Late Devonian (Frasnian) trilobites and brachiopods from the ... - Informit

Late Devonian (Frasnian) trilobites and brachiopods from the Soh area, Central Iran MANSOUREH GHOBADI POUR, LEONID E. POPOV, MEHRI HOSSEINI, ARTABAZ ADHAMIAN & MEHDI YAZDI GHOBADI POUR, M., POPOV, L.E., HOSSEINI, M., ADHAMIAN, A. & YAZDI, M., 2013:04:26. Late Devonian (Frasnian) trilobites and brachiopods from the Soh area, Central Iran. Memoirs of the Association of Australasian Palaeontologists 44, 149-158. ISSN 0810-8889. An asteropygine trilobite and brachiopod association, including new species Heliopyge sohensis and Leptagonia? lakhalensis, is described from the Soh area, north of Esfahan, Iran. The co-occurrence of Douvillina and Neocalmonia aff. quadricosta Pillet indicates a Frasnian age for the trilobite-bearing horizon. The underlying units of limestone (Bahram Formation equivalent) contain a diverse conodont assemblage characteristic of the upper Givetian hemiansatus to ansatus biozones. The faunal assemblage from Soh has an affinity to the contemporaneous faunas of Afghanistan, Chitral in Northern Pakistan and the eastern Pamir. Mansoureh Ghobadi Pour ([email protected]) Department of Geology, Faculty of Sciences, Golestan University, Gorgan, Iran and Department of Geology, National Museum of Wales, Cathays Park, Cardiff CF10 3NP, United Kingdom; Leonid Popov ([email protected]), Department of Geology, National Museum of Wales, Cathays Park, Cardiff CF10 3NP, United Kingdom; Mehri Hosseini ([email protected]), 18 Hajarol Asvadi Alley, Masjed Sayed Street, Esfahan, Iran; Artabaz Adhamian ([email protected]), Petroleum Engineering and Development Company, Tehran, P.O. Box 15855-543, Iran; Mehdi Yazdi, Department of Geology, Faculty of Sciences, University of Esfahan, Esfahan 81746, Iran. Received 19 November 2012 Keywords: Devonian, Frasnian, Iran, trilobites, Asteropyginae, brachiopods.

A SMALL fauna of trilobites and brachiopods was recovered from a unit of grey argillites at the base of an unnamed unit of upper Palaeozoic clastic deposits overlying carbonates provisionally referred to the Bahram Formation in the Soh area. In spite of the absence of diagnostic conodonts in the argillite unit, the Frasnian age of the assemblage is well constrained because of the occurrence of the trilobite Neocalmonia and the strophomenide brachiopod Douvillina, which are confined exclusively to that stage elsewhere (Morzadec 1992; Cocks & Rong 2000). The first reported occurrence of asteropygine trilobites in Iran was by Richter & Richter (1926); however, their material is now lost. The first verifiable record is that of Haas & Mensink (1970), who described Neocalmonia brinkmanni from the Upper Devonian Bahram Formation of Kale Sardar. Four years later, Brice et al. (1974) reported Heliopyge sharudensis (Pillet in Brice et al., 1974) from the Alborz Mountains. In addition, a number of asteropygine species have been described from several Middle to Upper Devonian (Givetian to Frasnian) localities in Iran (Fig. 1A), including the Khosh-Yeilagh Formation (Givetian) of the Eastern Alborz (Brice et al. 1974; Morzadec 2000); the Bahram Formation of Jajarm and Binalud, both in Khorosan (Weddige 1984); the Shishtu Formation (Lower Frasnian) of the Tabas Region (Haas & Mensink 1970; Morzadec 2000); the Bahram Formation (early Frasnian) of the Kerman Region (Morzadec 2000; Morzadec et al. 2002); and the Frasnian deposits of Chah-Riseh and Zefreh, both north-east of Esfahan (Morzadec 2002). Asteropygine trilobite genera previously reported from Iran include Bradocryphaeus, Neocalmonia, Heliopyge and Radiopyge.

