Reassessment of the Ordovician brachiopod Poramborthis and Poramborthidae

MICHAL MERGL

PORAMBORTHIS is a strophic orthid-like rhynchonelliformean genus which, since its erection by Havlíček (1949), has presented a phylogenetic enigma. The first described species, which was later referred to Poramborthis was recorded by Joachim Barrande. He assigned this remarkable taxon to the genus Orthis Dalman, 1828; this attribution was quite appropriate in the 19th century. In the ensuing 120 years eight species have been referred to Poramborthis and the family Poramborthidae has been established to accommodate them. However, the taxonomic position and affinity of the Poramborthidae Havlíček, 1950 has not been discussed for more than sixty years. The initial family rank of Poramborthidae was changed to subfamily level by Williams & Wright (1965). After Havlíček’s (1977) discussion, it reverted to family rank, a view adopted by Williams & Harper (2000). The family is monogeneric and has a stratigraphic range restricted to the Tremadocian. It inhabited the periphery of high-latitude Gondwana. In various palaeogeographic reconstructions, Poramborthis and the Poramborthidae have been considered as characteristic endemic taxa of the Mediterranean Province, in the European sector of Gondwana (Havlíček & Vaněk 1966; Havlíček

1976, 1989; Havlíček et al. 1994; Fortey & Cocks 2003; Mergl 2004).

HISTORY The genus Poramborthis was erected by Havlíček (1949). In his original description, the genus included five species: Poramborthis klouceki Havlíček, 1949; P. kettneri (Klouček, 1915); P. lamellosa (Růžička, 1927); P. grimmi (Barrande, 1879); and P. anomala Havlíček, 1949. All came from the Krušná Hora Beds, a now disused stratigraphical unit comprising the Třenice, Mílina and part of the Klabava formations in modern stratigraphic nomenclature (see Chlupáč et al. 1998). The type species P. klouceki occurs in the Mílina Formation and was the stratigraphically youngest species of the genus known to Havlíček (1949). Havlíček referred all these taxa to the family Porambonitidae Davidson, 1853. This suggests that Havlíček was uncertain where to place the genus. Significantly, in the present collection of the National Museum in Prague, there is Havlíček’s manuscript label with the name ‘Eoporambonites’ attached to specimens of Orthis Grimmi Barrande, 1879 (= Poramborthis grimmi). This generic name was a nomem nudum and the new generic name Poramborthis

MERGL, M., 2011:??:??. Reassessment of the Ordovician brachiopod Poramborthis and Poramborthidae. Memoirs of the Association of Australasian Palaeontologists 41, 351-358. ISSN 0810-8889.

The history, morphology and distribution of the genus Poramborthis and the family Poramborthidae are reviewed. Although the rectimarginate commissure and presence of a low notothyrial platform are suggestive of an orthid affinity, other features - especially the digitate mantle canal system, costellate ornament with subcircular pits in the interspaces and the sessile spondylium - argue for a syntrophiidine affinity. The associated brachiopod fauna, with dominant eoorthids, early plectorthoideans and tritoechiids, indicate communication with Laurentia and various low-latitude Gondwana microcontinents, representing a high-latitude counterpart of the orthide-syntrophioidean association. The uniqueness of the Mediterranean province in the late Cambrian and Tremadocian is thus challenged.

Michal Mergl (mmergl@kbi.zcu.cz), Department of Biology, Faculty of Education, University of West Bohemia in Plzeň, Klatovská 51, 30619 Plzeň, Czech Republic. Received 3 June 2011.

Keywords: Tremadocian, Czech Republic, Brachiopoda, Porambonitoidea, taxonomy.

AAP Memoir 41 (2011)352

AAP Memoir 41 (2011) 353

later replaced this label. Subsequently the valid generic name Eoporambonites was erected by Popov et al. (2005) for another Early Ordovician porambonitoid taxon. Havlíček (1949) noted that Poramborthis is a genus combining orthid characters; namely a strophic shell, distinct interareas, the presence of the a cardinal process, and short brachiophore plates, with finely capillate and fenestrate ornamentation, which is also characteristic of Porambonites Pander, 1830.

