◄ Carnets Geol. 17 (8) ►
Contents
[1. Introduction]
[2. Material and methods]
[3. Geologic setting, presumed origin of the specimeny]
[4. Systematic palaeontology]
[5. Conclusions] and ...
[Bibliographic references]
Charles University, Institute of Geology and Palaeontology, Albertov 6,
CZ–128 43, Prague 2 (Czech Republic)
Charles University, Institute of Geology and Palaeontology, Albertov 6,
CZ–128 43, Prague 2 (Czech Republic)
Published online in final form (pdf) on October 16,
2017
DOI 10.4267/2042/62768
[Editor: Bruno Granier; language editor: Robert W. Scott]
Reexamination of the type specimen described by Barrande in 1887 as "Tige d'une Cystidée indéterminée" shows that this unique specimen represents an articulated but incomplete remnant of the gogiid eocrinoid Akadocrinus jani Prokop. The specimen is preserved as an external mould in shale from the mid-Cambrian Jince Formation, and comprises a proximal part of a stem associated with a slightly disarticulated distal portion of a theca, composed of over twenty polygonal plates. With the exception of the basal-most plates, all other preserved thecal plates bear ellipsoidal marginal epispires, and substantiate assignment of this specimen to the epispire-bearing phase in ontogenetic development of Akadocrinus.
• Echinodermata;
• Blastozoa;
• Eocrinoidea;
• Drumian;
• Cambrian;
• Barrandian area;
• Příbram–Jince Basin;
• Czech Republic.
Nohejlová M. & Fatka O. (2017).- Revision of the Barrande's specimen "Tige d'une Cystidée indéterminée" (Cambrian, Echinodermata, Eocrinoidea).- Carnets Geol., Madrid, vol. 17, no. 8, p. 153-160.
Révision de la "Tige d'une Cystidée indéterminée" décrite par Barrande (Cambrien, Echinodermata, Eocrinoidea).- La réétude du spécimen-type décrit par Barrande en 1887 comme une "tige de Cystidée indéterminée" montre que ce spécimen unique pourrait être attribué à l'espèce d'éocrinoïde gogiidé Akadocrinus jani Prokop. Ce spécimen correspond à une empreinte préservée dans une argilite de la Formation de Jince (Cambrien moyen, République Tchèque). Il présente la partie proximale de la tige articulée à un fragment de thèque distale, composée d'une vingtaine de plaques polygonales. À l'exception des plaques basales, les plaques thécales portent des épispires ellipsoïdales. Cet indice morphologique suggère que ce spécimen pourrait représenter les prémices d'un stade adulte.
• Echinodermata ;
• Blastozoa ;
• Eocrinoidea ;
• Cambrien ;
• Drumien ;
• aire barrandienne;
• Bassin de Příbram-Jince
Basin ;
• République tchèque.
Remains of disarticulated echinoderm skeletons are quite common in Cambrian and Ordovician sediments of the Barrandian area (Barrande, 1887; Havlíček & Vaněk, 1966; Havlíček, 1971; Mergl & Prokop, 2006). However complete specimens are more rare (Barrande, 1887; Pompeckj, 1896; Prokop, 1964; Fatka & Szabad, 2014a; Zamora et al., 2015; Nohejlová & Fatka, 2016). After more than a century of intensive research, the Czech scientists Havlíček & Vaněk (1966) and more recently Prokop & Petr (2000) brought together a list of all Ordovician echinoderm taxa in the Prague Basin, including their stratigraphic ranges. Similarly, Ubaghs (1967a, 1967b, 1967c), Fatka (1990) and Fatka et al. (2004) compiled exhaustive lists of Cambrian echinoderm species for the Skryje-Týřovice and Příbram-Jince basins. One of the known groups of blastozoan echinoderms is a paraphyletic class Eocrinoidea, which ranges from the Cambrian to the Silurian (Sprinkle, 1995).
