Note

Scene/la barrandei (Mollusca) from the Middle Cambrian of Baltoscandia

VIVIANNE BERG-MADSEN & JOHN S. PEEL

Berg-Madsen, V. & Peel, J. S.: Scene/la barrandei (Mollusca) from the Middle Cambrian of Bal­ toscandia. Norsk Geologisk Tidsskrift, Vol. 66, pp. 81-86, Oslo 1986. ISSN 0029--196X.

Metoptoma barrandei Linnarsson, 1879 is redescribed on the basis of the holotype from the Exsulans Limestone (Middle Cambrian) of Scania, southem Sweden, and additional specimens of similar age from the Mjøsa district of southern Norway and from Bornholm, Denmark. The low, cap-shaped shell, with fine radiating ribs crossing concentric growth lines, promotes assignment to Scene/la Bill­ ings, 1872, originally described from the Lower Cambrian of Canada.

V. Berg-Madsen, Paleontologiska lnstitutionen, Box 558, S-751 22 Uppsala, Sweden. Present address: Geological1nstitute, Box 6801, S-10691, Stockholm, Sweden. J. S. Peel, Grønlands Geologiske Undersøgelse, Øster Voldgade 10, DK-1350 København K, Den­ mark.

The horizon of the Exsulans Limestone is widely firmed by Linnarsson (1882). A similar, but un­ recognised in the Middle Cambrian of Baltoscan­ determined specimen was mentioned from dia, and in several areas it can be recognised as slightly older strata at Gislov. None of these ad­ the first well-developed carbonate deposit. One ditional specimens, nor the ones mentioned by minor but widespread member of its fauna is a Dames (1881) from the equivalent Acrothele small cap-shaped fossil described by Linnarsson granulata conglomerate on Oiand, are now avail­ (1879) as Metoptoma barrandei. The species is re­ able for study. Lindstrom (1888) reported other corded from Denmark, Norway and Sweden but, unlocated material in his list of Swedish fossil with one exception (Henningsmoen 1962), subse­ faunas in the collections of the Swedish Museum quent authors have maintained its generic assign­ of Natura! History, Stockholm. ment to Metoptoma Phillips, 1836, a name widely Gronwall (1902) collected six specimens from employed during the last century for Lower Pal­ the Exsulans Limestone at Borregård, Bornholm aeozoic cap-shaped shells. Metoptoma, however, (Fig. 1), but only four of these are currently is a gastropod now considered to range in age available at the Geological Museum, Copenha­ from the Lower Carboniferous to the Permian gen. The collections of Christian Poulsen in the (Knight et al. 1960) and Linnarsson's species same institution contain two specimens from the should clearly be placed elsewhere. Available same locality and recent field work has produced specimens of M. barrandei have been examined three additional specimens. The Bornholm sped­ with prompt assignment to Scenel/a Billings, mens are much smaller than Linnarsson's origi­ 1872, originally described from the Lower Cam­ nal, a feature of the fauna from the Danish Ex­ brian of Newfoundland, Canada. The systematic sulans Limestone and Kalby marl in general, position of Scenella is the subject of some debate when compared to Scania (Berg-Madsen 1981). in the literature, but the genus is here considered Strand (1929) recorded 4 specimens from the to be an untorted mollusc, a monoplacophoran in Mjøsa district of southern Norway, but only two the sense of several recent authors. of these have been located in the Palaeontolog­ The holotype of Scenel/a barrandei was col­ ical Museum, Oslo. The best preserved of these, lected by von Schmalensee at Kiviks-Esperod in the original of Strand (1929, fig. 3a) is illustrated Scania (Fig. 1C) in 1877 and described by Lin­ here (Fig. 3A). Henningsmoen (1962) tentatively narsson (1879). Additional possible fragments assigned the species to Helcionella, a genus con­ from the Exsulans Limestone at Andrarum were sidered by some authors to Iie in dose connection noted, and the identification of these were con- with Scenel/a (Runnegar & Jell 1976). 