Late Silurian Cephalopods from Langkawi, Malaysia, with Peri-Gondwanan Faunal Affinity

Journal of Systematic Palaeontology

ISSN: 1477-2019 (Print) 1478-0941 (Online) Journal homepage: http://www.tandfonline.com/loi/tjsp20

Late Silurian cephalopods from Langkawi, Malaysia, with peri-Gondwanan faunal affinity

Shuji Niko, Masatoshi Sone & Mohd Shafeea Leman

To cite this article: Shuji Niko, Masatoshi Sone & Mohd Shafeea Leman (2018) Late Silurian cephalopods from Langkawi, Malaysia, with peri-Gondwanan faunal affinity, Journal of Systematic Palaeontology, 16:7, 595-610, DOI: 10.1080/14772019.2017.1316322 To link to this article: https://doi.org/10.1080/14772019.2017.1316322

Published online: 25 May 2017.

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Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tjsp20 Journal of Systematic Palaeontology, 2018 Vol. 16, No. 7, 595–610, https://doi.org/10.1080/14772019.2017.1316322

Late Silurian cephalopods from Langkawi, Malaysia, with peri-Gondwanan faunal afﬁnity Shuji Nikoa*, Masatoshi Sone b and Mohd Shafeea Lemanc aDepartment of Environmental Studies, Faculty of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashihiroshima, Hiroshima 739-8521, Japan; bDepartment of Geology, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia; cGeology Programme, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia (Received 14 April 2016; accepted 21 March 2017; published online 25 May 2017)

Nine species of late Pridoli (latest Silurian) orthocerid cephalopods are described from the Upper Setul Limestone of Pulau Langgun, Langkawi Islands, Malaysia. These are the orthoceratids Michelinoceras (Michelinoceras) cf. michelini (Barrande, 1866), Michelinoceras? sp., Kopaninoceras setulense sp. nov., Mimogeisonoceras? langgunense sp. nov., Kionoceras? sp. and Orthocycloceras sp.; the arionoceratids Arionoceras mahsuri sp. nov. and Caliceras mempelamense sp. nov.; and the geisonoceratid Murchisoniceras? sp. This is the first detailed record with taxonomic descriptions of Silurian cephalopods from Southeast Asia. The assemblage belongs to the newly defined Kopaninoceras Fauna that is interpreted to have been widely distributed along the northern (African to Asian) margin of Gondwana and around the Prototethys Ocean during the late Silurian. The Kopaninoceras Fauna includes a local assemblage from the Kurosegawa Belt of south-west Japan, which possibly represents its northernmost occurrence. The distribution of the Kopaninoceras Fauna implies that the cephalopod faunas of Kazakhstan and adjacent areas in Central Asia have closer affinities with peri- Gondwanan faunas than with Baltica or Siberia, corroborating conclusions drawn by earlier researchers based on the benthic faunas. http://zoobank.org/urn:lsid:zoobank.org:pub:DDE20872-C142-4B78-B5F2-2E604C3C8689 Keywords: Orthocerida; Kopaninoceras; Silurian; Langkawi; Malaysia; Gondwana

Introduction taxonomic descriptions, of Silurian cephalopods from Southeast Asia, and provides palaeobiogeographical Silurian sediments are rather uncommon in Southeast insights into the distribution of peri-Gondwanan marine Asia. Our information on Silurian cephalopods from this faunas. region is extremely limited compared with the Ordovician The fossil beds are found on the north-western coast of cephalopods, which are better studied (e.g. Stait & Burrett Pulau Langgun, known internationally as the Teluk Mem- 1987; Niko & Sone 2014, 2015). So far as is known, pelam section (Fig. 1C). Fifty-two specimens of cephalo- ‘Michelinoceras spp.’ from the Linwe and Nyaungbaw pods were examined in this study, which are housed in the formations in Shan State, Myanmar (Thein 1973; Aung Department of Geology, University of Malaya, Kuala 2012) and ‘Ormoceras sp.’ from the Upper Setul Lime- Lumpur (with the prefix UM). They were collected in situ stone of Langkawi (Jones 1981, p. 66) are the only (samples UM10581–10631) and from a float block reported Silurian occurrences. In addition, some Silurian (UM10632) of the Upper Setul Limestone of Jones (1981) cephalopods, including Michelinoceras and Kopaninoce- (D the Mempelam Limestone Formation of Cocks et al. ras, were reported from the Baoshan and Tenchong blocks 2005). of western Yunnan (Mu et al. 1986; Zhang et al. 2014) but In this paper, we use the traditional stratigraphical have never been studied in detail. terms of Jones (1981) for each unit of the Setul Formation, We recovered nine taxa, including four new species, of such as the Upper Setul Limestone and the Upper Detrital latest Silurian orthoconic and cyrtoconic nautiloids from Member, while new formation names as given by Cocks Teluk (D inlet) Mempelam in Pulau (D island) Langgun, et al. (2005) include equivalent strata in Perlis (mainland Langkawi Islands, northern Peninsular Malaysia Malaysia). This is for convenience to focus on our palae- (Fig. 1A–C). This is the first detailed record, with ontological findings within Pulau Langgun of Langkawi.

*Corresponding author. Email: [email protected]

Published online 25 May 2017 596 S. Niko et al.