From the Barrandian area, nine Cambrian and Ordovician species assigned to eocrinoids were known in the second half of the 19th century (Barrande, 1846, 1887). Seven species were based on specimens from the Ordovician of the Prague Basin, particularly: Archaeocystites medusa Barrande, 1887; Ascocystites drabowensis Barrande, 1887; Ascocystites micraster Barrande, 1887; Ascocystites cf. micraster Barrande, 1887; Cardiocystites bohemicus Barrande, 1887; Mimocystites bohemicus Barrande, 1887; and Macrocystella sp., two last named taxa are recently classified as rhombiferans by Paul (1968) and other authors (see Prokop & Petr, 2000; Mergl & Prokop, 2006). The scarce material collected from the Cambrian of the Příbram-Jince and Skryje-Týřovice basins allow the description of only two species, Acanthocysties briareus Barrande, 1887 and Lichenoides priscus Barrande, 1846 (see Ubaghs, 1967a; Sprinkle, 1973).
Continuing discoveries of new material combined with revisions of already described species have resulted in a clearer understanding of eocrinoid systematics. Four mid-Cambrian eocrinoid genera are now known: Acanthocystites Barrande, 1887; Akadocrinus Prokop, 1962; Lichenoides Barrande, 1846 and Luhocrinus Prokop & Fatka, 1985 (see Nardin et al., 2017), while only two genera of the Barrandian area, Ascocystites Barrande, 1887 and Cardiocystites Barrande, 1887, are currently accepted as Ordovician eocrinoids.
However, Barrande (1887) also described and figured several incompletely or quite poorly preserved echinoderm remains. The morphology of some of these imperfectly known taxa has been properly reconstructed only recently, and an understanding of systematic position of these previously poorly-known forms is now possible (e.g., Chlupáč & Kordule, 2002; Fatka et al., in press). The aim of this contribution is to revise an original specimen, based on this new understanding, erroneously described by Barrande. He classified it as the "Tige d'une Cystidée indéterminée". It comes from the mid-Cambrian Jince Formation of the Příbram-Jince Basin.
The original description of "Tige d'une Cystidée
indéterminée" by Barrande (1887)
was based on a single specimen, housed in the original collection of Joachim Barrande
in the National Museum Prague (inventory number L9052). This specimen
is preserved as an external natural mould of the original calcite ossicles in
fine greywacke. It was collected from an unknown site in the mid-Cambrian Jince
Formation in the Příbram–Jince Basin (Fig. 1 
). The
original external mould was photographed with a digital Canon EOS 70 D
camera. New latex casts were made, coated with ammonium chloride and also
photographed as part of the current research.
|
Figure 1:
Maps showing location of fossil sites. A – Czech Republic and Cambrian
rocks of Příbram-Jince Basin. B – Simplified geological maps showing
distribution of mid-Cambrian Jince Formation and location of fossil sites. C –
Stratigraphic distribution of Akadocrinus
jani sequence accessible at four localities within Jince Formation of Příbram–Jince
Basin. 1, Vystrkov Hill locality; 2, slope Vinice near Jince (= östlicher Ende
von Vinice, in der Nähe von Jinec in Želízko, 1897, p. 323); 3,
Chramostův mlýn (= Chramosta-Mühle in Želízko,
1897, p. 323); 4,
Felbabka within Příbram–Jince Basin. Geology modified from Havlíček
(1971); biostratigraphic zones after Fatka & Szabad (2014a). |
The mid-Cambrian Jince Formation of the Příbram–Jince
Basin (Fig. 1 ) is well-known as a classical source of diverse and usually
well-preserved skeletal fauna (e.g., Barrande, 1846; Šnajdr,
1958;
Geyer et al., 2008), including
echinoderms (see above). Rich associations of disarticulated as well as
articulated trilobites, agnostids, echinoderms, brachiopods, hyoliths,
organic-walled microfossils and ichnofossils associated with remains of bivalved
arthropods, helcionelloid molluscs, and foraminifers have been studied from this
locality for nearly two hundred years (summary see Fatka et
al., 2004).
