Pragian and lower Emsian (Lower Devonian ...

Pragian and lower Emsian (Lower Devonian) conodonts from Liujing, Guangxi, South China JIAN-FENG LU, WEN-KUN QIE and XIU-QIN CHEN

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LU, J.-F., QIE, W.-Q. & CHEN, X.-Q., July 2016. Pragian and lower Emsian (Lower Devonian) conodonts from Liujing, Guangxi, South China. Alcheringa 40, 275–296. ISSN 0311-5518. Lower Devonian (Pragian and Emsian) conodonts are described from the Liujing section in Guangxi, South China, highlighting the phylogeny of early polygnathids and establishing the basis for faunal correlations with deposits throughout the world. Records of Eognathodus kuangi sp. nov. and E. nagaolingensis Xiong increase the biodiversity of the Pragian eognathodids in South China and represent intermediate stages and probably the latest eognathodids in the evolutionary succession from Eognathodus to Polygnathus. During this evolutionary succession, the degeneration of the sulcus (or the flattening of the upper platform surface) is the most important morphological change, especially in the eognathodid lineage. Polygnathus trilinearis, P. pireneae and P. sokolovi are recognized together for the first time in South China. The contemporaneous occurrences of the kitabiformis and sokoloviformis morphs of P. pireneae with P. sokolovi and their respective similarities to P. kitabicus and P. sokolovi suggest that the latter two species are phylogenetically linked with P. pireneae. Evidence from the Liujing section also favours Polygnathus probably having evolved from Eognathodus in a tropical or subtropical area. Jian-feng Lu* [lujfi[email protected]] and Xiu-qin Chen [[email protected]], Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, PR China; Wen-Kun Qie [[email protected]], Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, 39 East Beijing Road, Nanjing 210008, PR China. *Also affiliated with University of Chinese Academy of Sciences, Beijing 100049, PR China. Received 14.9.2015; revised 30.11.2015; accepted 5.12.2015. Key words: conodonts, Eognathodus, Polygnathus, phylogeny, early diversification.

THE latest Pragian and early Emsian polygnathids are fundamentally important for understanding the early evolution of polygnathids. Over the past 40 years, the phylogeny of early polygnathids has been one of the most extensively investigated topics in Devonian conodont studies, and various evolutionary models have been offered by reseachers (Philip & Jackson 1967, Klapper & Johnson 1975, Weddige 1977, Weddige & Ziegler 1979, Lane & Ormiston 1979, Bardashev 1986, Mawson 1987, Bultynck 1989, Yolkin et al. 1994, 2011, Bardashev et al. 2002, Martínez-Pérez et al. 2011, Baranov et al. 2014, Martínez-Pérez & Valenzuela-Ríos 2014). Among them, the proposal of Yolkin et al. (1994, 2008, 2011) has been widely accepted. Based on the polygnathid successions from the stratotype section (GSSP) of the lower Emsian boundary in the Kitab State Geological Reserve, Uzbekistan and Yolkin et al. (1994, 2008, 2011) proposed several phylogenetic lineages of early polygnathids, one of which was applied to form the basis of conodont zonations from the latest Pragian to the early Emsian. During the past 20 years, parts of the phylogenetic lineages of early polygnathids proposed by Yolkin et al.

© 2016 Australasian Palaeontologists http://dx.doi.org/10.1080/03115518.2016.1129490

(1994, 2008, 2011) have been documented in the Iberian Peninsula (García-López et al. 2002a, MartínezPérez et al. 2011, Martínez-Pérez & Valenzuela-Ríos 2014) and northeast Asia (Baranov et al. 2014). However, the derivation of Polygnathus Hinde, 1879 and the evolution of Polygnathus across the Pragian–Emsian boundary have rarely been discussed. Moreover, there are some important and representative regions where the evolutionary stages of early polygnathids need to be evaluated. One of these key areas is South China, which was located in the equatorial or tropical belt in the Palaeotethys (Torsvik & Cockes 2004, 2013) during the Devonian and where Lower Devonian stata crop out extensively. The definitive Pragian to early Emsian conodonts have been reported only from the Liujing section, Guangxi, within this region. This section has yielded Eognathodus nagaolingensis Xiong, 1980, E. sulcatus Philip, 1965, Polygnathus dehiscens Philip & Jackson, 1967 and P. pireneae Boersma, 1973 (Wang & Wang 1978, Ruan et al. 1979, Xian et al. 1980, Wang & Ziegler 1983, Kuang et al. 1989, Wang 1989). However, owing to the taxonomic revision of E. sulcatus and P. dehiscens, new and detailed studies are being undertaken. Recently, conodonts from the Liujing section in Guangxi, South China, were resampled and analyzed. The main goal of this study is the detailed description

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of the Pragian and Emsian conodonts from the Liujing section. Additionally, we specifically discuss the derivation of Polygnathus and early diversification of Polygnathus across the Pragian–Emsian boundary.

Geological setting and stratigraphy

and the lower part of the Najiao Formation in ascending order (Wang et al. 1964, Kuang et al. 1989, Zhong et al. 1992). The Nahkaoling Formation is divided into the Gaoling Member and the Mahuanling Member in ascending order, and is overlain conformably by the Yukiang Formation that is divided into four lithological units: the Xiayiling Member, the Shizhou Member, the Daliancun Member and the Liujing Member in ascending order. Strata from the Lianhuashan Formation up to the Xiayiling Member of the Yukiang Formation are marked mainly by sandstone, mudstone and siltstone, which are intercalated with thin beds or lens of bioclastic, argillaceous limestone in the upper part of


The Liujing section is located about 60 km to the east of Nanning, Guangxi, South China (Fig. 1). In this section, the Lower Devonian is divided into five lithological units: the Lianhuashan Formation, the Nahkaoling Formation (=the Nagaoling Formation), the Yukiang Formation (=Yujiang Formation), the Moding Formation

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Fig. 1. Composite map showing China (A), Guangxi (B), the Liujing section (C) and the global reconstruction of terranes at 400 Ma (Early Devonian: Emsian) (D, modified from Torsvik & Cocks 2013). Abbreviations: Ib, Iberia; Kz, Kazakh terranes (including the South Tien-Shan); NC, North China; SC, South China. The Kazakh terranes are shown diagrammatically, according to Torsvik & Cocks (2004, fig. 5).

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DEVONIAN CONODONTS FROM SOUTH CHINA

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the Gaoling Member. The Shizhou Member is composed mainly of mudstone and calcareous–argillaceous siltstone, intercalated with bioclastic limestone and marl in the uppermost and lowermost parts. The overlying Daliancun Member and the Liujing Member consist mainly of limestone, bioclastic limestone and marl. The Moding Formation, conformably underlain by the Yukiang Formation, is represented by grey, thick-bedded dolomitic limestone in its basal part.


Materials and methods Thirty-three limestone samples were collected from the upper part of the Gaoling Member of the Nahkaoling Formation to the lower part of the Moding Formation (Fig. 2, Table 1); they were reduced percussively and then dissolved in dilute acetic acid (5–10%). All residues were then washed, air-dried and finally handpicked using a stereo microscope. Specimens coated with gold were photographed using a scanning electron microscope in the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences. All images were further processed using Adobe Photoshop CS4. Arrows (→) in the synonymy lists indicate a morpho-lineage.