82 V. Berg-Madsen & J. S. Pee/ NORSK GEOLOGISK TIDSSKRIFr 66 (1986) �es�\:: Whitfield, 1872. The latter was placed in a family A Palaeacmaeidae, together with Palae/ophacmaea Donaldson, 1962. Yochelson & Stanley (1981) NORWAY l ! subsequently removed Donaldson's genus from l l the Mollusca and suggested that this fate should also be shared by Scene/la, a step formalised by Yochelson & Gil Cid (1984). Runnegar & Jell (1976) placed the scenellidae within the super­ family Helcionellacea of the redefined monopla­ O BORNHOLM OLAND cophoran order Cyrtonellida Horny, 1963. ;J Knight et al. (1960) had regarded helcionella­ SWED ceans as gastropods, white Starobogatov (1970) I had not induded the Helcionellacea within the Monoplacophora. 'SCANIA N Harper & Rollins (1982) considered only the /' 'IS\BORNHOLM Tergomya of Horny (1965a,b) to be true mono­ ,' 1� placophorans. Scene/la, a cydomyan sensu Fig. I. Map of localities in Baltoscandia (A), the Mjøsa district Horny, was thus exduded from the Monopla­ of Norway (B), Scania, Sweden (C), and Bornholm, Denmark cophora and transferred to the gastropods. (D). The present material offers no new dues as to the placement of Scene/la within the host of con­ tradicting attempted dassifications mentioned Systematic description above. The thesis of Harper & Rollins (1982) concerning a very restricted dass Monoplacoph­ Scene/la Genus Billings, 1872 ora, equal to the Tergomya of Horny, offers an Type species. - Scene/la reticulata Billings, 1872 attractive grouping of one lineage of untorted from the Lower Cambrian of Conception Bay, molluscs. lts implication, however, that all other Newfoundland, Canada. previously supposed monoplacophorans are torted gastropods is not immediately acceptable. Discussion. - There is a considerable disagree­ Groups such as the helcionellaceans may be un­ ment concerning the suprageneric dassification torted, but not tergomyan monoplacophorans. of Scene/la. Knight & Yochelson (1960) question­ The complexity of this early period in molluscan ably assigned the genus to the family Palaeac­ history is emphasised by the recent description by maeidae of the monoplacophoran order Trybli­ Linsley & Kier (1984) of a new dass of untorted diodidae, the latter also induding 'dassical' molluscs, the Paragastropoda. Paragastropods monoplacophorans such as Pilina Koken, 1925, resemble torted gastropods in their anisotrophic, Neopilina Lemche, 1957 and Tryblidium Lind­ conispiral, coiling, while Scene/la and all the un­ strom, 1884. torted molluscs mentioned in the previous dis­

Horny (1965a,b) considered Tryblidium-like cussion have cap-shaped, isostrophically coiled forms to belong to a subdass Tergomya, charac­ shells. terised by musde scars forming a partial ring on Arguments presented by Yochelson & Stanley the dorsal surface, behind the apex. The subdass (1981) and Yochelson & Gil Cid (1984) concern­ Cydomya of Horny (1965,a,b) induded forms in ing the possible coelenterate affinities of Scene/la which the apex lay within the ring of musdes. or many species assigned to Scene/la illustrate Scene/la was assigned to the Cydomya on the ba­ some of the difficulties associated with the dassi­ sis of musde scars described by Rasetti (1954) fication of Cambrian faunas. It is considered pre­ from the Middle Cambrian of British Columbia. mature, however, to contemplate such a drastic Starobogatov (1970) did not recognise Hornfs step as exduding Scene/la from the Mollusca, subdasses. Following an interpretation of the particularly at a time when the dassification of supposed function of musdes based on musde early molluscs is in its present stage of flux. scar patterns, he exduded Scene/la from the Monoplacophora. Runnegar & lell (1976) recognised a family Scene/la barrandei (Linnarsson, 1879) Scenellidae, exduding Palaeacmaea Hall & Figs. 2, 3. NORSK GEOLOGISK TIDSSKRIFT 66 (1986) Note 83

