Furongian linguliform brachiopods from the Alborz Mountains ... - Informit

Furongian linguliform brachiopods from the Alborz Mountains, Iran LEONID E. POPOV, MANSOUREH GHOBADI POUR, MEHRI HOSSEINI & LARS E. HOLMER POPOV, L.E., GHOBADI POUR, M., HOSSEINI, M. & HOLMER, L.E. , 2009:12:24. Furongian linguliform brachiopods from the Alborz Mountains, Iran. Memoirs of the Association of Australasian Palaeontologists 37, 103-122. ISSN 0810-8889. Micromorphic linguliform brachiopods are described for the first time from the Furongian part of the Cambrian Mila Formation, eastern Alborz Mountains, Iran. The assemblage is dominated by acrotretides, including Dactylotreta lamellosa n. sp. and Ottenbyella hyrcanica n. sp. as well as species of the new genera Tapuritreta (T. angusta n. sp.) and Sadrocarta (S. delicatus). The siphonotretide Siphonobolus sp. also occurs in abundance, which is unusual for Furongian lingulate faunas. The newly discovered assemblage shows little similarity to contemporaneous faunas of Laurentia, Baltica and Kazakhstanian terranes, but S. delicatus is also known from the middle Furongian Series of the Malyi Karatau Range in southern Kazakhstan. Leonid E. Popov ([email protected]), Department of Geology, National Museum of Wales, Cathays Park, Cardiff CF10 3NP, United Kingdom; Mansoureh Ghobadi Pour ([email protected]), Department of Geology, Faculty of Sciences, Golestan University, Gorgan, Iran; Mehri Hosseini ([email protected]), Nonmetallic Material Co., 404 Yas House, Tohid St., Esfahan 8173837311, Iran; Lars E. Holmer ([email protected]), Institute of Earth Sciences, Palaeobiology, Uppsala University, SE-752 36 Uppsala, Sweden. Received 28 April 2009. Keywords: Cambrian, Furongian, Brachiopoda, Linguliformea, Siphonotretida, Alborz Mountains, Iran.

FURONGIAN linguliform brachiopods from Gondwana are poorly known. The best documented peri-Gondwanan faunas have been described from Kazakhstanian terranes (Popov & Holmer 1994; Holmer et al. 2001) and North China (Mei 1993); with the exception of Dactylotreta and Treptotreta, most acrotretides described from the middle Cambrian to Furongian of Australia (Rowell & Henderson 1978; Henderson & MacKinnon 1981; Engelbretsen 1996) became extinct by the beginning of the Furongian. This paper analyses linguliform brachiopods from the Furongian part of the Mila Formation of the eastern Alborz Mountains in northern Iran. There are no previous descriptions of micromorphic linguliform brachiopods from the Cambrian of Iran. GEOLOGICAL AND GEOGRAPHICAL SETTING The Mila Formation was first defined by Stöcklin et al. (1964) and it conformably overlies the Early Cambrian Lalun Formation. The Mila Formation is subdivided into five members, of

which the lower four comprise dolomites and bioclastic limestones of middle to late Cambrian age. The fifth member (mostly consisting of argillites and siltstones with a bed of quartzose sandstone at the base) was originally referred to the Early Ordovician (Stöcklin et al. 1964). The biostratigraphy of the Mila Formation is based on trilobites (Kushan 1973, Wittke 1984, Peng et al. 1999), but the trilobite faunas from the Mila Formation of the Simeh-Kuh section, the source of the brachiopods studied here, have not been documented in detail. All studied brachiopods come from Member 3 of the Mila Formation in the Simeh-Kuh section, which is located in the eastern Alborz Range, northeastern Iran, about 13 km NW of Damghan (Fig. 1). The geographic coordinates of the zero point in the section in the base of Member 3 of the Mila Formation are N 36°12’40.2”, E 54°13’40.3”, at 1361 m above sea level. In this section, the base of the Furongian coincides with a fault at the lower boundary of Member 3, which is underlain by the dolomites of the Member 1. Six informal units are recognised within Member

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AAP Memoir 37 (2009)

Fig. 1. Map of north-central Iran showing the position of Simeh-Kuh section northwest of Damghan.

3, which are characterised below (Fig. 2): Unit 1. A basal bed of intercalated pink sandstone and argillite, about 21 m thick, followed by light grey argillite (10 m thick) and by a bed of light brown dolomite about 5 m thick, which is succeeded by 8 m of grey argillite at the top. Total thickness is up to 44 m. Unit 2. Bedded, bioclastic limestone (total up to 128.5 m thick), comprising four subunits: (a) thin to medium bedded grey limestone up to 27.5 m thick; (b) grey limestone with lenses of light-brown calcareous sandstone up to 7.5 m thick. Sample A-8 with numerous echinoderm fragments, sponge spicules and microbrachiopods. Acrotretidae gen. et sp. indet. was taken from the interval about 7 m above the base of the subunit; (c) light-grey, bedded, bioclastic (echinoderm) limestone, nodular in the upper part, up to 68.5 m thick,

individual beds varying from 10 to 30 cm thick, (d) grey limestone, with abundant echinoderm fragments and numerous Billingsella shell beds, totalling about 25 m thick. Most of the brachiopod specimens were collected from the uppermost part of Unit 2. Samples A-3 and A-3/1 with the brachiopods Dactylotreta lamellosa n. sp. and Ottenbyella hyrcanica n. sp. were taken at 20.95 m above the base of subunit 2d. Samples A-2, A-2a and ‘Ts’ with the brachiopods Dictyonina? cf. perforata Palmer, 1954, Ottenbyella hyrcanica n. sp., Sadracarta delicatus (Holmer et al., 2001), Tapuritreta angusta n. gen., n. sp., Siphonobolus sp. and Zhanatellidae gen. et sp. indet., and the conodont Westergaardodina sp. were collected from the interval covering the uppermost metre from its top. Other components of the assemblage include silicified echinoderm fragments and sponge spicules (Fig. 2).