Systematic palaeontology All specimens described and illustrated herein are deposited in the collections of the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGP). Only Pa elements are described. Order OZARKODINIDA Dzik, 1976 Family SPATHOGNATHODONTIDAE Hass, 1959 Eognathodus Philip, 1965 Type species. Eognathodus sulcatus Philip, 1965. Eognathodus kuangi sp. nov. (Fig. 3A–F) 1980 Eognathodus cf. sulcatus Philip; Xiong in Xian et al., p. 83, pl. 30, figs 35–37. 1983 Eognathodus sulcatus Philip; Wang & Ziegler, pl. 1, fig. 14. Etymology. To honour Guo-dung Kuang from the Guangxi Institute of Geological Survey, in recognition of his geological research in Guangxi over more than 50 years. Holotype. NIGP 163163 from sample AGP-LJ-74 of the Gaoling Member of the Nahkaoling Formation. Paratype. NIGP 163164 from sample AGP-LJ-74 of the Gaoling Member of the Nahkaoling Formation. Material. Three Pa elements.

Fig. 2. Stratigraphical column of the Pragian–Emsian succession at the Liujing section with conodont ranges. Abbreviations: Eog, Eognathodus; Oza, Ozarkodina; Pan, Pandorinellina; Pol, Polygnathus.

Diagnosis. Representative Pa elements of Eognathodus kuangi have an elongate, narrow platform whose upper surface is remarkably flat and smooth, and a relatively

58.1 56.1 6.54 6.04 5.74 4.24 3.63 3.36 2.74 2.24 2.24 1.24 0 8.60 5.65 5.40 2.58 0 31.47 15.47 10.37 9.76 8.79 7.66

97 96 92 91 90 89 95 94 88 93 87 86 85 82 84 83 80 78 77 76 75d 75a 75 74

3 3

Eog. kuangi

2 2

Eog. nagaolingensis

8 1 1 1 1 14 15 46

3 1 1

Pan. exigua philipi

1

1

Pol. trilinearis

7

6

1

Pol. sokolovi

38

13 1 23

1

Pol. pireneae

82

4 6 1 4 6 9 9 9 6 5 10 13

Oza. prolata

7

1 2

4 1

38

1

1

1

1

Pol. nothoperbonus

1

8 4

2 3 6 3 6

Oza. midundenta

36

2 5 2 2 3 5

6 3 4 3 1

Pol. perbonus

33

5 9

3 1

3 3 2 2 1 4

Pol. excavatus excavatus

25

2 4 2 1 1 5

1 1

6 1 1

Pol. excavatus ‘114’

Table 1. Distribution and number of conodont taxa at the Liujing section. Abbreviations: Eog, Eognathodus; Oza, Ozarkodina; Pan, Pandorinellina; Pol, Polygnathus.

Total number

Metres above sample AGP-LJ-69



Sample levels (m)

Samples (AGP-LJ)


8

1

2

5

Pan. steinhornensis miae

23 14 20 9 14 11 19 20 19 12 8 24 39 2 1 14 1 37 1 1 1 1 15 20 326

Total number

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Fig. 3. A–F, Eognathodus kuangi sp. nov. NIGP 163163 (holotype), 163164 (paratype), AGP-LJ-74; A, D, upper, B, E, lower, and C, F, lateral views. G–K, Eognathodus nagaolingensis Xiong, 1981. NIGP 163161, 163162, AGP-LJ-74; G, I, upper, H, J, lower, and K, lateral views. L–P, Pandorinellina exigua philipi (Klapper, 1969). L–M, NIGP 163165, 163166, AGP-LJ-74; L, M, lateral views. N–P, NIGP 163167–163169, AGP-LJ-75; N, O, P, lateral views. Q. Pandorinellina steinhornensis miae (Bultynck, 1971). NIGP 163170, AGP-LJ-97; Q, upper view. Scale bars = 100 μm.

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wide basal cavity that gradually tapers posteriorly in the posterior half of the platform. Description. Free blade approximately one-third of total length of unit and composed of more than six laterally compressed denticles. Platform elongate, narrow, notably flat and smooth, and ornamented with two lateral marginal rows of nodes, which may be fused together to form short transverse ridges in the posterior part, and converging with the free blade at anterior end of platform (Fig. 3A, D). Posterior end of platform narrow and pointed, bearing one row of nodes. Basal cavity symmetrical or slightly asymmetrical, situated in posterior half of blade and visibly protruding laterally outside platform margins (Fig. 3B, E). Posterior half of basal cavity progressively tapers posteriorly and continues to terminus. In lateral view, platform thick; upper margin more or less straight and deflected downwards posteriorly, lower margin weakly concave (Fig. 3C, F). Remarks. Xiong (in Xian et al. 1980, pl. 30, figs 35– 37) first reported and illustrated this species from the Gaoling Member of the Nahkaoling Formation, and tentatively named it Eognathodus cf. sulcatus owing to its relatively large posterior basal cavity and the lack of the medial row of nodes. Later, Wang & Ziegler (1983, pl. 1, fig. 14) illustrated this species again from the Nahkaoling Formation but as E. sulcatus. Our specimens derive from the same interval from which Xiong (in Xian et al. 1980) and Wang & Ziegler (1983) reported this species. Eognathodus kuangi can be easily differentiated from Polygnathus trilinearis and P. zeravshanicus by its flat and smooth upper platform surface and the lack of a third row of nodes (comparing Fig. 3A, D with Polygnathus trilinearis described later). These features also make it readily distinguishable from E. sulcatus and E. kindlei Lane & Ormiston, 1979. Eognathodus kuangi closely resembles E. nagaolingensis in having a flat and smooth platform, but differs from the latter by its comparatively narrow platform and the progressively constricted posterior part of the basal cavity (comparing Fig. 3A–B with Fig. 3G–J). In contrast, the basal cavity in E. nagaolingensis is comparatively much wider and rounded, and strongly constricted in the posterior part of the blade. Moreover, in E. kuangi, the basal cavity is positioned in the posterior half of the platform and extends to its terminus, whereas the basal cavity expansion in E. nagaolingensis is restricted to the anterior 50% of the posterior half of the platform and extends as a narrow trough to the posterior end. Distribution. In Liujing, this species occurs together with Eognathodus nagaoingensis and Pandorinellina exigua philipi (Klapper 1969) in sample AGP-LJ-74 from the upper part of the Gaoling Member. Eognathodus nagaolingensis Xiong, 1980 emend. (Fig. 3G–K)

