Carnets de Géologie / Notebooks on Geology - Article 2002/01 (CG2002_A01_CCE)

Tools for linguloid : the genus Obolus (Brachiopoda) as an example

Christian C. EMIG1

Abstract: This study points out some basic problems of linguloid systematics and proposes solutions for them. A taxonomic examination of the unique species of the genus Obolus found in the Upper Cambrian of Estonia and Russia, O. apollinis (= O. ruchini, O. transversus, O. rebrovi and Ungula convexa) is used as an example of a methodology employing all of the characters valid for distinguishing species of both extant and fossil Lingulidae. These characters are: - umbonal region; - body musculature; - septa or ridges; - main mantle canals - as established and figured by EMIG (1982, 1983) and BIERNAT and EMIG (1993). All of them have been determined to be taxonomically stable and have been studied and compared to take into account intraspecific variability; they should be used to describe or to redescribe any taxon of the superfamily . Characters of the shell and valves, such as shape, size, and dimensional ratios have no taxonomic value. Key Words: Taxonomy; Obolus; Brachiopoda; Cambrian - Ordovician; Estonia

Citation: EMIG C. (2002).- Tools for linguloid taxonomy: the genus Obolus (Brachiopoda) as an example.- Carnets de Géologie / Notebooks on Geology, Maintenon, Article 2002/01 (CG2002_A01_CCE) Résumé : Des outils pour la taxinomie des Lingulidoida : le genre Obolus (Brachiopoda) pris comme exemple.- Cette étude met en exergue des problèmes fondamentaux de la systématique des Linguloïdes et propose des solutions méthodologiques basées sur les caractères utilisés pour identifier les espèces de Lingulides actuelles et fossiles. L'unique espèce du genre Obolus, O. apollinis (= O. ruchini, O. transversus, O. rebrovi and Ungula convexa), récoltée dans divers gisements du Cambrien moyen et supérieur en Estonie et Russie, sert ici d'exemple. Les caractères sont : - la région umbonale ; - la musculature du corps ; - les septums et crêtes internes ; - les canaux du manteau ; selon la description et la représentation faites par EMIG (1982, 1983) et BIERNAT et EMIG (1993). Tous ces caractères se sont révélés taxinomiquement stables tout en présentant une relative variabilité intraspécifique ; ils sont donc à être utilisés pour décrire ou redécrire tous les taxons de la superfamille des Linguloidea. Il convient de souligner que les caractères de la coquille ou des valves, tels que formes, tailles, rapports dimensionnels n'ont aucune valeur taxinomique. Mots-Clefs : Taxinomie ; Obolus ; Brachiopoda ; Cambrien - Ordovicien ; Estonie strata were classified as belonging to the genera Introduction Ungula PANDER, 1830, Oepikites KHAZANOVITCH et POPOV, 1984, and Schmidtites SCHUCHERT et As stated by EMIG (1977) diagnoses of the LEVENE, 1929, all representatives of the family extant species of the genera BRUGUIÈRE, (: Linguloidea). Other 1797, and Glottidia DALL, 1870, are too poor to specimens studied are in the collections of the permit discrimination between species. Museum of Geology in the Institute of Geology Consequently, all species referred to these of the University of Tartu, Estonia; they were genera have been redescribed by EMIG (1982, collected by L. POPOV from: 1983) using a new taxonomy based on morpho- (1) localities along the Sarya and anatomical characters. Recently, these Volkhov rivers (Ingra, Russia: Middle Cambrian) characters have been used successfully by and identified as Obolus apollinis EICHW ALD, BIERNAT and EMIG (1993), GAGNIER et alii (1996) 1829, and MÁRQUEZ-ALIAGA et alii (1999) to revise the (2) the locality Sarya River (Ingria taxonomy of Palaeozoic and Mesozoic Russia, Middle Cambrian) identified as O. ruchini genera and species. KHAZANOVITCH et POPOV, 1984, During recent field trips to Estonia hundreds of well preserved specimens were collected from the Upper Cambrian (PUURA, 1996) near Tallinn. Previously, from these