Jafarian (2000) published a comprehensive review of the Upper Devonian brachiopod faunas from Iran. According to the faunal lists given in that publication, the Frasnian brachiopod associations reported from the Alborz, Anarak, Chah-Riseh, Kerman and Tabas regions are dominated by atrypides, rhynchonellides and spiriferides, whereas strophomenides and productides are absent. The low diversity brachiopod association recovered from the Soh area is unusual, because the strophomenides Douvillina and Leptagonia, and the productide Productella represent the most distinctive components of the fauna. Other associated groups include bivalve and scaphopod molluscs, which await further study. GEOLOGICAL SETTING The Devonian sediments in the Soh area were first identified by Stöcklin during geological mapping (Zahedi 1973). Subsequently Zahedi (1973) reported the presence of a well exposed, presumably Middle to Upper Devonian sequence in the Negheleh valley. Weddige (1984) assigned the Devonian sequence of the Soh area to the Padeha and Bahram formations. Later, conodont studies by Long & Adhamian (2000) and Adhamian (2003) revealed the presence of Givetian sediments. The studied fossil locality is situated north of Esfahan, about 12 km north-east of Soh village, at the Lakhal Mountain on the western side of the Joor Maadan valley. Geographical coordinates of the stratigraphic base of the section are 51º 33′ 45″ E and 33º 29′ 53″ N (Fig. 1B). The lower to middle part of the exposed sequence comprises a basal unit of sandstone and an overlying unit of limestone and dolomite up to 270 m

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Figure 1. A, Geographic map showing the position of the Devonian sections with Asteropyginae trilobites in Iran. 1, Eastern Alborz, Khosh-Yeilagh Formation (Givetian) (Brice et al. 1974); 2, Jajarm, Bahram Formation (Richter & Richter 1926); 3, Binalud, southwest of Mashhad, Bahram Formation (Givetian) (Weddige 1984); 4, Tabas Region, Shishtu Formation (Lower Frasnian) (Haas & Mensink 1970); 5, Kerman Region, Bahram Formation (early Frasnian) (Morzadec et al. 2002); 6, Chah-Riseh and Zefreh, NE of Esfahan (Frasnian) (Morzadec 2002); 7, Soh (Frasnian) (this paper). B, Geographic map of the Soh area showing the position of the studied section. C, Stratigraphic column showing the sequence of Middle and Upper Devonian sediments and the position of the fossil locality.

thick, which are considered here as stratigraphic equivalents of the Bahram Formation. The middle part of the carbonate unit contains a diverse conodont fauna (Fig. 1C), including Belodella resima (Philip, 1965); Bipennatus bipennatus bipennatus (Bischoff & Ziegler, 1957); Icriodus lindensis Weddige, 1977; Icriodus arkonensis Stauffer, 1938; Icriodus struvei Weddige, 1977; Icriodus sp.; Icriodus “expansus” Branson & Mehl, 1938; Icriodus cf. “expansus” Branson & Mehl, 1938; Icriodus obliquimarginatus Bischoff & Ziegler, 1957; Polygnathus linguiformis klapperi Clausen, Leuteritz & Ziegler, 1979; Polygnathus pseudofoliatus Wittekindt,

1966; Polygnathus xylus xylus Stauffer, 1940; Polygnathus parawebbi Chatterton, 1974; and Neopanderodus aequabilis Telford, 1975, indicating a Givetian age within the hemiansatus-ansatus (= middle varcus) conodont biozones (Adhamian 2003). The carbonate sequence is topped by a bed of carbonate breccia up to 0.6 m thick, deposited in a very shallow, storm dominated environment. The overlying formally unnamed unit of late Palaeozoic clastic sediments in the upper part of the sequence was deposited mainly in a terrestrial depositional system. It comprises mainly alternating argillites and sandstones lacking