ALCHERINGA 1980 Eognathodus nagaolingensis Xiong in Xian et al., pp. 82–83, text-fig. 51, pl. 30, figs 32–34. 1989 Eognathodus sulcatus Philip; Kuang et al., pl. 34, fig 1. Material. Two Pa elements. Emended diagnosis. Representative Pa elements of Eognathodus nagaolingensis have an elongate, relatively wide platform whose upper surface is remarkably flat and smooth, and a wide and large basal cavity that is restricted mainly to the anterior portion of the posterior half of the platform and strongly constricted at the posterior end of the platform. Description. Free blade broken, only posterior part preserved. Platform elongate, relatively wide, notably flat and smooth lacking any nodes on its upper surface. Platform margins smooth or serrated, and decorated at posterior end with nodes, which may be fused to form short transverse ridges (Fig. 3G). Platform widest at its midlength, gently tapering anteriorly and posteriorly. Basal cavity symmetrical or slightly asymmetrical, and visibly protruding laterally outside platform margins, forming more or less semi-circular lobes (Fig. 3H, J). Posterior end of basal cavity strongly and abruptly constricted, continuing to the posterior end as a narrow trough. In lateral view, platform thick, with straight upper margin and weakly concave lower margin (Fig. 3K). Remarks. The holotype of Eognathodus nagaolingensis reported by Xiong (in Xian et al. 1980, text-fig. 51, pl. 30, figs 32–34) was also from the Gaoling Member of the Nahkaoling Formation at the Liujing section. According to the original description and illustrations of the holotype of this species, the platform is slightly symmetrical, wide and characteristically covered by several longitudinally arranged large nodes in the posterior half and several randomly distributed small nodes adjacent to the large ones. Moreover, the platform margins are represented by one row of nodes on each side. The holotype has a basal cavity similar to the new specimens; however, it has a total length of 1.5 mm, which is twice as long as the new material. The holotype is interpreted to be a senile specimen covered with nodes on its upper surface. Eognathodus nagaolingensis was compared with Polygnathus zeravshanicus Bardashev & Ziegler, 1992 by Bardashev et al. (2002, p. 394). However, both can be easily distinguished by the medial row of denticles that runs from the anterior to the posterior ends of the platform in P. zeravshanicus. Distribution. In Liujing, this taxon, occurring 0.9 m below the first occurrence of Polygnathus trilinearis (Cooper 1973), is considered to be Pragian in age and possibly ranges within the Eognathodus kindlei Zone.

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Pandorinellina Müller & Müller, 1957 Type species. Pandorina insita Stauffer, 1940.


Pandorinellina (Fig. 3L–P)

exigua

philipi

(Klapper

1969)

1969 Spathognathodus exiguus philipi Klapper, pp. 16–19, pl. 4, figs 30–38; pl. 5, figs 1–7. 1973 Pandorinellina exigua philipi (Klapper); Klapper in Ziegler, pp. 321–322, Ozarkodina–pl. 2, fig. 11. 1980 Pandorinellina exigua philipi (Klapper); Klapper & Johnson, p. 450. (with synonymy list) 1982 Pandorinellina exigua philipi (Klapper); Hose et al., pl. 7, figs 10–11. 1982 Spathognathodus exiguus Philip; Wang, pp. 443– 444, pl. 1, figs 10–12. non 1990 Pandorinellina exigua philipi (Klapper); Bischoff & Argent, pp. 458–459, pl. 4, figs 19–28. 1992 Pandorinellina exigua philipi (Klapper); Mawson et al., figs 9K–L, 11R, 13O. 2003 Pandorinellina exigua philipi (Klapper); Farrell, pp. 146–147, pl. 10, figs 11–19. (with synonymy list) 2003 Pandorinellina exigua philipi (Klapper); Mawson & Talent, p. 347, pl. 1, fig. 19. Material. Forty-six Pa elements. Description. Anterior third of blade composed of three to four laterally compressed denticles and remarkably higher than posterior two-thirds that are usually arched in a convex curve. Posteriormost denticle of anterior third of blade commonly the highest and most stout, with its posterior edge dropping abruptly and vertically to anterior end of posterior convex arc. Anterior third of blade slightly offset to right side. In some specimens (Fig. 3O–P), denticles above basal cavity slightly larger and higher. Lower margin of anterior third of blade straight to slightly convex, with anteriormost end highest. Lower margin of posterior third of blade slightly or distinctly arched concave. Mid-region of blade possessing two asymmetrical, rounded and laterally extended lobes. Basal cavity is restricted to area under two lobes and extending under anterior and posterior blades by a conspicuously narrow groove. In some specimens (not illustrated here), a narrow expansion of basal cavity may extend for a short distance posterior to lobes. Remarks. The position of the basal cavity, the remarkably high anterior denticles, the convex arc of the upper margin of the posterior third of the blade, the grooves under the anterior and posterior blades and the outline of the lower margins permit the assignment of our specimens to Pandorinellina exigua philipi. The aforementioned development of the groove under the posterior blade easily distinguishes P. exigua philipi from P. exigua exigua (Philip 1966).

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Distribution. According to Mawson (1987) and Mawson & Talent (2003) this taxon ranges from the Eognathodus sulcatus Zone to the Polygnathus nothoperbonus Zone. However, Farrell (2003) extended its range from the Pedavis pesavis pesavis Zone to the Polygnathus costatus patulus Zone. This subspecies has been recorded from North America (Yukon Territory, Alaska, Nevada, Arctic Archipelago), Australia and Asia (Tajikistan, South China). Pandorinellina steinhornensis miae (Bultynck 1971) (Fig. 3Q) 1971 Spathognathodus steinhornensis miae Bultynck, pp. 25–31, pl. 4, figs 13–14; pl. 5, figs 1–14, textfigs 19–21. 1980 Pandorinellina steinhornensis miae (Bultynck); Klapper & Johnson, p. 451. (with synonymy list). 1982 Pandorinellina steinhornensis miae (Bultynck); Hose et al., pl. 7, figs 12–13. 1983 ? Pandorinellina steinhornensis miae (Bultynck); Wang & Ziegler, pl. 4, fig. 13. 1995 Pandorinellina steinhornensis miae (Bultynck); Furey-Greig, pl. 1, fig. 18. 1999 ? Pandorinellina steinhornensis miae (Bultynck); Talent & Mawson, pl. 5, figs 11–12, 19–24. 1999 Pandorinellina steinhornensis miae (Bultynck); Talent et al., pl. 2, figs 4–5, 6? 2002a Ozarkodina miae (Bultynck); García-López et al., pl. 3, figs 16–17. 2007 Pandorinellina miae (Bultynck); Suttner, pp. 44–45, pl. 20, fig. 7. (with synonymy list) Material. Eight Pa elements. Description. Blade low, bearing 13–17 denticles with anteriormost part broken. Denticles subequal in size, closely spaced and laterally compressed. Cusp above basal cavity and a few denticles in anterior end of blade are somewhat larger and higher. Anterior blade usually much longer than posterior blade. Denticular height gradually diminishing posteriorly. Lower margin of blade usually straight and horizontal. Blade slightly or distinctly curved inwardly in posterior part. Basal cavity asymmetrical, cardiform and positioned posterior to midlength of blade. Posterior part of basal cavity clearly restricted and extending under posterior blade as a narrow groove. Remarks. A restricted asymmetrical basal cavity positioned posterior to the midlength, curvature of the blade posterior of the basal cavity, relatively even denticles with a prominent cusp and several prominent denticles in the anterior part of the blade allow identification of these specimens as Pandorinellina steinhornensis miae. This subspecies closely resembles P. steinhornensis steinhornensis (Ziegler 1956). However, in the latter subspecies, denticles are quite even without the

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Fig. 4. A–L, Polygnathus excavatus excavatus Carls & Gandl, 1969. A–D, NIGP 161866, 163171, AGP-LJ-85; A, D, upper, and B, C, lower views. E–H, NIGP 163172, 163173, AGP-LJ-86; F, H, upper, and E, G, lower views. I–J, NIGP 163174, AGP-LJ-90; J, upper, and I, lower views. K–L, NIGP 163175, AGP-LJ-97; K, upper, and L, lower views. M–R, Polygnathus excavatus ‘114’ Carls & Valenzuela-Ríos, 2002. NIGP 163176, 163177, AGP-LJ-86; N, Q, upper, M, R, lower, and O, P, enlarged views. Scale bars = 100 μm.