In 1950, only a year after the definition of Poramborthis, Havlíček (1950) erected the family Poramborthidae. In his original diagnosis of the family, he noted a biconvex strophic shell, the lack of a fold and sulcus, long dental plates converging towards the valve floor, a long ventral muscle field, divergent vascula media, orthid-like brachiophores, and a rudimentary or absent cardinal process. The absence of a spondylium-like structure and the lack of strong and long brachiophore supporting plates distinguished the genus from other members of the Porambonitidae. Radial rows of circular pits on the shell surface, similar to those in Porambonites, were also noted (Havlíček 1950, p. 130).

The first report of Poramborthis outside Bohemia was by Sdzuy (1955). He described two new species, P. catilla Sdzuy, 1955 and P. gemmata Sdzuy, 1955 from the Lower Tremadocian (Leimitz Shales) of Bavaria, Germany. Havlíček & Josopait (1972) described Poramborthis hispanica Havlíček, 1972, a Spanish Lower Tremadocian species closely related to the Bavarian P. catilla.

In 1977, Havlíček defended the family rank of Poramborthidae and discussed its relationships with the Orthidae Woodward, 1852 and the Eoorthidae Walcott, 1908, and to the Cambrian genera Wimanella Walcott, 1908 and Diraphora Bell, 1941. He omitted any reference to porambonitoid features and emphasised similarity with the smooth or finely costellate surfaces of various Cambrian genera. To Havlíček (1977), the pinnate mantle canal system and blade-like brachiophores were the significant

differences distinguishing the Poramborthidae from the Orthidae and Eoorthidae. However, uncertainty concerning arrangement of a mantle canal system is also apparent in this discussion (Havlíček 1977, p. 37).

Since Havlíček’s (1977) review of Bohemian species of Poramborthis, new material has been recorded from Bavaria and Bohemia. Mergl (1985) reported a very rare, unnamed new species of Poramborthis in the Mílina Formation (Tremadocian). Sdzuy et al. (2001) described unique material from the Vogtendorf Formation (Tremadocian) of Bavaria. Two well preserved species, Poramborthis vonhorstigi Villas, 2001 and P. cf. klouceki Havlíček, 1949 differ from each other by the subcircular outline and much finer capillate ornamentation of the latter species. Fragments of shells with a characteristic porambonitoid-like microornament have been observed near the top of the Klabava Formation (Dapingian) (Mergl 2004).

MORPHOLOGY Specimens of Poramborthis show considerable variations in size and ornament, but other features are rather uniform. However, some features, for instance the length of the dental plates, vary in the different species.

Width of adult specimens ranges from 30-35 mm in P. grimmi to 15–20 mm in P. klouceki. The shell is strophic, usually with large, clearly defined and wide interareas in both valves. However, the interarea may also be very low and short, producing a subcircular shell outline, such as in P. cf. klouceki. The shell is thin in small individuals and anteriorly, but larger shells show a moderately thickened shell posteriorly. The shell outline of all known species range from transversally elliptical to subcircular, generally with obtuse cardinal extremities. The maximum width is situated at midlength to anterior third; however, the outline changes rapidly with ontogeny, with maximum width at the hinge line in small specimens. The shell convexity is moderate, producing an orthid-like appearance