1 CNRS UMR 6540, Centre d'Océanologie, Rue de la Batterie-des-Lions, 13007 Marseille (France) e-mail: [email protected]

Manuscript online since November 27, 2002

1 Carnets de Géologie / Notebooks on Geology - Article 2002/01 (CG2002_A01_CCE)

superfamily Linguloidea. (3) the Sayas River locality identified as O. transversus (PANDER, 1830), (4) from Ladoga and Suma River Main taxonomic characters localities (Ingria Russia: Upper Cambrian) The main taxonomic criteria used to identified as Ungula convexa PANDER, 1830. discriminate between linguloid taxa were It is of fundamental importance that the established and figured by EMIG (1982, 1983) taxonomic criteria used here to define the and BIERNAT and EMIG (1993). They are listed Cambrian genus Obolus are applied in the below, illustrated for the genus Obolus on Fig. 1 revision of the systematics of and within the and described in Tables 1 and 2.

Figure 1: Diagrams of the main taxonomic characters of Obolus apollinis. A. Umbonal regions (internal view), see also Fig. 2, 3; B. Average disposition of muscles and main mantle canals (drawn from a real specimen); C. Variability in musculature (established from more than 20 specimens) and main mantle canals (on 3 specimens). Muscle terminology as established by EMIG (1982):

1 Anterior Oblique; 2 Anterior Lateral Oblique; 3 Median Lateral Oblique; 4 Anterior Internal Oblique; 4' Median Internal Oblique; AA Anterior Adductor; PA Posterior Adductor.

2 Carnets de Géologie / Notebooks on Geology - Article 2002/01 (CG2002_A01_CCE)

Umbonal region of each valve: internal its systematics (see POPOV et alii, 1989; PUURA, view, and when needed external view and 1996 for reviews), because many species have profile; been assigned to this genus without regard to its taxonomic characteristics stated above; Body muscle imprint or scars on the internal side of each valve: arrangement and The genus Obolus has been redefined based variability; on a study of four species: i.e. O. apollinis, O. ruchini, O. transversus (= O. rebrovi Septa or ridges on the valves: when KHAZANOVITCH et POPOV, 1984), and Ungula present convexa (Table 2). Consequently, three of these Main mantle canals (vascula lateralia), and species must be considered junior synonyms of secondary ones (vascula media) when present: O. apollinis, the type-species, originally disposition and variability. described by EICHW ALD (1829). Most of these features are used to define All of the specimens of the above cited species, but some appear to have generic value species show so many similarities in their also, for example the septa in the extant genus characters that they are described and Glottidia. Some serve as criteria to define discussed herein under the name Obolus higher taxa among the Linguloidea, for example apollinis. Furthermore their original descriptions the ridge in the dorsal valve between the (EICHW ALD, 1829; PANDER, 1830; KHAZANOVITCH anterior oblique muscles, a characteristic and POPOV, 1984; POPOV et alii, 1989) do not perhaps of the entire superfamily. Symmetrical establish valid distinctions between them. musculature is a defining characteristic of the The shell ranges from subcircular to a family Obolidae and asymmetrical musculature subtriangular in outline, the former being most serves to distinguish the Lingulidae. All of these common (Fig. 1). Externally, the valves are criteria exhibit great variability, so when the smooth with fine growth lines, some of which erection of a new linguloid genus or species is are stronger. Sometimes weak radial marks are contemplated its characteristics must be present. The insides of both valves shows a measured and compared not only with a single thickened visceral area, ranging from a very related taxon but also with all possible relatives. slight elevation to a very well developed The description of fossil taxa should be based on thickened area, common in large specimens. In no less than 20 to 30 well-preserved specimens, the ventral valve there is a heart-like none fragmentary. To attain this requisite depression between the anterior and posterior number, several hundred specimens may have adductor muscles. POPOV et alii (1989) stated to be collected, prepared and studied in detail. that Obolus differs from Ungula in having a Furthermore a species should be defined only on subcircular, thinner and flatter shell and lacking the basis of its occurrence in at least three a heart-like depression in the ventral visceral discrete geographic populations, as suggested area: However these characteristics have no by WILEY (1981). taxonomic value because they occur in both In addition, it is highly desirable that the full Obolus and Ungula. range and limits of variability of diagnostic Umbonal regions: characters be figured, and that the figures be integrated into the definition of the species as The pseudointerarea always overhangs the has been done here in Fig. 1 for Obolus internal valve surface, except at the level of the apollinis. pedicle groove, which is generally continuous with the internal side of the valve. Laterally it is External features, such as the shape, size, limited by well-marked and elevated flexure and dimensional ratios of the valves, have been lines, which are aligned with the Anterior (or demonstrated to have no taxonomic value Median) Internal Oblique - Anterior Oblique (EMIG, 1982, 1983; BIERNAT and EMIG, 1993). muscles. The flexure line is sometimes Consequently, they cannot be used to define accentuated by a narrow groove. Furthermore, either genus or species but may be given in the ventral valve the pseudointerarea, additional to the diagnosis. Only exceptionally is triangular and slightly concave, extends shell form diagnostic of a species, for example laterally over about 30 to 60 per cent of the the quadrangular shape of the shell of Lingula umbonal region of which the beak is rather adamsi when compared to those of the other rounded. A rather narrow subparallel pedicle species of Lingula (EMIG, 1982). groove medially divides the ventral pseudointerarea (Fig. 1A, 2). The length of the The Obolus example pedicle groove ranges between 1.3 and 3.8 mm (mean = 2.2 mm; n = 31). In larger specimens Among the lingulid taxa of the Middle the groove sometimes is less prominent or Cambrian to Ordovician (Tremadocian) in unimpressed anteriorly over half to one-third of Estonia and Russia, the genus Obolus (Table 1) the length of the pseudointerarea. has been the subject of controversy regarding

