Lower and Middle Ordovician Conodonts from the Thung Song and Thung Wa Areas, Southern Peninsular Thailand

Paleontological Research, vol. 10, no. 3, pp. 215–231, September 30, 2006 6 by the Palaeontological Society of Japan

Lower and Middle Ordovician conodonts from the Thung Song and Thung Wa areas, southern peninsular Thailand

SACHIKO AGEMATSU1, KATSUO SASHIDA1, SIROT SALYAPONGSE2 AND APSORN SARDSUD2

1Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki, 305-8572, Japan (e-mail: [email protected]) 2Geological Survey Division, Department of Mineral Resources, Rama VI, Bangkok, 10400, Thailand

Received September 12, 2005; Revised manuscript accepted May 18, 2006

Abstract. Lower and Middle Ordovician conodonts from the Thung Song Group, in the Thung Song and Thung Wa areas of southern peninsular Thailand, are described and illustrated here for the ﬁrst time. These conodonts are divided into faunas A, B, and C, which are middle to late Arenigian, middle Arenigian to Darriwilian or Caradocian, and late Arenigian to early Caradocian, respectively. Fauna A resembles faunas in Australia, South China, the Argentine Precordillera, and North America. Fifteen species belonging to twelve genera were studied systematically.

Key words: conodont, Ordovician, Thailand, Thung Song, Thung Wa

Introduction north and Sra (or Sa) Kaeo-Chanthaburi to the south (Figure 1). Lower Paleozoic to Cenozoic sedimentary The Ordovician Thung Song Group (Bunopas, rocks on a Precambrian basement are widely present 1981, 1992; Wongwanich et al., 1990) of southern in the Shan-Thai Block. Bunopas (1992) divided these peninsular Thailand consists mainly of argillaceous sedimentary rocks into five stratigraphic belts, desig- limestones, which are locally well exposed, form con- nated BS-1 to BS-5 (Figure 1). The Lower to Middle spicuous karst topography, and contain several index Paleozoic strata of BS-3, in which the present study macrofossils. Although this area is one of the strato- sections are located, consist of the following three types for the Lower Paleozoic in Thailand (Wongwa- stratigraphic units (Bunopas, 1992): the Cambrian nich et al., 1990), its lithostratigraphy and chronostra- Tarutao Group, the Ordovician Thung Song Group, tigraphy have not been fully studied. Furthermore, and the Silurian to Devonian Thong Pha Phum detailed correlation of this group within southern pen- Group. The Thung Song Group, the type locality of insular Thailand has not yet been undertaken. During which is in the Thung Song area, Nakorn Sri Tham- our field work in March of 2003, we collected sixteen marat Province, mainly comprises carbonate rocks limestone samples in the Thung Song and Thung Wa (Javanaphet, 1969) with sporadic macrofossils such as areas to extract conodonts. We recovered twelve gen- trilobites, brachiopods, and orthoceratid nautiloids era and sixteen species of Ordovician conodonts and (Kobayashi and Hamada, 1964; Hamada, 1964; Stait have established three conodont zones in this area. and Burrett, 1984; Cocks et al., 2005). Wongwanich Most of these conodonts are reported for the first et al. (1990) subdivided the Thung Song Group in this time in Thailand. This study describes the conodonts area into the Khao Ngiap Limestone, Khao Nui Lime- and discusses the correlation of the conodont faunas. stone,andthePaKaeFormation, in ascending order. Cocks et al. (2005) reviewed the Ordovician sequences Geologic setting distributed in the southern peninsular Thailand, and temporarily termed these rocks, in ascending order, The geologic framework of Thailand consists of two the Thung Song Limestone, the Satun Shale, and the principal elements, the western Shan-Thai and eastern Pa Kae Formation. The composition of the Thung Indochina blocks (Bunopas, 1981). According to Bu- Song Group is complicated because continuous sec- nopas (1981), these two blocks have a suture zone be- tions comprising the lower to upper Thung Song tween them, which is called the Nan-Uttradit to the Group have not yet been observed, and only parts of 216 Sachiko Agematsu et al.

tions of quartz grains. Fossils were not observed in thin section samples. We collected nine samples from the thickly bedded limestone.

TUW 1 section This section is located along a road about 10 km northeast of Thung Wa City (7100808N, 99460 509E) and is composed of thickly bedded limestones, some several tens of cm thick. Limestones of this section strike N20E and dip 15 to S, total about 20 m thick, are brownish gray, and are characterized by a stylolitic texture parallel to the bedding plane. The limestones consist of lime mudstone to wackestone, based on microscopic observation. Fine-grained clasts of ostracods, gastropods and bivalves, and silt-sized to very ﬁne-grained quartz are contained in a micritic matrix. The stylolitic texture consists of veins of dolo- mitized micrite. We collected six samples from this section.

TUW 2 section This section is located about 6 km east of Thung Wa City, and most of its lithological features coincide with those of the TUW 1 section. The limestones are dark gray and strike N30E and dip 45 to S. The total Figure 1. 1, Index map showing the study areas and strati- thickness of this section is about 80 m, and we col- graphic belts on the Shan-Thai Block of Thailand by Bunopas lected eight samples from it. The microscopic charac- (1992). 2, Index map showing the two studied sections (TUW 1 and TUW 2). teristics of these limestones are similar to those of the TUW 1 section. the Ordovician rocks are exposed locally. In this Conodont faunas paper, we provisionally use ‘‘Thung Song Group’’ as the Ordovician limestone discussed here. We attempted to extract conodont specimens from 23 samples in the three sections by using acetic acid, Study sections and separated specimens from residues with a heavy liquid (sodium polytungstate). Conodonts were recov- Ordovician conodonts have been recovered from ered from nearly all samples, although the abundance three sections, the TUS section in the Thung Song of specimens was low. Most of the conodonts are coni- area, and the TUW 1 and TUW 2 sections in the form elements, and are black, with a Color Alterna- Thung Wa area (Figure 1). The location and lithostra- tion Index of 5 (Epstein et al., 1977). We selected five tigraphy of each section are described below. samples from the TUS section, three from the TUW 1 section and eight from the TUW 2 section for our TUS section study; the conodonts in the other samples were not This section is located on the roadside about 10 km well preserved and contained too few specimens to southeast of Thung Song City (8000420N, 99440 identify. In total, we identified twelve genera and fif- 590E) and is characterized by repetitions of bedded teen species of conodont in these three sections (Fig- limestone with several-mm to 1-cm-thick laminations, ures 2–4, Table 1). These conodonts are divided into and thickly bedded limestone several tens of cm thick. faunas A, B, and C. Fauna A consists of conodonts The total thickness of this section is 30 m. These lime- from the samples TW-15, 16, and 17 in the lower part stones are pale gray and strike N30E and dip 35 to of the TUW 2 section. Conodonts of fauna B are ob- N. Under microscopic observation, this limestone is a tained from the samples TW-10, 11, 12, 13, and 14 in lime mudstone with silt- to very fine-sand sized quartz the middle to upper part of the TUW 2 section. Con- in a micritic matrix. Laminations consist of aggrega- odonts from the TUS section constitute fauna C. Ordovician conodonts from Thung Song 217

Figure 2. Columns of studied three sections showing the stratigraphic distribution of conodonts.