3.1. Presumed origin of the specimen
The exact site at which the studied specimen was
collected is not known. The associated label bears the name "Ginetz". Barrande
and his collectors used the cumulative designation "Ginetz"
for several sites near the town of Jince (= Ginetz
- German transcription used in maps in 19th century; Šnajdr,
1958; Chlupáč, 1999). However, lithology of the rock sample
combined with knowledge of outcrops excavated by Barrande
and his collectors
provided enough evidence to assess probable localities. The lithological
character of the rock sample and the occurrence of an internal mould of a prone,
well-articulated exoskeleton of the agnostid
Peronopsis integra Beyrich, 1845, at the sample surface
(Fig. 2 )
indicate that the sample originates from the range from upper levels of the Hypagnostus
parvifrons Biozone through the middle part of the Paradoxides
(P.)
paradoxissimus gracilis Biozone of Fatka & Szabad
(2014a).
These are the levels of richly fossiliferous shales and fine greywackes that
have been intensively quarried since the middle of the 19th century (Šnajdr,
1958). Fossils were collected from four major areas in the Příbram-Jince
Basin (Chlupáč, 1999, p. 11):
););); and).3.2. Age
The occurrence of the agnostid Hypagnostus parvifrons indicates an age corresponding to middle and higher levels of the Baltic Paradoxides (P.) paradoxissimus Biozone (see Axheimer & Ahlberg, 2003). These levels are supposed to be equivalent to the Caesaraugustan Regional Stage in the West Gondwanan chronostratigraphic sequence (see Geyer et al., 2008; Gozalo et al., 2011), and thus correspond to the Drumian Stage of Cambrian Series 3 (see discussion in Fatka et al., 2014).
Phylum Echinodermata Brugière, 1791 (ex Klein, 1734)
Subphylum Blastozoa Sprinkle, 1973
Class Eocrinoidea Jaekel, 1918
Order Gogiida Broadhead, 1982
Family Eocrinidae Jaekel, 1918
Akadocrinus Prokop, 1962
Type species. Akadocrinus jani Prokop, 1962. Jince Formation, Hypagnostus parvifrons Biozone, Drumian, Příbram–Jince Basin, Barrandian area, Czech Republic.
Occurrence. The genus Akadocrinus is known from three localities in the Příbram–Jince Basin; (1) the slope named Vinice (near Jince), (2) north-eastern slope of Vystrkov Hill near Jince, and (3) the Felbabka locality. All these localities are situated in the range from the Paradoxides (E.) pusillus through the Paradoxides (P.) paradoxissimus gracilis biozones of Fatka & Szabad (2014a), from the latest Cambrian Stage 5 into the Drumian in age (Fig. 1.D).
Remarks. The endemic eocrinoid genus Akadocrinus includes two separate species: A. jani Prokop, 1962, and A. knizeki Fatka & Kordule, 1991, both known from the middle part of the Jince Formation (Fatka et al., 2004). The species A. nuntius Prokop, 1962, is considered to be synonymous with the type species A. jani Prokop, 1962 (Sprinkle, 1973, p. 106; Nohejlová & Fatka, 2016, p. 142).
Akadocrinus jani Prokop, 1962
(Figs. 2
- 3 )
1887 "Tige d'une Cystidée indéterminée"; Barrande, p. 189, pl. 2, fig. 33.
(full synonymy see Nohejlová & Fatka, 2016, p. 143-144)
Material. The type specimen housed in the National Museum Prague under number L9052; exact locality unknown.
Description. The rock slab measures 34.2 x 22.8 mm; its thickness ranges around 14 mm. On
the slab, few complete and incomplete fossils are seen; only the largest remnant
was described and figured by Barrande (1887). It is 23 mm long and from three to
five mm wide, an incompletely preserved fossil composed of two distinct parts,
(1) a longer and narrower, transversally segmented and well-articulated section
(S in Fig. 2.B ) around 16.7 mm in length, and (2) a shorter and wider,
bottle-shaped section composed of more than twenty irregularly polygonal plates,
which are slightly disarticulated. Almost all these plates (except the plates
nearest to the narrow section) show distinctive undulate margins. Nearly all
plates with straight margins show a smooth surface (sp in Fig.
2.A ), while plates
with distinctive undulate margins bear fine granulation (gp in Fig.