3 Carnets de Géologie / Notebooks on Geology - Article 2002/01 (CG2002_A01_CCE)

Figure 2: Obolus apollinis: Internal umbonal region of the ventral valve: profile view from the beak and a frontal view. On the dorsal valve, the subtriangular On each side of the pseudointerarea is a flat, pseudointerarea is slightly concave and broad lateral umbonal plate, which largely rounded; it has an extent similar to that of the overhangs the Oblique muscle scars. These ventral pseudointerarea, i.e. it occupies from 30 plates are commonly as wide as the length of to 60 per cent of the umbonal region. The the pedicle groove. Nevertheless, such plates median length of the pseudointerarea ranges appear rather fragile and are partly broken in from 0.6 and 3.4 mm (mean = 1.6 mm; n = many specimens. Pseudointerarea and lateral 34). The flexure lines are well-marked and umbonal plates overhang the scars of the elevated: they are more or less aligned with the Anterior and Internal Oblique muscles three postero-lateral muscles, i.e. the Median sometimes so far that they are hidden Lateral Oblique muscle, the Anterior (or Median) completely. These features may vary in their Internal Oblique muscle and the Anterior Lateral expression in relation to the degree of internal Oblique muscle. Anteriorly, the flexure lines on thickening of the valve. either side extend towards the Anterior Lateral Arrangement and variability of the Oblique muscle (Fig. 1B, 3). musculature: The clearly established existence of flexure lines on the dorsal valve (Fig. 3) is cited here for The muscle system of Obolus was first the first time as regards the genus Obolus, described by BULMAN (1939). The absence in the because their lack was used by POPOV et alii obolids of the Internal Posterior Oblique muscle, (1989) to distinguish the genus Obolus from the considered by this author as an undivided genus Ungula. Consequently, this character Median Internal Oblique muscle, is an important cannot be used to separate the genera. feature because the muscle arrangement is bi- symmetrical in the obolids and asymmetrical in