Figure 1. Poramborthis klouceki Havlíček, 1949, Upper Tremadocian, Mílina Formation; locality Horní Kvaň, Barrandian, Czech Republic. A-B, juvenile ventral valves showing small triangular ventral muscle field, PCZCU 1791, PCZCU 1792. C, F, large ventral valve with trilobate ventral muscle field, PCZCU 1793. D, G, R, ventral valves showing variable development of dental plates, and detail of ventral muscle field, PCZCU 1794, PCZCU 1796. E, medium-sized complete shell, PCZCU 1795. H, ventral valve with asymmetry of the sessile spondylium, PCZCU 1797. I, J, ventral valve with well developed sessile spondylium, PCZCU 1798. K, S, dorsal valve showing mantle canals and raised notothyrial platform, and detail of notothyrial platform and dorsal muscle field, PCZCU 1799. L, dorsal valve showing mantle canal system, PCZCU 1800. M, incomplete dorsal valve showing digitate pattern of dorsal mantle canal system, PCZCU 1801. N, large dorsal valve showing small notothyrial platform, PCZCUI 1802. O-P, dorsal valve with well preserved sites of diductors on a weakly raised notothyrial platform bounded by broadly diverging brachiophore (= crural) bases, PCZCU 1803. Q, dorsal valve in oblique view showing weakly raised notothyrial platform and dorsal adductor imprints, PCZCU 1804.

AAP Memoir 41 (2011)354

in all known species.The ventral muscle field of the type species

is long and bounded by subparallel dental plates converging onto the valve floor. The outline of the ventral muscle field ranges from long and parallel-sided in P. klouceki to broadly triangular or transversely broadly ovate in P. vonhorstigi. The diductor scars have oblique anterior edges and their surface is striated with growth lines. The adductor scar is undivided, parallel-sided to narrowly triangular, with elongate tongue-like scars at its anterior border. Anterior border of the muscle field is trilobate, with a forwardly extended adductor scar (Figs 1C, F). Thickness and position of the dental plates varies (Figs 1D, F, G, I). There are specimens with subvertical and thick dental plates in P. klouceki, but other individuals show basally converging thin plates which form a structure similar to a sessile

spondylium. Asymmetry of dental plates also occurs (Fig. 1H).

The dorsal notothyrial platform is variably developed but is usually very low with a broadly triangular outline. Its height increases with shell size. The diductor attachment structure is broadly triangular, as long as the brachiophore bases, with a simple ridge separating the diductor muscle bases (Figs 1S, 2F). This ridge has been interpreted as a cardinal process by some authors (Havlíček 1949, 1977; Sdzuy et al. 2001), but more likely represents a blade-like ridge of shell deposits between the bundles of diductor muscles. The brachiophore bases are broadly divergent, converging toward the valve floor.

The dorsal adductor muscle field consists of a larger posteromedian pair of scars and smaller anteromedian scars (Figs 1P, S, 2G). The scars are generally weakly impressed in P. klouceki

Figure 2. Poramborthis grimmi (Barrande, 1879), Lower Tremadocian, Třenice Formation; locality Holoubkov, abandoned mine “V Ouzkém”, Barrandian, Czech Republic. A, ventral valve showing muscle field, 3RO 21524a. B, ventral valve showing digitate vascula media, 3RO 21457. C, dorsal valve showing deep scars of the muscle field, SBNM L39309. D, ventral valve with muscle scars on surface of sessile spondylium, SBNM L 39310. E, dorsal valve showing mantle canal system, SBNM L39311. F, incomplete dorsal valve with raised notothyrial platform showing distinct attachment sites of diductor muscles; the specimen referred by Havlíček (1977) to Poramborthis cf. hispanica Havlíček, 1972, 3RO 21678. G, dorsal valve interior with distinct impressions of dorsal muscle field, SBNM L 39312. H, exterior of the shell, 3RO 21572. I, detail of costellate ornamentation, SBNM L 39313. J, rows of circular pits in interspaces, PCZCU 1805.

AAP Memoir 41 (2011) 355

but fairly deeply impressed in P. vonhorstigi. However, some specimens of P. klouceki (Fig. 1K, S) show deeply impressed posterior scars which are twice the size of the smaller elongate anteromedian scars.