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AAP Memoir 44 (2013) any fossils except rare plant remains, such as Lepidodendron sp. and Sigillaria sp. A general regressive trend during the transition from carbonate to clastic deposition is complicated by a short term excursion of shallow marine environment in the base of the clastic sequence, represented by an horizon of grey kaolinitic argillite, about 1.5 m thick. It contains the trilobites Heliopyge sohensis n. sp.and Neocalmonia aff. quadricosta (Pillet, 1969); the brachiopods Douvillina sp., Leptagonia? lakhalensis n. sp. and Productella cf. subaculeata (Murchison, 1840), bivalve and scaphopod molluscs, and ostracods preserved as external and internal moulds. The depositional environment during formation of this unit was a quiet one. This is confirmed by the occurrence of some complete or almost complete trilobite carapaces, articulated strophomenide shells and productide shells with long spines, suggesting that there was little reworking of the skeletal remains. SIGNIFICANCE OF THE FAUNA The trilobite Neocalmonia aff. quadricosta is similar to the species originally described from the lower Frasnian of Central Afghanistan and from the Frasnian deposits exposed in Chah-Riseh and Zefreh quarry north-east of Esfahan (Morzadec 2002). The stratigraphic range of the brachiopod Douvillina is also confined to the Frasnian (Harper & Boucot 1978; Cocks & Rong 2000). Therefore the Frasnian age of the argillite bed in the base of the predominantly terrestrial clastic sequence, overlying the Givetian limestone unit, is well established. This is the first report on the occurrence of Leptagonia and Productella in the Frasnian of Iran; however, according to Jafarian (2000) both genera are rather common in the Famennian where Productella is represented by the species P. baitalensis Reed, 1922 and P. subaculeata (Murchison 1840). Both trilobites and brachiopods from this small faunal assemblage suggest a strong affinity to the contemporaneous faunas from Afghanistan (Morzadec 2002), the Chitral Region in Pakistan (Reed 1922; Feist et al. 2001) and the eastern Pamir (Reed 1922; Karapetov 1971). Another important feature of the trilobite assemblage from Soh, and the contemporaneous trilobite faunas from Iran, Afghanistan and Pakistan, is a late appearance of the subfamily Asteropyginae. According to Lieberman & Kloc (1997), the subfamily is confined to the Lower Devonian of Europe and North Africa and the Middle Devonian of western USA. However, this group survived until the Givetian-Frasnian in Iran, Afghanistan (Morzadec 2002) and Pakistan (Feist et al. 2001). The diachronous occurrences of asteropygine trilobites suggest the existence of an easterly directed migration route along North Gondwana. SYSTEMATIC PALEONTOLOGY Most of the figured specimens are deposited in the National Museum of Wales, Cardiff (NMW) and the Natural History Museum of Esfahan (NMET). A small sample of unfigured material including some paratypes is housed in the Museum of the Esfahan University Geology Department (EUIT and EUIMT). Brachiopods (by L.E. Popov) Abbreviations for parameters measured on specimens are (in millimetres): W = maximum shell width; Lv, Ld = maximum length of ventral and dorsal valves; Iw = maximum width of interarea; Dl, Dw = length and width of ventral disc; Ml,

Mw = length and width of muscle field. Order STROPHOMENIDA Öpik, 1934 Superfamily STROPHOMENOIDEA King, 1846 Family RAFINESQUINIDAE Schuchert, 1893 Subfamily LEPTAENINAE Hall & Clarke, 1894 Leptagonia M‛Coy, 1844 Type species. Producta analoga Phillips, 1836. Carboniferous, Viséan (probably from Pendleside Limestone Group), Bowland, Yorkshire, England. Leptagonia? lakhalensis n. sp. (Figs 2A-I, 3E) Derivation of name. After Lakhal Mountain near the type locality. Holotype. NMW 2012.7G.1 (Lv=21.4, W=34.0, Dl=16.5, Dw=21.0), ventral valve internal mould, from the Frasnian of Lakhal Mountain in the Soh area, Central Iran. Paratypes. One ventral valve external mould (NMW 2012.7G.2 [Lv=26.6, W=38.3, Ml=8.4, Mw=10.0]); three ventral valve internal moulds (NMW 2012.7G.8 [Lv=21.4, W=34.3], 10, 39 [plaster cast, original is in the Esfahan University Museum]); one dorsal valve external and internal mould (NMW 2012.7G. 12); four dorsal valve external moulds (NMW 2012.7G.9 [Ld=19.0, W=28.7], 11, 14, EUIT 8272 [plaster cast NMW 2012.7G.37]); four dorsal valve internal moulds (NMW 2012.7G.5, 6, 13, 38 [plaster cast, original is in the Esfahan University Museum]). Total of five ventral and nine dorsal valves. Locality and horizon as for the holotype. Diagnosis. Leptagonia? with concavoconvex shell geniculated at 16-18 mm from umbo; up to 7 strong rugellae on disc; radial ornament multicostellate with up to 10 ribs per 3 mm; short median ridge in front of ventral muscle field; no dorsal muscle platform; dorsal median septum commonly absent, occasionally present in posterior half of mature specimens. Description. Shell concavoconvex, geniculated about 16-18 mm from umbo, transverse, subrectangular, with maximum width at hinge line. Cardinal extremities slightly acute. Ventral valve with low, apsacline interarea. Delthyrium completely covered by a convex, narrow, triangular pseudodeltidium perforated apically by a small, rounded foramen. Lateral profile of ventral valve from umbo to point of geniculation almost flat. Geniculation accentuated by strong concentric rim, continuing in a trail strongly curved dorsally. Dorsal valve flattened, with an almost linear, anacline interarea and a small, convex chilidium divided medially by a furrow. Radial ornament finely and equally multicostellate with 7-10 rounded ribs per 3 mm in the area of the valve geniculation. Concentric ornament with up to seven strong rounded rugae covering the shell surface posterior to the geniculation and with very fine, crowded, concentric fila. Ventral valve interior with small teeth and thin, straight, widely divergent dental plates. Ventral muscle field strongly impressed, surrounded by strong muscle bounding ridges in mature individuals, open anteriorly in juveniles, occupying about one quarter of maximum valve length.