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Fig. 2. Stratigraphical column of the Mila Formation in the Simeh-Kuh section north-west of Damghan showing the stratigraphical position of brachiopod samples and stratigraphical ranges of described brachiopod taxa.

Unit 3. Grey to olive argillite (individual beds up to 25 cm thick) intercalating with siltstone and sandstone (individual units up to 11 cm thick), total 19 m thick. Beds of sandstone often show hummocky cross-bedding. Unit 4. Dolomitic limestone, varying from brown and orange to grey in colour, about 1.6 m thick. Sample A-1 taken at 23 cm from the base of the unit contains rare conodonts, including Rotundoconus sp. and Proconodontus (probably a fragment of P. tenuiserratus), echinoderm fragments and the microbrachiopod Siphonobolus sp. Unit 5. Olive argillite with nodules of brightyellow, slightly calcareous siltstone with lingulides and a few trilobites up to 2.7 m thick. Unit 6. Brown (grey on the weathered surface) sandy limestone, thick to medium bedded, up to 4.5 m thick.

In the Simeh-Kuh section the Mila Formation is overlain conformably by the Lashkarak Formation which contains early Tremadocian trilobites, including Asaphellus inflatus Lu, 1962 at 13 m above the base (Ghobadi-Pour 2006) (Fig. 2). SYSTEMATIC PALAEONTOLOGY Abbreviations for parameters measured on specimens are (in millimetres): W, L, T = maximum width, length, thickness of the shell; Lv, Ld = maximum length of ventral and dorsal valve; Iw, Il = maximum width and length of pseudointerarea; Pw = width of median groove or pedicle groove; Pl = median length of pseudointerarea; Cw, Cl = width, length of cardinal muscle field; Sa = length of dorsal median septum;

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Sm = position of maximum height of dorsal median septum. The morphological terminology used here follows that of Holmer & Popov (2000). The illustrated and described material is housed in the National Museum of Wales, Cardiff (NMW). Class LINGULATA Gorjansky & Popov, 1985 Order LINGULIDA Waagen, 1885 Superfamily LINGULOIDEA Menke, 1828 Family ZHANATELLIDAE Koneva, 1986 Zhanatellidae gen. et sp. indet. (Fig. 3I, L) Material. NMW2008.35G.1, incomplete ventral valve from sample Ts. Remarks. A single incomplete ventral valve of subcircular outline has a characteristic microornament of densely packed, regular hemispherical pits varying from 4 to 6 µm in diameter suggesting attribution to the Zhanatellidae. However, it differs from Zhanatella Koneva, 1986 in the absence of an emarginature in the umbonal part of the ventral valve and in the lack of the characteristic elevated concentric rugellae. Zhanatella utahensis Popov et al., 2002 (from the Cambrooistodus minutus Subzone of the Notch Peak Formation, Utah) has lenticular pits twice as large as those illustrated here (Fig. 3I). The Iranian specimen resembles juvenile Thysanotos (as revised by Popov & Holmer 1994), but it apparently lacks marginal spines and has the finer and uniformly pitted microornament with only slight variation in the diameter of pits. Order SIPHONOTRETIDA Kuhn, 1949 Superfamily SIPHONOTRETOIDEA Kutorga, 1848 Family SIPHONOTRETIDAE Kutorga, 1848 Siphonobolus Havlíček, 1982 Type species. By original designation Siphonotreta simulans Růžička, 1927; Early Ordovician, Tremadocian, Třenice Formation, Bohemia. Siphonobolus sp. (Figs 3A-H, J-K; 4A-G) Material. Figured: NMW 2008.35G.2, ventral valve, sample A-2; NMW 2008.35G.3, 4, ventral valves, sample A-2a; 2008.35G.5, dorsal valve, sample A-2a; 2008.35G.8, ventral valve, sample A-1. Other specimens: 2008.35G.7, 9-11, 12.1-9, incomplete ventral valves, sample A-1; 2008.35G.13,1-27, 14, sample A-2. Description. Shell ventribiconvex, slightly

AAP Memoir 37 (2009) elongate suboval to subcircular in outline. Ventral valve low, subconical with a lateral profile gently convex anterior to the umbo and almost straight, steeply inclined downward between the umbo and posterior margin. Foramen relatively small, teardrop-shaped, up to 90 µm wide. Ventral umbo with a crescentic area posterior to the foramen accentuated by growth mark, which may represent a rudiment of the protegulum (Fig. 4G). Dorsal valve gently convex in the lateral profile with maximum height slightly anterior to the marginal umbo. Dorsal pseudointerarea vestigial, elevated above the valve floor. Dorsal larval shell smooth about 250-270 µm wide surrounded by a distinct halo with a median mound about 50-60 µm in diameter in the central part probably representing a rudiment of the embryonic shell or protegulum (for discussion, see Popov et al. 2009). This mound surrounded by two pairs of inflated lobes, becoming more strongly swollen towards the outer boundary of the larval shell (Fig. 3C, D). Postlarval shell ornamented by concentric rugellae and fine, densely spaced, slightly irregular tubercles about 20 µm across (Fig. 4D) arranged in concentric rows. Hollow spines 25-20 µm in diameter developed only in peripheral parts of the valves (Fig. 4A-B, D-E). Ventral interior with a free, high, cylindrical internal pedicle tube. Dorsal interior without distinct characters. Remarks. As recently demonstrated by Williams et al. (2004), most of the Cambrian siphonotretides, like Gorchakovia, Helmersenia and Schizambon lack hollow spines. However, two Furongian species of Siphonobolus recently described from Iran (Popov et al. 2009) have short hollow spines in both valves and also show a free internal pedicle tube, which is otherwise not known from other Cambrian siphonotretide genera. Siphonobolus sp. is among the oldest known siphonotretides. Schizambon reticulatus MacKinnon in Shergold et al., 1976 from Antarctica (where it occurs together with Irvingella? sp. suggesting correlation with Elvinia Biozone of Laurentia), is probably the only contemporaneous siphonotretid species, but unlike the Iranian species it lacks an internal pedicle tube. It also has fine radial ornamentation and a large foramen anterior to the ventral umbo suggesting attribution to Schizambon. Siphonobolus sp. shows distinct similarity to Siphonobolus priscus Popov et al., 2009 from the lower Shirgesht Formation (Cambrian, Furongian) of the Derenjal Mountains, Central Iran in having a free pedicle tube, a relatively small foramen, a high, undivided dorsal pseudointerarea and strongly granulated shell surface. It also has closely similar morphology of the dorsal larval