Fauna A 1981), Protoprioniodus yapu Cooper, 1981, Cooper- Fauna A includes relatively abundant specimens ignathus aranda (Cooper, 1981), Periodon sp., Proto- and consists of eight species of conodont, Protopan- panderodus leonardii Serpagli, 1974, and Erraticodon derodus gradatus Serpagli, 1974, Paroistodus originalis patu Cooper, 1981. C. nyinti, P. yapu, C. aranda,and (Sergeeva, 1963), Cooperignathus nyinti (Cooper, P. leonardii are known to have short stratigraphic

V Figure 3. SEM photos of conodonts. Scale bar indicates 100 mm. 1, 2. Protopanderodus leonardii Serpagli, lateral and aboral views of the a/b element, IGUT-ag1826, ag1838, sample TW-15. 3, 4. Panderodus nogamii (Lee). 3, lateral and aboral views of the f element, IGUT-ag1796, sample TS-5; 4, posterior and aboral views of the a element, IGUT-ag1798, sample TS-10. 5, 6. Walliserodus costatus Dzik. 5, lateral and aboral views of the symmetrical a/b element, IGUT-ag1799, sample TW-2; 6, lateral and aboral views of the asymmetrical a/b element, IGUT-ag1800, sample TW-2. 7, 9–11. Acodus sp. 7, lateral and aboral views of the b element, IGUT-ag1805, sample TW- 10; 9, lateral and aboral views of the f element, IGUT-ag1804, sample TW-10; 10, lateral and aboral views of the e element, IGUT-ag1801, sample TW-10; 11, posterior and aboral views of the c element, IGUT-ag1802, sample TW-10. 8. Scolopodus sp., postero-lateral and aboral views of IGUT-ag1795, sample TS-5. 12, 13. Periodon aculeatus Hadding. 12, lateral and aboral views of the a element, IGUT-ag1807, sample TW-10; 13, lateral and aboral views of the e element, IGUT-ag1809, sample TW-13. 14, 15. Periodon sp. 14, lateral and aboral views of the b element, IGUT-ag1839, sample TW-16; 15, lateral and aboral views of the b element, IGUT-ag1837, sample TW-15. 16– 20. Paroistodus originalis (Sergeeva). 16–18, lateral and aboral views of the q element, IGUT-ag1814, 1831, 1822, sample TW-15; 19, 20, lateral and aboral views of the r element, IGUT-ag1834, 1828, sample TW-15. 21–23. Triangulodus larapintinensis (Crespin). 21, lateral and aboral views of the e element, IGUT-ag1810, sample TW-13; 22, lateral and aboral views of the f element, IGUT-ag1813, sample TW-14; 23, lateral and aboral views of the a element, IGUT-ag1812, sample TW-14. 24. Oistodus sp., lateral and aboral views, IGUT- ag1806, sample TW-10. 25. Erraticodon sp., lateral and aboral views of the b element, IGUT-ag1797, sample TS-8. 26. Erraticodon patu Cooper, aboral view of the f element, IGUT-ag1816, sample TW-15. 218 Sachiko Agematsu et al.

Figure 3. Ordovician conodonts from Thung Song 219

Figure 4. 220 Sachiko Agematsu et al.

Table 1. List of conodonts obtained from the TUS, TUW 1 and Fauna B TUW 2 sections. Number indicates the number of element recov- Fauna B is composed of Protopanderodus gradatus, ered from each 1 kg sample. Acodus sp., Triangulodus larapintinensis (Crespin, 1943), Periodon aculeatus Hadding, 1913, and Oisto- dus sp. P. aculeatus has been reported from the Areni- gian, Darriwilian, and Caradocian strata in North America (Sweet and Bergstro¨ m, 1962; Bradshaw, 1969; Barnes and Poplawski, 1973; Landing, 1976; Stouge, 1984; Johnston and Barnes, 1999, 2000; Pyle and Barnes, 2003), Sweden (Hadding, 1913; Lind- stro¨ m, 1955; Lo¨ fgren, 1978), Poland (Dzik, 1976, 1994), Scotland (Armstrong, 1997), Argentina (Alba- nesi, 1998), and China (Wang and Luo, 1984; Wang and Bergstro¨ m, 1999a; Wang and Qi, 2001). T. larapintinensis has been known from New South Wales, the Georgina Basin, and the Amadeus Basin in Aus- tralia, and indicates a middle Arenigian age (Cooper, 1981; Stait and Druce, 1993; Zhen et al., 2003b). Oisto- dus sp. has been reported from several areas of North America (Sweet and Bergstro¨ m, 1962; Bergstro¨ mand Sweet, 1966; Webers, 1966), Britain (Rhodes, 1953), Norway (Hamar, 1964), Sweden (Lo¨ fgren, 1978, 2003), Poland (Dzik, 1994), and Estonia (Viira et al., 2001). This species is known from lower Darriwilian to Ashgillian. These lines of biostratigraphic evidence imply an age for the fauna B of middle Arenigian to Darriwilian or Caradocian (Figure 2). The TUW 1 section yields a few conodont specimens, which are identiﬁed as Protopanderodus gradatus and Walliserodus costatus Dzik, 1976 (Table 1). P. gradatus is a predominant species both of the faunas AandB.W. costatus is present in the middle part of the TUW 1 section. This species was originally described by Dzik (1976) from the lower Darriwilian strata in the Mo´ jcza Limestone in Poland, and it has rather a short stratigraphic range. W. costatus also has been reported from the upper Arenigian in Swe- den (Lo¨ fgren, 1978) and from the upper Arenigian to ranges, middle to late Arenigian, in Australia and lower Darriwilian in Argentina (Albanesi, 1998; Alba- Argentina (e.g., Cooper, 1981; Albanesi et al., 1998, nesi et al., 1998). Based on these biostratigraphic 2004). Therefore, the age of fauna A is inferred to be occurrences, the age of the fauna from the TUW 1 sec- middle to late Arenigian (Figure 2). tion is inferred to be late Arenigian to early Darriwi-