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Figure 2. A-I, Leptagonia? lakhalensis n. sp.; A, B, EUIT 8272 (NMW 2012.7G.37), latex cast of dorsal valve interior, internal mould; C, NMW 2012.7G.2, latex cast of ventral valve exterior; D, NMW 2012.7G.38, latex cast of dorsal valve exterior; E, NMW 2012.7G.1, holotype, ventral valve internal mould; F, NMW 2012.7G.4, latex cast of dorsal valve interior; G, NMW 2012.7G.39, ventral valve internal mould; H, NMW 2012.7G.5, latex cast of dorsal valve interior; I, NMW 2012.7G.6, latex cast of dorsal valve interior. J-M, Productella cf. subaculeata (Murchison, 1840); J, NMW 2012.7G.21, latex cast of ventral valve exterior; K, NMW 2012.7G.24, latex cast of ventral valve interior; L, NMW 2012.7G.22, latex cast of ventral valve exterior; M, NMW 2012.7G.22, latex cast of ventral valve exterior. All scale bars are 3 mm. All specimens from Upper Devonian, Frasnian of Lakhal Mountain in the Soh area, Central Iran.

Ventral adductor muscle scar narrow, completely dividing semicircular diductor muscle scars. Short median ridge present in front of the adductor scars. Dorsal valve interior with a double cardinal process joined laterally with low, straight, widely diverging socket plates. Dorsal adductor

scars weakly impressed, slightly thickened only in gerontic specimens. Dorsal median septum usually absent, but sometimes present together with a pair of incipient side septa in posterior half of gerontic individuals.

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Figure 3. A-E. Douvillina sp.; A, NMW 2012.7G.40, latex cast of ventral valve interior of juvenile specimen; B, NMW 2012.7G.41, latex cast of ventral valve exterior of juvenile specimen; C, NMW 2012.7G.16, ventral valve internal mould; D, NMW 2012.7G.42, latex cast of ventral valve interior; E, NMW 2012.7G.15, dorsal view of conjoined valves with Leptagonia? lakhalensis sp. nov., NMW 2012.7G.14, dorsal valve exterior (latex casts). All scale bars are 3 mm. All specimens from the Upper Devonian, Frasnian of Lakhal Mountain in the Soh area, Central Iran.

Remarks. The subfamily Leptaeninae is rare in the Upper Devonian and is represented only by Leptagonia. This genus is characterised by a strongly impressed ventral muscle field, bordered by an elevated rim, and a well developed dorsal muscle platform (see Cocks & Rong 2000, p. 247, fig. 1541a-d). However, the dorsal adductor muscle platform is absent in the specimens from Soh, except for a single dorsal valve of a gerontic specimen (Fig. 2I), which exhibits a slightly thickened dorsal adductor muscle field bordered by a low rim. Therefore the generic affiliation of Leptagonia? lakhalensis is considered here as provisional. There are some other Late Devonian leptaenid species that lack a dorsal muscle platform. In particular, Leptagonia rotunda (Karapetov, 1971) from the lower Frasnian Schuchertella pamirica – Mucrospirifer aff. muralis Biozone of Ak-Baital in the eastern Pamir, Tajikistan, is similar in that respect to L.? lakhalensis. However, it differs from the Iranian species in having a prominent dorsal median ridge, finer concentric rugae (up to 11 instead of seven as in L.? lakhalensis) and a larger ventral muscle field occupying about one third of valve length. Another similar taxon is Leptagonia barunkhuraica Alekseeva, 2011, from the Barunkhurai Depression of southern Mongolia. It also exhibits a gently impressed dorsal adductor muscle field bordered by a low rim. However, L.? lakhalensis differs from this taxon in having a shell almost twice as large with the point of geniculation situated further from the ventral umbo, in having finer radial ornament, an incipient dorsal median septum developed only in gerontic individuals and in the absence of the ventral sulcus on the trail. There are no previous records of Leptagonia in the Frasnian of Iran, but Jafarian (2000, pl. 3, fig. 4a-c) reported on the occurrence of Leptagonia in the late Famennian of the Chah-Riseh area, north-east of Esfahan. The single illustrated specimen is characterised by the numerous fine rugae covering the disc and by its short trail, unlike L.? lakhalensis, but features of the ventral and dorsal valve interiors remain unknown.