2.A ). All
well-preserved plates have quite similar dimensions; average sizes range around
1.51 mm in diameter.
|
Figure 2:
Akadocrinus
jani Prokop, 1962 (specimen L9052); Drumian, Jince Formation, Příbram–Jince
Basin, exact locality and stratigraphical level unknown (= "Tige d'une Cystidée
indéterminée" of Barrande, 1887). Scale bar 5 mm. A
– Photograph of latex casts whitened with ammonium chloride. Abbreviations: sp
– smooth internal surface of thecal plate, gp – external surface of thecal
plate with fine granulation, a – holaspid agnostid Peronopsis, b – valve of the bradoriid Konicekion, c
– part of the eocrinoid stem. B – Drawing of specimen L9052 made in CorelDraw X6
showing in grey color the most basal thecal plates. Abbreviations: T – theca,
S – stem. |
Remark. On the rock surface, five other skeletal remains are
preserved; they represent a cross-section of an isolated eocrinoid columnal (d
in Fig. 3.A ), a broken part of an eocrinoid stem (c in
Figs. 2.A
& 3.A ), an
indeterminable echinoderm plate (e in Fig. 3.A ), an isolated valve of a tiny
bradoriid arthropod Konicekion (b in Fig. 2.A ), and an articulated prone exoskeleton of a holaspid agnostid Peronopsis
(a in Figs. 2.A
& 3.A ).
Discussion. The morphology and dimension
of the partially preserved fossil agrees well with an incomplete medial part of
an eocrinoid echinoderm (Fig. 3.B ). The wider section composed of slightly
disarticulated polygonal plates we interpret here as the distal part of the
theca (T in Fig. 2.B ). Almost all thecal plates, except the most-basal, bear
roundish to ellipsoidal epispires, bounded by a low rim. The narrower,
transversally segmented section we assign to partially preserved proximal part
of stem, composed of well-articulated columnals (S in Fig. 2.B
). Barrande's
preserved echinoderm remnant is consistent with the morphology of the eocrinoid
echinoderm Akadocrinus Prokop,
1962 (Fig. 3.B ). Mature
specimens of Akadocrinus have thecal plates, around 1.69
mm in largest surface dimension, which is only slightly larger than the diameter
of plates in Barrande's specimen.
Similar also is the length of the stem fragment; in mature specimens of A. jani, the length of observed parts of the stem is quite variable. Although we do not have a specimen with a complete stem at our disposal, preserved remains of stems are usually more than 20 mm long (see Nohejlová & Fatka, 2016). This preserved part is only slightly shorter, composed of several tens of low columnals; their heights range around 0.16 mm.
|
Figure 3:
Photographs of external moulds. Scale bar 5 mm. A – Akadocrinus jani Prokop,
1962 (specimen L9052) (= "Tige d'une Cystidée indéterminée" of Barrande,
1887). Abbreviations: a – holaspid specimen of the agnostid Peronopsis,
c – part of the eocrinoid stem, d – cross-section of an isolated eocrinoid
columnal, e – indeterminable echinoderm plate. B – Well preserved specimen of Akadocrinus
jani Prokop, 1962 (specimen L42231); Drumian, Jince Formation, Příbram–Jince
Basin, slope Vinice near Jince. Dashed line represents preserved part of the
specimen L9052. |
The specimen classified by Barrande (1887) as "Tige d'une Cystidée indéterminée" belongs to the proximal part of stem associated with the basal part of the theca of an eocrinoid Akadocrinus jani Prokop, 1962. The presence of irregularly shaped marginal epispires in most thecal plates assigns this specimen to the epispire-bearing phase in eocrinoid ontogeny (see Nohejlová & Fatka, 2016).
We would like to express our thanks to Ron Parsley (New Orleans, U.S.A.) for reviewing the manuscript. We are very grateful to Élise Nardin (Toulouse, France) for her insightful review and translation in French. This research was funded by grant No. 898416 "Revision of eocrinoids echinoderms from Cambrian of the Barrandian area" from GA UK (Grant Agency of Charles University), and by the project PRVOUK Q45 of the Ministry of education, youth and sports of Czech Republic. English language proofreading by Petr Daneš.
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