Fig. 2. Scenellabarrandei (Linnarsson, 1879), holotype, SGU TypeNo. 4532a,b, x 4.5; Exsulans Limestone, Middle Cambrian, Ki­ viks-Esperi.id, Scania, Sweden. A, dorsal view; B, postero-dorsal view of latex impression of counterpart to A, showing the arched dorsum of early growth stages; C, lateral view of B; D, photographic restoration produced by combining A and B.

Metoptoma barrandei Linnarsson, 1879, p. 24, (SGU), Uppsala, Type No. 4532a,b, counterparts pl. 3, figs. 35-37. of the same specimen figured here as Fig. 2. ?Metoptoma sp. Dames, 1881, p. 420. ?Metoptoma barrandei Linnarsson, 1882, p. 7. Other figured material. - Palaeontological Mu­ Metoptoma barrandei Gronwall, 1902, pp. 21, seum, Oslo, PO 25303 (Fig. 3A); Geological Mu­ 41-42, 166. seum, University of Copenhagen, Nos. MGUH Metoptoma barrandei Strand, 1929, p. 342, pl. 1668 (Fig. 30-F), MGUH 16.781 (Fig. 3G,H), l, figs. 3a-b. MGUH 16.782 (Fig. 3B,C). Helcionella? barrandei Henningsmoen, 1962, p. 22. Description. - A small, cap-shaped, bilaterally ?Metoptoma barrandei Martinsson, 1974, p. symmetrical mollusc with sub-central apex; the 204. apex lying nearer to the margin interpreted as an­ Metoptoma barrandei Berg-Madsen, 1981, p. terior. In dorsal view, the periphery is ovoid, 226. with an approximate length:width ratio of 4:3. The anterior and posterior margins tend toward Holotype. - Geological Survey of Sweden parallelism, with a slight posterior widening in 84 V. Berg-Madsen & J. S. Peel NORSK GEOLOGISK TIDSSKRIIT 66 (1986)

Fig. 3. Scenel/a barrandei (Linnarsson, 1879). A, dorsal view PMO 25303, Stensviken, zone le�. Mjøsa district, Norway, x 3.5 (Strand 1929, fig.3a). B, C, dorsal and lateral views, MGUH 16.782, Exsulans Limestone, Borregård, Bornholm, Denmark, x 5. (C. Poulsen collection). d, lateral view, MGUH 1668, Exsulans Limestone, Borregård, Bornholm, Denmark, x 4.5 (Gronwall 1902). E, oblique lateral view, as D, x 10. F, lateral view, as D, E, x 3.5. G, H, MGUH 16.781, Exsulans Limestone, Borregård, Bornholm, Denmark, lateral and dorsal views of latex impression x 5. Note the repaired shell injury (small swelling) to the lower right in H (collected by V. Berg-Madsen 1981).