4 Carnets de Géologie / Notebooks on Geology - Article 2002/01 (CG2002_A01_CCE)

Figure 3: Obolus apollinis: Internal umbonal region of the dorsal valve: frontal view and postero-lateral view with well-marked flexure lines. scars is narrow and poorly developed. One may the lingulides. This phylogenetic character was infer that, as in extant lingulides, the overlooked in the diagnosis of the family importance of this ridge generally increases with Obolidae by HOLMER and POPOV (2000). However, the size of the specimen. it is a character which should perhaps be applied Main mantle canals: at superfamily level, thus implying a revision of the higher taxa in the order Lingulida. The vascula lateralia are described as arcuate, submarginal by POPOV et alii (1989). No New characteristics of musculature in Obolus observation is given on the vascula media. are established: muscle scars "deeply" impressed into the inner surface of the valves, As a result of this study, a new diagnosis for in particular the postero-lateral scars; in the Obolus EICHW ALD, 1829, is provided (Table 1) as ventral valve, the muscle succession Anterior well as for the unique species Obolus apollinis Oblique - Internal Oblique is more or less EICHW ALD, 1829, remaining in the genus (Table aligned with the flexure lines of the 2). Furthermore, Ungula convexa described by pseudointerarea, covered by the lateral PANDER (1830) was considered by subsequent umbonal plates until about the middle of the designation (ROWELL, 1965: see HOLMER and Anterior Oblique muscle, and less extended POPOV, 2000) as the type species of Ungula but antero-laterally than in Ungula; in the this species is now assigned to Obolus and composite muscle formed by the Anterior considered a synonym of Obolus apollinis. Thus, Adductor and the Anterior Lateral Oblique, the a new type species for Ungula must be proposed latter is located in the posterior part of the scar; (paper in preparation): that is Ungula ingrica in the inner side of the dorsal valve the lateral (EICHW ALD, 1829), originally described under umbonal plates overhang the alignment of Obolus ingricus, and new diagnoses will be muscles: Median Lateral Oblique - Anterior provided for the species and for Ungula. Lateral Oblique - Anterior Internal Oblique (or Median Internal Oblique) until about the middle The genus Obolus now represented by only of the Anterior Lateral Oblique muscle; the one species is an example of what occurs when Anterior Adductor muscles are elongate and the taxonomic characters discussed above are slightly convergent posteriorly as observed also applied. Furthermore, this genus along with the in the obolid Schmidtites celatus (unpublished genus Lingula, both of which have provided a data) (Fig. 1, 2, 3). name for the family, share an occurrence unique among the inarticulated brachiopods: Septa or ridges: that is many more or less complete fossils specimens have been assigned to one or the On the ventral valve a narrow to well- other genus based solely on the shape of the developed median ridge extends over several shell. millimetres at the level of and between the posterior adductor muscles (Fig. 1, 2). This Because Obolus was selected as the ridge was first cited as the "Seitensepta" by genotype at a family level (see HOLMER and MICKW ITZ (1896). On the dorsal valve, a median POPOV, 2000) the taxonomic criteria used here ridge at the level of the anterior oblique muscle

5 Carnets de Géologie / Notebooks on Geology - Article 2002/01 (CG2002_A01_CCE)

Previous diagnosis New diagnosis from HOLMER and POPOV (2000)

Bi-symmetrical muscle arrangement (*)

Ventral valve: Triangular umbonal region; the pseudointerarea reduced, slightly concave, Ventral propareas with deep, narrow with elevated flexure lines.

pedicle groove. Lateral umbonal plates, overhanging the internal side. Posterior adductor muscle paired, separated by short median septum.

Dorsal valve: Rounded umbonal region with reduced, Dorsal pseudointerarea lacking flexure slightly concave, pseudointerarea with lines. elevated flexure lines. Dorsal median ridge vestigial or absent. Lateral umbonal plates flat and large overhanging the internal surface. Posterior adductor muscle unpaired.