U Figure 4. SEM photos of conodonts. Scale bar indicates 100 mm. 1–5. Protoprioniodus yapu Cooper. 1, 2, lateral and aboral views of the f element, IGUT-ag1835, ag1820, sample TW-15; 3, 4, posterior and aboral views of the g element, IGUT-ag1821, ag1832, sample TW- 15; 5, posterior and aboral views of the b element, IGUT-ag1824, sample TW-15. 6–11. Cooperignathus nyinti (Cooper). 6, 7, anterior and aboral views of the e element, IGUT-ag1825, ag1818, sample TW-15; 8, 9, lateral and aboral views of the f element, IGUT-ag1833, ag1830, sample TW-15; 10, lateral and aboral views of the c element, IGUT-ag1819, sample TW-15; 11, lateral and aboral views of the b element, IGUT-ag1836, sample TW-15. 12–15. Cooperignathus aranda (Cooper). 12, 13, anterior and aboral views of the e element, IGUT-ag1829, ag1827, sample TW-15; 14, lateral and aboral views of the c element, IGUT-ag1815, sample TW-15; 15, lateral and aboral views of the b element, IGUT-ag1817, sample TW-15. 16–19. Protopanderodus gradatus Serpagli. 16, lateral and aboral views of the a/b element, IGUT- ag1811, sample TW-13; 17, lateral and aboral views of the a/b element, IGUT-ag1803, sample TW-10; 18, lateral and aboral views of the c element, IGUT-ag1808, sample TW-12; 19, lateral and aboral views of the e element, IGUT-ag1823, sample TW-15. Ordovician conodonts from Thung Song 221 lian and corresponds with that of the fauna B from the all of which are contained in fauna A in this study. TUW 2 section (Figure 2). However, it is difﬁcult to The Coolibah Formation in the Georgina Basin yields correlate these faunas in detail due to the small size a conodont fauna comparable to that of the Horn Val- of the collection from the TUW 1 section. ley Siltstone, including several index species such as C. aranda (¼ P. nyinti)andParoistodus originalis (Stait Fauna C and Druce, 1993). Zhen et al. (2003b) reported two Fauna C is also composed of a few specimens of conodont faunas, the Mount Arrowsmith and Koo- three species of conodont. However, we distinguish nenberry faunas, from the Tabita Formation, western fauna C from faunas A and B, because fauna C does New South Wales. These faunas share several species, not share any species with the other faunas. The fauna C. aranda, C. nyinti, E. patu, Protopanderodus grada- C consists of Panderodus nogamii (Lee, 1975), Scolo- tus, Protopanderodus leonardii,andP. yapu,withthe podus sp., and Erraticodon sp. P. nogamii has been re- fauna A. P. leonardii has been reported from the Hen- ported from several areas of Gondwana, including sleigh Siltstone in New South Wales (Zhen et al., Korea, Malaysia, Australia, and Argentina, ranging 2003a), and this species is present in fauna A. How- from Darriwilian to early Caradocian (Cantrill and ever, fauna A does not yield Juanognathus variabilis Burrett, 2003). Albanesi (1998) and Albanesi et al. Serpagli, 1974 and Acodus comptus (Branson and (1998) showed that P. nogamii ranges from late Areni- Mehl, 1933), which are dominant species of the Hen- gian to early Darriwilian in Argentina. We cannot sleigh Siltstone. Therefore, the age of fauna A corre- state a precise age for this zone, but tentatively place lates with that of the Horn Valley Siltstone, the Cool- it in the late Arenigian to early Caradocian (Figure 2). ibah Formation, and the Tabita Formation (Figure 5). The conodont fauna of the Hensleigh Siltstone is Correlations slightly older than fauna A. Faunas B and C consist of only a few specimens and Argentine Precordillera their ages range through a relatively long stratigraphic Most of the conodont species in fauna A of this interval. Therefore, we will discuss only the correla- study are known from the San Juan Formation in the tion of fauna A here. Argentine Precordillera (Serpagli, 1974; Albanesi, Regional correlations within Thailand and Malaysia 1998; Albanesi et al., 1998, 2004). The Arenigian con- To date, Lower and Middle Ordovician conodont odont biostratigraphy of the San Juan Formation is faunas have been reported from the Thong Pha shown in Figure 5. Albanesi et al. (1998) reported Pro- Phum area in western Thailand (Agematsu et al., topanderodus gradatus and Paroistodus originalis from 2006), the Satun area (Agematsu et al., in press) the Yanso section in the Argentine Precordillera. and Tarutao Island (Teraoka et al., 1982) of southern These species have relatively long stratigraphic distri- peninsular Thailand, the Peris area in peninsular Ma- butions ranging from the Prioniodus elegans to L. var- laysia (Metcalfe, 1980) and from the Langkawi Is- iabilis zones and the Oepikodus evae to L. variabilis lands, Malaysia (Igo and Koike, 1967) (Figure 1). zones, respectively. Protopanderodus leonardii,which However, conodont faunas from these areas do not has a somewhat older age, is reported from the Parois- contain species in common with fauna A of this study. todus proteus to O. evae zones by Albanesi et al. Based on several lines of previously reported faunal (1998), and from the Prioniodus elegans to Baltonio- evidence (Igo and Koike, 1967; Metcalfe, 1980; Ter- dus navis zones by Serpagli (1974). According to Al- aoka et al., 1982; Agematsu et al., 2006, in press), banesi et al. (2004), P. originalis, P. gradatus, P. leo- most of the faunas from the Tarutao Islands and the nardii,andCooperignathus aranda occur from the Perlis area are older than fauna A, and the faunas Niquivil section in the Argentine Precordillera. Strati- from the Thong Pha Phum area, the Satun area, and graphic distribution of P. originalis and P. gradatus the Langkawi Islands are younger than fauna A. ranges from the O. evae to Tripodus laevis zones. P. leonardii is known from the Pariostodus proteus to Australia Oepikodus intermedius zones. C. aranda is restricted An early to middle Arenigian conodont fauna, which in its stratigraphic range to an interval from the upper- has been reported from the Horn Valley Siltstone most part of the O. evae Zone to the lower part of the in the Amadeus Basin (Cooper, 1981), includes Coop- T. laevis Zone. To sum up, the age of fauna A of this erignathus aranda (¼ Protoprioniodus aranda Cooper, study corresponds to that of the uppermost part of the 1981), C. nyinti (¼ Protoprioniodus nyinti Cooper, O. evae Zone and the O. intermedius Zone of the San 1981), Eratticodon patu,andProtoprioniodus yapu, Juan Formation (Figure 5). 222 Sachiko Agematsu et al.

Figure 5. Age of the fauna A, B, and C in the Thung Song and Thung Wa areas and Ordovician conodont zones in Australia, Ar- gentine Precordillera, South China, Newfoundland, and North American Midcontinent.