Family DOUVILLINIDAE Caster, 1939 Subfamily DOUVILLININAE Caster, 1939 Douvillina Oehlert, 1887 Type species. Orthis dutertrei Murchison, 1840 (attributed to de Verneuil by Oehlert, 1887), Frasnian, Ferques Limestone Formation, Ferques, Boulonnais, France. Douvillina sp. (Fig. 3) Material. Three external moulds of conjoined valves (NMW 2012.7G.15 [Lv=28.0, Ld=26.5,W>32.6], 17, 18); four ventral valve internal moulds: (NMW 2012.7G.16 [Lv=24.8, Ml=6.1,Mw=8.6], 20, 40 [plaster cast, original is in the Esfahan University Museum], 42 [plaster cast, original is in the Esfahan University Museum]); two ventral valve external moulds (NMW 2012.7G.19 [Lv=25.1, W=32.1], 41 [plaster cast, original is in the Esfahan University Museum]). Total three pairs of conjoined valves and six ventral valves from the Frasnian of Lakhal Mountain in the Soh area, Central Iran. Description. Shell concavoconvex, transverse, semioval in outline, about three-fifths as long as wide with maximum width at hinge line. Cardinal extremities with small ears, acute and slightly alate. Ventral valve gently convex with an uneven lateral profile more strongly curved at about one-quarter valve length from the anterior margin. Ventral interarea low, apsacline, with a narrow convex pseudodeltidium. Hinge line of the ventral valve finely denticulate with 5-6 denticles per 3 mm. Dorsal valve weakly concave with a linear, anacline interarea. Radial ornament unequally parvicostellate with up to 20 accentuated costae in the umbonal area and two generations of up to 50 accentuated ribs inclined in the middle and anterior parts of the shell, with about 4-5 ribs per 5 mm along the anterior margin of mature specimens. Interspaces between accentuated ribs covered by 3-7 very fine parvicostellae. Ventral valve interior with rudimentary teeth and a transverse, bilobed, douvillinid-type muscle field completely


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surrounded by strong muscle bounding ridges, about onequarter as long as valve in mature specimens. Prominent median ridge bisects entire ventral muscle field. Area around ventral muscle field densely pustulose. Dorsal valve interior unknown. Remarks. The presence of a denticulate hinge line and a characteristic douvillinid-type ventral muscle field (Harper & Boucot 1978; Rong & Cocks 1994; Cocks & Rong 2000) leave no doubts about the generic assignment of the Iranian specimens despite the lack of information on the dorsal valve interior. In size, external shape and characters of the radial ornament they are most similar to the material described by Reed (1922) as Stropheodonta (Douvillina) dutertii var. asiatica from the Frasnian deposits (presently referred to the Shogrām Formation) of Chitral Province in northern Pakistan; however, specimens from Chitral illustrated by Reed (1922, p. 36, pl. 6, figs 16-17; pl. 7, fig. 1, 1a-b) are incompletely preserved and the interior of both valves is inadequately known, making more detailed comparisons impossible. The material described by Karapetov (1971) as Brachioprion birmanica (Reed, 1908) from the Frasnian of Ak-Baiotal represents a species of Douvillina. It has a strongly differentiated, parvicostellate radial ornament similar to the specimens from Soh, but is characterised by a significantly larger ventral muscle field that occupies almost two-fifths of the valve length. The Soh specimens show some similarity to Douvillina dutertii (Murchison, 1840) and Douvillina thomosi (Rigaux, 1908), from the Frasnian of France, as revised by Brice (1988). The Iranian material can be easily distinguished from both in having strongly differentiated radial ornament with only 4-5 accentuated ribs per 5 mm along the anterior margin of mature specimens, and a less transverse outline of the ventral muscle field. In addition, the Iranian specimens have less alate cardinal extremities than those of D. dutertii. They differ from Douvillina immatatrix Reed, 1929 from the Frasnian of Padaukpin, Northern Shan States, Burma, in having a transverse, semioval, not subquadrate, shell outline, acute and slightly alate cardinal extremities, and less numerous parvicostellae between the accentuated ribs. Order PRODUCTIDA Waagen, 1883 Suborder PRODUCTIDINA Waagen, 1883 Superfamily PRODUCTOIDEA Gray, 1840 Family PRODUCTELLIDAE Schuchert, 1929 Productella Hall, 1867 Type species. Productus subaculeatus Murchison, 1840, Upper Devonian, Frasnian, Ferques, Boulonnais, France. Productella cf. subaculeata (Murchison, 1840) (Fig. 2J-M) Material. Three ventral valve external moulds (NMW 2012.7G.21 [Lv=11.6. W=13.4], 22 [Lv=12.4. W=16.2], 23); one ventral valve internal mould (NMW 2012.7G.24); Three dorsal external moulds (NMW 2012.7G.25, 26, 38). Total of four ventral and three dorsal valves from the Frasnian of Lakhal Mountain in the Soh area, Central Iran. Remarks. All three ventral valves of Productella from Soh are characterised by a moderately convex lateral profile that is more strongly curved in the posterior third of the valve,