The mantle canal system is weakly impressed and is interpreted as digitate (Figs 1K-M, 2A-B). Young dorsal shells of P. klouceki show narrow and gently diverging canals of vascula media extending from the anteromedian part of the anterior adductor scar. The second pair of undivided canals of vascula myaria extends in between the anterior and posterior pairs of adductor scars. These canals are also well defined in P. cf. klouceki (Sdzuy et al. 2001, pl. 2, fig. 9). However, the vascula genitalia are less clearly impressed. In some specimens (Fig. 1M) the proximal parts of these canals are discernible. The simple vasculum medium canal is less clear from two thirds of valve length and, as seen in P. grimmi, it branches into several subsidiary, less clearly impressed canals. Terminal canals of the vascular system are weakly impressed along the shell periphery, forming parallel striations in the valve floor. These fine canals are visible only in the large shells. Juvenile shells display a smooth periphery.

The ventral valve mantle canal system is digitate, consisting of arcuate broadly divergent vascula media and four or more blind canals impressed on the posteromedian valve floor close to the dental plates.

The ornamentat ion of Poramborthis is multicostellate, formed by fine to very fine, sometimes flat-topped costellae with superimposed concentric fila. New fila originate exclusively by dichotomous branching. New costellae are always narrower than the primary costella and their breadth increases slowly in P. grimmi but rapidly in P. vonhorstigi. This results in the variable density of the costellation on shells of different sizes. At a particular growth line the sizes of costellae are almost uniform. At growth lamellae, there is sometimes a rapid leap in the size of costellae. A new growth band has a uniformly sized costellation. The costellae are separated by deep, slit-like, narrow interspaces that accommodate subcircular, flat-bottomed pits which are fairly evenly arranged on the shell surface (Figs 2I, J). Pit size and density are largely uniform within individuals of the same species, but differ in size and density between species. The pits are prominent in P. vonhorstigi, P. gemmata and P. grimmi, and small to very small in P. anomala and P. klouceki. Size of the pits in other species (P. catilla, P. hispanica) is not easy to evaluate because of poor preservation. Concentric lamellae are commoner in large specimens and

are usually absent in small- to medium-sized individuals. Lamellae may be prominent and coarse as in P. vonhorstigi but usually weak in P. klouceki.

AFFINITYDespite its general orthid-like shape, Poramborthis should be referred to the Porambonitoidea. Similarities with other Early Ordovician syntrophiidines are: moderately convex biconvex shell, radial multicostellate ornament with shallow pits aligned in interspaces, sessile spondylium and digitate mantle canal system. The differences concern the absence of a fold and sulcus in Poramborthis.

Syntrophioides Schuchert & Cooper, 1931 is the stratigraphically youngest member of the family Eostrophiidae Ulrich & Cooper, 1936. This middle Cambrian genus from the Urals and southern U.S.A. is remarkably similar to Poramborthis. It also has a wide hinge line, almost rectimarginate shell and poorly developed spondylium with anteriorly extended adductor scar. However, Syntrophioides differs mainly inits smooth shell, shorter ventral muscle field and the absence of a cardinal process. It might be the ancestor of Poramborthis.

The Family Huenellidae Schuchert & Cooper, 1931 is characterised by costate or costellate shells, but also includes the smooth and rectimarginate Eosyntrophopsis Yadrenkina, 1989 and the finely ramicostellate and weakly uniplicate Rhabdostrophia Neuman, 1989. Their smooth, strophic, rectimarginate to weakly uniplicate shells with wide hinge lines and smooth exteriors are similar to Poramborthis. These genera differ from Poramborthis in their arrangement of socket plates, which converge to form a notothyrial platform-like structure. This advanced feature suggests that Eosyntrophopsis is unlikely to be an ancestor of Poramborthis. Rectostrophia is younger that Poramborthis, occurring in the Dapingian and Darriwilian rocks of Norway.