Shell circular to rounded triangular, (*) Nota: The Posterior Internal Oblique dorsibiconvex to subequally biconvex. muscle (numbered 4": EMIG 1982) is at Visceral area of both valves weakly present only known in Lingula, Glottidia and thickened, extending to midvalve. Vascula Lingularia, which have an asymmetrical lateralia of both valves submarginal, arcuate. muscle arrangement.

Table 1: Obolus EICHWALD, 1829: the previous diagnosis and the proposed one emended (in italics the non- taxonomic characters, without generic significance). A diagnosis cannot be based on features should be applied to the genera and their without taxonomic value, or even more species in all the Obolidae. The same remark is significantly on chacters without phylogenetic valid for all the Lingulidae (see Lingulidae in value, or include only a part of the characters http://paleopolis.rediris.es/BrachNet/). that define a taxon. A species should not be identified by any of the characters that define the genus and vice versa, so that the diagnosis Recommendations for each hierarchical taxon is clearly Taxonomy is a tool based primarily on a differentiated (Recommendation 13A). diagnosis of each taxon. When comparing the Taxonomy is a tool based primarily on a diagnoses in Tables 1 and 2, remember that the diagnosis of each taxon. When comparing the definition of the term diagnosis as given in ICZN diagnoses in Tables 1 and 2, remember that the (1999), differs slightly in the French and English definition of the term diagnosis as given in ICZN versions: "Énoncé écrit établissant l'ensemble (1999), differs slightly in the French and English des caractères d'un taxon qui suffisent à le versions: "Énoncé écrit établissant l'ensemble distinguer des autres taxons auxquels il peut des caractères d'un taxon qui suffisent à le être utilement comparé" and "A statement in distinguer des autres taxons auxquels il peut words that purposes to give those characters être utilement comparé" and "A statement in which differentiate the taxon from other taxa words that purposes to give those characters with which it is likely to be confused". A which differentiate the taxon from other taxa diagnosis should also comply with with which it is likely to be confused". A Recommendation 13A (ICZN, 1999) as well as diagnosis should also comply with recommendation 13B that concerns the Recommendation 13A (ICZN, 1999) as well as languages in which a diagnosis should be given. recommendation 13B that concerns the languages in which a diagnosis should be given.

6 Carnets de Géologie / Notebooks on Geology - Article 2002/01 (CG2002_A01_CCE)

Previous diagnosis New diagnosis from PUURA (1996)

including Fig. 1 Synonyms:

O. ruchini, O. transversus, O. rebrovi, Ungula convexa Muscle scars deeply impressed, in particular the postero-lateral ones.

Ventral valve: Umbonal region with pseudointerarea forming a beak; reduced subtriangular pseudointerarea, slightly concave, with laterally elevated flexure lines and medially a narrow subparallel pedicle groove. Pseudointerarea generally slightly Ventral pseudointerarea narrow and overhanging the visceral area, but pedicle triangular, with well-defined flexure lines and groove continuous with the internal valve narrow and deep pedicle groove. surface. Lateral umbonal plates overhanging the internal surface until about the middle of the Anterior Oblique muscle. Anterior Oblique and Internal Oblique muscles more or less aligned with the flexure lines of the pseudointerarea. Dorsal valve: Rounded umbonal region; pseudointerarea reduced, triangular, slightly concave, with elevated flexure lines. Lateral umbonal plates overhanging the internal side until about the middle of the Dorsal pseudointerarea narrow, with wide, Internal Oblique muscle. slightly concave median groove; propareas More or less extended median ridge at the high, reduced, without flexure lines; with level of the anterior oblique muscle scars. narrow median ridge. Anterior adductor muscles subparallel to slightly convergent posteriorly. Median Lateral Oblique muscle, Anterior Internal Oblique (or Median Internal Oblique) muscle and Anterior Lateral Oblique muscle separated and placed in a line.

Vascula lateralia on both sides arcuate, peripherally placed (submarginal). Vascula media (dorsal) - no data.