Figure 1. A, tectonic division map of Southeast Asia (in part), showing the location of the Langkawi Islands off Peninsular Malaysia. B, geological map of the Langkawi Islands, indicating the Teluk Mempelam locality in Pulau Langgun (after Jones 1981). C, Teluk Mempelam section (base map after Jones 1981, ﬁg. 19) on the north-western coast of Langgun, showing the stratigraphical extent of the Silurian Upper Setul Limestone and the location of cephalopod sampling. Late Silurian cephalopods from Langkawi, Malaysia 597

Geological setting between the septa) and the maximum width (diameter) of each camera, as defined by Niko & Ozawa (1997). The Setul Formation (Setul Group in Cocks et al. 2005)is a thick carbonate-dominated succession, ranging in age Subclass Nautiloidea Agassiz, 1847 from Early Ordovician to Early Devonian. It occurs in the Order Orthocerida Kuhn, 1940 Shan-Thai (D Sibumasu) Block that underlies part of Superfamily Orthoceratoidea M’Coy, 1844 Myanmar, Thailand, Malaysia and possibly Sumatra Family Orthoceratidae M’Coy, 1844 (Fig. 1A). The Tenchong and Baoshan blocks in western Subfamily Michelinoceratinae Flower, 1945 Yunnan are generally considered the northern extension Genus Michelinoceras Foerste, 1932 of Shan-Thai. The whole Shan-Thai Block is believed to be a crustal fragment once forming the margin of north Type species. Orthoceras michelini Barrande, 1866. Gondwana until its breakup by Early Permian rifting Subgenus Michelinoceras Foerste, 1932, emend. (e.g. Shi & Archbold 1998; J. R. Ali et al. 2013; Cocks & Kiselev & Gnoli, 1992 Torsvik 2013). The entire Ordovician–Devonian succession in Langkawi thus represents sediments deposited on Michelinoceras (Michelinoceras) cf. michelini the continental shelf of Gondwana. It was most likely situ- (Barrande, 1866) ated at a stable passive margin at that time. (Fig. 2A‒D) The Upper Setul Limestone represents the Silurian por- tion of the Setul Formation and consists of grey to dark Compares with: grey micritic limestones with intercalations of thin shales, interpreted by C. A. Ali & Mohamed (2013) to have 1866 Orthoceras michelini Barrande: pl. 221, figs 12‒19. formed in a relatively deep marine environment. It is best 1870 Orthoceras michelini Barrande; Barrande: pl. 381, exposed along the Teluk Mempelam section in north- figs 3‒16, pl. 442, figs 20‒23; pl. 447, figs 12(?), 13(?). western Pulau Langgun, where the succession ranges 1909 Orthoceras michelini Barrande; Gortani & Vinassa from Middle Ordovician to Early Devonian and is about de Regny: 205. 120 m thick (Jones 1981). 1932 Michelinoceras michelini (Barrande); Foerste: 51, Silurian ages for the Upper Setul Limestone are well con- 72. trolled by its conodonts (Igo & Koike 1966, 1968, 1973;Igo 1968 Michelinoceras michelini (Barrande); Ristedt: 245, 1984;Idris1989), trilobites (Kobayashi & Hamada 1971) pl. 1, figs 1, 2. and crinoids (Lee 2001, 2005). The age is further constrained 1970 Michelinoceras michelini (Barrande); Barskov & by the occurrence of Early Devonian graptolites and tentacu- Kiselev: pl. 3, fig. 1. litids in the overlying basal beds of the Upper Detrital Mem- 1972 Michelinoceras michelini (Barrande); Barskov: 36, ber. The graptolites belong to the Monograptus uniformis pl. 1, figs 1, 2, pl. 2, figs 1‒3. Zone of the basal Lochkovian (earliest Devonian) (Jones 1977 Michelinoceras grande (Meneghini, 1857); Serpagli 1981, p. 66). The tentaculitids include Styliolina and Nowa- & Gnoli: 162, pl. 2, figs 1, 2, 3a, b, 4, text-fig. 7a [not kia, also indicative of an Early Devonian age (Jones 1981). 5a, b D Columenoceras grande (Meneghini); see Gnoli Based on the available results, three age-levels are con- & Serpagli 2009]. firmed within the Upper Setul Limestone of the Teluk 1982 Michelinoceras grande (Meneghini); Gnoli: 82, pl. Mempelam section: (1) late Llandovery (Telychian) at 5 m 2, figs 2, 3. above the base; (2) Wenlock to early Ludlow (late Silurian) 1992 Michelinoceras michelini (Barrande); Gnoli & at 30 m above the base; and (3) late Pridoli (latest Silurian) Kovacs: 381, pl. 2, figs 1a, b. at 35 m below the top. The (floating) scyphocrinoid lobo- 1992 Michelinoceras (Michelinoceras) michelini liths, collected from the beds marked Number 21 in the (Barrande); Kiselev & Gnoli: 74. section map of Jones (1981, fig. 19), were assigned a late 1998 Michelinoceras (Michelinoceras) michelini Prodoli–early Lochkovian (Lee 2005) or a late Pridoli age (Barrande); Gnoli & Histon: 314, pl. 1, figs 1, 2. (Cocks et al. 2005, p. 711). Our cephalopod assemblage is 1999 Michelinoceras (Michelinoceras) michelini from the immediately overlying beds, Number 20 of Jones (Barrande); Histon: 236, pl. 2, figs 5, 7. (1981) and, based on the fauna described below, we recon- 2006 Michelinoceras (Michelinoceras) michelini firm its age to be late Pridoli, not Lochkovian. (Barrande); Serventi et al.: 44, pl. 2, figs 1a, b, 2. 2011 Michelinoceras (Michelinoceras) michelini (Barrande); Serventi: 17, fig. 3.8. Systematic palaeontology Material. Five specimens, UM10581–10585. Silurian, The term ‘cameral form ratio’ used in the descriptions late Pridoli, Upper Setul Limestone, Pulau Langgun, below refers to the ratio between the length (the distance Langkawi Islands, Malaysia. 598 S. Niko et al.