The presence of subcircular pits in the finely costellate shells is one of the diagnostic features of the Tetralobulidae Ulrich & Cooper, 1936 and is present in many porambonitoids (Carlson 2002). The same ornament is typical for Poramborthis. Other features warranting the attribution of Poramborthis to the Tetralobulinae Ulrich & Cooper, 1936 are: wide hinge line, rounded quadrate to widely elliptical outline, sessile spondylium, long robust but discrete socket plates, digitate mantle canal system and distinct dorsal muscle field. The first members of the subfamily are known from the lower Cambrian but most species are present in strata

AAP Memoir 41 (2011)356

of Tremadocian to Darriwilian age (Ulrich & Cooper 1938). Tetralobula Ulrich & Cooper, 1936 differs in its uniplicate commissure and the presence of a low, wide median ridge supporting the spondylium. A median ridge and uniplicate commissure are absent in all but one species of Poramborthis. Poramborthis grimmi, the earliest and the largest species of the genus, has a short massive median ridge in front of sessile spondylium, and a weak flattening of the median sector in large ventral valves to form a weakly uniplicate commissure. Another significant difference of Tetralobula is the position of petaloid discrete socket plates which do not form a planar platform structure similar to the notothyrial platform of Poramborthis.

DISTRIBUTION Poramborthis is known from three areas of Central and SW Europe. The stratigraphically earliest species P. grimmi and P. anomala are from the Třenice Formation (Tremadocian) of the Barrandian in Bohemia (Czech Republic). The third Bohemian species, referred with uncertainty by Havlíček (1977) to the Spanish species P. hispanica, is probably conspecific with P. anomala. These species are associated with several eoorthids and the tritoechiid Protambonites, cystoids and rare trilobites. Younger beds in the Třenice Formation (Mergl 2009) yielded another smaller and as yet unnamed Poramborthis, similar to P. klouceki. That species is associated with the rhynchonelliformeans Jivinella, Apheoorthina and Kvania, diverse lingulates of the Leptembolon association, and trilobites of the Illaenid–Cheirurid Biofacies.

The type species P. klouceki is fairly abundant near the top of the Mílina Formation, of probable late Tremadocian age. It is associated with rare P. sp. (Mergl 1984), and again with the rhynchonelliformeans Jivinella and Kvania, abundant lingulates of the Leptembolon association, and trilobites of the Illaenid – Cheirurid Biofacies.

The Bavarian (Germany) P. catilla and P. gemmata are known from the two lower zones of the Leimitz Shales, referred to the Lower Tremadocian by Sdzuy (1955). The former is abundant in Sdzuy’s bed 9 which, unlike other beds at the Leimitz locality, is almost devoid of trilobites. The second species is represented by a single valve from an older bed, and is there associated with abundant trilobites, amongst which Leimitzia, Pharostomina, Triarthus and Niobella predominate, indicating a deeper-water environment of the Nileid Biofacies.

The stratigraphically younger Bavarian species P. vonhorstigi and P. cf. klouceki are

abundant in the Vogtendorf Formation, which is of late Tremadocian age (Sdzuy et al. 2001). The associated fauna consists of Ranorthis, Kvania, cystoids and rare trilobites. This association is comparable with that in Bohemia, having common cystoids, and trilobites of the Illaenid–Cheirurid Biofacies.

The Spanish species P. hispanica is known from the Tremadocian of the Iberian Chains in northeast Spain. It is associated with Protambonites and Billingsella and rare undescribed trilobites (Havlíček & Josopait 1972).

In summary, several species in Central and SW Europe are restricted to the Tremadocian. A single, younger species referable to Poramborthis sp. is known from the top of the Klabava Formation, of Dapingian age. That species was briefly described by Mergl (1991) but the material is very poorly preserved and the interior is unknown. However, the microornament of radial rows of pits, and absence of a distinct fold or sulcus, indicate affinity to Poramborthis or to another porambonitoidean taxon.