South China costatus van Wamel, 1974) was reported by An et al. The fauna A of this study contains several species in (1985). This species occurs mainly in the Oepikodus common with South China. Conodont zones estab- evae Zone. Therefore, fauna A can be correlated lished in South China by Wang et al. (1996) are shown with the O. evae Zone in South China. in Figure 5. Protopanderodus gradatus and Parois- todus originalis are known from a relatively long North America interval, Arenigian to Darriwilian (An et al., 1985; The fauna A of this study includes several species, Wang et al., 1996). Hubei is a representative area for which are common to faunas from Newfoundland (Ji the conodont fauna of the South China Province, and Barnes, 1994; Pohler, 1994; Johnston and Barnes, from which Cooperignathus aranda (as Oelandoudus 1999, 2000). Conodont biostratigraphy of the Cow Ordovician conodonts from Thung Song 223

Head Group in Newfoundland by Johnston and 1981; Zhen et al., 2003b), South China (An et al., Barnes (1999) is shown in Figure 5. Protopanderodus 1985), and the peri-Lanrentia areas (Johnston and gradatus, Paroistodus originalis,andProtopanderodus Barnes, 1999, 2000). These lines of faunal evidence leonardii are reported from the Prioniodus elegans to suggest that a signiﬁcant relation between fauna A of Tripodus laevis zones (Stouge and Bagnoli, 1988; Poh- this study and faunas of the Gondwana and Laurentia ler, 1994; Johnston and Barnes, 1999, 2000). Accord- areas. ing to Pohler (1994) and Johnston and Barnes (1999, The quantity of specimens in fauna A is insufﬁcient 2000), stratigraphic distributions of Cooperignathus for a detailed correlation with faunas of other areas. aranda (¼ Protoprioniodus aranda,partly),Cooper- However, fauna A seems to have a close relation with ignathus nyinti (¼ P. aranda, partly), and Protoprio- faunas of Australia and Newfoundland. The Mt. Ar- niodus yapu (¼ P. aranda, partly) range from the rowsmith and Koonenberry Gap faunas, which are de- upper part of the Oepikodus evae Zone to the T. laevis scribed by Zhen et al. (2003b) in New South Wales, Zone. share six species, P. gradatus, P. leonardii, P. yapu, Er- Conodont faunas from the North American Mid- raticodon patu, C. aranda,andC. nyinti,withfaunaA. continent areas share several species with fauna A of All taxa of fauna A of this study, except for E. patu, this study. Conodont zones established in the North are common to contemporaneous faunas from the St. American Midcontinent areas are shown in Figure 5. Pauls Member of the Green Point Formation, Cow C. aranda (¼ New genus A, partly) and C. nyinti Head Group, western Newfoundland (Johnston and (¼ New genus A, partly) are known to occur from Barnes, 1999). Johnston and Barnes (1999) organized the upper part of the Reutterodus andius Zone to the Arenigian conodont biofacies in western Newfound- lowerpartoftheT. laevis Zone (Sweet et al., 1971; land into six paleoenvironments, namely, peritidal Repetski, 1982). Ethington and Clark (1982) and shelf, shallow subtidal shelf, deep subtidal shelf, shelf- Repetski (1982) reported P. gradatus and C. aranda edge and upper slope, proximal lower slope, and distal (¼ Protoprioniodus aranda)fromtheR. andius to lower slope. The St. Pauls Member is a representative Histiodella sinuosa zones and the upper part of the R. succession of distal lower slope, and an interval from andius Zone to the lower part of the T. laevis Zone, the upper part of the Orpikodus evae Zone to the Tri- respectively. These lines of biostratigraphic evidence podus laevis Zone of this member yields Periodon- imply that fauna A of this study is contemporary with dominated faunas (Johnston and Barnes, 1999). Al- those of the upper part of the O. evae Zone to the T. though the frequency of the predominant taxa of laevis Zone in Newfoundland and the upper part of fauna A is different from that of the St. Pauls faunas, the R. andius Zone to the lower part of the T. laevis fauna A seems to be close to the biofacies represent- Zone in North American Midcontinent. ing the most offshore paleoenvironment in western Newfoundland. Paleobiogeographc implications Among the species of fauna A, Paroistodus origina- Summary lis is a widespread species around the world. Proto- panderodus gradatus, Protopanderodus leonardii,and 1. Three faunas of Ordovician conodonts occur Cooperignathus aranda are reported from Australia from the Lower and Middle Ordovician limestones in (Cooper, 1981; Stait and Druce, 1993; Zhen et al., the Thung Song and Thung Wa areas of southern pen- 2003b), South China (An et al., 1985), Argentina (Ser- insular Thailand. The faunas, A, B, and C, are charac- pagli, 1974; Albanesi, 1998; Albanesi et al., 2004), teristic of the middle to late Arenigian, middle Areni- North American Midcontinent (Sweet et al., 1971; gian to Darriwilian or Caradocian, and late Arenigian Ethington and Clark, 1982; Repetski, 1982), and the to early Caradocian, respectively. peri-Laurentia areas (Stouge and Bagnoli, 1988; Fa˚h- 2. The lower part of the TUW 2 section, which ræus and Roy, 1993; Ji and Barnes, 1994; Pohler, yields fauna A, correlates with the Horn Valley Silt- 1994; Johnston and Barnes, 1999, 2000; Pyle et al., stone, the Coolibah Formation, and the Tabita Forma- 2003). Cooperignathus nyinti is distributed in re- tion in Australia; the uppermost part of the O. evae stricted areas, including Australia (Cooper, 1981; Zone and the O. intermedius Zone of the San Juan Zhen et al., 2003b), North American Midcontinent FormationinArgentina;theO. evae Zone in South (Ethington and Clark, 1982), and the peri-Laurentia China; upper part of the O. evae Zone to the T. laevis areas (Johnston and Barnes, 1999, 2000; Pyle et al., Zone in Newfoundland; and the upper part of the R. 2003). Protoprioniodus yapu also has been known andius Zone to the lower part of the T. laevis Zone from restricted areas, including Australia (Cooper, in the North American Midcontinent. 224 Sachiko Agematsu et al.