Figure 2. A–D, Michelinoceras (Michelinoceras) cf. michelini (Barrande, 1866); A, B, UM10582; A, dorsoventral thin section, venter left; B, partial enlargement of A to show details of siphuncle; C, D, UM10583; C, dorsoventral thin section, venter on right; D, partial enlargement of C to show details of septal neck. E–G, Michelinoceras? sp.; E, F, UM10587; E, longitudinal thin section; F, partial enlargement of E to show details of siphuncle; G, UM10586, partial enlargement to show details of siphuncle in longitudinal thin section. Scale bar: A, C, E D 10 mm; B, D, F, G D 3 mm. Late Silurian cephalopods from Langkawi, Malaysia 599

Description. Longiconic orthocones with very gradual Remarks. Kopaninoceras differs from Michelinoceras in conch expansion and circular cross section. The largest having a characteristic septal neck shape reflecting the specimen (UM10584) attains 9 mm in approximate conch conical appearance and larger expansion angle of the diameter. Shell surface probably smooth. In serial pol- conch. About 20 species of Kopaninoceras were previ- ished sections, sutures directly transverse. Camerae rela- ously known from the middle Silurian to the Early Devo- tively long to very long indicating approximate cameral nian of the Anti-Atlas Range, Morocco (Gnoli 2003; form ratios (length/maximum width) of 0.8‒1.6. Kroger€ 2008); the Armorican Massif, France (Babin Siphuncle cylindrical and narrow, with wall consisting of 1966, reported as Orthoceras jucundum); Sardinia, Italy orthochoanitic septal necks and thin connecting rings. (Serpagli & Gnoli 1977); the Carnic Alps, Austria (Gnoli Position of siphuncle nearly central. Septal neck length & Histon 1998); the Prague Basin, Bohemia (Barrande exceptionally long, attaining 1.89 mm at approximate 1870; Kiselev 1969); the Uppony Mountains, Hungary conch diameter of 7 mm. Connecting rings cylindrical. (Gnoli & Kovacs 1992); Podolia in Ukraine (Barskov & No cameral or endosiphuncular deposits were detected. Kiselev 1970); southern Fergana, Uzbekistan (Barskov & Kiselev 1970); the northern Urals, Russia (Kiselev 1969); Remarks. Since the Langkawi specimens are not in a Nyalam, southern Tibet (J. Chen 1975); Ninglang, South good state of preservation, their identification as Micheli- China (J. Chen 1981); and the Yokokurayama area in the noceras (M.) michelini is with the reservation that the Kurosegawa Belt, south-western Japan (Niko et al. 1989). details of the shell surface and cameral deposits need to In addition, three species of Kopaninoceras were reported be clarified for the Langkawi form. Nevertheless, other from the Wenlock–Pridoli of the Rutog Country, western features described above appear identical with those of Tibet (T. Chen & Zhang 2010), although the details are the syntypes from the Prague Basin of Bohemia, Czech unknown. Republic (see Barrande 1866). In addition to its type locality, M. (M.) michelini is found worldwide in North Kopaninoceras setulense sp. nov. Africa, Europe, central to East Asia, Australia and North (Fig. 3) America (Serventi 2011). Diagnosis. Species of Kopaninoceras having conch Subgenus incertae sedis expansion angles of 5–7, weakly depressed cross section and smooth surface. Sutures oblique. Camerae mostly Michelinoceras? sp. long. Nearly central siphuncular position in adoral shells. (Fig. 2E‒G) Derivation of name. After the Upper Setul Limestone. Material. Two specimens, UM10586 and UM10587. Silurian, late Pridoli, Upper Setul Limestone, Pulau Lang- Material. Holotype: UM10632. Paratypes: UM10589, gun, Langkawi Islands, Malaysia. 10590, 10599–10601. Other than the type series, 13 poorly preserved specimens (UM10588, 10591–10598, Description. Longiconic orthocones with very gradual 10602–10605) are assigned to Kopaninoceras setulense conch expansion. The largest specimen, UM10586, sp. nov. Silurian, late Pridoli, Upper Setul Limestone, attains 16 mm in approximate conch diameter. Cam- Pulau Langgun, Langkawi Islands, Malaysia. erae moderate to relatively long, indicating cameral form ratios (length/maximum width) of approximately Description. Longiconic orthocones with moderate 1.6. Sutures probably transverse; siphuncle narrow and expansion, with angle of 5–7. Transverse section of central in position. Septal necks orthochoanitic to conch weakly depressed and subcircular. Lateral diame- faintly suborthochoanitic, long, attaining 1.40 mm at ter/dorsoventral diameter ratio of conch at apical end of approximate conch diameter of 9 mm. Connecting the holotype approximately 1.1. Shell surface smooth. rings cylindrical with weak constrictions at the septal Holotype an incomplete phragmocone measuring foramen. No cameral or endosiphuncular deposits were 67.5 mm in length, with dorsoventral diameters of 4 mm detected. near the apex and 5.5 mm near the adoral ends. The larg- Remarks. Two incomplete phragmocones are assigned est specimen (paratype UM10600) consisting of the questionablytoasecondspeciesofMichelinoceras, incomplete phragmocone and the apical part of the body readily separated from the associated Michelinoceras chamber attains approximately 10 mm in dorsoventral (M.)cf.michelini by its shorter camerae and septal diameter. Sutures oblique, inclined towards dorsum. Cam- necks. erae mostly long, but their length ranging from moderate to very long, with cameral form ratios (length/maximum dorsoventral width) of 0.9‒2.0. Septa deeply concave. Genus Kopaninoceras Kiselev, 1969 Siphuncle situated subcentrally in apical, then nearly cen- Type species. Orthoceras jucundum Barrande, 1870. tral in adoral, shell part. Siphuncular wall consisting of 600 S. Niko et al.