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development of a prominent cusp and a few prominent denticles on the anterior part of the blade; the outer lobe is markedly constricted posteriorly whereas the inner lobe is usually not clearly delimited posteriorly from a tapering groove.


Distribution. According to Farrell (2003, fig. 9), this taxon ranges from the lower part of the Eognathodus sulcatus Zone into the upper part of the Polygnathus inversus Zone. Zone: Australia, North America (Nevada, Alaska, Canadian Cordillera), Asia (Tajikistan, South China), Europe (Sierra de Guadarrama, Sardinia, Cantabria, Barrandian, Carnic Alps, Armorican Massif, Catalonian Coastal Ranges, Asturias) and Morocco. Family POLYGNATHIDAE Bassler, 1925 Polygnathus Hinde, 1879 Type species. Polygnathus dubius Hinde, 1879. Polygnathus excavatus excavatus Carls & Gandl, 1969 (Fig. 4A–L) 1969 Polygnathus webbi excavata Carls & Gandl, pp. 193–195, pl. 18, fig. 11. 1971 Polygnathus dehiscens Philip & Jackson; Fåhræus, pp. 677–678, pl. 77, figs 4–6, 10–12? 1976 Polygnathus dehiscens Philip & Jackson; Bultynck, pp. 61–62, pl. 11, figs 6, 8–9, 14. 1978 Polygnathus dehiscens Philip & Jackson → Polygnathus gronbergi Klapper & Johnson; Mashkova & Apekina in Kim et al., pl. 75, fig. 3. 1978 Polygnathus lenzi Klapper; Wang & Wang, pp. 340–341, pl. 41, figs 1–3?, 12–14, 24–26. 1985 Polygnathus dehiscens Philip & Jackson; Ziegler & Wang, pl. 1, fig. 1. 1986 Polygnathus dehiscens Philip & Jackson; Barca et al., pl. 29, figs 3–5. 1994 Polygnathus excavatus Carls & Gandl; Yolkin et al., pp. 150–152. (with synonymy list) 2002 Eocostapolygnathus excavatus (Carls & Gandl) alpha morphotype; Bardashev et al., text-figs 9, 14.11. 2004 Polygnathus excavatus Carls & Gandl; Slavík, p. 465, fig. 11.26–11.28?, 11.29. 2011 Polygnathus excavatus Carls & Gandl; Izokh et al., p. 51, pl. 1, figs 11–12. 2011 Polygnathus foveolatus Philip & Jackson; Izokh et al., p. 54, pl. 3, figs 21–24. 2011 Polygnathus excavatus excavatus Carls & Gandl; Martínez-Pérez et al., pp. 49–50, fig. 6a. 2014 Polygnathus arthuri Baranov et al., pp. 657–659, fig. 7G–L. 2014 Polygnathus carlsi Martínez-Pérez & ValenzuelaRíos, pp. 144–145, fig. 8e–h. 2014 Polygnathus excavatus Carls & Gandl; Baranov et al., p. 662, figs 9D, E, 11E–Q, 15A–O.

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2014 Polygnathus excavatus excavatus Carls & Gandl; Martínez-Pérez & Valenzuela-Ríos, p. 145, fig. 9m–n. 2014 Polygnathus ramoni Martínez-Pérez & ValenzuelaRíos, pp. 148, 150, 152, fig. 8i–l. 2014 Polygnathus sobolevi (Bardashev et al.); Baranov et al., p. 662, fig. 12O–S. Material. Thirty-three Pa elements. Description. Free blade high and composed of laterally compressed denticles; height decreasing gradually posteriorly (Fig. 4A, H, K). Platform asymmetrical with carina positioned near to inner side. Carina, flanked by adcarinal grooves, extending to posterior end of platform and varying from strongly fused denticles in anterior part of platform to a row of small discrete denticles in posterior part. Adcarinal grooves unequally developed, outer one being much wider, deeper and extending far more posteriorly than inner one. Platform margins more or less subparallel in anterior part and ornamented with well-developed, short transverse ridges (Fig. 4A, F, H), which are separated from carina by adcarinal grooves. Posterior part of platform (tongue) slightly or distinctly deflected inwardly and ornamented by interrupted transverse ridges (Fig. 4A, F, H, J–K). On lower side, basal cavity is asymmetrical, large and deep to moderately deep. Remarks. The clearly asymmetrical platform bearing two unequally developed adcarinal grooves and a carina positioned near to the inner platform margin easily distinguish our specimens from Polygnathus kitabicus. The tongue covered with interrupted transverse ridges in the new specimens allows them to be distinguished from P. excavatus ‘114’ Carls & Valenzuela-Ríos, 2002, whose tongue is ornamented by semi-crossed transverse ridges (comparing Fig. 4F, H with Fig. 5A, C). In addition, the latter may also have a comparatively smaller and shallower basal cavity. Specimens reported as Polygnathus arthuri and P. sobolevi Bardashev et al., 2002 by Baranov et al., 2014 from northeast Asia, and P. carlsi and P. ramoni by Martínez-Pérez & Valenzuela-Ríos (2014) from the Spanish Central Pyrenees all have a deep or moderately deep and large basal cavity, a slightly or distinctly deflected posterior part of the platform, a well-developed outer adcarinal groove, which is wider and deeper than the inner one, and a carina positioned close to the inner margin and extending to the posterior termination. Although they may differ slightly from the typical P. excavatus excavatus in the various outlines of the anterior part of the platform, we interpret them to reflect intraspecific rather than systematically informative features. More importantly, they also share the almost identical stratigraphical range with the latter. Thus, the minor differences between these species and P. excavatus excavatus suggest that taxonomic splitting of the latter is probably

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Fig. 5. A–D, Polygnathus excavatus ‘114’ Carls & Valenzuela-Ríos, 2002. A–B, NIGP 163178, AGP-LJ-88; A, upper, and B, lower views. C–D, NIGP 163179, AGP-LJ-97; C, upper, and D, lower views. E–N, Polygnathus pireneae Boersma, 1973. E–F, NIGP 75196, re-illustrated from Wang (1989, pl. 29, fig. 15); F, upper, and E, lower views. G–J, M–N, NIGP 163180, 161863, 163183, AGP-LJ-78; H, I, M, upper, and G, J, N, lower views. K–L, NIGP 163181, AGP-LJ-80; L, upper, and K, lower views. O–R, Polygnathus nothoperbonus Mawson, 1987. M–N, NIGP 161865, AGP-LJ-85; N, upper, and M, lower views. O–P, NIGP 163182, AGP-LJ-86; P, upper, and O, lower views. Scale bars = 100 μm.


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Fig. 6. A–B, Polygnathus nothoperbonus Mawson, 1987. NIGP 163184, AGP-LJ-97; A, upper, and B, lower views. C–N, Polygnathus perbonus (Philip, 1966). C–D, NIGP 161867, AGP-LJ-85; D, upper, and C, lower views. E–H, NIGP 163185, 163186, AGP-LJ-86; F, H, upper, and E, G, lower views. I–J, NIGP 163187, AGP-LJ-92; I, upper, and J, lower views. K–L, NIGP 163188, AGP-LJ-93; K, upper, and L, lower views. M–N, NIGP 163189, AGP-LJ-97; M, upper, and N, lower views. O–R, Polygnathus pireneae Boersma, 1973 sokoloviformis morph. NIGP 163190, 161864, AGP-LJ-78; O, R, upper, and P, Q, lower views. Scale bars = 100 μm.