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Fig. 3. A-H, J. Siphonobolus sp., Cambrian, Furongian, Mila Formation; A-C, NMW 2008.35G.5, incomplete dorsal valve, interior, exterior and oblique lateral view of exterior showing larval shell with L1-posterior lobe, L2-anterior lobe and M-posteromedian mound (embryonic shell), sample A-2a; D, H, K, NMW 2008.35G.4, incomplete ventral valve, exterior, oblique lateral view, umbonal area showing foramen, sample A-2a; E, NMW 2008.35G.3, ventral valve fragment showing internal pedicle tube, sample A-2a; F, NMW 2008.35G.8, ventral valve fragment showing internal pedicle tube, sample A-1; G, J, NMW 2008.35G.6, dorsal valve, exterior, oblique lateral view, sample A2; I, L, Zhanatellidae gen. et sp. indet., Cambrian, Furongian, Mila Formation, sample A-2a; NMW 2008.35G.1, ventral valve, shell surface showing finely pitted microornament, exterior.

shell, with a smooth median mound and two pairs of lateral lobes (Popov et al. 2009). However, the spinose ornamentation is rarely preserved in the specimens from the Mila Formation (Fig. 4D, E), probably due to significant exfoliation and

fragmentation of the external surface in most of the specimens. The spines on the shells from the Mila Formation are less densely spaced and have about 1.5-2 times smaller diameter at the base when compared with Siphonobolus priscus.

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Fig. 4. A-G. Siphonobolus sp., Cambrian, Furongian, Mila Formation; A-F, NMW 2008.35G.2, ventral valve, sample A-2, exterior, oblique lateral view of exterior, anterior margin with broken hollow spines, enlargement of tuberculate microornament, oblique posterior view, umbonal area; G, 2008.35G.8, ventral valve, sample A-1, umbonal area showing foramen and rudiment of protegulum. H-L. Acrotretidae gen. et sp. indet., Cambrian, Furongian, Mila Formation, sample A-8; H, I, NMW 2008.35G.149, dorsal valve, interior, oblique lateral view of interior; J-L, NMW 2008.35G.148, ventral valve, exterior, oblique posterior view showing deltoid pseudointerarea, posterior view of the umbonal area showing pedicle foramen.


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Fig. 5. Dactylotreta lamellosa n. sp., Cambrian, Furongian, Mila Formation, sample A-3/1; A, B, NMW 2008.35G.15, holotype, ventral valve exterior, oblique posterior and ventral views; C, D, NMW 2008.35G.16, ventral valve exterior, ventral and oblique posterior views; E, F, NMW 2008.35G.17, ventral valve interior and posterior view of pseudointerarea; G, NMW 2008.35G.18, ventral valve exterior showing apical process; H, NMW 2008.35G.21, incomplete dorsal valve interior; I, J, NMW 2008.35G.19, incomplete dorsal valve exterior, larval shell with pitted microornament; K, L, NMW 2008.35G.20, incomplete dorsal valve interior, oblique lateral view showing blade-like, triangular median septum.

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Order ACROTRETIDA Kuhn, 1949 Superfamily ACROTRETOIDEA Schuchert, 1893 Family ACROTRETIDAE Schuchert, 1893 Dactylotreta Rowell & Henderson, 1978 Type species. By original designation Dactylotreta redunca Rowell & Henderson, 1978; Cambrian, Furongian (Idamean Stage), Georgina Limestone; Glenormiston district, western Queensland, Australia. Dactylotreta lamellosa n. sp. (Fig. 5) Derivation of name. Due to characteristic, regular lamellose ornamentation of the ventral valve. Holotype. NMW2008.35.15, ventral valve, Cambrian, Furongian, Mila Formation, sample A-3/1, Simeh-Kuh, eastern Alborz Mountains, Iran. Paratypes. Figured; NMW2008.35.16-18, ventral valves, NMW2008.35.19-21, dorsal valves. Other specimens; NMW2008.22-39, 63.1-4, ventral valves, NMW2008.40-49, 64.1-3, dorsal valves. All from sample A-3/1. Diagnosis. Ventral valve high, conical, with a procline to catacline deltoid pseudointerarea bearing a shallow intertrough; lateral valve slopes almost straight in transverse profile and with a straight sagittal profile of the anterior slope. Dorsal valve flattened, with a convex umbonal region and a moderately high, blade-like, triangular median septum. Postlarval shell with numerous, fine regularly spaced growth lamellae more pronounced in the ventral valve. Description. Ventral valve high, conical, subcircular in commissural outline. Lateral profile with almost straight anterior slope and posterior slope slightly concave in the umbonal region; lateral slopes almost straight in transverse profile (Fig. 5A, D). Deltoid pseudointerarea procline to catacline, bisected medially by a weakly defined, shallow intertrough. Pedicle foramen small, circular, about 40 µm in diameter, directed posteroventrally, enclosed within the larval shell (Fig. 5D). Dorsal valve almost flat with a slightly convex umbonal region. Dorsal valve larval shell subcircular, about 220 µm wide, bisected medially by a shallow groove, ornamented by fine, hemispherical pits of two slightly varying sizes (Fig. 5J). Dorsal pseudointerarea subtriangular, occupying about half of the maximum valve width, and with a broad, subtriangular groove