Figure 3. Kopaninoceras setulense sp. nov. A‒D, holotype, UM10632; A, side view; B, dorsoventral thin section, venter on right; C, partial enlargement of B to show the details of camerae and siphuncle (note the conical shape of the septal foramen); D, cross thin section of apical end, venter down; E, F, paratype, UM10600; E, dorsoventral thin section, venter on right; F, partial enlargement of E to show the details of well-preserved (upper) and probably deformed (lower) septal necks. Scale bar: A, B, E D 10 mm; C, D, F D 3 mm.

orthochoanitic (to suborthochoanitic by possible deforma- cylindrical. Diameters of the connecting rings range 0.37– tion) septal necks and thin connecting rings. The well- 0.46 mm in the holotype. No cameral or endosiphuncular preserved septal foramen indicates the conical shape deposits were detected. (Fig. 3C). Length of septal necks exceptionally long, attaining 1.63 mm in the holotype and 1.92 mm at the last Remarks. This is the most abundant species in the pres- septum of paratype UM10600. Connecting rings ent fauna, as their accumulated shells form a cephalopod Late Silurian cephalopods from Langkawi, Malaysia 601 limestone. Among all the previously known species of the not preserved. No cameral or endosiphuncular deposits genus, Kopaninoceras ankhorense Barskov in Barskov & were detected. Kiselev, 1970 (p. 68, pl. 3, figs 3a, b, v; see also Barskov Remarks. This new species is the most similar to species 1972, p. 40, pl. 1, figs 7a, b, pl. 2, figs 16, 17) from south- of Mimogeisonoceras among previously known orthocer- ern Fergana is the most similar to K. setulense sp. nov. in atoids in sharing the general conch shape, imbricated sur- having a depressed conch, mostly long camerae, and face ridges, a subcentral siphuncular position, and the nearly central siphuncular position in the adoral part of septal neck shape. However, its placement in Mimogeiso- the shell. A major difference between the two species lies noceras is still questionable, essentially because the avail- in the surface ornamentation: the transverse ridges devel- able information on the internal structure of the type oped in K. ankhorense are absent from the new species. species, M. ljubovae Shimansky, 1968 (p. 54, 55, pl. 1, Kopaninoceras kobayashii Niko, Hamada & Yasui, 1989 figs 3a, b) from the Early Carboniferous of the southern (p. 61, figs 2A, B) from the Yokokurayama Group in the Urals, is insufficient. The new species differs from M. lju- Kurosegawa Belt is also similar to K. setulense, but has bovae in having deeper concavities of the septa and finer shorter camerae and a more eccentric position of the surface ridges. siphuncle. Some orthoceratoids from the late Silurian (Wenlock– Ludlow) of the Carnic Alps also have a surface ornamen- Genus Mimogeisonoceras Shimansky, 1968 tation similar to that of the new species. They were Type species. Mimogeisonoceras ljubovae Shimansky, reported as Orthoceras amoenum Barrande by Heritsch 1968. (1929, pp. 22, 61, 87, 88, 90, pl. 5, figs 586, 587, 592‒ 598, 600‒605, pl. 6, fig. 606), O. aff. amoenum by Mimogeisonoceras? langgunense sp. nov. Heritsch (1929, p. 61, pl. 5, figs 591, 599) and (Fig. 4A‒D) Merocycloceras? cf. declivis Ristedt by Histon (1999,p. 242). These Austrian species, however, have longer septal Diagnosis. Orthoconic conchs with an expansion angle of necks than Mimogeisonoceras? langgunense does. The approximately 5 . Surface ornamented by imbricate fine genus Merocycloceras Ristedt, 1968 (type species Mero- ridges. Sutures slightly oblique. Septal curvature deep. cycloceras declivis Ristedt, 1968, p. 247, pl. 1, figs 8–11) Siphuncle near central in position, having short septal is diagnosed only by the apical shells; therefore, a direct necks. comparison with Mimogeisonoceras is not possible at this Derivation of name. After Pulau Langgun, where the stage. new species was recovered. Subfamily Kionoceratinae Hyatt in Zittel, 1900 Material. Holotype: UM10609. Paratypes: UM10610 Genus Kionoceras Hyatt, 1884 and UM10611. Apart from the type series, seven poorly preserved specimens (UM10606‒10608, 10612‒10615) Type species. Orthoceras doricum Barrande, 1868. are assigned to Mimogeisonoceras? langgunense sp. nov. Silurian, late Pridoli, Upper Setul Limestone, Pulau Lang- Kionoceras? sp. gun, Langkawi Islands, Malaysia. (Fig. 5H, I) Description. Longiconic orthocones with gradual conch Material. UM10616. Silurian, late Pridoli, Upper Setul expansion, with an expansion angle of approximately 5. Limestone, Pulau Langgun, Langkawi Islands, Malaysia. Transverse sections of conch are circular. Holotype Description. A single deformed specimen of the longi- UM10609, consisting of an incomplete phragmocone and conic conch, 63 mm in length, was available for study. an apical part of the body chamber, attains 42 mm in Shell surface ornamented by longitudinal ridges. Internal length and 7 mm in diameter near the adoral end. Paratype structure unknown. UM10611 an incomplete phragmocone attaining 9 mm (slightly deformed) in diameter. The shell surface is orna- Remarks. This species appears distinct from any other in mented by fine transverse ridges, the adjoining ridges the Langkawi fauna. It is assigned as a species of Kiono- being imbricated. The adoral side of each ridge is steeper ceras with some reservation, since its longitudinal ridges than the apical side. There are 2‒3 lirae in 1 mm of conch over the surface ornamentation resemble those in other length in the holotype. Sutures slightly oblique. Deeply species of the genus. Nevertheless, several other Silurian concave septa from moderate to long camerae. Approxi- orthocerid genera, such as Mongoceras Miagkova, 1967 mate cameral form ratios (length/maximum width) 1.1‒ and Parakionoceras Foerste, 1928, also possess similar 2.0. Siphuncle narrow with a nearly central position. Sep- longitudinal ridges. More information about the internal tal necks orthochoanitic to faintly suborthochoanitic and structure of the Langkawi species is required for making a short, 0.44‒0.49 mm in the holotype. Connecting rings more definite generic assignment. 602 S. Niko et al.