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unnecessary, and the treatment of these supposedly separate species from northeast Asia and the Spanish Central Pyrenees as junior synonyms of P. excavatus excavatus in the present study is justified. Distribution. From the base of the Polygnathus excavatus Zone to the lower P. nothoperbonus Zone in Australia, North America (Nevada), Asia (Uzbekistan, South China, Kolyma), Europe (Spanish Pyrenees, Sierra de Guadarrama, Sardinia, Cantabria, Barrandian) and Morocco.


Polygnathus excavatus ‘114’ Carls & Valenzuela-Ríos, 2002 (Figs 4M–R, 5A–D) 1969 Polygnathus lenzi Klapper, pp. 14–15, pl. 6, figs 9–13, 16–18. 1969 Polygnathus webbi excavata Carls & Gandl, pp. 193–195, pl. 18, figs 9–10, 12–13. non 1975 Polygnathus gronbergi Klapper & Johnson, p. 73, pl. 1, figs 17–28. non 1975 Polygnathus dehiscens Philip & Jackson → Polygnathus gronbergi Klapper & Johnson; Klapper & Johnson, pl. 1, figs 9–12. 1976 Polygnathus dehiscens Philip & Jackson; Bultynck, pp. 61–62, pl. 11, figs 1–5, 10–11, 13. non 1977 Polygnathus gronbergi Klapper & Johnson; Klapper in Ziegler, pp. 449–450, Polygnathus pl. 8, figs 1, 5. 1978 Polygnathus dehiscens Philip & Jackson; Mashkova & Apekina in Kim et al., pl. 74, fig. 9; pl. 75, figs 1–2. non 1978 Polygnathus gronbergi Klapper & Johnson; Mashkova & Apekina in Kim et al., pl. 74, figs 6, 8; pl. 75, figs 4–6. 1978 Polygnathus sp. Mashkova & Apekina in Kim et al., pl. 75, fig. 8. 1978 Polygnathus lenzi Klapper; Wang & Wang, pp. 340–341, pl. 41, figs 7–9. non 1979 Polygnathus gronbergi Klapper & Johnson; Lane & Ormiston, p. 61, pl. 6, figs 6–7, 13. non 1980 Polygnathus gronbergi Klapper & Johnson; Bultynck & Hollard, pp. 42–43, pl. 2, figs 6–7. 1983 Polygnathus dehiscens Klapper & Johnson; Wang & Ziegler, pl. 5, fig. 1. 1990 Polygnathus gronbergi Klapper & Johnson; García-Alcalde et al., fig. 10.3–10.4. 1994 Polygnathus excavatus Carls & Gandl; Yolkin et al., pp. 150–152. (with synonymy list) non 2002 Eocostapolygnathus gronbergi (Klapper & Johnson) alpha morphotype; Bardashev et al., text-figs 9, 14.14. 2002 Polygnathus excavatus ssp. 114 Carls & Valenzuela-Ríos, p. 321. 2002a Polygnathus excavatus ssp. 114 Carls & Valenzuela-Ríos; García-López et al., pl. 4, figs 19–24.

ALCHERINGA 2002a Polygnathus gronbergi Klapper & Johnson; García-López et al., pl. 5, figs 15–16. 2011 Polygnathus excavatus Carls & Gandl; Izokh et al., p. 51, pl. 1, figs 13–14. 2014 Polygnathus excavatus 114 Carls & ValenzuelaRíos; Martínez-Pérez & Valenzuela-Ríos, pp. 145– 146, fig. 9m–n. 2014 Polygnathus settedabanicus Baranov et al., p. 672, fig. 14H–J. Material. Twenty-five Pa elements. Description. Free blade high and composed of laterally compressed denticles; height decreasing gradually posteriorly (Figs 4Q, 5C). Platform asymmetrical with carina positioned near to inner margin. Adcarinal grooves, which flank carina, are unequally developed, outer one being much wider, deeper and extending far more posteriorly than inner one. Platform margins more or less subparallel and ornamented with short transverse ridges, which are separated from carina by adcarinal grooves in anterior part. Posterior part of platform (tongue) slightly or distinctly deflected inwardly and ornamented by semi-crossed transverse ridges, resulting in carina and adcarinal troughs not extending to posterior end of platform (Figs 4N–Q, 5A, C). On lower side, basal cavity is asymmetrical, moderately large and deep but not inverted. Remarks. In the original diagnosis given by Klapper & Johnson (1975, p. 73, pl. 1, figs 17–28), Polygnathus gronbergi has a basal cavity which ‘is at least slightly inverted at the posterior end’. However, after examination, Yolkin et al. (1994, p. 144) argued that the posterior part of the basal cavity in P. gronbergi was not inverted but just closed, and the basal cavity started to invert at its posterior end during the evolutionary stage of P. nothoperbonus Mawson, 1987. Consequently, two paratypes of P. gronbergi (Klapper & Johnson 1975, pl. 1, figs 19–20, 23–24) were identified as P. nothoperbonus by Yolkin et al. (1994, p. 152). Moreover, they suggested that P. gronbergi should be treated as a subspecies of P. excavatus. Later, Carls & Valenzuela-Ríos (2002) pointed out the great difference in the posterior part of the basal cavity between P. excavatus gronbergi sensu Yolkin et al. 1994 and P. gronbergi sensu Klapper & Johnson 1975, and stressed that the former was phylogenetically much older than the latter. Accordingly, P. excavatus gronbergi sensu Yolkin et al. 1994 was provisionally termed P. excavatus ssp. 114 and the original diagnosis of P. gronbergi was adopted by them. Here, taxonomic treatment of P. excavatus gronbergi proposed by Carls & Valenzuela-Ríos (2002) is followed, because we agree with their opinion that the posterior part of the basal cavity in specimens illustrated as P. gronbergi by Klapper & Johnson (1975, pl. 1, figs 17–28) is clearly inverted.


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Fig. 7. A–B, Polygnathus pireneae Boersma, 1973 sokoloviformis morph. NIGP 163191, AGP-LJ-78; A, upper, and B, lower views. C–J, Polygnathus pireneae Boersma, 1973 kitabiformis morph. NIGP 161861, 163192–163194, AGP-LJ-78; C, F, G, I, upper, and D, E, H, J, lower views. K–O, Polygnathus sokolovi Yolkin et al., 1994. NIGP 163195, 161862, 163196, AGP-LJ-78; K, N, O, upper, and L, M, lower views. P–Q, Polygnathus trilinearis (Cooper, 1973). NIGP 163197, AGP-LJ-75; P, upper, and Q, lower views. Scale bars = 100 μm.

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The new specimens are similar to the representative Pa elements of Polygnathus excavatus ‘114’ in their unequally developed adcarinal grooves and the presence of a posterior part of the platform that is covered by semi-crossed transverse ridges. Distribution. From the middle Polygnathus excavatus Zone to the P. nothoperbonus Zone. Zone: North America (Alaska, Nevada, Yukon Territory), Asia (Uzbekistan, South China, Kolyma), Europe (Spanish Pyrenees, Sierra de Guadarrama, Cantabria) and Morocco.