a hinge line slightly shorter than maximum shell width and a very low ventral interarea lacking a delthyrial cover. Both valves are ornamented by slightly irregular concentric rugellae weakening in the anterior third of the valve, with long spines evenly distributed along the entire ventral valve surface. Up to three pairs of long, posteriorly directed spines are present close to the hinge region (Fig. 2L). The ventral valve interior, observed in a single internal mould, has incipient teeth and a faint median ridge bisecting a poorly defined muscle field. The dorsal valve interior is unknown. In characters of external morphology, including shell outline, size and arrangement of spines on the ventral valve, the Iranian material falls into the range of variation characteristic of Productella subaculeata, as described by Brousmiche (1973). In particular, they show a close resemblance to the specimen of P. subaculeata illustrated by Mottequin (2008, fig. 4) from the Grands Breux Formation (Boussu-en-Fagne Member) of the Namur-Dinant Basin in Belgium. However, the absence of data on the dorsal valve interior makes their taxonomic assignment provisional. The material described and illustrated by Gourvennec (2006, pl. 1, figs 2–5), as Productella sp. cf. subaculeata, from the Frasnian deposits exposed north-east of Kozan in the Taurus Mountains, Turkey, have significantly finer and more densely arranged spines on the ventral valve, unlike the specimens from Soh. The Iranian material differs from Productella baitalensis Reed, 1922 from the Upper Devonian (Famennian) of Ak-Baital in the eastern Pamir in having coarser, irregularly arranged spines with rounded, rather than elongate bases. Trilobites (by M. Ghobadi Pour) Order PHACOPIDA Salter, 1864 Family ACASTIDAE Delo, 1935 Subfamily ASTEROPYGINAE Delo, 1935 Heliopyge Haas & Mensink, 1970 Type species. Asteropyge (Comura) helios Richter & Richter, 1926, Frasnian, Liénaux Formation of Nismes, Belgium. Heliopyge sohensis n. sp. (Fig. 4) 2002 Heliopyge sp. nov.; Morzadec, p. 416, fig. 5.6. Derivation of name. After the type locality near Soh village. Holotype. NMET235, pygidium, from the Frasnian of Lakhal Mountain in the Soh area, Central Iran. Paratypes. One articulated carapace (EUIT3168b), one attached cephalon and thorax (NMET220b), one attached thorax and pygidium (NMET222a), 13 cephala (including NMET227, NMET251a, NMW 2012.7G.44, NMET223a, NMET271, NMET220a, NMET264b), two external moulds of cephala (NMW 2012.7G.28, 32), one glabella (NMET223d), two librigenae (NMET220c, NMET264), three hypostomes (NMET242, NMET222b, NMW2012.7G.43), one incomplete thorax (NMET220d), two external moulds of pygidia (NMW2012.7G.33, 34) and 21 internal moulds of pygidia (including NMET251b, NMET225, NMET235, NMET261, NMET268, NMET221, NMET224, NMET264a, EUIT8262, NMW 2012.7G.30, NMW 2012.7G.27, 29).


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Figure 4. Heliopyge sohensis n. sp.; A, EUIMT3168b, paratype, articulated exoskeleton, internal mould, dorsal view; B, NMET225, paratype, pygidium, latex cast of external mould, dorsal view; C, NMET235, holotype, pygidium, latex cast of external mould, dorsal view; D, NMET221, paratype, pygidium, latex cast of external mould, dorsal view; E, NMET268, paratype, pygidium, latex cast of external mould, dorsal view; F, NMET222a, paratype, thoracopygon, latex cast of external mould, dorsal view; G, NMET264, paratype, pygidium, internal mould, dorsal view; H, NMW 2012.7G.30, paratype, pygidium, latex cast of external mould, dorsal view showing abnormal growth of pygidial spines; I, NMET220, paratype, cephalon and incomplete thorax, latex cast of external mould, dorsal view; J-L, NMET271, paratype, cephalon, latex cast of external mould, J, dorsal view, K, lateral view of the right eye, L, anterior view; M, NMET231a, paratype, broken hypostome, internal mould, ventral view; N, NMET242, paratype, distorted hypostome, internal mould, ventral view. All scale bars are 2 mm. All specimens from Upper Devonian, Frasnian of Lakhal Mountain in the Soh area, Central Iran.