Figure 4. A–D, Mimogeisonoceras? langgunense sp. nov.; A–C, holotype, UM10609; A, longitudinal thin section; B, partial enlargement to show details of surface ornamentation; C, partial enlargement to show details of camerae and septal necks; D, paratype, UM10611, side view. E–G, Orthocycloceras sp., UM10617; E, partial enlargement of F to show details of siphuncle (arrow indicates suborthochoanitic septal neck); F, longitudinal thin section (arrow indicates cameral deposits); G, side view. Scale bar: A, F D 10 mm; B, E D 4.7 mm; C D 3 mm; D D 6 mm; G D 20 mm. Late Silurian cephalopods from Langkawi, Malaysia 603

Figure 5. A–F, Arionoceras mahsuri sp. nov. A, paratype, UM10625, longitudinal thin section; B, F, paratype, UM10619; B, dorsoventral thin section, venter on right; F, partial enlargement of B to show details of siphuncle; C‒E, holotype, UM10618; C, dorsoventral thin section, venter on left; D, dorsoventral polished section, venter on left; E, partial enlargement of C to show details of siphuncle. G, J, Murchisoniceras? sp., UM10631; G, dorsoventral thin section, venter on left; J, partial enlargement of G to show details of septal necks. H, I, Kionoceras? sp., UM10616; H, side view; I, partial enlargement of H to show details of surface ornamentation. Scale bar: A–C, G D 10 mm; D D 24 mm; E, F, J D 3 mm; H D 15 mm; I D 30 mm.

In addition, Kobayashi & Hamada (1971, p. 88) Type species. Orthocycloceras alayense Barskov, 1972. reported the occurrence of ‘a longitudinally striated ceph- Remarks. Orthocycloceras was proposed by Barskov alopod’ from the Upper Setul Limestone; this is presum- (1972) based on the type species – Orthocycloceras ably the same species as the present form. alayense Barskov, 1972 – from the late Silurian of Isfara in Tajikistan. Gnoli (1982) considered Euthyocycloceras Subfamily Leurocycloceratinae Sweet, 1964 J. Chen, 1981 (type species, E. qujingense J. Chen, 1981) Genus Orthocycloceras Barskov, 1972 from Qujing, eastern Yunnan (South China), as a 604 S. Niko et al. synonym of Orthocycloceras: we agree with this assign- 2003;Kroger€ 2008); the Armorican Massif, France (Babin ment. Orthocycloceras is known also from the Carnic 1966; Babin et al. 1979); the Montagne Noire, France Alps (Gnoli & Histon 1998); the Graz Palaeozoic area, (Ristedt 1968, reported as Psilorthoceras chaubetae Ris- Austria (Histon et al. 2010); Sardinia, Italy (Serpagli & tedt, 1968); Sardinia, Italy (Meneghini 1857; Serpagli & Gnoli 1977; Gnoli 1982); the Prague Basin, Czech Repub- Gnoli 1977); the Carnic Alps, Austria (Gnoli & Histon lic (Barrande 1868, reported as Orthoceras lynx Barrande, 1998); the Prague Basin, Czech Republic (Barrande 1866; 1868); Kazakhstan (Barskov 1972); Fergana, Uzbekistan Barskov 1966); erratic boulders in Poland (Dzik 1984); (Barskov 1972); south-eastern Afghanistan (Barskov Fergana, Uzbekistan (Barskov & Kiselev 1970); and the 1972); and the Yokokurayama area, Japan (Kobayashi Yokokurayama area, Japan (Kobayashi 1984). In addition, 1984). some forms of Arionoceras have been reported from the late Silurian (Ludlow–Pridoli) of Rutog, western Tibet Orthocycloceras sp. (T. Chen & Zhang 2010), although they were not studied (Fig. 4E‒G) in detail. Material. UM10617. Silurian, late Pridoli, Upper Setul Arionoceras mahsuri sp. nov. Limestone, Pulau Langgun, Langkawi Islands, Malaysia. (Fig. 5A‒F) Description. A single specimen of the incomplete longi- Diagnosis. Species of Arionoceras having a conch conic orthocone was available for this study. The annu- lated phragmocone indicates gradual conch expansion. expansion angle of approximately 8 . Camerae relatively The approximate conch diameter near the adoral end is long for the genus with cameral form ratios (length/maxi- ‒ 14 mm. Annulations low and slightly oblique. Annula- mum width) of 1.5 2.0. Septal curvature shallow. tions and interspaces covered by lirae that run parallel to Siphuncle narrow and slightly closer to venter in the the annulations. Cameral length short to very short. adoral part of the shell. Constrictions of connecting rings Siphuncle situated subcentrally and lacking endosiphun- at septal foramen very weak. cular deposits. Siphuncle diameter relatively large for the Derivation of name. After Mahsuri, the legendary family. Septal necks short and suborthochoanitic. Con- woman who lived in Langkawi. necting rings cylindrical. Cameral deposits developed at episeptal-mural and hyposeptal positions (Fig. 4F). Material. Holotype: UM10618. Paratypes: UM10619, 10620 and 10625. Other than the type series, seven poorly Remarks. This specimen can be referred to Orthocyclo- preserved specimens (UM10621‒10624, 10626–10628) ceras rather than Leurocycloceras Foerste, 1928 are assigned to Arionoceras mahsuri sp. nov. Silurian, (type species, L. raymondi Foerste, 1928)orFlowerina late Pridoli, Upper Setul Limestone, Pulau Langgun, Zhuravleva & Kiselev, 2001 (type species, L. bucheri Langkawi Islands, Malaysia. Flower, 1941). It displays the short and suborthochoanitic septal necks characteristic of Orthocycloceras, while typi- Description. Longiconic orthocones with relatively rapid cal species of Leurocycloceras and Flowerina have long expansion, expansion angle of approximately 8, and cir- and straight septal necks. In addition, cameral deposits of cular cross section. The holotype, consisting of an incom- Flowerina bulge into the siphuncle and encase the septal plete phragmocone and the apical end of the body necks (see Flower 1941; Zhuravleva & Kiselev 2001), a chamber, attains 99 mm in length and 18.5 mm in width feature not seen in the Langkawi form. at the adoral end. Shell surface probably smooth. In the The external conch morphologies of the present form serial polished sections, sutures are directly transverse. suggest a relationship with Orthocycloceras sp. reported Cameral length moderate to short for the family and rela- by Histon et al.(2010, pl. 1, ﬁgs 11, 12) from the late Silu- tively long for the genus. Form ratios (length/maximum rian of the Graz Palaeozoic in Austria. More detailed width) of camerae are 1.5‒2.0. Septa exhibiting a shallow information on the siphuncular structure of the Austrian curvature. Siphuncle narrow, with ratios of connecting species will be necessary for making an adequate compar- ring diameter per corresponding conch diameter of 0.08‒ ison with the Malaysian form. 0.12. Position of siphuncle central in apical part of shell, then slightly translocated to venter in adoral part, where Family Arionoceratidae Dzik, 1984 position ratios of siphuncle (distance of central axis of Genus Arionoceras Barskov, 1966 siphuncle per corresponding conch diameter) indicating approximately 0.46. Siphuncular wall composed of ortho- Type species. Orthoceras arion Barrande, 1866. choanitic to faintly suborthochoanitic septal necks and Remarks. About 15 reliable species of Arionoceras were thin connecting rings. Septal necks very short, 0.48‒ previously known from the middle to late Silurian of: the 0.50 mm long in the holotype. Connecting rings cylindri- Tindouf Basin and the Anti-Atlas Range, Morocco (Gnoli cal with very weak constrictions at septal foramen. Late Silurian cephalopods from Langkawi, Malaysia 605