Polygnathus nothoperbonus Mawson, 1987 (Figs 5O–R, 6A–B) 1975 Polygnathus aff. P. perbonus (Philip); Klapper & Johnson, p. 74, pl. 2, figs 1–10. 1980 Polygnathus aff. P. perbonus (Philip); Klapper & Johnson, p. 454. 1980 Polygnathus perbonus (Philip); Xiong in Xian et al., pl. 22, figs 25–28, 35–36; pl. 23, figs 9–12; pl. 31, figs 9–12. 1982 Polygnathus perbonus (Philip); Bai et al., p. 59, pl. 3, fig. 3, 6? 1983 Polygnathus aff. perbonus (Philip); Wang & Ziegler, pl. 5, figs 4–5. 1987 Polygnathus nothoperbonus Mawson, p. 276, pl. 32, figs 11–15; pl. 33, figs 1–2; pl. 36, fig. 7 (with synonymy list). 1990 Polygnathus nothoperbonus Mawson; Uyeno, p. 85, pl. 7, figs 4–5; pl. 9, figs 5–6, 13–14. 2002a Polygnathus dehiscens Philip & Jackson → Polygnathus nothoperbonus Mawson; García-López et al., pl. 5, figs 6–10. 2002b Polygnathus nothoperbonus Mawson; GarcíaLópez et al., pl. 1, figs 15–16. 2003 Polygnathus nothoperbonus Mawson; Mawson & Talent, p. 346, pl. 1, figs 1–4; pl. 2, figs 4–5. 2005 Polygnathus nothoperbonus Mawson; Jin et al., p. 62, pl. 4, figs 1–6; pl. 12, figs 1–2, 13–14. 2007 Polygnathus nothoperbonus Mawson; Kim et al., p. 263, pl. 126, figs 8–9. 2011 Polygnathus nothoperbonus Mawson; Izokh et al., p. 52, pl. 1, figs 15–17. 2011 Polygnathus nothoperbonus Mawson; MartínezPérez et al., pp. 58–59, fig. 6d–f. (with synonymy list) 2013 Polygnathus nothoperbonus Mawson; Lu, pp. 317–318, pl. 2, figs 4–8; pl. 3, figs 1–4. 2014 Polygnathus nothoperbonus Mawson; Baranov et al., pp. 668, 670, fig. 13A–L. 2014 Polygnathus yakutensis Baranov et al., pp. 672– 673, fig. 14M–N. Material. Seven Pa elements. Description. Free blade high and composed of laterally compressed denticles; height decreasing gradually posteriorly (Fig. 6A). Platform slightly or distinctly asym-

ALCHERINGA metrical with carina positioned near to inner platform margin. Anterior platform margins more or less subparallel and of equal height. Carina flanked by unequally developed adcarinal grooves, outer one being much wider, deeper and extending far more posteriorly than inner one. Platform margins ornamented with short transverse ridges, which are separated from carina by adcarinal grooves. Posterior part of platform (tongue) distinctly deflected inwardly. Transverse ridges crossing tongue are variable but usually interrupted (Figs 5R, 6A). On lower side, basal cavity is medium-sized, flat and shallow, and not inverted even at posterior end (Figs 5O, Q, 6B). Remarks. Yolkin et al. (1994) recognized two forms of this species. In the early form, the posterior basal cavity is flat or even slightly convex, whereas in the late form, the basal cavity is narrower and its posterior part is clearly inverted. In our collections, only the early form is present. Polygnathus nothoperbonus, initially named P. aff. perbonus by Klapper & Johnson (1975), can be confused with P. perbonus because both species have a medium-sized basal cavity and somewhat similar ornamentation. However, they can be distinguished by P. nothoperbonus having a shallow or flat basal cavity, which is even inverted posteriorly in the late form, whereas P. perbonus possesses a deeper and V-shaped basal cavity that is not inverted posteriorly (comparing Figs 5Q, 6B with Fig. 6C, G, J). Distribution. From the base of the Polygnathus nothoperbonus Zone to the lower part of the P. inversus Zone: Australia, North America (Arctic Archipelago, Alaska, Nevada), Asia (Uzbekistan, Tajikistan, South China, Kolyma) and Europe (SW-Harz Mountains, Armorican Massif, Spanish Pyrenees, Cantabria). Polygnathus perbonus (Philip 1966) (Fig. 6C–N) 1966 Roundya perbona Philip, p. 449, pl. 4, figs 7–8, text-fig. 6. (Sa element) 1969 Polygnathus linguiformis foveolata Philip & Jackson; Carls & Gandl, p. 196, pl. 18, figs 17–18, 22. 1971 Polygnathus dehiscens Philip & Jackson; Fåhræus, pp. 677–678, pl. 77, figs 1–3, 7–9. 1975 Polygnathus perbonus (Philip); Klapper & Johnson, p. 74, pl. 2, fig. 11–19. (with synonymy list) 1980 Polygnathus perbonus (Philip); Pickett, p. 69, text-fig. 2. 1980 Polygnathus perbonus (Philip); Xiong in Xian et al., p. 96, pl. 22, figs 15–16, 21–22, 33–34; pl. 23, figs 9–10; pl. 31, figs 9–12. 1981 Polygnathus perbonus (Philip); Wang, p. 403, pl. 1, figs 9–21, text-fig. 1. 1981 Polygnathus perbonus (Philip); Xiong, pl. 1, figs 25–26. 1982 Polygnathus perbonus (Philip); Bai et al., p. 59, pl. 3, fig. 6.


ALCHERINGA


1982 Polygnathus perbonus (Philip); Wang, p. 443, pl. 2, figs 22–24. 1983 Polygnathus perbonus (Philip); Wang & Ziegler, pl. 5, figs 2–3. 1985 Polygnathus perbonus (Philip); Ziegler & Wang, pl. 1, figs 4–5. 1989 Polygnathus perbonus (Philip); Kuang et al., pl. 34, figs 6–7. 1989 Polygnathus perbonus (Philip); Wang, p. 118, pl. 29, figs 10–14. 1992 Polygnathus perbonus (Philip); Bardashev & Ziegler, pl. 4, figs 34–37, 40; pl. 5, figs 9–10, 13–16. 1992 Polygnathus perbonus (Philip); Mawson et al., fig. 8E–K. 1994 Polygnathus perbonus (Philip); Bai et al., p. 181, pl. 16, fig. 6. 2002 Eolinguipolygnathus foveolatus (Philip & Jackson) alpha morphotype; Bardashev et al., p. 409, textfigs 10, 15.10–15.11. 2002 Eolinguipolygnathus foveolatus (Philip & Jackson) beta morphotype; Bardashev et al., p. 409, text-figs 10, 15.12. 2003 Polygnathus perbonus (Philip); Mawson & Talent, pp. 346–347, pl. 1, figs 5, 16–18; pl. 2, figs 1–3, 6. (with synonymy list) 2005 Polygnathus perbonus (Philip); Jin et al., p. 63, pl. 4, figs 7–8, 10–11; pl. 12, figs 17–18; pl. 13, figs 1–2, 5–10, 17–18. 2007 Polygnathus perbonus (Philip); Boncheva et al., fig. 5O. 2013 Polygnathus perbonus (Philip); Lu, pp. 318–319, pl. 3, figs 5–7; pl. 4, figs 1–2. 2014 Polygnathus dehiscens Philip & Jackson; Baranov et al., pp. 660–662, fig. 10A–D. 2014 Polygnathus michaelmurphyi Baranov et al., p. 668, fig. 8A–K. 2014 Polygnathus perbonus (Philip); Baranov et al., pp. 670, 672, fig. 14K–L. Material. Thirty-six Pa elements. Description. Free blade high and composed of laterally compressed denticles, its height decreasing gradually posteriorly (Fig. 6F, H, M). Platform somewhat asymmetrical with carina positioned slightly near to inner platform margin. Anterior platform margins more or less subparallel and of equal height. Carina flanked by unequally developed adcarinal grooves, outer one being much wider, deeper and extending far more posteriorly than inner one. Platform margins ornamented with short transverse ridges, which are separated from carina by adcarinal grooves in anterior part. Posterior part of platform (tongue) distinctly deflected inwardly and usually covered by crossed (locally discontinuous, Fig. 6H) transverse ridges, resulting in carina and adcarinal troughs extending only to anterior end of tongue (Fig. 6D, F, I, K, M). On lower side, basal cavity is medium-sized, deep and V-shaped.