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Figure 5. Neocalmonia aff. quadricosta Pillet, 1969; A, NMW2012.7G.36, articulated exoskeleton, internal mould, dorsal view; B, NMET237, incomplete articulated exoskeleton, latex cast of external mould, dorsal view; C, NMET226, incomplete exoskeleton, with disarticulated pygidium, latex cast of external mould, dorsal view. All scale bars are 2 mm. All specimens from Upper Devonian, Frasnian of Lakhal Mountain in the Soh area, Central Iran.

Diagnosis. Pygidium with axis including 9-10 rings and a terminal piece, 4-6 anterior rings bearing median tubercle; five pairs of broad pleural furrows and five pairs of pleural spines and a posteromedian spine; pleural spines narrow, posteriorly directed, increasing in length so that the third pair is the longest, then shortening posteriorly with the median spine being shortest; interpleural furrows with long fenestrae extending about a third to half furrow length. Description. Cephalon about 50% to 65% as long as wide, excluding genal spines, almost semicircular, with moderately long genal spines. Glabella subpentagonal in outline, with a rounded anterior margin; lateral profile of frontal lobe gently declined anteriorly. S1 gently curved anteriorly, S2 nearly transverse or very slightly inclined anteriorly, S3 straight, declined posteriorly. Axial furrows moderately deep, divergent anteriorly. Occipital ring less than 10% of cephalic length, higher than remainder of glabella, with a strong posteromedian spine directed upward. Occipital furrow shallow and wide. Surface of glabella covered by coarse, widely spaced tubercles. Anterior border narrow, sicklelike. Eyes large, slightly less than half as long as cephalon. Visual surface steeply inclined in front and almost vertical in posterior part, including up to 26 dorsoventral files with a maximum of seven lenses. Eye socle thick, covered by fine tubercles. Palpebral lobes well defined, higher than glabella. Anterior branches of facial suture cutting the anterior margin of the cephalon; posterior branches sigmoidal, curved anteriorly then curved backwards before crossing the lateral margin. Librigena small, sloping towards cephalic margin. Posterior border furrow shallow and narrow. Posterior border widening abaxially, merged with moderately long genal spines that are about half as long as sagittal length of cephalon. Hypostome elongate, suboval, with a very gently convex, elongate, suboval middle body, a long anterior lobe and a shorter (sag.) posterior lobe, separated by a narrow and very shallow middle furrow. Macula poorly defined, situated

on posterior side of middle furrow. Two small spines on moderately wide (sag.) posterior border. Anterior wings wide, inclined dorsally abaxially. Hypostomal suture curved forwards. Thorax of 11 segments with pointed pleural ends. Thoracic axis well defined, occupying about 30% of thoracic width; axial rings with a large posteromedian node. Pygidium about two-thirds as long as wide, subtriangular, with gently curved lateral sides, bearing five pairs of narrow, moderately long, radially arranged pleural spines, the third pair being longest. Median spine triangular, with a thick base and concave lateral sides, shorter than lateral spines. Pygidial axis about 30% of pygidial width at anterior margin, with up to ten axial rings and a small terminal piece. First 4-6 large, well defined rings bearing a median tubercle, others decreasing gradually in length and width posteriorly. Axial furrows converging posteriorly, constricted slightly at the level of the fifth axial ring. Pleurae with five, rarely (less than 10% of the specimens) six pairs of pleural ribs curved posteriorly. Posterior pleural band of segments much thicker than anterior bands, bearing a node on their distal third. Pleural furrows wide and shallow. Interpleural furrows broad, with openings originating near axial furrow and extending more than half of furrow length. Border furrow narrow; pygidial border gently convex in cross section. Remarks. A pygidium from the Soh area was briefly described and illustrated by Morzadec (2002) as Heliopyge sp. nov. It came from the same locality as the types of Heliopyge sohensis n. sp. and is considered conspecific herein. Heliopyge sohensis differs from Heliopyge caelata Haas & Mensink, 1970, from the Givetian of Rhuck, western Afghanistan, in having a more acute anterior border on the cephalon, a pygidium usually with only five (not six) pairs of pleural ribs and significantly shorter pygidial spines. The new species also resembles Heliopyge mariamae Farsan, 1981, from the Middle Devonian to Frasnian of Robat-ePai, western Afghanistan; however, unlike that species, H.