AAP Memoir 37 (2009) about one third as wide as the pseudointerarea. Postlarval shell ornamented with numerous fine, regularly spaced growth lamellae more prominent in the ventral valve. Ventral umbo occluded with the apical process perforated by the subconical internal pedical tube. Apical pits deep, almost circular, situated posterolaterally of the internal foramen (Fig. 5G). Dorsal interior with large, elongate, cardinal muscle fields extending anteriorly to the midvalve and bordered laterally by a low rim. Median buttress elongate, subtriangular, narrowing anteriorly. Dorsal median septum moderately high, triangular, blade-like, with highest point situated anteriorly to mid-length (Fig. 5L). Remarks. Dactylotreta is one of the few acrotretides that cross the base of the Furongian (defined by the first appearance of Glyptagnostus reticulatus) into the Tremadocian (Popov & Holmer 1994; Holmer et al. 2001). However, most of the species presently assigned to Dactylotreta are from the Middle Cambrian, whereas Dactylotreta redunca Rowell & Henderson, 1978 and Dactylotreta unda Engelbretsen, 2006 are the only Furongian species yet recorded. Dactylotreta lamellosa can be distinguished from D. redunca and D. unda in having anterior and lateral slopes of the ventral valve almost straight in cross section, as well as in having numerous, regular growth lamellae covering the ventral valve. It also differs from D. redunca in having a blade-like, triangular, dorsal median septum and a relatively low dorsal pseudointerarea. It has a distinctly shorter dorsal pseudointerarea and a slightly curved anterior edge of the dorsal median septum in comparison to D. unda. Among mid Cambrian species of the genus, the dorsal valve of Dactylotreta septata Holmer et al., 2001 from the Sarykumy Formation of the North Balkhash Region in Kazakhstan is similar in having a blade-like, triangular median septum and a low dorsal pseudointerarea. However, unlike the Iranian shells, it has a dorsal median sulcus, a gently concave lateral profile of the ventral valve anterior to the umbo, becoming convex in the anterior half of the shell; moreover, it lacks regular lamellose ornamentation on the ventral valve. Dactylotreta bacula Gonzáles-Gómez, 2005, from the latest Middle Cambrian Val d’Homs Formation of the Montagne Noir, France, also has a blade-like, triangular median septum, but D. lamellosa differs in having a procline to catacline deltoid pseudointerarea, an almost straight sagittal profile of the ventral anterior slope, and lacks a septal rod on the dorsal median septum.


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Fig. 6. Ottenbyella hyrcanica sp. nov., Cambrian, Furongian, Mila Formation, sample Ts; A-D, NMW2008.35G.57, ventral valve, exterior, oblique posterior and oblique lateral views, posterior view of umbonal area showing larval shell and pedicle foramen, sample Ts; E, I, NMW2008.35G.58, ventral valve, umbonal areas showing larval shell, oblique posterior view of ventral pseudointerarea, sample A-2; F, H, J, NMW2008.35G.59, ventral valve exterior, oblique lateral, posterior and ventral views, sample A-2; G, N, O, NMW2008.35G.60, ventral valve, lateral view, oblique posterior view and interior, sample A-2a; K, L, NMW2008.35G.61, ventral valve, posterior view, interior, sample Ts; M, NMW2008.35G.65, ventral valve, interior, sample Ts.


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Ottenbyella Popov & Holmer, 1994 Type species. By original designation Ottenbyella carinata (Moberg & Segerberg, 1906), from the Bjørkåsholmen Limestone of Sweden and the Oslo Region, Norway. Ottenbyella hyrcanica n. sp. (Figs 6-7) Derivation of name. After Hyrcania, ancient Iranian region located southeast of the Caspian Sea. Holotype. NMW2008.50 (L=0.78, W=0.94, Iw0.53, Pw=0.32, Cl=0.28, Cw=0.52, Sa=0.56, Sm=0.42, Sp=0.24) Cambrian, Furongian, Mila Formation, sample Ts, Simeh-Kuh, eastern Alborz Mountains, Iran. Paratypes. Figured; NMW2008.35G.51 (L=0.64, W=0.70), 53 (L=0.80, W=0.86, Tw=0.54, Pw=0.26, Cw=0.54, Sa=0.50, Sp=0.24), 54, dorsal valves, sample Ts; NMW2008.35G.58, 59, ventral valves, sample A-2; NMW2008.35G.60, ventral valve, sample A-2a; NMW2008.35G.61, 65, ventral valves, sample Ts. Other specimens; NMW2008.35G.62, ventral valve, sample A-2; NMW2008.35G.66-72, ventral valves and NMW2008.35G.73-77 dorsal valves, sample TS; NMW2008.35G.78-95, ventral valves, sample A-3/1; NMW2008.35G.96-98, ventral valves, sample A-2a. Diagnosis. Ventral valve high, conical, up to three-quarters as high as long; ventral deltoid pseudointerarea slightly procline to almost catacline, with a very weakly defined interridge; pedicle tube not differentiated, foramen facing posteroventrally. Dorsal valve gently convex, without median sulcus. Ventral valve interior with an elongate apical process projecting anterior to the internal foramen. Dorsal cardinal muscle fields relatively small, short, weakly impressed, occupying about half of valve width and onethird of valve length; dorsal median septum low, triangular, originating on average 24 µm from the pseudointerarea and extending anteriorly to about two thirds valve length; dorsal median buttress low, elongate, lacking lateral nodes. Description. Shell strongly ventribiconvex, transversely oval to subcircular in commissural outline. Ventral valve high, conical, 65-75% as high as long, with lateral slopes gently and evenly convex in a transverse profile; sagittal profile of the anterior slope almost straight (Fig. 6G, H). Deltoid pseudointerarea slightly procline to almost catacline, bisected by a very