Diameters of connecting rings 0.69‒0.85 mm in the holotype, approximately 0.9 mm in paratype UM10619 at 9 mm in conch diameter. No endosiphuncular or cameral deposits were observed.

Remarks. With regard to its conch expansion angle, narrow siphuncle diameter and position, Arionoceras mahsuri sp. nov. resembles the two other late Silurian species of Arionoceras, namely Arionoceras arion (Barrande, 1866, pl. 221, figs 24, 25; also Barrande 1868, pl. 347, figs 1‒4; 1870, pl. 408, figs 9‒14; Dzik 1984, pl. 30, figs 5, 6) and Arionoceras densiseptum Kobayashi, 1984 (p. 246, pl. 3, figs 3‒5). Apart from its type locality in the Prague Basin (Barskov 1966), A. arion is also known to occur in the Armorican Massif (Babin et al. 1979, p. 73, pl. 8, figs 5‒11) and southern Fergana (Barskov & Kiselev 1970, p. 70, pl. 3, fig. 6; Barskov 1970, p. 41, pl. 2, fig. 12a, b). Arionoceras densiseptum is known only from a Ludlow limestone of the Yokokurayama Group. The relatively long camerae and shallow septal curvature of A. mahsuri allow it be readily distinguished from these two species.

Genus Caliceras Kolebaba, 1975

Type species. Orthoceras capillosum Barrande, 1868.

Remarks. Dzik (1984) considered Caliceras a junior subjective synonym of Arionoceras, and relocated the for- mer to the family Arionoceratidae. Although this familial grouping is reasonable, we disagree about the synonymy of Caliceras with Arionoceras. This is because Caliceras differs clearly from Arionoceras in having a smaller angle of conch expansion and a much longer body chamber. Moreover, constrictions at the aperture and transverse lirae seen on the shell surface of Caliceras are absent from Arionoceras. Previously, three to four species of Caliceras were Figure 6. Caliceras mempelamense sp. nov., holotype, known from the middle and late Silurian of North Africa UM10629. A, dorsoventral thin section, venter on right; B, par- and Europe – more precisely, from the Anti-Atlas Range tial enlargement to show details of apertural shell modification and surface ornamentation; C, partial enlargement to show (Gnoli 2003, reported as Arionoceras aff. capillosum) and details of siphuncle. Scale bar: A D 10 mm; B, C D 4.7 mm. the Prague Basin (Barrande 1868; Kolebaba 1975). The new species below represents the first confirmation of Caliceras from Asia. Material. Holotype: UM10629. Silurian, late Pridoli, Upper Setul Limestone, Pulau Langgun, Langkawi Islands, Caliceras mempelamense sp. nov. Malaysia. (Fig. 6)