3. Several common species between fauna A and Cooperignathus aranda (Cooper, 1981). Zhen, Percival and Webby, faunas of other areas indicate that fauna A has a close 2003b, p. 188, 190, fig. 12a–p. Oelandodus costatus relation with the Mt. Arrowsmith and Koonenberry van Wamel, 1974. An, Du and Gao, 1985, pl. 6, fig. 20 (only). Gap faunas of New South Wales and the St. Pauls Protoprioniodus aranda Cooper, 1981, p. 175, 176, pl. 30, figs. 1, 6, 7, fauna of western Newfoundland. 10, 12; Ethington and Clark, 1982, p. 86, 87, pl. 9, figs. 27–29 (only); Fa˚hræus and Roy, 1993, p. 30, 31, text-fig. 5.21–23; Poh- ler, 1994, pl. 6, figs. 10–12; Johnston and Barnes, 2000, p. 42, pl. Systematic paleontology 6, figs. 26, 30 (only); Norford, Jackson and Nowlan, 2002, pl. 3, figs. 4–6; Pyle, Barnes and Ji, 2003, figs. 8.18, 8.19. Conodont taxa herein are only classified to genus Protoprioniodus nyinti Cooper, 1981. Stait and Druce, 1993, p. 317, and species. Genera and species are listed in alphabet- pl. 19, fig. M (only); Pyle, Barnes and Ji, 2003, figs. 8.22, 8.23 (only). ical order. Element terminology basically follows that Protoprioniodus simplicissimus McTavish, 1973. Ji and Barnes, 1994, of Barnes et al. (1979). p. 54, pl. 16, figs. 10, 11 (only).

Genus Acodus Pander, 1856 Materials.—Eight specimens; 1 a elements, 3 b ele- Type species.—Acodus erectus Pander, 1856 ments, 2 c elements, 2 e elements (IGUT-ag1815, 1817, 1827, 1829). Remarks.—The a, b, c, and e elements are recog- Acodus sp. nized in our collection. Zhen et al. (2003b) described Figures 3.7, 3.9–3.11 a, b, c, e, f, and g elements in a seximembrate apparatus of this species. The f and g elements are also re- Materials.—Four specimens; 1 c element, 1 b ele- ported from New Mexico (Repetski, 1982). However, ment, 1 e element, 1 f element (figured specimens are f and g elements are not recognized in Cooper’s listed here with IGUT number; IGUT-ag1801, 1802, (1981) collection from the Horn Valley Siltstone, 1804, 1805). which yielded more than 200 elements of this species. Remarks.—We agree with Zhen et al. (2003a), who Discussion of the apparatus of this species requires redefined the genus Acodus. Our collection contains c, more specimens of f and g elements. Although John- b, e and f elements of Acodus sp. The c, e and f ele- ston and Barnes (2000) relegated the elements of ments are similar to those of Acodus comptus (Bran- Protoprioniodus yapu to a part of an apparatus of P. son and Mehl, 1933) described by Zhen et al. (2003a). aranda (¼ Cooperignathus aranda), we follow the con- However, the b element of Acodus sp. differs from cept of Zhen et al. (2003b) that P. yapu is one of the that of Acodus comptus in the asymmetrical unit, species of the genus Protoprioniodus McTavish, 1973. which has three blade-like costae and a keeled poste- The specimen of Oelandodus costatus in An et al. rior margin. Basal margin is a trapezoid in aboral (1985; pl. 6, fig. 20) has a stout cusp with a conspicuous view. costa on the posterior face and a ledge-like costa, Occurrence.—Bed TW10 in the TUW 2 section. which is parallel to a basal margin, on the inner and outer lateral processes. On the basis of these charac- Genus Cooperignathus Zhen et al., 2003b teristics, the specimen of An et al. (1985) is identified with the e element of C. aranda. Type species.—Protoprioniodus nyinti Cooper, 1981 Occurrence.—Bed TW-15 in the TUW 2 section. Remarks.—Conodonts belonging to this genus, which is established by Zhen et al. (2003b), have a seximembrate apparatus composed of ramiform and pec- Cooperignathus nyinti (Cooper, 1981) tiniform elements with adenticulate processes. All elements have a ledge-like costa above the basal margin. Figures 4.6–4.11 Two species, C. aranda and C. nyinti are included in New genus A, Sweet, Ethington and Barnes, 1971, pl. 1, fig. 19 this genus. (only); Repetski, 1982, p. 56, pl. 27, figs. 3, 4 (only). Cooperignathus nyinti (Cooper, 1981). Zhen, Percival and Webby, 2003b, p. 184–188, figs. 10a–n, 11a–o. Cooperignathus aranda (Cooper, 1981) Protoprioniodus nyinti Cooper, 1981, p. 176, 178, pl. 29, figs. 1–8, 11, 12; Pyle, Barnes and Ji, 2003, figs. 8.20, 8.21 (only). Figures 4.12–4.15 Protoprioniodus aranda Cooper, 1981. Ethington and Clark, 1982, p. New genus A, Sweet, Ethington and Barnes, 1971, pl. 1, fig. 22 86, 87, pl. 9, figs. 24–26, 30 (only); Johnston and Barnes, 2000, (only); Repetski, 1982, p. 56, pl. 27, figs. 1–6. p. 42, pl. 6, figs. 23, 24 (only). Ordovician conodonts from Thung Song 225

Materials.—Twenty-six specimens; 4 b elements, 2 c lower part. The poor preservation of the specimen elements, 9 e elements, 11 f elements (IGUT-ag1818, prevents a species identification. 1819, 1825, 1830, 1833, 1836). Occurrence.—Bed TS-8 in the TUS section. Remarks.—Our collection contains b, c, e, and f ele- et al ments. Cooper (1981) and Zhen . (2003b) recog- Genus Oistodus (Pander, 1856) nized five and six types of elements in an apparatus of this species, respectively. The b and c elements show a Type species.—Oistodus lanceolatus (Pander, 1856) symmetry transition series by the position of an ante- riolateral process. The e element can be distinguished Oistodus sp. from that of Cooperignathus aranda byawavybasal margin in anterior and posterior views and a more Figure 3.24 acute angle, about 30, between a costa on the poste- Drepanoistodus? venustus (Stauffer, 1935). Lo¨ fgren, 1978, p. 57, pl. rior face of a cusp and a ledge-like horizontal costa on 1, figs. 9, 10. the inner and outer lateral processes. The f element is Drepanoistodus?aff.venustus (Stauffer, 1935). Lo¨ fgren, 2003, fig. 7ac (only). a crescent unit with a ledge-like costa above the basal Drepanoistodus cf. D. venustus (Stauffer, 1935). Viira, Lo¨ fgren, margin. On the basis of the size of the outer lateral Ma¨gi and Wickstro¨ m, 2001, fig. 9h. process, Zhen et al. (2003b) distinguished a g element Oistodus abundans Branson and Mehl, 1933. Rhodes, 1953, p. 294, from an f element. However, f elements have a grad- pl. 21, figs. 91, 92. ual variation in conspicuousness of their outer lateral Oistodus venustus Stauffer, 1935. Rhodes, 1953, p. 295–296, pl. 22, figs. 168–170; Sweet and Bergstro¨ m, 1962, p. 1232, pl. 168, figs. processes. Therefore, it is difficult to separate f and g 10, 11; Hamar, 1964, p. 269, pl. 3, figs. 3–6, 9, 11, text-fig. 6.10; elements in our collection. Webers, 1966, p. 34–35, pl. 2, figs. 18, 19; Bergstro¨ mandSweet, Occurrence.—Bed TW-15 in the TUW 2 section. 1966, p. 341–342, pl. 35, figs. 20, 21. ‘‘Oistodus’’ sp. A. Leslie, 2000, p. 1136, figs. 3.30–3.32. Paltodus? venustus (Stauffer, 1935). Dzik, 1994, p. 76–78, text-fig. Genus Erraticodon Dzik, 1978 12c (only).