weekly defined interridge, accentuated by slight undulations of growth lines, to almost undivided (Fig 6H, I). Pedicle tube not differentiated; foramen circular, about 55-60µm in diameter, facing posteroventrally, situated within the larval shell (Fig 6D, E). Dorsal valve very gently and evenly convex, about 85-90% as long as wide. Dorsal pseudointerarea low, about 60% as wide as valve. Dorsal median groove shallow, subtriangular, occupying about 55-60% of pseudointerarea width. Larval shell of both valves subcircular, about 140 µm wide, with microornament of hemispherical pits from 1 to 3 µm in diameter (Fig. 7G). Dorsal larval shell divided by a shallow median cleft (Fig. 7D). Ventral interior with an elongate apical process occluding the apex and projecting anterior to the internal foramen (Fig. 6M). Ventral vascula lateralia baculate, divergent. Dorsal interior with weakly impressed, elongate, suboval cardinal muscle scars, occupying almost 60% of the valve width and 35% of valve length. Dorsal median septum low, subtriangular, extending anteriorly about two thirds valve length. Dorsal median buttress low, elongate, subtriangular, widening posteriorly. Remarks. Ottenbyella hyrcanica n. sp. is presently the only known Cambrian species of the genus. It differs from the Ordovician species, including the type species Ottenbyella carinata (Moberg & Segerberg, 1906), Ottenbyella ibexiana Holmer et al., 2005, from the upper part of the ‘Paltodus’ spurius Subzone of the Fillmore Formation, Utah, and Ottenbyella shidertensis (Holmer & Popov, 1994); from the Floian, Olenty Formation of north-eastern Central Kazakhstan and the Emanuel Formation of Western Australia (Brock & Holmer 2004) in the complete absence of a dorsal median sulcus, a very weakly defined interridge and a more strongly developed apical process. Ottenbyella hyrcanica also has a less transverse shell outline in comparison with O. carinata, a dorsal median ridge originating at some distance from the dorsal pseudointerarea, unlike O. shidertensis, and it lacks lateral nodes on the median buttress unlike O. ibexiana. Sadracarta n. gen. Derivation of name. After Sadracarta - a legendary founder of the ancient Hyrcanian Kingdom on the southern coast of the Caspian Sea. Type and only species. Eoscaphelasma? delicata Holmer, Popov, Koneva & Bassett, 2001, Cambrian, Furongian, Pseudagnostus pseudangustilobus – Acrocephalaspina Biozone,


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Fig. 7. Ottenbyella hyrcanica sp. nov., Cambrian, Furongian, Mila Formation, sample Ts; A-C, NMW2008.35G.50, holotype, dorsal valve, interior, oblique lateral and oblique posterior views of interior, sample Ts; D-G, NMW2008.35G.54, dorsal valve, umbonal area showing larval shell, exterior, oblique lateral view, pitted microornament of larval shell; H, I, NMW2008.35G.53, dorsal valve, oblique lateral view, interior; J-L, NMW2008.35G.51, dorsal valve exterior, oblique posterior, oblique lateral and dorsal views.

Malyi Karatau, southern Kazakhstan. Diagnosis. Shell ventribiconvex. Ventral valve moderately convex to subconical with a low, strongly procline to almost catacline deltoid pseudointerarea curved posteriorly near the apex and bearing a broad and shallow, weakly defined intertrough; pedicle foramen small, circular, facing posteriorly, enclosed within the larval shell. Dorsal valve gently convex with a low

and narrow pseudointerarea mostly occupied by a weakly defined median groove. Larval shell ornamented by circular, flat-based pits about 4-5 µm in diameter, separated by broad, flat-topped interspaces covered by unevenly distributed small hemispherical pits less than 1 µm across, dorsal larval shell gently grooved medially; some larger hemispherical pits about 2-3 µm in diameter also occasionally present (Figs 8E, F, 9F). Ventral interior with a very weakly defined to almost

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Fig. 8. Sadracarta delicatus (Holmer, Popov, Koneva & Bassett), Cambrian, Furongian, Mila Formation; A, B, E, NMW2008.G35.99, ventral valve, exterior, oblique posterior view, larval shell showing flat-bottomed pits, sample A-2; C, D, F, NMW2008.G35.100, ventral valve, oblique lateral view, exterior, larval shell, sample A-2; G, H, I, NMW2008.G35.101, ventral valve, oblique lateral view of interior, interior, oblique posterior view showing pseudointerarea, sample A-2a; J, NMW2008.G35.102, ventral valve exterior, sample A-2; K, NMW2008.G35.103, ventral valve, oblique posterior view, sample A-2; L, NMW2008.G35.104, ventral valve, oblique lateral view of interior showing rudimentary apical process, sample A-2.

absent apical process, usually expressed as a fine rim anterior to the internal foramen, may be grooved medially (Fig. 8G). Dorsal interior with large, weakly impressed, elongate suboval cardinal muscle scars; a very fine dorsal median ridge may be present.

Discussion. The type species of the genus was originally assigned to Eoscaphelasma (Holmer et al. 2001), but it differs from all other scaphelasmatids in having a small, circular foramen enclosed within the larval shell, as well as lacking the characteristic groove on the larval ventral valve, anterior to the pedicle foramen in


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Fig. 9. Sadracarta delicatus (Holmer, Popov, Koneva & Bassett), Cambrian, Furongian, Mila Formation; A, NMW2008.G35.105, dorsal valve interior, sample A-2a; B, C, NMW2008.G35.106, dorsal valve, interior, oblique lateral view of interior, sample A-2; D-F, NMW2008.G35.107, dorsal valve, oblique lateral view, exterior, umbonal area showing larval shell, sample A-2a.

