TY - JOUR

T1 - Nonmineralized triradial conulariids from the lowermost Cambrian Stage 2 of the Olenek Uplift, Siberian Platform

AU - Sarsembaev, Zhiger A.

AU - Marusin, Vasiliy V.

N1 - Funding Information: This research was supported by the Russian Foundation for Basic Research (grant number 20-35-70016; paleontology, SEM-study) and by the Russian Science Foundation (grant number 21-17-00052; paleontology, manuscript preparation). Fieldworks at the Olenek Uplift were financially supported by the National Geographic Committee for Research and Exploration (grants 8227-07, 8637-09, NGS-372R-18). We thank D.V. Grazhdankin, N.V. Bykova, V.I. Rogov, K.E. Nagovitsin, and B.B. Kochnev (IPGG SB RAS, Novosibirsk) for their help during the fieldwork. Insightful comments of D.V. Grazhdankin and T.A. Ivanovskaya on the early draft of the manuscript are warmly appreciated. The authors are grateful to M.V. Khlestov (IGM SB RAS, Novosibirsk) for guidance during the SEM study and to N.V. Bykova for linguistic improvements of the manuscript. We also thank the reviewers, H. Van Iten (Hanover College, USA) and A. Kouchinsky (Swedish Museum of Natural History), who provided the in-depth critical analysis of our work and hence developed it considerably. The authors declare no conflict of interest. Publisher Copyright: Copyright © The Author(s), 2022. Published by Cambridge University Press on behalf of The Paleontological Society.

PY - 2022/7/11

Y1 - 2022/7/11

N2 - In the early Cambrian fossil record, triradial symmetry is typical for anabaritids and occurs among carinachitids. The former are an extinct group of minute benthic cnidarians covered with a calcareous tubular exoskeleton. The origin of the anabaritids is poorly understood, but previously reported triradial pyramid-shaped steinkerns and molds of the oldest conulariids, Vendoconularia, from the upper Ediacaran of the White Sea region suggested the anabaritids were closely related to conulariids. However, triradial symmetry could originate independently in different lineages in the late Ediacaran and early Cambrian. Herein we describe a new taxon, Ilankirus kessyusensis new genus new species, from the base of the Cambrian Stage 2 of the Olenek Uplift (Siberian Platform). These fossils occur as ornamented steinkerns in the shape of trilateral pyramids and lack any relics of a mineralized exoskeleton. Abundant plastic deformations and fractures of the casts suggest the organism was weakly if at all mineralized. The steinkerns are encrusted with a thin patina of iron-rich chlorite (chamosite) formed because of a multistage diagenetic replacement of authigenic glauconite (glauconite-berthierine-chamosite) under reducing conditions of oxygen-depauperate pore- and seawater. Both lacking two major autapomorphies of the crown-group conulariids (mineralized periderm and quadrate cross section of the oral region of the periderm), the late Ediacaran triradial Vendoconularia and Terreneuvian Ilankirus represent stem-group conulariids. UUID: http://zoobank.org/a2ce04fa-36a5-485a-806c-f13f4749fc7f

AB - In the early Cambrian fossil record, triradial symmetry is typical for anabaritids and occurs among carinachitids. The former are an extinct group of minute benthic cnidarians covered with a calcareous tubular exoskeleton. The origin of the anabaritids is poorly understood, but previously reported triradial pyramid-shaped steinkerns and molds of the oldest conulariids, Vendoconularia, from the upper Ediacaran of the White Sea region suggested the anabaritids were closely related to conulariids. However, triradial symmetry could originate independently in different lineages in the late Ediacaran and early Cambrian. Herein we describe a new taxon, Ilankirus kessyusensis new genus new species, from the base of the Cambrian Stage 2 of the Olenek Uplift (Siberian Platform). These fossils occur as ornamented steinkerns in the shape of trilateral pyramids and lack any relics of a mineralized exoskeleton. Abundant plastic deformations and fractures of the casts suggest the organism was weakly if at all mineralized. The steinkerns are encrusted with a thin patina of iron-rich chlorite (chamosite) formed because of a multistage diagenetic replacement of authigenic glauconite (glauconite-berthierine-chamosite) under reducing conditions of oxygen-depauperate pore- and seawater. Both lacking two major autapomorphies of the crown-group conulariids (mineralized periderm and quadrate cross section of the oral region of the periderm), the late Ediacaran triradial Vendoconularia and Terreneuvian Ilankirus represent stem-group conulariids. UUID: http://zoobank.org/a2ce04fa-36a5-485a-806c-f13f4749fc7f

KW - ORDOVICIAN

KW - FOSSIL

KW - MICROSTRUCTURE

KW - GLAUCONITE

KW - MEDUSOZOA

KW - ROCKS

KW - MODE

KW - LIFE

UR - http://www.scopus.com/inward/record.url?scp=85129040845&partnerID=8YFLogxK

U2 - 10.1017/jpa.2022.21

DO - 10.1017/jpa.2022.21

M3 - Article

VL - 96

SP - 791

EP - 802

JO - Journal of paleontology

JF - Journal of paleontology

SN - 0022-3360

IS - 4

M1 - PII S002233602200021

ER -