Type species.—Erraticodon balticus Dzik, 1978 Materials.—Two specimens (IGUT-ag1806). Remarks.—According to Leslie (2000), his ‘‘Oisto- Erraticodon patu Cooper, 1981 dus’’ sp. A is similar to Oistodus venustus, but it is a Figure 3.26 different species. ‘‘O.’’ sp. A has a more strongly com- Erraticodon patu Cooper, 1981, p. 166–168, pl. 32, ﬁgs. 1–6, 8; Zhen, pressed cusp with more marked costa than O. venus- Percival and Webby, 2003b, p. 195–198, ﬁgs. 16a–k, 17a–o. tus, and is divided into two morphotypes, A1 and A2. Our specimens have a laterally compressed and con- Materials.—One specimen; 1 f element (IGUT- spicuously costate cusp. An anterobasal corner is ag1816). rounded and forms an angle of about 80.Abasal Remarks.—Our specimen conforms with the f (lon- margin turns up at a position two-thirds of the way chodiniform) element described by Cooper (1981). from the posterior end. These characteristics corre- This element is distinguished from that of Erraticodon spond to those of the type A1 of ‘‘O.’’ sp. A (Leslie, balticus by having the anterior, posterior, and lateral 2000). processes, which are of similar length and bear three Occurrence.—Bed TW-10 in the TUW 2 section. to four discrete denticles. Occurrence.—Bed TW-15 in the TUW 2 section. Genus Panderodus Ethington, 1959 Erraticodon sp. Type species.—Paltodus unicostatus Branson and Figure 3.25 Mehl, 1933

Materials.—One specimen; 1 b element (IGUT- Panderodus nogamii (Lee, 1975) ag1797). Figures 3.3, 3.4 Remarks.—The specimen of our collection is a hin- deodelliform element with a long cusp and denticulate Panderodus sp. Serpagli, 1974, p. 59, pl. 24, figs. 12, 13, pl. 30, figs. 12, 13. anterolateral and posterior processes, which are dis- Panderodus nogamii (Lee, 1975). Cantrill and Burrett, 2003, p. 410– tally broken. Cusp has keeled anterolateral and poste- 415, pl. 1, figs. 1–16; Zhang, Barnes and Cooper, 2003a, p. 16, rior costae, which connect to the processes in their pl. 5, figs. 1–5. 226 Sachiko Agematsu et al.

Parapanderodus nogamii (Lee, 1975). Watson, 1988, p. 124, 125, pl. pl. 3, fig. 15; Wang and Bergstro¨ m, 1999a, pl. 2, figs. 6, 7; Wang 3, figs. 1, 6. and Bergstro¨ m, 1999b, p. 339, 340, pl. 2, figs. 6, 11, 12; Albanesi Parapanderodus paracornuformis (Ethington and Clark, 1982). Al- and Barnes, 2000, figs. 5.20–24; Viira, Lo¨ fgren, Ma¨gi and Wick- banesi, 1998, p. 116, 117, pl. 12, figs. 8–10, 12, 13 (only), text- stro¨ m, 2001, figs. 6.l, m. fig. 9. Protopanderodus nogamii (Lee, 1975). Zhen, Percival and Webby, Materials.—Thirty-two specimens; 16 r elements, 16 2003b, p. 207, 209, fig. 23a–q. q elements (IGUT-ag1814, 1822, 1828, 1831, 1834). Protopanderodus primitus (Druce). Cooper, 1981, p. 174, 175, pl. 27, figs. 3, 4; Agematsu, Sashida, Salyapongse and Sardsud, 2006, Remarks.—The distinction of Paroistodus parallelus figs. 7.1–3. and P. originalis is still in dispute. These species have Protopanderodus? primitus Cooper, 1981. Stait and Druce, 1993, p. been distinguished from each other mainly by the 307, 308, text-figs. 13.A–C, 18.D, E, G–K. presence of longitudinal costae on lateral faces. How- Scolopodus cf. bassleri (Furnish, 1938). Igo and Koike, 1967, p. 23, ever, some researchers regard this morphological fea- pl.3,figs.7,8,text-fig.6B. Scolopodus nogamii Lee, 1975, p. 179, pl. 2, fig. 13, text-fig. 3L. ture as variation within a species (e.g., Johnston and Barnes, 2000). We consider that there is some differ- Materials.—Eight specimens; 5 a elements, 3 f ele- ence in biostratigraphic distribution between P. paral- ments (IGUT-ag1796, 1798). lelus and P. originalis, because our specimens, which Remarks.—This species has been fully described by were obtained from a single level, consist of only acos- Cantrill and Burreitt (2003). On the basis of the tate elements. Panderodus apparatus reconstructed by Sansom et al. Occurrence.—Bed TW-15 in the TUW 2 section. (1994), Cantrill and Burreitt (2003) recognized six Genus Periodon Hadding, 1913 types of element as components of the apparatus of this species: a, b, c, e, f, and g elements. The a and f Type species.—Periodon aculeatus Hadding, 1913 elements are contained in our collection. Remarks.—We follow the concept of Johnston and Occurrence. —Beds TS-5, 7, 8, 10, and 11 in the TUS Barnes (2000), who described a, b, c, e, f, and g ele- section. ments in an apparatus of a Periodon species. Genus Paroistodus Lindstro¨ m, 1971 Periodon aculeatus Hadding, 1913 Type species.—Oistodus parallelus Pander, 1856 Figures 3.12, 3.13 Remarks.—Two element forms, drepanodontiform Periodon aculeatus Hadding, 1913, p. 33, pl. 1, fig. 14; Lindstro¨ m, and oistodontiform, have been described as an appa- 1955, p. 110, pl. 22, figs. 10, 11, 14–16, 35; Sweet and Bergstro¨ m, ratus of the Paroistodus species (e.g., Lo¨ fgren, 1978). 1962, p. 1235, pl. 171, figs. 3, 9; Bradshaw, 1969, p. 1159, 1160, Lo¨ fgren (1997) subdivided drepanodontiform ele- pl. 137, figs. 1–6; Barnes and Poplawski, 1973, p. 780, 781, pl. 5, figs. 15–18; Landing, 1976, p. 636, pl. 3, figs. 3–6, 14; Dzik, 1976, ments in her huge collection into 6 types. However, figs. 34i–r; Lo¨ fgren, 1978, p. 74, 75, pl. 10, fig. 1, pl. 11, figs. 12– Johnston and Barnes (2000) redescribed a Paroistodus 26; Wang and Luo, 1984, p. 271, 272, pl. 6, figs. 10–16, pl. 9, fig. apparatus consisting of two element types, r (oisto- 32, pl. 11, fig. 5; Pohler, 1994, p. 33, pl. 4, figs. 25–27, 30–32; dontiform) and q (drepanodontiform) elements. We Armstrong, 1997, p. 774, 775, pl. 2, figs. 13–21, text-fig. 3; Alba- follow their concept in this paper, because drepano- nesi, 1998, p. 170, 171, pl. 15, figs. 16, 17, pl. 16, figs. 19, 20; Wang and Bergstro¨ m, 1999a, pl. 2, fig. 20; Johnston and Barnes, dontiform elements exhibit a gradual change of their 2000, p. 32–35, pl. 13, figs. 12, 13, 17, 18, 20–31, pl. 14, figs. 1–7, morphology and subdivision of those elements is quite text-figs. 4, 5; Wang and Qi, 2001, pl. 2, figs. 8–11; Pyle and difficult. Barnes, 2003, figs. 15.6–15.8.