CONCLUSIONSThe morphology of Poramborthis indicates that, despite significant differences concerning absence of a septalium in the dorsal valve, the genus is best assigned to the Tetralobulidae Ulrich & Cooper, 1936. The lack of both a septalium and uniplicate commissure was the main reason for the erection of Poramborthidae by Havlíček (1950). Evolutionary trends in the transition from a septalium to an “orthoid” notothyrial platform were documented in plectorthoideans by Benedetto (2007), and a similar transition is suggested for Poramborthis. A rectimarginate or weakly uniplicate commissure is also known in other porambonitoideans. Thus the family Porambonitidae Havlíček, 1950 is considered a junior subjective synonym of Tetralobulidae.

Late Cambrian-Tremadocian syntrophiidines are typical of low-latitude carbonate platforms and terranes associated with Gondwana, South and North China, and Laurentia. Their associated fauna consists of orthides (Apheoorthis and Eoorthis), Billingsella and pelmatozoan echinoderms, indicating a relatively complex trophic structure (Bassett et al. 2001). The high-latitude northern Gondwana craton and associated microplates in late Cambrian and early Tremadocian time were mostly occupied by lower-diversity lingulate brachiopod associations with Hyperobolus, Westonia- l ike obolids, micromorphous acrotretids and siphonotretids, which during the Tremadocian evolved into the distinctive late Tremadocian-Floian Thysanotos-Leptembolon fauna (Popov & Holmer 1994; Bassett et al.

AAP Memoir 41 (2011) 357

2002). In northern Gondwana, occurrences of rhynchonelliformean brachiopods are very localised, but the low diversity and composition of these associations is analogous to those of low latitudes. Accepting a porambonitoidean affinity for Poramborthis, the composition of brachiopod associations in low latitude Gondwana consists of syntrophiidines (Poramborthis), eoorthids (Eoorthis, Apheoorthina, Jivinella), plectorthoideans (Kvania, Ranorthis) and the tritoechiid Protambonites. In the Late Cambrian to early Tremadocian, the billingsellid-dominated associations in Algeria and Spain (Colchen & Havlíček 1968; Havlíček & Josopait 1972) with Billingsella precede these orthide-syntrophiidine associations. The tritoechiid Protambonites is known from Spain (Havlíček & Josopait 1972; Villas et al. 1995), Bohemia (Havlíček 1977) and the South Urals (Popov et al. 2001), but unlike the latter, Protambonites is known in southwest and central Europe only in the early Tremadocian.

The reassignment of Poramborthis to porambonitoideans is further evidence that challenges the Early Ordovician endemicity of the Mediterranean province. The composition of the rhynchonelliformean associations in southwest and central Europe is a mixture of taxa which have their origin and close relatives in tropical Gondwana platforms and terranes, and also in Laurentia (eoorthids and tetralobulids), as well as on the temperate South American shelves of Gondwana (plectorthoideans) and also on temperate eastern margins of Baltica and Gondwana (tritoechiids).

REPOSITORY Figured material is housed in the palaeontological collections of the University of West Bohemia in Plzeň, Czech Republic (PCZCU), in the palaeontological collections of the Museum of Dr. B. Horák in Rokycany, Czech Republic (3RO VH) and in the palaeontological collections of the National Museum, Prague, Czech Republic (SBNM).

ACKNOWLEDGEMENTSThis study was supported by a grant from the Grant Agency of the Czech Republic GAČR 205/09/1521. The author is greatly indebted to L.R.M. Cocks, D.A.T. Harper and I.G. Percival for valuable comments which significantly improved the quality of the text.

REFERENCESBarrande, J., 1879. Systême silurien du Centre de la

Bohême. Ière partie: Recherches Paléontologiques. Volume 5. Classe des Mollusques. Ordre des Brachiopodes. Prague and Paris, 226 p.

Bassett, M.G., PoPov, L. & HoLMer, L.e., 2002. Brachiopods: Cambrian-Tremadoc precursors to Ordovician radiation events. 13-23 in Crame, J.A & Owen, A.W. (eds), Palaeobiogeography and Biodiversity Change: the Ordovician and Mesozoic-Cenozoic Radiations. Geological Society, London, Special Publication 194.