289

Remarks. The tongue ornamented with continuous or crossed transverse ridges distinguishes Polygnathus perbonus from P. excavatus excavatus and P. excavatus ‘114’, both of which have the posterior part of the platform covered by interrupted or semi-crossed transverse ridges. For the differences between P. perbonus and P. nothoperbonus, see remarks under the latter. Distribution. From the upper part of the Polygnathus excavatus Zone into the P. nothoperbonus Zone: Australia, North America (Nevada, Yukon Territory, Michigan), Asia (Uzbekistan, Tajikistan, South China, Kolyma) and Europe (Spanish Pyrenees, west Bulgaria, Cantabria). Polygnathus pireneae Boersma, 1973 (Figs 5E–N, 6O–R, 7A–J) 1973 Polygnathus pireneae Boersma, pp. 287–288, pl. 2, figs 1–12. 1977 Polygnathus boucoti Savage, pp. 58–59, pl. 1, figs 13–16, text-fig. 2 (only). 1977 Polygnathus pireneae Boersma; Klapper in Ziegler, pp. 489–490, Polygnathus–pl. 8, fig. 6. 1977 Polygnathus sp. n. R; Al-Rawi, pp. 57–58, pl. 5, fig. 47. 1979 Polygnathus pireneae Boersma; Lane & Ormiston, p. 62, pl. 3, figs 15–17; pl. 5, figs 2–3, 9–10, 30– 34. 1980 Polygnathus pireneae Boersma; Klapper & Johnson, p. 454. 1982 Polygnathus pireneae Boersma; Murphy & Matti, pp. 39–41, pl. 1, figs 33–35, 38. 1985 Polygnathus pireneae Boersma; Norford & Orchard, pl. 3, fig. 22. 1985 Polygnathus pireneae Boersma; Savage et al., pl. 1, figs 21–26. non 1988 Polygnathus pireneae Boersma; Xiong et al. in Hou et al., pp. 316–317, pl. 119, fig. 1. 1989 Polygnathus pireneae Boersma; Wang, p. 119, pl. 29, fig. 15. 1989 Polygnathus pireneae Boersma Form B; Yolkin et al., p. 238, pl. 1, fig. 6. non 1991 Polygnathus pireneae Boersma; Uyeno, pl. 1, figs 21–22. non 1992 Polygnathus pireneae Boersma; Mawson et al., pp. 48, 51, fig. 7A–F. 1992 Polygnathus pireneae Boersma; Weyant, fig. 3. 1992 Polygnathus pireneae Boersma; Bardashev & Ziegler, pl. 4, figs 15–21. 1994 Polygnathus pireneae Boersma; Valenzuela-Ríos, pp. 73–75, pl. 9, figs 27–29. non 1999 Polygnathus pireneae Boersma; Talent & Mawson, pl. 8, figs 19, 21–22. non 2000 Polygnathus pireneae Boersma; Wang et al., pl. 1, fig. 1. 2002 Eoctenopolygnathus boersmai (Bardashev); Bardashev et al., p. 398, text-figs 9, 13.4.

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2002

Eoctenopolygnathus pireneae (Boersma); Bardashev et al., p. 400, text-figs 7, 9, 11.25, 13.3. 2002 Eognathodus trilinearis (Cooper) → Eocostapolygnathus sokolovi (Yolkin et al.); Bardashev et al., p. 394, text-figs 7, 9, 11.24, 14.4. 2002 Polygnathus pireneae Boersma–Polygnathus kitabicus Yolkin et al.; Valenzuela-Ríos, pl. 2, fig. 13. 2007 Polygnathus pireneae Boersma; Kim et al., p. 264, pl. 125, figs 1–3. 2011 Polygnathus pireneae Boersma; Izokh et al., p. 51, pl. 1, figs 1–7. 2014 Polygnathus pireneae Boersma; Martínez-Pérez & Valenzuela-Ríos, pp. 147–148, fig. 9a–d.


Material. Thirty-eight Pa elements. Description. Free blade broken in most cases with posterior part preserved and bearing several discrete laterally compressed denticles. Platform relatively broad and flat, ornamented by marginal nodes or short transverse ridges. Carina, consisting of rounded and discrete nodes, situated at the centre of platform and extending to posterior termination of platform. At posterior end of platform, carina may be fused with marginal nodes or short transverse ridges (Fig. 7A). No adcarinal grooves developed on upper platform surface, even at anterior end. Outer platform margin strongly deflected inwardly in a round and smooth curve (Figs 5E–N, 7C–J) or a distinct and sharp angularity (Figs 6O–R, 7A–B), whereas inner platform margin is usually slightly curved. Platform widest at inwardly deflected point of platform and tapering anteriorly and posteriorly. On lower side, basal cavity clearly asymmetrical, deep and broad, visibly protruding outside (Figs 6O–R, 7A–J) or reaching only (Figs 5E–N) platform margins. Remarks. Polygnathus pireneae was first described and illustrated from the Spanish Central Pyrenees by Boersma (1973). Later, this species was reported or figured by various reseachers throughout the world (see the synonymy list above) and interpreted to be the first polygnathid. According to the original description (Boersma, 1973, pp. 287–288, pl. 2, figs 1–12), P. pireneae, whose small holotype and paratypes probably represent the juvenile specimens, is characterized by a basal cavity, which only reaches the platform margins. Subsequently, when defining and describing P. kitabicus, Yolkin et al. (1994) made a descriptive comment that P. pireneae had an enlarged basal cavity whose flanks could protrude beyond the platform margins. Although the width of the basal cavity in P. pireneae is varied, the upper platform surface is completely flat or even convex without the development of adcarinal grooves, by which P. pireneae differs from its descendant P. kitabicus. Martínez-Pérez & Valenzuela-Ríos (2014, pp. 142–144, fig. 8a–d) introduced a new species, P. arogonensis, from the Spanish central Pyrenees. This species is very similar to P. pireneae in having a