Diagnosis. Species of Caliceras with an endogastric Description. Longiconic cyrtocone with a weak endo- conch curvature and a conch expansion angle of approxi- gastric curvature. Cross sections of conch circular. Conch expansion gradual with an expansion angle of approximately 4 . Camerae short to very short. Siphuncle subcentral. Connecting rings indicating weak constrictions at mately 4 . Holotype composed of incomplete phragmo- septal foramen. cone and body chamber with peristome, measuring 50.5 mm in length and 9.5 mm in diameter at the peri- Derivation of name. After Teluk Mempelam, from stome. Body chamber long, 31 mm in length, approxi- which the new species was recovered. mately four times as long as the conch diameter at the last 606 S. Niko et al. septum. Aperture oblique, slightly inclined towards ven- Material. UM10630 and UM10631. Silurian, late Pri- ter. Transverse constriction of apertural modification prodoli, Upper Setul Limestone, Pulau Langgun, Langkawi vided by inward shell wall thickening. Depth of this Islands, Malaysia. constriction deeper on the venter than on the dorsum. Sur- face ornamentation not visible, but the presence of fine Description. Longitudinal sections of the two specimens transverse lirae recognizable in longitudinal section. In were examined. They are longiconic orthocones with serial polished sections, sutures directly transverse. Cam- gradual conch expansion and subcircular cross sections. eral length short to very short. Form ratios (maximum The larger specimen (UM10630) attains 9 mm in approxi- width per length) of camerae ranging from 2.3 to 3.4. mate conch diameter. No distinct surface ornamentation Septa relatively shallow; siphuncle subcentral in position recognized. Camerae very short. Sutures slightly oblique. with position ratios (distance of central axis of siphuncle Siphuncle subcentral in position. Septal necks short and from ventral shell wall surface per corresponding conch suborthochoanitic. No connecting rings preserved. Endo- diameter) of 0.46‒0.47. Siphuncular wall consisting of siphuncular and cameral deposits unknown. suborthochoanitic septal necks and thin connecting rings. The neck length is short, approximately 0.3‒0.5 mm. Con- Remarks. This form is assigned to Murchisoniceras with necting rings cylindrical with weak constrictions at septal reservation, because it has short camerae and subortho- foramen, measuring 0.69‒0.87 in diameter. No cameral or choanitic septal necks similar to those of the type species endosiphuncular deposits were detected. of Murchisoniceras, Orthoceras murchisoni (see Barrande 1868,pl.254,figs 4‒6, pl. 303, figs 11, 12, pl. 320, figs 5‒ Remarks. Caliceras mempelamense sp. nov. is similar to 10, pl. 231, figs 1‒12, pl. 331, figs 1‒7; Barrande 1870,pl. the two species of Caliceras from the Prague Basin men- 408, figs 1‒8, pl. 445, figs 12, 13, pl. 455, figs 1‒3; Babin tioned below. It is nevertheless different from Orthoceras 1966,p.358,pl.16,fig. 7), known from the late Silurian capillosum, the type species of Caliceras (see Barrande of Bohemia. Among species of other Silurian genera, it is 1868, pl. 325, figs 19‒33; 1870, pl. 357, figs 4‒7, pl. 394, also similar to Bandoceras gifuense Niko, 2016,thetype figs 16‒19; Kolebaba 1975, p. 389, pl. 1, figs 1‒4, pl. 2, species of the pseudorthoceratid genus Bandoceras Niko, figs 1‒6, pl. 3, figs 1‒6, pl. 4, figs 1‒3, text-fig. 4.1‒6) in 2016, from the Hitoegane Formation of the Hida-Gaien having a greater conch curvature with a lower expansion Belt, Central Japan, but the exogastric conch curvature and angle (approximately 4 versus 6‒7 in C. capillosum) transverse surface ornamentation developed in Bandoceras and a more eccentric position of the siphuncle. The new are not recognized in the species from Langkawi. species can be separated from Caliceras spinari Kole- baba, 1975 (p. 390, pl. 4, figs 5, 6, text-fig. 5.1‒7) by having much shorter camerae. The Kopaninoceras Fauna and its palaeobiogeography Family Geisonoceratidae Zhuravleva, 1959 Genus Murchisoniceras Babin, 1966 Nine species of orthocerid cephalopods from the Upper Type species. Orthoceras murchisoni Barrande, 1868. Setul Limestone are described. Among the genera of this latest Silurian fauna, Michelinoceras is a cosmopolitan Remarks. Murchisoniceras was originally included in genus distributed widely in North America, Europe, Asia the family Geisonoceratidae by Babin (1966). Subse- and Australia (e.g. Sweet 1964). The global occurrences quently, it was relocated to the family Flowerinidae by of the other genera – Kopaninoceras, Orthocycloceras, Zhuravleva & Doguzhaeva (2004) based on the observa- Arionoceras and Caliceras – are indicated on the palaeo- tion that episeptal deposits in the specimen of Orthoceras geographical map (Fig. 7). Their distributions appear to murchisoni illustrated by Barrande (1868, pl. 321, figs 6, have been more or less confined to the Prototethys margin, 10), the type species of Murchisoniceras, pass through the or to northern peri-Gondwana, during the late Silurian. septal foramen into cameral deposits in more posterior It is noteworthy that the Silurian cephalopod fauna of chambers and are fused with hyposeptal deposits. How- Langkawi in the Shan-Thai Block shares affinities in com- ever, these calcareous deposits in Barrande’s specimen position with faunas found widely in North Africa (Tindouf appear uniform, implying secondary precipitation, and Basin and Anti-Atlas Range), Variscan Europe (Armorican lack any internal structure. We consider, therefore, that Massif, Montagne Noire, Sardinia, Carnic Alps, Graz the deposits are unlikely to be biogenic but are more likely Palaeozoic, Prague Basin and Uppony Mountains), Baltica sedimentary. Because of this uncertainty, we do not (northern Urals and erratic boulders in Poland), Central accept the transfer of Murchisoniceras to Flowerinidae. Asia (Kazakhstan, Uzbekistan and Tajikistan), southern Afghanistan, western Tibet (Rutog), southern Tibet (Nya- Murchisoniceras? sp. lam), western Yunnan (Baoshan and Tenchong blocks), (Fig. 5G, J) South China and Japan. These cephalopod assemblages are Late Silurian cephalopods from Langkawi, Malaysia 607