Benedetto, J.L., 2007. New Upper Cambrian-Tremadoc rhynchonelliformeans brachiopods from northwestern Argentina: evolutionary trends and early diversification of plectorthoideans in the Andean Gondwana. Journal of Paleontology 81, 261-285.

BeLL, W.C., 1941. Cambrian Brachiopoda from Montana. Journal of Paleontology 15, 193-255.

CarLson, s.J., 2002. Syntrophiidina. 929-960 in Williams, A., Brunton, C.H.C., Carlson, S.J. et al., Treatise on Invertebrate Paleontology, part H, Brachiopoda, Revised, Volume 4: Rhynchonelliformea (part). Geological Society of America, Boulder, and University of Kansas, Lawrence.

Chlupáč, I., havlíček, v., kříž, J., kukal, Z., ŠtorCh, P., 1998. Palaeozoic of the Barrandian (Cambrian to Devonian). Czech Geological Survey, Prague, 183 p.

ColChen, M. & havlíček, v., 1968. Le niveau à Billingsella cf. lingulaeformis Nikitin di Cambrien de la Sierra de la Demanda (Longroño, Espagne). Bulletin Societé geologique de France, série7, 10, 133-137.

daLMan, J.W., 1828. Upställning och Beskrifning af de i sverige funne Terebratuliter. Kongliga vetenskapsakademien Hanglingar för Ar 1827, 85-155.

Fortey, r.a. & CoCks, l.r.M., 2003. Palaeontological evidence bearing on global Ordovician-Silurian continental reconstructions. Earth-Science Reviews 61, 245-307.

havlíček, v., 1949. Orthoidea a Clitambonoidea z českého tremadoku. Sborník Státního geologického Ústavu Československé Republiky, Oddíl paleontologický 16, 93-144.

havlíček, v., 1950. Ramenonožci českého ordoviku. Rozpravy Ústředního ústavu geoloogického 13, 1-133.

havlíček, v., 1976. Evolution of Ordovician brachiopod communities in the Mediterranean province. 349-358 in Bassett, M. (ed.), The Ordovician System: proceedings of a Palaeontological Association symposium. University of Wales Press, Cardiff.

havlíček, v., 1977. Brachiopods of the order Orthida in Czechoslovakia. Rozpravy Ústředního Ústavu geologického 44, 1-327.

havlíček, v., 1989. Climatic changes and development of benthic communities through the Mediterranean Ordovician. Sborník geologických věd, Geologie 44, 79-116.

AAP Memoir 41 (2011)358

havlíček, v. & JosopaIt, v., 1972. Articulate brachiopods from the Iberian Chains, Northern Spain (Middle Cambrian - Upper Cambrian - Tremadoc). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 140, 328-353.

havlíček, v. & vaněk, J., 1966. The biostratigraphy of the Ordovician of Bohemia. Sborník geologických věd, Paleontologie 8, 7-69.

havlíček, v., vaněk, J. & Fatka, o., 1994. Perunica microcontinent in the Ordovician (its position within the Mediterranean Province, series division, benthic and pelagic associations). Sborník geologických věd, Geologie 46, 23-56.

MerGL, M., 1983. New brachiopods (Cambrian Ordovician) f rom Alger ia and Morocco (Mediterranean Province). Časopis pro mineralogii a geologii 28, 337 348.

MerGL, M., 1984. Fauna of the Upper Tremadocian of central Bohemia. Sborník geologických věd, Paleontologie 26, 9-46.

MerGL, M., 1991. Arenig (Lower Ordovician) orthide brachiopods from Prague Basin, Bohemia. Časopis pro mineralogii a geologii 36, 1, 1 13.

MerGL, M., 2004. The earliest brachiopod-bryozoan dominated community in the Ordovician of peri-Gondwana and its ancestors: a case study from the Klabava Formation (Arenigian) of the Barrandian, Bohemia. Journal of the Czech Geological Society 49(3-4), 127–136.