larger specimens (Fig. 2A). Smaller specimens Discussion. - Growth ornamentation of Scenella and earlier growth stages show an apparent slight barrandei is irregular in its expression (Fig. 2C), narrowing toward the posterior. In lateral view, but a tendency towards the periodic development the anterior face is concave beneath the slightly of more conspicuous growth elements is evident overhanging apex, but becomes slightly convex (Fig. 3A,E). The holotype from Scania is larger, as the margin is approached. The posterior face is perhaps more mature, than the examples from shallowly convex, but somewhat irregular, due to Norway and Denmark, and clearly shows allo­ the rugose growth ornament. The protoconch is metric growth. The allometry is indicated by the not certainly known, but was seemingly shallowly loss of the arched dorsum, which is conspicuous cap-shaped. Early growth stages often show a in the early stages of the holotype (Fig. 2B) but pronounced arching of the dorsal surface pos­ also characterises the specimens from Bornholm terior to the apex (Fig. 2B); the arching becomes (Fig. 3B,H). In addition, smaller specimens and subdued with growth such that a more uniformly earlier growth stages seem to narrow posteriorly, convex dorsum characterises the adult. whereas the fully grown holotype narrows Ornamentation of concentric, rugose growth slightly anteriorly. lines crossed by fine radiating threads. Shell In the absence of definitive paired muscle scars thickness, structure and musculature unknown. of the type described by Rasetti (1954), place- NORSK GEOLOGISK TIDSSKRIFf 66 (1986) Note 85 ment of Linnarsson's species in Scene/la cannot the Ptychagnostus gibbus Zone in the Middle be conclusive. It is, however, considered to be Cambrian of Scandinavia. the most satisfactory generic assignment at this time. The generic name Metoptoma Phillips, 1836, is widely used in older literature for Lower Acknowledgments. -Jan Ågård, Institute of Historical Geology Palaeozoic cap-shaped molluscs. However, the and Palaeontology, Copenhagen, took the photographs. David L. Bruton. Oslo, Sven Laufeld, Uppsala, and Søren Floris, Co­ holotype of Metoptoma oblonga Phillips, 1836, penhagen kindly lo an ed specimens in their care. J. S. Peel pub­ the type species, is from the Lower Carbonif­ lishes with permission of the Director, Geological Survey of erous of England, and Knight et al. (1960) con­ Greenland. MGUH, PMO and SGU denote specimens in the sidered this genus of patellinid gastropod to Geological Museum, Copenhagen, Palaeontological Museum, Oslo, and Geological Survey of Sweden, Uppsala, respectively. range from the Lower Carboniferous to the Per­ This is a contribution to Project Tornquist (IGCP Accession mian. Metoptoma has an apex which overhangs No. 86). the periphery, whereas the apex is more centrally Manuscript received January 1985 placed in S. barrandei. Muscle scars in Metop­ toma take the form of a horse-shoe shaped band below the apex, in contrast to 6 pairs of discrete muscle scars in Scene/la (Rasetti 1954). References Scene/la barrandei seemingly has a more quad­ Berg-Madsen, V. 1981: The Middle Cambrian Kalby and Bor­ rate form in dorsal perspective than S. reticulata regård Members of Bornholm, Denmark. Geo/. For. Sthlm. Billings, 1832, as illustrated by Knight (1941, pl. Forh. 103, 215-231. 2, fig. Sa). Both species have conspicuous, cord­ Berg-Madsen, V. & Peel, J. S. 1978: Middle Cambrian mono­ like radial lines, which are more prominent than placophorans from Bornholm and Australia, and the system­ atic position of the bellerophontiform molluscs. Lethaia 11, the fine striations recorded by Knight (1941) in 113-125. Helcionella subrugosa. Dames, W. 1881: Geologische Reisenotizen aus Schweden. H. subrugosa ( d'Orbigny, 1850), the type spe­ Zeitschr. Deutsch. geo/. Gesell. 