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AAP Memoir 44 (2013) sohensis has only nine (not 11) axial rings on the pygidium and a single large interpleural opening on each interpleural furrow instead of the two small interpleural openings in H. mariamae. Heliopyge shahrudensis (Pillet in Brice et al. 1974) from the Givetian of the Khosh-Yeilagh Formation of the eastern Alborz has longer and thicker pygidial spines, whereas pygidial openings are smaller and fewer in number (four pairs instead of five) in comparison to H. sohensis. The new species differs from Heliopyge afghanica (Haas & Mensink 1970) in having finer pygidial spines, wider interpleural furrows with larger fenestrae, a more acute anterior border on the cephalon and a stout spine on the occipital ring. Neocalmonia Pillet, 1969 Type species. Neocalmonia quadricosta Pillet, 1969; Upper Devonian, lower Frasnian of Badragha in central Afghanistan. Neocalmonia aff. quadricosta Pillet, 1969 (Fig. 5) Material. Two articulated carapaces (NMET237, NMW2012.7G.36) and one with disarticulated pygidium (NMET226), from the Frasnian of Lakhal Mountain in the Soh area, Central Iran. Description. Carapace elongate oval, about two thirds as wide as long (excluding spines). Cephalon semicircular with moderately long genal spines. Glabella subpentagonal in outline, frontal lobe gently declined anteriorly in lateral profile, covered by coarsely tuberculate ornament. S3 straight, posteromedially directed; S2 almost transverse, S1 curved anteriorly. Occipital ring well defined, with a median tubercle. Fixigena with long, slightly divergent genal spines terminating opposite the fifth segment of the thorax. Palpebral area well defined, slightly lower than palpebral lobes. Eyes large, comprising almost half cephalic length. Visual surface of eye covered by 23 dorsoventral files with 6-7 lenses each. Thorax with 11 segments; pleural ends pointed. Pygidium subtriangular. Four pairs of short pleural spines with the second pair longest and fourth pair shortest. Median spine short and thick. Axis with up to nine axial rings and a small terminal piece. Pleura of supradevonicus-type, with five pairs of posterior pleural bands lacking any openings. Remarks. Due to the small number of specimens and their insufficient preservation, precise species determination is impossible. However, the observed characters are mainly within the range of morphological variation for Neocalmonia quadricosta Pillet 1969, but there are some minor differences. In particular, specimens from Soh differ from the types of N. quadricosta described by Pillet (1969) and revised by Morzadec (2002), as well as those from the Frasnian of Dashte-Nawar (southern Afghanistan) (Haas & Mensink 1970) in having a small median tubercle on the occipital ring and fewer pygidial axial rings. Specimens from Soh also differ from N. quadricosta from the Frasnian of Kuh-e-Kaftar in the Chah-Riseh area and Kuh-e-Zard in the Zefreh area, both north-east of Esfahan (Morzadec 2002), in having a slightly different visual surface lens formula, fewer pygidial axial rings, and in the presence of a distinct median tubercle on the occipital ring. Neocalmonia aff. quadricosta is similar to Neocalmonia

brinkmanni Haas & Mensink, 1970, from the Frasnian of Kale Sardar, eastern Central Iran, but the latter species has 12 axial rings on the pygidial axis and a different visual surface lens formula. Neocalmonia aff. quadricosta shows some similarity to Neocalmonia yazdii described by Morzadec (2002) from the Middle Frasnian Shishtu Formation of the Shotori Range in eastern Central Iran, but differs in having a well defined median tubercle on the occipital ring and a visual surface covered by 23 dorsoventral files with 6-7 lenses each. The types of Neocalmonia yazdii lack a tubercle on the occipital ring and have only 20 rows with five lenses on the visual surface. Neocalmonia imperfecta Pillet, 1969, from the Frasnian of Afghanistan differs from the Iranian specimens in having 12 axial rings on the pygidium, five pleural furrows, thinner and longer pleural spines and in lacking a triangular median spine on the pygidium (Pillet et al. 1969; Haas & Mensink 1970). ACKNOWLEDGEMENTS Mansoureh Ghobadi Pour thanks the National Museum of Wales for logistical support on her visits to Cardiff; her work in Iran is supported by Golestan University. Leonid Popov acknowledges support from the National Museum of Wales. Mehri Hosseini, Artabaz Adhamian, and Mehdi Yazdi acknowledge support from the Geology Department of the Esfahan University. We thank Dr James Valentine and Dr Jed Day for their useful and constructive comments on the manuscript. REFERENCES

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