MerGL, M., 2009. Succession of fossil associations in the Třenice Formation (Tremadocian, Ordovician) at Holoubkov (Prague Basin). Geoscience Research Reports for 2008, 101-103.

neuMan, r.B., 1989. Brachiopoda. 57-72 in Neuman R.B. & Bruton, D.L. Brachiopods and trilobites from the Ordovician Lower Hovin Group (Arenig/Llanvirn), Hølonda area, Trondhein Region, Norway: New and revised taxa and paleogeographic interpretation. Geological Survey of Norway, Bulletin 414.

Pander, C.H., 1830. Beiträge zur Geognosie des Russischen Reiches. K. Krya, St. Petersburg, 165 p.

popov, l.e., egerquIst, e. & Zuykov, M.a., 2005. Ordovician (Arenig-Caradoc) syntrophiidine brachiopods from the east Baltic region. Palaeontology 48, 739-761.

PoPov, L. & HoLMer, L.e., 1994. Cambrian-Ordovician lingulate brachiopods from Scandinavia, Kazakhstan, and South Ural Mountains. Fossils and

Strata 35, 1-156. popov, l.e., vInn, o. & nIkItIna, o.I., 2001.

Brachiopods of the redefined family Tritoechiidae from the Ordovician of Kazakhstan and South Urals. Geobios 34(2), 131-155.

růžIčka, r., 1927. Fauna vrstev Eulomových rudního ložiska u Holoubkova (V Ouzkém). Část II. Rozpravy České Akademie pro vědy, slovesnost a umění, Třída II, 36(60), 1-21.

sCHuCHert, C. & CooPer, G.a., 1931. Synopsis of the brachiopod genera of the suborders Orthoidea and Pentameroidea, with notes on the Telotremata. American Journal of Science (series 5) 22, 241-255.

sdZuy, k., 1955. Die Fauna der Leimitz Schiefer (Tremadoc). Abhandlungen der Senckenbergischen Naturforschenden Gesellschaft 492, 1-74.

sdZuy, k., haMMann, W. & vIllas, e., 2001. The Upper Tremadoc fauna from Vogtendorf and the Bavarian Ordovician of the Frankenwald (Germany). Senckenbergiana lethaea 81, 207-261.

ulrICh, e.o. & Cooper, g.a., 1936. New genera and species of Ozarkian and Canadian brachiopods. Journal of Paleontology 10, 616-631.

ulrICh, e.o. & Cooper, g.a., 1938. Ozarkian and Canadian Brachiopoda. Geological Society of America, Special Papers 13, 1-323.

vIllas, e., arbIZu, M., bernardeZ, e., MendeZ-bedIa, I. & araMburu, C., 1995. Protambonites primigenius (Brachiopoda, Clitambonitidina) y el límite Cámbrico-Ordovícico en la Serie de los Cabos (Zona Asturoccidental-Leonesa, NO de Espana). Revista Española de Paleontologia 10, 140-150.

WaLCott, C.d., 1908. Cambrian geology and paleontology, No. 3. Cambrian Brachiopoda, description of new genera and species. Smithsonian Miscellaneous Collections 53(1810), 53-137.

WIllIaMs, a.W. & harper, d.a.t., 2000. Orthida. 714-844 in Williams, A. Brunton, C.H.C., Carlson, S.J. et al., Treatise on Invertebrate Paleontology, part H, Brachiopoda, Revised, Volume 3: Linguliformea, Craniiformea and Rhynchonelliformea (part). Geological Society of America, Boulder, and University of Kansas, Lawrence.

WoodWard, s.P., 1851-1856. A Manual of the Mollusca. John Weale, London, 488 p.

yadrenkIna, a.g., 1989. Brakhiopody, 65-81, 183-186 in Obut A.M. (ed.), Ordovik Sibirskoi Platformy: Fauna i Stratigrafiia Lenskoi Fatsialnoi Zony. Institut Geologii i Geofiziki, Trudy 751.