Scaphelasma (Holmer & Popov 2000, Fig. 64.1f), Eoscaphelasma (Holmer & Popov 2000, Fig. 65.2e) and Kotylotreta (Holmer et al. 2001, pl. 45, fig. 14). In addition, the new genus differs from Eoscaphelasma (Koneva et al. 1990) in having a strongly procline to almost catacline deltoid pseudointerarea, which is curved posteriorly in the umbonal area. Among Cambrian brachiopods, flat-based pits on the larval shell are typical mostly of the Family Scaphelasmatidae (Holmer et al. 2001; Williams 2003), but rare in the genera of the Family Acrotretidae, which usually have hemispherical pits on the larval shell. The only presently know exceptions are Linnarssonella Rowell, 1966 and Stilpnotreta Henderson & MacKinnon, 1981 (see also, Williams 2003, p. 77; Holmer et al. 2001, pl. 36, fig. 7). Stilpnotreta is also similar to Sadracarta in its simple dorsal valve morphology, but the new genus differs in having a strongly ventribiconvex shell with a well developed, strongly procline to almost catacline, deltoid pseudointerarea and a rudimentary and weakly defined apical process. Sadracarta is also similar to the late Cambrian Opisthotreta Palmer, 1954, but unlike Sadracarta it has a subequally biconvex shell with a strongly apsacline deltoid pseudointerarea and a distinct apical process anterior to the internal foramen.

Sadracarta delicatus (Holmer, Popov, Koneva & Bassett, 2001) (Figs 8, 9) 2001 Eoscaphelasma? delicata Holmer, Popov, Koneva & Bassett; p. 142, pl. 44, figs 1-2; pl. 46, figs 6, 8-15. Holotype. NMW 98.61G.286, dorsal valve; Cambrian, Furongian, Pseudagnostus pseudangustilobus – Acrocephalaspina Biozone; Kyrshabakty section, Malyi Karatau, sample 1378-12. Material. Figured; NMW 2008.35G.99, 100, 102-104, ventral valves, sample A-2; NMW 2008.35G.101, ventral valve, sample A-2a; NMW 2008.35G.105, 107, dorsal valves, sample A-2a; NMW 2008.35G.106, dorsal valve, sample A-2. Other specimens; NMW 2008.35G.108-110, 132-134, ventral valves, sample A-2a; NMW 2008.35G.111, 112, dorsal valves, sample A-2a; NMW 2008.35G.113-126, ventral valves and 2008.35G.127-131, dorsal valves, sample A-2. Remarks. Iranian shells are closely similar to the topotypes of Sadracarta delicatus from the Kyrshabakty Section in Malyi Karatau, but differ slightly in having a weaker dorsal median ridge, which is rarely observed in gerontic specimens.

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Fig. 10. Tapuritreta angusta n. gen., n. sp., Cambrian, Furongian, Mila Formation; A, B, NMW 2008.35G.144, ventral valve posterior and oblique lateral views, sample Ts; C-E, NMW 2008.35G.143, ventral valve valve, oblique posterior view, interior, oblique lateral view of interior showing apical process; F, G, J, K, NMW 2008.35G.145, ventral valve, interior, oblique anterior view of interior, posterior view showing pseudointerarea, oblique lateral view of exterior; H, I, L, NMW 2008.35G.146, ventral valve, exterior, posterior view showing pseiudointerarea, oblique lateral view.

In addition to the original description, which does not contain information on the detailed morphology of the larval shell, the Iranian shells show a subcircular larval shell up to 220 µm wide. The ventral larval shell narrows towards the foramen, which is about 25-30 µm in diameter. The dorsal larval shell is bisected medially by a

shallow groove. The pitted ornament consists of circular flat-based pits about 4-5 µm in diameter separated by flat-topped interspaces of variable width, covered by unevenly distributed small hemispherical pits less than 1µm with a small number of larger pits varying from 1-3 µm in diameter (Figs 8E, F, 9F).


117

Fig. 11. Tapuritreta angusta n. gen., n. sp., Cambrian, Furongian, Mila Formation, sample Ts; A, NMW 2008.35G.136, dorsal valve exterior; B, G, NMW 2008.35G.135, holotype, dorsal valve, oblique lateral view of interior, interior; C-F, NMW 2008.35G.137, conjoined valves, pitted microornament on dorsal larval shell, posterior, dorsal and lateral views of the shell; H, I, NMW 2008.35G.138, dorsal valve, interior, oblique lateral view of interior; J, K, NMW 2008.35G.139, dorsal valve, exterior, oblique lateral view of exterior, L, NMW 2008.35G.140, dorsal valve interior.

118


Tapuritreta n. gen.

Tapuritreta angusta n. sp. (Figs 10, 11)

Type and only species. Tapuritreta angusta n. sp. Cambrian, Furongian, Mila Formation, sample Ts, Simeh-Kuh, eastern Alborz Mountains, Iran.

Derivation of name. Latin angustus, narrow, constricted; alluding to less transverse shell outline in comparison to other acrotretids.

Derivation of name. After the Ancient Kingdom of Tapuria in northern Iran.

Holotype. NMW 2008.35G.135, dorsal valve (L=1.04, Il=0.10, Iw=0.76, Pw=0.46, Cl=0.40, Cw=0.80, Sa=0.92, Sm=0.62, Sp=0.30), Cambrian, Furongian, Mila Formation, sample Ts, Simeh-Kuh, eastern Alborz Mountains, Iran.