Paroistodus originalis (Sergeeva, 1963) Materials.—Two specimens; 1 a element and 1 e element (IGUT-ag1807, 1809). Figures 3.16–3.20 Remarks.—The a and e elements are included in Oistodus originalis Sergeeva, 1963, p. 98, pl. 7, figs. 8, 9, text-fig. 4. our collection. Three denticles are present on the Paroistodus parallelus (Pander, 1856). Johnston and Barnes, 2000, p. 31, 32, pl. 10, figs. 10, 15–17, 20 (only). antero-basal part of the e element. The ramiform a Paroistodus originalis (Sergeeva, 1963). Lindstro¨ m, 1971, p. 48, 49, element has an acute antero-basal corner, and the figs. 8, 12; Lo¨ fgren, 1978, p. 69–71, pl. 1, figs. 22–25, text-fig. basal margins of the anterior process and the basal 28; An, Du and Gao, 1985, pl. 5, figs. 4, 5, 22; Stait and Druce, cavity form a 90 angle. On the basis of the character- 1993, p. 306, text-fig. 18.F; Lo¨ fgren, 1994, figs. 6.13–16; Lo¨ fgren, istics of Periodon flabellum (Lindstro¨ m, 1955) and P. 1995, figs. 7.u–y; Lo¨ fgren, 1997, p. 926, 927, pl. 1, figs. 13–16, 18–20, 22–33, text-figs. 5.H–O; Albanesi, 1998, p. 143, 144, pl. aculeatus, suggested by Pohler (1994) and Johnston 8, figs. 17–23, test-figs. 17, 18; Bednarczyk, 1998, pl. 1, figs. 6, and Barnes (2000), our specimens are identified with 18; Lehnert, Keller and Bordonaro, 1998, p. 56, pl. 2, fig. 10, P. aculeatus. Ordovician conodonts from Thung Song 227

Occurrence.—Beds TW-10 and 13 in the TUW 2 Protopanderodus leonardii Serpagli, 1974 section. Figures 3.1, 3.2 Protopanderodus leonardii Serpagli, 1974, p. 77–79, pl. 16, figs. 1–4, Periodon sp. pl. 27, figs. 12–16, text-fig. 18; Albanesi, 1998, p. 129, pl. 11, figs. Figures 3.14, 3.15 1–4, text-fig. 14E; Johnston and Barnes, 2000, p. 40, 41, pl. 9, figs. 22, 26–28, text-figs. 7.1, 2, 6, 9; Zhen, Percival and Webby, 2003b, p. 207, figs. 22l–r. Materials.—Four specimens; 1 a element and 3 b elements (IGUT-ag1837, 1839). Materials.—Four specimens; 4 a/b elements (IGUT- Remarks. —The two types of b (ligonodiniform and ag1826, 1838). cladognathiform) elements are included in our collec- Remarks.—Our specimens have a postero-lateral tion. However, it is impossible to assign the specimens costa on one lateral surface and are antero-posteriorly to a named species because they are poorly preserved asymmetrical. These elements correspond to an asym- and an e element is not present. metrical element of the ‘‘Acontiodus’’-like element Occurrence.—Beds TW-15 and 16 in the TUW 2 (Serpagli, 1974) and the a/b element of Johnston and section. Barnes (2000). The c and e elements of Johnston and Barnes (2000) are not recognized due to the smallness Genus Protopanderodus Lindstro¨ m, 1971 of our collection. Occurrence.—Bed TW15 in the TUW 2 section. Type species.—Acontiodus rectus Lindstro¨ m, 1955 Remarks.—We use the apparatus reconstruction of Genus Protoprioniodus McTavish, 1973 McCracken (1989) and Johnston and Barnes (2000), which includes a/b, c, and e elements. The a/b and c Type species.—Protoprioniodus simplicissimus elements form a symmetry transition series. Most spe- McTavish, 1973 cies of this genus have a trimembrate apparatus (John- Remarks.—We follow the concepts of Sweet (1988) ston and Barnes, 2000). and Zhen et al. (2003b) on this genus. An apparatus of the Protoprioniodus species has a ramiform- Protopanderodus gradatus Serpagli, 1974 pectiniform configuration of adenticulate elements. Figures 4.16–4.19 Protopanderodus gradatus Serpagli, 1974, p. 75–77, pl. 15, figs. 5–8, Protoprioniodus yapu Cooper, 1981 pl. 26, figs. 11–15, pl. 30, figs. 1a, 1b, text-fig. 17; Landing, 1976, Figures 4.1–4.5 p. 639, pl. 4, figs. 8, 9, 11, 12; Ethington and Clark, 1982, p. 84, 85, pl. 9, figs. 16, 17, 20, 21; An, Du and Gao, 1985, pl. 5, figs. 2, Oelandodus costatus van Wamel, 1974. An, Du and Gao, 1985, pl. 6, 3, 15; Stouge and Bagnoli, 1988, p. 136, 137, pl. 14, figs. 9–12; fig. 21 (only). Pohler, 1994, pl. 6, fig. 5; Albanesi, 1998, p. 128, 129, pl. 11, Protoprioniodus yapu Cooper, 1981, p. 178, pl. 30, figs. 3–5, 8, 9, 11, figs. 13–16, pl. 15, figs. 12, 13, text-fig. 14.B; Lehnert, Keller 13; Zhen, Perval and Webby, 2003b, p. 210, figs. 24a–d. and Bordonaro, 1998, p. 57, pl. 3, figs. 4, 5; Johnston and Protoprioniodus aranda Cooper, 1981. Johnston and Barnes, 2000, Barnes, 2000, p. 40, pl. 8, figs. 7–9, text-figs. 6.7–11; Zhen, Per- p. 42, pl. 6, figs. 17, 22 (only). cival and Webby, 2003b, p. 204, 207, figs. 22a–k. Materials.—Nineteen specimens; 6 b elements, 6 f Materials.—Eighty specimens; 63 a/b elements, 10 c elements, 7 g elements (IGUT-ag1820, 1821, 1824, elements, 7 e elements (IGUT-ag1803, 1808, 1811, 1832, 1835). 1823). Remarks.—Zhen et al. (2003b) divided Cooper’s Remarks.—The a/b and c elements in our collection (1981) P elements into Pa and Pb elements. These correspond to the ‘‘Scolopodus’’-like element of Ser- two elements are recognized in our collection (f and g pagli (1974), which comprises a symmetry transition elements). The f element has a cusp with a longitudi- series, and their forms change gradually. Protopander- nal costa on the outer face, which extends to a short odus cf. P. gradatus described by Johnston and Barnes outer lateral process, but the g element lacks the pro- (2000) differs from P. gradatus in that the former pos- cess. The g element is also characterized by having a sesses an asymmetrical a/b (acontiodontiform) ele- wider cusp and a shorter posterior process with an ment in its apparatus. Our specimens do not contain arched upper margin than those of the f element. The any acontiodontiform-type a/b elements. b elements are strongly laterally compressed and their Occurrence.—Beds TW-1, 2, and 3 in the TUW 1 cuspshaveaninnermidcostainclinedtotheinner section and beds TW10-17 in the TUW 2 section. side. Long, slender posterior process and short ante- 228 Sachiko Agematsu et al. rior process are adenticulated. Our b elements are Occurrence.—Beds TW-13 and 14 in the TUW 2 identical to an asymmetrical S element of Cooper section. (1981). Symmetrical c elements and e elements are not included in our collection. Genus Walliserodus Serpagli, 1974 Occurrence.—Bed TW-15 in the TUW 2 section. Type species.—Paltodus debolti Rexroad, 1967 Genus Scolopodus Pander, 1856