Figure 7. Late Silurian palaeogeographical reconstruction (based on Scotese & McKerrow 1990; Scotese 2001; Cocks & Torsvik 2013), showing the distribution of the Kopaninoceras Fauna with the occurrences of Kopaninoceras, Orthocycloceras, Arionoceras and Calice- ras. Locality numbers: 1, Langkawi (this report); 2, western Yunnan (Tenchong and Baoshan blocks); 3, Nyalam country (southern Tibet in the northern India block); 4, Rutog Country, western Tibet; 5, southern Afghanistan; 6, Kurosegawa Belt of Japan; 7, Qujing and Nin- glang countries of eastern Yunnan (South China); 8, Carnic Alps, Graz Palaeozoic, Prague Basin and Uppony Mountains; 9, Sardinia; 10, Armorican Massif and Montagne Noire; 11, Tindouf Basin and Anti-Atlas Range; 12, Podolia; 13, northern Urals; 14, Kazakhstan; 15, Fergana and Isfara (Uzbekistan and Tajikistan). Tectonic block abbreviations: ST, Shan-Thai (Sibumasu); SC, South China; IC, Indochina; A, Argo.

characterized by the chief occurrence of Kopaninoceras in the Kurosegawa Belt indicates low latitudes at 5–15 in association with Michelinoceras, Orthocycloceras, Ariono- the northern hemisphere (Shibuya & Sasajima 1981). The ceras and Caliceras; hence, they are defined as the Kopani- Kurosegawa Belt is interpreted to have formed as an noceras Fauna. The main habitats of this fauna are island arc on the northern margin of South China during interpreted to have been distributed along the northern the middle Palaeozoic (Yoshikura et al. 1990; Hada & (African to Asian) shelf margin of Gondwana and around Yoshikura 1999; Cocks & Torsvick 2013). Taking these the Prototethys Ocean during the late Silurian (Fig. 7). into consideration, the Yokokurayama fauna appears to Of particular interest are strong similarities between the represent the northernmost occurrence of the Kopaninoce- Silurian cephalopods of Langkawi and the Japanese ras Fauna, which possibly had links with other faunal sta- Kurosegawa Belt: their similarities are notable in familial tions in peri-Gondwana (Fig. 7). and generic compositions and the moderate level of diver- The distribution of the Kopaninoceras Fauna further sity. The late Silurian cephalopod fauna of the Yokokur- reveals that the cephalopod faunas of Kazakhstan and ayama Group (Kurosegawa Belt) documented by adjacent areas (Uzbekistan and Tajikistan) in Central Asia Kobayashi (1984) and Niko et al.(1989) includes: the have closer affinities with peri-Gondwanan faunas than orthoceratids Michelinoceras alticameratum Kobayashi, with Baltica or Siberia (Fig. 7). A similar distributional 1984 (? D M. mizobuchii Kobayashi, 1984), Kopaninoce- pattern was previously pointed out by Fortey & Cocks ras kobayashii Niko et al., 1989, Leurocycloceras? sp. (2003), based on Siluro–Ordovician benthic faunas, and Orthocycloceras gomiense Kobayashi, 1984 (? D O. including brachiopods and trilobites. Fortey & Cocks aff. gomiense); the arionoceratid Arionoceras densiseptum (2003) then suggested that these Central Asian terranes Kobayashi, 1984; and the geisonoceratids Protokionoce- were likely located much closer to Gondwana during the ras fessicancellatum Kobayashi, 1984 and a geisonocera- early Palaeozoic. This view, which we share, should be tid gen. et sp. indet. Silurian palaeomagnetic data from further tested. We nevertheless place these Kazakh 608 S. Niko et al. terranes in question on the western side of the Prototethys Barskov, I. S. 1966. [Cephalopods of Late Ordovician and Silu- following more general reconstructions (e.g. Scotese rian of Kazakhstan and Middle Asia]. Avtoreferat Dissertat- 2001). sii na Soiskanie Uchenoi Stepeni Kandidata Geologo- Mineralogicheskikh Nauk. Izdatel’stovo Moskovskogo Uni- versitete, Moscow, 200 pp. [in Russian.] Barskov, I. S. 1972. [Late Ordovician and Silurian cephalopod Acknowledgements molluscs of Kazakhstan and Middle Asia]. Akademia Nauk SSSR, Moscow, 112 pp. [in Russian.] € Barskov, I. S. & Kiselev, G. N. 1970. [Revision of some Silu- Many thanks to Christian Klug (University of Zurich) and rian Michelinoceratinae (Cephalopoda, Orthocerida)]. Pale- David Evans (Natural England) for their helpful com- ontologicheskii Zhurnal, 1970(3), 66‒70, pl. 3. [in Russian.] ments on the original manuscript. Local support was Chen, J. 1975. [Fossil nautiloids from the Mount Jolmo Lungma ‒ ‒ gained from the Langkawi Development Authority Region]. Pp. 268 294, pls 1 9 in Tibetan Scientific Expedition Team,AcademiaSinica(ed.)Report of scientific expedition in (LADA). 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