Diagnosis. Shell ventribiconvex to almost convexiplanar with commissural length equal to or slightly exceeding maximum shell width. Ventral valve with a procline, undivided pseudointerarea and small, circular foramen enclosed within the larval shell. Dorsal valve with a low, orthocline pseudointerarea divided by the median groove. Larval shell covered by fine, hemispherical pits varying from 1 to 3µm in diameter; dorsal larval shell bisected by a shallow median cleft. Ventral interior with an apical process as a strong, wide ridge with steep lateral slopes, excavated medially, undercut anteriorly and widening posteriorly. Internal foramen situated near the junction of the apical process with the posterior valve slope. Apical pits shallow, situated laterally to the internal foramen. Ventral mantle canals baculate with a pair of slightly divergent vascula lateralia. Dorsal interior with a high, blade-like, triangular median septum. Dorsal cardinal muscle fields weakly impressed, occupying about one third valve length. Remarks. Among other Cambrian acrotretides, Tapuritreta most closely resembles Treptotreta (Henderson & MacKinnon, 1981) and Angulotreta (Palmer, 1954) in having a dorsal valve with a blade-like triangular median septum, but differs considerably from both genera in the ventral valve morphology, including having an undivided deltoid pseudointerarea, and a ridge-like, apical process with steep lateral and anterior slopes, excavated medially and widening posteriorly. The dorsal median septum of Tapuritreta also lacks the superstructures that are characteristic of the type species of Angulotreta (Holmer & Popov 2000, Fig. 53.1f, g). Dicondylotreta Mei, 1993 is similar in the morphology of the apical process, but Tapuritreta can be distinguished from that genus in having a pedicle foramen enclosed entirely by the larval shell as well as a high blade-like triangular median septum. Tapuritreta also has a superficial similarity to the Ordovician genus Cyrtonotreta (Holmer 1989) in the morphology of the apical process, but differs in having baculate, rather than pinnate mantle canals, and in the absence of an interridge and dorsal median sulcus.

Paratypes. Figured; NMW 2008.35G.136 (L=1.00, W=0.94), 138 (L=0.92, Il=0.12, Iw=0.58, Pw=0.32, Cl=0.32, Cw=0.64, Sa=0.70, Sm=0.44, Sp=0.20), 138, 139 (L=0.80, W=0.86), 140 (L=0.84, W=0.82, Il=0.08, Iw=0.50, Pw=0.26, Cw=0.46, Sa=0.70, Sm=0.44, Sp=0.20), dorsal valves; NMW 2008.35G.143-146, ventral valves. Other specimens; NMW 2008.35G.141, 142, 147.1-2, dorsal valves; NMW 2008.35G.147.3-6, ventral valves. All from sample Ts. Diagnosis. As for genus. Description. Shell strongly ventribiconvex to almost convexiplanar; commissural outline subcircular with length almost equal or slightly exceeding maximum width. Ventral valve conical, almost as high as long. Deltoid pseudointerarea catacline, may be slightly procline or apsacline, undivided (Fig 10A, I, J). Pedicle foramen small, circular, placed within the larval shell. Dorsal valve very gently convex with a low, orthocline pseudointerarea occupying about 60% of maximum shell width, divided by a broad, shallow median groove about 55-60% as wide as the pseudointerarea. Larval shell about 140 µm wide, ornamented by fine, hemisphaerical pits varying from 1 to 3µm in diameter (Fig. 11C). Ventral interior with an apical process forming a wide, high ridge defined laterally by steep slopes and undercut anteriorly (Fig. 10E, G). Internal foramen situated near the posterior termination of the apical process. Cardinal muscle fields weakly impressed, situated posterolaterally on the posterior slope of the valve. Mantle canals baculate with a pair of divergent vascula lateralia (Fig. 10F). Dorsal interior with weakly impressed cardinal muscle fields occupying about 35% of sagittal valve lendth. Dorsal median septum blade-like, triangular, extending anteriorly about 80-85% valve length and with highest point at about mid-valve. Median buttress, low and narrow, widening considerably near the dorsal pseudointerarea.


119

Fig. 12. Dictyonina? cf. perforata Palmer, Cambrian, Furongian, Mila Formation, sample Ts; A, B, NMW 2008.35G.150, incomplete dorsal valve, exterior, oblique lateral view; C, NMW 2008.35G.151, ventral(?) valve fragment.

Acrotretidae gen. et sp. indet. (Fig. 4H-L) Material. NMW 2008.35G.148, ventral valve; NMW 2008.35G.149, dorsal valve; sample A-8. Remarks. These specimens resemble ‘Treptotreta’ mutabilis Mei, 1993 from the middle Cambrian Taitzuia and Liopeishania trilobite biozones of North China in having a broadly conical ventral valve with a procline deltoid pseudointerarea with a very weak intertrough (Fig. 4J, K), a pedicle foramen crossing the boundary of the larval shell (Fig. 4L) and a moderately high, triangular dorsal median septum. Both taxa may be congeneric, but it is unlikely that they belong to Tapuritreta, which has a pedicle foramen entirely enclosed within the boundaries of the larval shell. The apical process in ‘Treptotreta’ mutabilis was described and illustrated by Mei (1993, pl. 2, fig. 19), and it forms a high median septum bridging anterior and posterior valve slopes, and is perforated medially by the internal pedicle tube. This morphology is rather different from Tapuritreta, but resembles the apical process of Acrotreta (Holmer & Popov 1994). Acrotreta has a pedicle foramen, which is also not enclosed within the larval shell. It is possible that Iranian shells and ‘Treptotreta’ mutabilis may represent early Acrotreta, but their generic affiliation requires further study. Class PATERINATA Williams, Carlson, Brunton, Holmer & Popov, 1996 Order PATERINIDA Rowell, 1965 Superfamily PATERINOIDEA Schuchert, 1893 Family PATERINIDAE Schuchert, 1893 Dictyonina Cooper, 1942 Type species. By original designation, Trematis pannula White, 1874 from the Early to early Middle Cambrian Pioche Shale, Nevada, USA.