Type species.—Scolopodus sublaevis Pander, 1856 Walliserodus costatus Dzik, 1976 Figures 3.5, 3.6 Scolopodus sp. Walliserodus costatus Dzik, 1976, p. 421, pl. 41, fig. 2, text-figs. 14m, Figure 3.8 n; Dzik, 1978, pl. 15, fig. 7; Dzik, 1994, p. 56, pl. 12, figs. 1–6, text-fig.2a;Albanesi,1998,p.113,114,pl.14,figs.15–19,text- Materials.—Two specimens; 2 nongeniculate ele- fig. 7. Walliserodus cf. ethingtoni Fa˚hræus, 1966. Lo¨ fgren, 1978, p. 113, pl. ments (IGUT-ag1795). 4, figs. 13, 14. Remarks.—Eighteen sharp-edged costae extend from the proclined cusp to the short base. Outline of Materials.—Two specimens; 2 a/b elements (IGUT- the basal margin is oval in aboral view. Although in ag1799, 1800). form and number of costae our specimens resemble Remarks.—Dzik (1994) described three species be- Scolopodus quadratus Pander, 1856, they cannot be longing to this genus, and distinguished elements in identified further due to their poor preservation. their apparatuses into six forms. The a/b element in- Occurrence.—Beds TS-5 and 11 in the TUS section. cludes four forms, indicatingasymmetrytransitionse- ries. Symmetrical and asymmetrical a/b elements are Genus Triangulodus van Wamel, 1974 recognized in our collection. Occurrence.—Bed TW-2 in the TUW 1 section. Type species.—Paltodus volchovensis Sergeeva, 1963 Acknowledgments

Triangulodus larapintinensis (Crespin, 1943) We are grateful to W.C. Sweet for his most helpful Figures 3.21–3.23 review of the manuscript. We are much indebted to Oistodus larapintinensis Crespin, 1943, p. 231, pl. 31, figs. i.6, 9, 12, the reviewer, R.S. Nicoll, and an anonymous reviewer 13. for reading of the manuscript and offering many useful Triangulodus larapintinensis (Crespin, 1943). Stait and Druce, 1993, comments and suggestions. We would like to thank p. 315, 317, figs. 14a–c, 21d–f, h–j; Zhen, Percival and Webby, the Department of Mineral Resources of Thailand for 2003b, p. 212–216, figs. 28a–v. Trigonodus larapintinensis (Crespin, 1943). Cooper, 1981, p. 180, pl. providing facilities for our research in Thailand. The 27, figs. 5, 6, 11, 12, 16, 17; Watson, 1988, p. 129, pl. 2, figs. 12– fieldwork was funded by a grant from the Mombusho 14, 18–20, 22, 23. International Scientific Research (Number 11440148 to K. Sashida). Materials.—Three specimens; 1 a element, 1 e element, 1 f element (IGUT-ag1810, 1812, 1813). References Remarks.—We follow an apparatus reconstruction of Zhen et al. (2003b). Our collection yields a, e, and Agematsu, S., Sashida, K., Salyapongse, S. and Sardsud, A., f elements. The f element has an erect cusp, which 2006: Ordovician conodonts from the Thong Pha Phum slightly curves and twists inward. This element agrees area, western Thailand. Journal of Asian Earth Sciences, with a scandodontiform P element of Cooper (1981) vol. 26, p. 49–60. Agematsu, S., Sashida, K., Salyapongse, S. and Sardsud, A., in and Pa element of Zhen et al. (2003b). Recurved ois- press: Ordovician conodonts from the Satun area, south- todontiform e element is identified with the M ele- ern peninsular Thailand. Journal of Paleontology. ment of Zhen et al. (2003b). Although Zhen et al. Albanesi, G. L., 1998: Taxonomıá de conodontes de las secuen- (2003b) recognized Sa-Sc elements forming a symme- cias ordovicicas del Cerro Potrerillo, Precordillera Central try transition series, only one of these elements, the Sc de San Juan, R. Argentina. In,Hu¨ nicken, M. A. ed., Bio- stratigrafıá, biofacies y taxonomıá de conodontes de las se- element, which is characterized by a strongly asym- cuencias ordovicicas del Cerro Potrerillo, Precordillera metrical cusp with keeled anterior and posterior mar- Central de San Juan, R. Argentina, p. 101–249. Actas de gins, occurs in the TUW 2 section. la Academia Nacional de Ciencias, vol. 12. (in Spanish) Ordovician conodonts from Thung Song 229

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