Shell biconvex to slightly dorsibiconvex, Shell flattened, slightly dorsibiconvex, subcircular to subtriangular in outline, smooth subcircular in outline. with some concentric growth lines well marked.

Ventral visceral area slightly elevated Visceral area in both valves varying from extending to about mid-valve. slightly elevated to very strongly thickened, Dorsal visceral area large, strongly the ventral valve shows a heart-like depression impressed elongate oval Anterior Adductors between the anterior and posterior adductor muscle scars. muscles.

Table 2: The new diagnosis of Obolus apollinis EICHWALD, 1829, is compared to the previous diagnosis as translated and modified by PUURA (1996) from the paper of POPOV et alii (1989), concerning O. apollinis, O. ruchini, O. transversus, and Ungula convexa. Non-taxonomic characters are in italics.

7 Carnets de Géologie / Notebooks on Geology - Article 2002/01 (CG2002_A01_CCE)

A diagnosis cannot be based on features Warsaw, Vol. 38, N° 1/2, pp. 1-20. without taxonomic value, or even more BRUGUIÈRE J.G. (1797).- Vers, coquilles, significantly on chacters without phylogenetic mollusques et polypiers. Tableau value, or include only a part of the characters encyclopédique et méthodique des trois that define a taxon. A species should not be règnes de la nature, vol. 2. Agasse, Paris, Pl. identified by any of the characters that define 96-314. the genus and vice versa, so that the diagnosis BULMAN O.M. (1939).- Muscle systems of some for each hierarchical taxon is clearly inarticulate brachiopods.- Geological differentiated (Recommendation 13A). Magazine, Cambridge, Vol. 76, pp. 434-444. DALL W.H. (1870).- A revision of the Information on the sites where types are terebratulidae and lingulidae.- American deposited and their accessibility for study or Journal of Conchology, Vol. 6, pp. 88-168. revision is sometimes rather difficult to obtain EICHW ALD E. (1829).- Zoologia specialis, quam for linguloid taxa, contrary to Recommendation expositis animalibus tum vivis, tum fossilibus 72F of the ICZN (1999). None of the types of potissimum Rossiae in universum et Poloniae Obolus species are available from the Geological in specie, in usum lectionum publicarum in Museum in St-Petersburg (Russia) and the only Universitate Caesarea Vilnensi. Volume 1.- specimens of Obolus that can be studied Josephi Zawadski, Vilnae, 314 p. currently are in Tartu (Estonia). EMIG C.C. (1977).- Réflexions sur la taxonomie Finally, a scientific approach to systematics des espèces du genre Lingula (Brachiopodes, should be based on a good knowledge of the Inarticulés).- Comptes Rendus de l'Académie taxa, comparative morphology and anatomy. des Sciences, Paris, Vol. 285, pp. 523-525 Ecological requirements may also be criteria in EMIG C.C. (1982).- Taxonomie du genre Lingula systematics (ARNAUD and EMIG, 1987). (Brachiopodes, Inarticulés).- Bulletin du Systematics and taxonomy must propose new Muséum National d'Histoire Naturelle, Paris, ideas and test hypotheses. Systematics as a tool Sér. 4, Vol. 4, N° 3/4, pp. 337-367 to identify a taxon is but a technical EMIG C.C. (1983).- Taxonomie du genre Glottidia consequence. This paper is a first step in better (Brachiopodes Inarticulés).- Bulletin du understanding in linguloid taxonomy, as well as Muséum National d'Histoire Naturelle, Paris, in suggesting new hypotheses and cladistic Sér. 4, Vol. 5 (Sect. 4), N° 2, pp. 469-489. analyses. In these latter, a plesiomorphous or GAGNIER P.Y., BLIECK A., EMIG C.C., SEMPERE T., apomorphous condition has to be proved and VACHARD D. and VANGUESTAINE M. (1996).- discussed; that such a state exists cannot be New paleontological and geological data on based only on a simple computer calculation. the Ordovician and Silurian of Bolivia.- Journal of South America Earth Sciences, Vol. 9, N° 5/6, pp. 329-347. Acknowledgements HOLMER L.E. and POPOV L.E. (2000).- Lingulida. In: KAESLER This study was supported by a CNRS-Estonia R.L. (Ed.), Revised Brachiopoda.- grant for cooperation between France and Treatise on Invertebrate Paleontology, Estonia and through a grant by the French Geological Society of America, New York, and University of Kansas, Lawrence, Part H, Embassy in Tallinn. I thank Ivar PUURA and the Vol. 2, pp. 32-95. Institute of Geology staff (University of Tartu, INTERNATIONAL OMMISSION ON OOLOGICAL Estonia) for laboratory facilities and for help in C Z NOMENCLATURE (1999).- International code of collecting specimens, and Chantal BEZAC (Centre d'Océanologie, Marseille) for SEM preparations. zoological nomenclature, Fourth Edition, adopted by the International Union of I am most grateful to Nestor J. SANDER (USA) for Biological Sciences, The International Trust comments and English improvement of the for Zoological Nomenclature / The Natural earlier draft, as well as to the two referees, Art History Museum, London, xxix + 306 pp. BOUCOT (OSU, Corvallis, USA) and Fernando KHAZANOVITCH K.K. and POPOV L.E., In: ALVAREZ (Universidad de Oviedo, Spain). KHAZANOVITCH K.K., POPOV L.E. and MELNIKOVA L.M. (1984).- Inarticulate brachiopods, References ostracodes (bradoriids) and hyolithelminths from the Sablinka Formation of the ARNAUD P.M. and EMIG C.C. (1987).- La Leningrad District (in Russian).- population, unité fonctionnelle de la Paleontologicheskiy Zhurnal, Moscow, Vol. biocoenose. In: Biologie des Populations.- 1984, N° 4, pp. 33-47. Actes du Colloque National du Centre MÁRQUEZ-ALIAGA A., EMIG C.C. and BRITO J.M. National de la Recherche Scientifique, Lyon (1999).- Triassic lingulide brachiopods from 1986, pp. 69-72. the Iberian Range (Spain).- Géobios, Lyon, BIERNAT G. and EMIG C.C. (1993).- Anatomical Vol. 32, pp. 815-821. distinctions of the Mesozoic lingulide MICKW ITZ A. (1896).- Über die brachiopods.- Acta Palaeontologica Polonica, Brachiopodengattung Obolus EICHW ALD.-