Dictyonina? cf. perforata Palmer, 1954 (Fig. 12) cf. 1954 Dictyonina? perforata; Palmer, p. 766, pl. 89, figs 11, 14. cf. 2007 Dictyonina perforata Palmer; Robson & Pratt, p. 36, pl. 26, figs 10-18. Material. NMW 2004.22G.150, incomplete dorsal valve; NMW 2004.22G151, 152, shell fragments; all sample Ts. Remarks. These ventribiconvex shells with weakly convex dorsal valve are represented in our collection by a few incomplete ventral and dorsal valves. The larval shell is poorly preserved, whereas the postlarval shell is ornamented by pits arranged in characteristic honeycomb pattern. In the anterior part the shell these pits are transformed into perforations arranged in concentric rows (Fig. 12C). Among Cambrian paterinides, Dictyonina? perforata Palmer, 1954, originally described from the earliest Furongian (Paibian) Aphelaspis Biozone of Texas, USA, is the only taxon which is characterised by a perforated anterior part of the shell. However, original description of the species is based mostly on fragmentary material and a single complete ventral valve, which makes further comparison of the Iranian and North American shells difficult. Similar perforated shells are also characteristic of the Ordovician Dictyonites Cooper, 1956, but unlike Cambrian paterinids this genus is characterised by a smooth, rather than granulated surface of the larval shell. Robson & Pratt (2007) recently reported the presence of a pustulose ornament on the larval shell of Dictyonina? perforata. SIGNIFICANCE OF THE FAUNA The Paibian Stage coincides with an extinction of cosmopolitan micromorphic lingulate brachiopods, including the common acrotretides


120

Anabolotreta, Linnarssonia, Neotreta, Picnotreta, Rhondellina and Stilpnotreta. With the exception of Rhondellina, which occurs in Laurentia in the lower Aphelaspis Biozone (Rowell 1986) these genera became extinct in Laurentia (Robson & Pratt 2007; Streng & Holmer 2006), Siberia (Ushatinskaya 1994), South China (Peng & Engelbersten 2007) and Kazakhstanian terranes (Holmer et al. 2001) by the beginning of Furongian, but probably survived in equatorial Gondwana until the end of the Paibian (Idamean) according to Engelbersten (2006). After a period of stasis corresponding to the Paibian Stage, new lingulate brachiopod associations appear on the shelves of the major early Palaeozoic continents. These associations mostly have a low to medium diversity, and include many endemic taxa. In particular, Apsotreta, Linnarssonella and Curticia are entirely endemic to Laurentia, whereas Angulotreta and Ceratreta occur in Laurentia and Baltica (Bassett et al. 1999). The Kazakhstanian terranes, which occupied equatorial positions between Baltica and Gondwana, supported more diverse faunas, with early representatives of Eoconulidae, Ephippelasmatidae and Scaphelasmatidae. These families had a restricted geographical distribution in the Cambrian, but diversified later in the Ordovician (Popov & Holmer 1994; Holmer et al. 2001). Our knowledge of Furongian lingulate brachiopods of Siberia, South China and Gondwana is presently inadequate for a biogeographical analysis. The newly discovered Furongian brachiopod fauna from the Eastern Alborz is unusual in that it contains the siphonotretide Siphonobolus, which is numerically the most abundant taxon. Remarkably, Siphonobolus, Dactylotreta and Ottenbyella are otherwise typical of Tremadocian micromorphic brachiopod assemblages and the Broeggeria Association, which are mostly found in dysaerobic environments (Popov & Holmer 1994; 1995). By contrast, in the eastern Alborz, these brachiopods come from shallow water carbonates with echinoderm bioclastic limestones and brachiopod shell beds (accumulations of disarticulated valves of Billingsella), but their co-occurrence with sponge spicules, as pointed out earlier by Percival et al. (1999) and Holmer et al. (2005), remain characteristic. Due to the absence of trilobite data and the sporadic occurrence of linguliform brachiopods, no formal biostratigraphical biozonation was attempted for the Furongian deposits in the Simeh-Kuh section. The age of the fauna is defined mainly by the occurrence of Sadracarta delicatus (Holmer et al., 2001), which is otherwise known only from Furongian deposits of the Malyi Karatau Range in southern Kazakhstan, where it occurs

within the Pseudagnostus pseudangustilobusAcrocephalaspina, Eurudagnostus kazakhstanicus-Parabolina monstruosa and E u r u d a g n o s t u s o v a l i f o r m i s - P a re u l o m a trilobite biozones below the first appearance of euconodonts. These biostratigraphical units are correlated with the middle part of the Iverian Stage of Australia (Shergold & Geyer 2003). In Malyi Karatau, Sadracarta delicatus is present in the upper part of the stratigraphical range of the acrotretide Quadrisonia minor Rowell & Henderson, 1978 (Holmer et al. 2001). The latter taxon is also characteristic of the Elvinia and Taenicephalus biozones of Laurentia. Dictyonina? perforata Palmer, 1954 occurs in Laurentia in the earliest Furongian (Paibian) Aphelaspis Biozone. In the Simeh-Kuh section Dictyonina? cf. perforata seemingly occupies a somewhat higher stratigraphical position. ACKNOWLEDGEMENTS We thank Dr Glenn A. Brock (Macquarie University) and Dr. Michal Mergl (University of West Bohemia) for constructive critical comments on the manuscript. Leonid Popov acknowledges support from the National Museum of Wales for work in Iran. Mansoureh Ghobadi Pour acknowledges her visit to the National Museum of Wales, Cardiff with financial support from the Golestan University, Gorgan. Lars Holmer’s work was supported by grants from the Swedish Natural Sciences Research Council (VR). We are grateful to Dr Oliver Lehnert (University of Erlangen) for identification of conodonts. REFERENCES

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