Journal of Paleontology, 91(4), 2017, p. 672–684 Copyright © 2017, The Paleontological Society 0022-3360/17/0088-0906 doi: 10.1017/jpa.2016.157
Evolutionary implications of a new transitional blastozoan echinoderm from the middle Cambrian of the Czech Republic
Elise Nardin,1 Bertrand Lefebvre,2 Oldřich Fatka,3 Martina Nohejlová,3 Libor Kašička,4 Miroslav Šinágl,5 and Michal Szabad6
1Géosciences Environnement Toulouse (GET), Observatoire Midi-Pyrénées, CNRS/UPS/IRD/CNES, 14 avenue Édouard Belin, F-31400
Toulouse, France ⟨
elise.nardin@
get.omp.eu⟩ 2UMR CNRS 5276 Laboratoire de Géologie, Université Lyon 1, Géode, 2 rue Raphaël Dubois, F-69622 Villeurbanne Cedex, France
⟨
bertrand.lefebvre@univ-lyon1.fr⟩ 3Charles University, Institute of Geology and Palaeontology, Albertov 6, 128 43 Praha 2, Czech Republic ⟨
fatka@natur.cuni.cz⟩
⟨
martina.nohejlova@
natur.cuni.cz⟩ 4Koněprusy 45, 266 01 Beroun, Czech Republic ⟨
libor.kasicka@email.cz⟩ 5Osvobozeni 390, 26101 Příbram VII, Czech Republic ⟨
mira.sinagl@
seznam.cz⟩ 6Tisová 29, Bohutín 261 42, Czech Republic ⟨
geosz.pb@seznam.cz⟩
Abstract.—The primitive blastozoan Felbabkacystis luckae n. gen. n. sp. is described from the Drumian Jince Formation, Barrandian area (Czech Republic) from eleven fairly well-preserved specimens. Its unique body plan organization is composed of a relatively long, stalk-like imbricate structure directly connected to the aboral imbricate cup of the test and of an adoral vaulted tessellate test supporting the ambulacral and brachiolar systems. Its bipartite test, called prototheca, highlights the evolution of the body wall among blastozoans. Felbabkacystis n. gen. shows the combination of plesiomorphic (imbricate stalk-like appendage) and derived features (highly domed peristome, elongate epispires). The new genus is interpreted as a transitional form between calyx-bearing and theca-bearing blastozoans, and is attributed to the new family Felbabkacystidae. The lithology, the associated fauna, and the possession of a long stalk suggest that Felbabkacystis was probably a low-level suspension feeder living in relatively deep settings.
Introduction
The Cambrian succession of the Příbram-Jince Basin is famous for being abundantly fossiliferous. Numerous fairly well- preserved fossils from a large number of distinct fossil groups have been collected in the Cambrian Series 3 (latest Drumian) Jince Formation of the Příbram-Jince Basin (Barrandian area) for more than 230 years. During that time, those fossils have been intensively studied and include the primary producers (e.g., acritarchs and prasinophytes), different primary and higher consumers (like agnostids, brachiopods, echinoderms, foraminiferans, hyoliths, trilobites), and traces of their life activities (see Fatka et al., 2004 and references therein). Echino- derms are highly diverse in the Jince Formation (Fig. 1), being represented by numerous species including at least one
lepidocystoid (Vyscystis ubaghsi Fatka and Kordule, 1990), five eocrinoids (Acanthocystites briareus Barrande, 1887; Akadocrinus jani Prokop, 1962; A. knizeki Fatka and Kordule, 1991; Lichenoides priscus Barrande, 1846, and L. vadosus Parsley and Prokop, 2004), two (?)rhombiferans (Dibrachia- cystidae gen. indet. sp. indet., Vizcainoia sp.), one cinctan (Asturicystis havliceki Fatka and Kordule, 2001), three cteno- cystoids (Etoctenocystis bohemica Fatka and Kordule, 1985; Ctenocystoidea gen. indet. sp. indet.), and one edrioasteroid
(Stromatocystites pentangularis Pompeckj, 1896 and S. flexibilis Parsley and Prokop, 2004), in addition to one stylophoran (Ceratocystis perneri Jaekel, 1901) and the problematic Cigara dusli Barrande, 1887. This assemblage is mainly endemic from this basin; only a few of these genera allow comparison with fauna elsewhere (see Lefebvre and Fatka, 2003; Zamora et al., 2013). Here, we document a remarkable new blastozoan, Felbabkacystis n. gen., from the Jince Formation of Czech Republic interpreted to represent the oldest record of a unique morphology showing a mixture of plesiomorphic and more derived features.
Geological setting
The Jince Formation, with a thickness of about 450 m, is predominantly composed of greywacke interbedded with mud- stone to clayshale beds and locally contains subordinate sandy layers in the Příbram-Jince Basin. Fossiliferous layers are composed of relatively massive dark shales grading into fine- grained shales (Fatka and Szabad, 2014). Paleoenvironmental conditions might be interpreted as relatively deep, quiet water below storm base (mid offshore) on a siliciclastic platform. Fossil content is mostly represented by fragments and isolated elements spread over large surfaces. Well-preserved specimens
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