8 Carnets de Géologie / Notebooks on Geology - Article 2002/01 (CG2002_A01_CCE)

Mémoires de l'Académie Impériale des boundary beds in Baltoscandia.- Dr. Thesis, Sciences de St Pétersbourg, Classe physico- Univ. Uppsala, 136 pp. mathématique, St-Péterbourg, Vol. 4, N° 2, ROWELL A.J. (1965).- Inarticulata. In: MOORE pp. 1-216. R.C. (Ed.), Brachiopoda.- Treatise on PANDER C.H. (1830).- Beiträge zur Geognosie Invertebrate Paleontology, Geological des Russischen Reiches, St. Petersburg, 165 Society of America, New York, and University p. of Kansas, Lawrence, Part H, p. 260-296. POPOV L., KHAZANOVITCH K.K., BOROVKO N.G., SCHUCHERT C. and LEVENE C.M. (1929).- SERGEYEVA S.P. and SOBOLEVSKAYA R.F. Brachiopoda (generum et genotyporum (1989).- The Key sections and stratigraphy of index et bibliographia). In: Fossilium the phosphate bearing Obolus beds of the Catalogues, Vol. 1, Animalia, Pars 42. Junk, North-East of the Russian platform (in Berlin 140 p. Russian). Nauka Trudy, Leningrad, Vol. 18, WILEY E. O. (1981).- Phylogenetics. The theory pp. 1-222. and practice of phylogenetic systematics.- PUURA I. (1996).- Lingulate brachiopods and Wiley-Interscience, New-York, 439 p. biostratigraphy of the Cambrian-Ordovician

9