly difficult the identification of homologous structures and the construction of a phylogeny encompassing the whole phylum. The goal of this study is to clarify whether feeding appendages of blastozoans (brachioles) and crinoids (arms) are homologous (or not) and thus if those two groups belong (or not) to a same clade Pelmatozoa. In this context, the gogiid genus Alanisicystis -the oldest echinoderm known so far from the African continent, situated in Western Gondwana- is of particular interest. Its morphology was analyzed based on abundant and remarkably preserved specimens from the Issafen Formation (Cambrian Series 2, Stage 3; Morocco). This eocrinoid has a short stem composed of small, irregularly arranged circular plates. The theca is made of a mosaic of irregularly polygonal plates, ornamented with a fine granulation and numerous respiratory structures (epispires). Its aboral end consists of a single basal plate. The brachioles consist of two series of alternating flooring plates and two series of alternating cover plates. Those long appendages branch from the adoral end of the theca, at the edges of the oral fram

Skeletal elements controlled soft-tissue preservation in echinoderms from the Early Ordovician Fezouata Biota

International audienc

Skeletal elements controlled soft-tissue preservation in echinoderms from the Early Ordovician Fezouata Biota

International audienc