33, 405-441. Gronwall, K. A. 1902: Bornholms Paradoxideslag og deres eies of Helcionella Grabau and Shimer, 1909, fauna. Danm. geo/. unders., 2 række, 13, 230 pp. shows more strongly rugose growth ornamenta­ Harper, J. A. & Rollins, H. B. 1982: Recognition of Mono­ tion than S. barrandei. placophora and Gastropoda in the fossil record: a functional Runnegar & Jell (1976, Fig. 9C, 1-10) refer to morphological look at the bellerophont controversy. Proc. ll/rd N. Amer. Paleont. Convention l, 227-232. Helcione/la, a species which they consider to ap­ Henningsmoen, G. 1962: Liste over fossiler fra mellom-kam­ proach Latouchel/a Cobbold, 1921 in form. In brium in Norge. Fossil-Nytt-Årsber. Pal. Mus., Oslo, 17-24. this, coiling is better developed than in any of the Horny, R. J. 1965a: On the systematical position of Cyrto/ites above described species, causing the apex to be Conrad, 1838 (Mollusca). Cas. ndrod. Muz., odd. pfirod. hooked in lateral aspect, the transverse ornament 134, s--11. Horny, R. J. 1965b: Cyrtolites Conrad, 1938 and its position is strongly plicate and the apertural margins are among the Monoplacophora (Mollusca). Sb. narod. Muz. flared. Praze 21 B, 2, 57-70. Ka/bye/la poulseni Berg-Madsen & Peel, 1978 Knight, J. B. 1941: Paleozoic gastropod genotypes. Geo/. Soc. America, Special Paper 32, 510 pp. is distinguished from Scene/la barrandei by its di­ Knight. J. B., Cox, L. R., Keen, A. M., Batten, R. L., Yochel­ minutive size, elongate form with anterior apex, son. E. L. & Robertson, R. 1960: Systematic descriptions and the radial ornamentation. (Archaeogastropoda). In Moore, R. C. (edit.) Treatise on ln­ vertebrate Paleontology /, Mo/lusca l, Geo/. Soc. America & Kansas Univ. Press, 1169-1310. Distribution. - The holotype of Scene/la barran­ Knight. J. B. & Yochelson, E. L. 1960: Monoplacophora. In dei was collected from the type locality of the Ex­ Moore. R. C. (edit.) Treatise on Invertebrate Paleonto/ogy /, sulans Limestone, at the beach south of Kiviks­ Mol/usca /, Geo/. Soc. America & Kansas Univ. Press, 1177- Esperod (Fig. 1). A few unlocated specimens 1184. l, were recorded from the Exsulans Limestone at Lindstrom, G. 1888: List of the fossil faunas of Sweden. Cambrian and Lower Silurian. 24 pp. Norstedt, Stockholm. Andrarum by Linnarsson (1882). The Norwegian Linnarsson, G. 1879: Om faunan i kalken med Conocoryphe specimen from Stensviken was collected from a exsulans ("Coronatuskalken"). Sver. geo/. unders. C 35, 31 level containing the characteristic Exsulans pp. Limestone fauna - zone le� in Norway. All Linnarsson, G. 1882: De undre paradoxideslagren vid Andra­ rum. Sver. geo/. unders. C 54, 47 pp. specimens from Bornholm were collected from Linsley, R. M. & Kier, W. M. 1984: The Paragastropoda: a the Exsulans Limestone at Borregård. Scene/la proposal for a new class of Paleozoic Mollusca. Malacologia barrandei thus seems to be currently restricted to 25, 241-254. 86 V. Berg-Madsen & J. S. Peel NORSK GEOLOGISK TIDSSKRIFT 66 (1986)

Martinsson, A. 1974: The Cambrian of Norden. In Holland, C. Starobogatov, Y. I. 1970: Systematics of Early Paleozoic O. (ed.) Lower Palaeozoic Rocks of the World 2, London, Monoplacophora. Paleont. J. 1970, 3, 293-302. Wiley, 300 pp. Strand, T. 1929: The Cambrian beds of the Mjøsen district in Rasetti, F. 1954: Internal shell structures in the Middle Cam­ Norway. Nor. Geo/. Tidsskr. JO, 308-362. brian gastropod Scene/la and the problematic genus Steno· Yochelson, E.L. & Gil Cid, O. 1984: Reevaluation of the sys­ thecoides. l. Paleont. 26, 5'Hi6. tematic position of Scene/la. Lethaia 17, 33 1-340. Runnegar, B. & Jell, P. A. 1976: Australian Middle Cambrian Yochelson, E. L. & Stanley, G. O. 1981: An early Ordovician molluscs and their bearing on early molluscan evolution. Al­ patelliform gastropod Palaelophacmoea, reinterpreted as a cheringa l, 109-138. coelenterate. Lethaia 15, 323-330.