ALCHERINGA comparatively flat platform and a large basal cavity, but differs from the latter mainly by the poorly developed adcarinal troughs in the anterior half of the platform, a stronger inner arch of the outer posterior platform margin and the different joint positions of the inner and outer anterior margins with the free blade. Moreover, in the Spanish central Pyrenees, P. arogonensis ranged much higher than P. pireneae from the uppermost part of the lower P. excavatus excavatus Subzone into the lower P. nothoperbonus Zone. Our specimens are included in Polygnathus pireneae based on the combination of the following characters: large and capacious basal cavity and flat upper platform surface without the development of adcarinal grooves. However, they differ from most of the figured type materials in having a relatively broad platform. Two morphotypes of this species, which were initially proposed by Izokh et al. (2011) from the Zinzilban section, Uzbekistan, are also recognized in our material from sample AGP-LJ-78: in the P. pireneae sokoloviformis morphotype (Figs 6O–R, 7A–B), there is a distinct angularity of the outer platform margin just behind its midlength; in the P. pireneae kitabiformis morphotype (Fig. 7C–J), the outer platform margin behind its midlength deflects in a round and smooth convex curve. These two morphotypes can be readily distinguished from P. sokolovi and P. kitabicus by having a broad basal cavity visibly protruding outside the platform margins. In some specimens (Figs 6Q–R, 7C–F), remains of the basal filling exist, which is also evident in specimens figured by Izokh et al. (2011, pl. 1, figs 2–4). However, it is easy to distinguish the main body from the remains of the basal filling because, in upper view, the flanks of the basal cavity appear much smoother than the basal filling and a boundary between the flanks and the basal filling can also be clearly observed. Among the new specimens, another morphotype (Fig. 5E–N) is also evident whose basal cavity only reaches the platform margins. This morphotype closely resembles the type material of P. pireneae in the outlines of the basal cavity and upper platform surface. Actually, a specimen of this morphotype had already been reported by Wang & Ziegler (1983, fig. 4) and subsequently figured by Wang (1989, pl. 29, fig. 15; herein Fig. 5E–F) as P. pireneae from the base of the Shizhou Member. Distribution. According to Izokh et al. (2011), this species ranges from the Polygnathus pireneae Zone into the lower part of the P. kitabicus Zone in the Zinzilban section. However, it extends upwards into the middle P. excavatus Zone in the Spanish central Pyrenees (Martínez-Pérez & Valenzuela-Ríos 2014). This species occurs in North America (Alaska, California, Nevada, Yukon Territory) and Asia (Uzbekistan, Tajikistan, South China) and Spainish Pyrenees.

ALCHERINGA



Polygnathus sokolovi Yolkin et al., 1994 (Fig. 7K–O) non 1969 Polygnathus linguiformis dehiscens Philip & Jackson, Flood, pl. 2, fig. 4. non 1976 Polygnathus dehiscens Philip & Jackson; Lane & Ormiston, pl. 1, figs 17–20. 1979 ? Polygnathus dehiscens Philip & Jackson; Lane & Ormiston, p. 61, pl. 5, figs 24–26, 35–36. 1994 Polygnathus sokolovi Yolkin et al., p. 152, pl. 1, figs 5–8. (with synonymy list) 2004 ? Polygnathus sokolovi Yolkin et al.; Slavík, pp. 457, 459. 2007 Polygnathus sokolovi Yolkin et al.; Kim et al., p. 265, pl. 125, figs 4–5. 2011 Polygnathus sokolovi Yolkin et al.; Izokh et al., p. 52, pl. 2, figs 1–6. (with synonymy list) 2014 ? Polygnathus sokolovi Yolkin et al.; MartínezPérez & Valenzuela-Ríos, pp. 152–153, fig. 9h. Material. Seven Pa elements. Description. Free blade broken with its posterior part preserved and bearing several discrete, laterally compressed denticles. Platform flat and narrow, ornamented by rounded nodes on inner and outer margins. Carina situated at centre of platform and extending to posterior termination of platform. Carina composed of laterally compressed and fused denticles in anterior part of platform, and degrading into a row of several rounded and discrete denticles in posterior part, which may be fused with marginal nodes to form short transverse ridges (Fig. 7N). No adcarinal grooves developed on upper platform surface, even at anterior end of platform. In one specimen (Fig. 7N), platform displaying a slight and short depression at inner anterior margin. A distinct angularity of outer platform margin developed just behind midlength (Fig. 7K, N, O); in contrast, inner margin slightly curved. Platform widest at the inwardly deflected point of platform and tapering anteriorly and posteriorly with anterior end of platform being narrowest. On lower side, basal cavity is clearly asymmetrical and deep but does not protrude outside platform margins. Remarks. The angularity of the outer platform margin, the ornamentation of the upper surface and the shape and position of the basal cavity is very similar to the holotype (Yolkin et al. 1994, pl. 1, figs 7–8) and other representative specimens of Polygnathus sokolovi (Yolkin et al. 1994, pl. 1, figs 5–6; Izokh et al. 2011, pl. 2, figs 1–6). However, differing from the holotype in which single nodes may be intercalated between marginal nodes and the carina, the new specimens lack nodes between the outer platform margin and carina on the upper platform surface (Fig. 7K, N–O). This taxon closely resembles P. kitabicus but differs in having a distinctly angular outer platform margin.

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Distribution. According to Yolkin et al. (1994) and Izokh et al. (2011), this species ranges from the uppermost Polygnathus pireneae Zone into the lower part of the P. kitabicus Zone. However, Martínez-Pérez & Valenzuela-Ríos (2014) recently reported this species to range to the lower P. excavatus excavatus Zone in the Spanish Pyrenees. The species is reported from Australia, North America (Alaska?), Asia (Uzbekistan, South China) and Spain (?). Polygnathus trilinearis (Cooper 1973) (Fig. 7P–Q) 1973 Spathognathodus trilinearis Cooper, p. 80, pl. 3, figs 1, 6, 7. 1977 Eognathodus trilinearis (Cooper); Klapper in Ziegler, p. 125, Eognathodus pl. 1, fig. 4. 1992 Eognathodus trilinearis trilinearis (Cooper); Bardashev & Ziegler, pl. 4, figs 8–13. 1992 Polygnathus trilinearis (Cooper); Mawson et al., pp. 51, 53, fig. 9A–G. 1998 Polygnathus trilinearis (Cooper); Mawson, pl. 2, figs 1–3. 1999 Polygnathus trilinearis (Cooper); Talent & Mawson, p. 75, pl. 8, figs 18, 20? 2002 Eognathodus trilinearis (Cooper) alpha morphotype; Bardashev et al., p. 394, text-figs 7, 11.19 (only). 2002 Eognathodus trilinearis (Cooper) beta morphotype; Bardashev et al., p. 394, text-figs 7, 11.21. 2002 Eognathodus trilinearis (Cooper) → Eocostapolygnathus yolkini erinae Bardashev et al.; Badashev et al., p. 394, text-figs 7, 11.22, 15.3. 2006 Eognathodus trilinearis (Cooper); Bardashev et al., pl. 1, fig. 7. Material. One specimen. Description. Free blade broken with its posterior part preserved and bearing several laterally compressed denticles. Platform elongate, symmetrical and relatively flat with three rows of nodes. Medial row linear and straight, consisting of small and discrete nodes and not extending to anterior and posterior end of platform (Fig. 7P). Two lateral marginal rows composed of small and discrete nodes in anterior half of platform and short transverse ridges in posterior half, these converging with free blade at anterior end of platform. Platform widest around its midlength and gradually tapering anteriorly and posteriorly, forming a rhombic outline. Posterior end slightly broken, apparently not pointed but relatively wide and rounded. On lower side, basal cavity is wide and asymmetrical, visibly protruding beyond platform margins and restricted to posterior three-quarters of platform (Fig. 7Q). Remarks. The general platform outline, the development of three rows of nodes, and the shape and position of

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the basal cavity allow us to assign our specimen to Polygnathus trilinearis. However, our specimen differs slightly from the holotype by having a medial row that does not extend to the posterior end of the platform and a flat platform lacking troughs, the latter of which is also evident in a specimen from southeastern Australia (Mawson et al. 1992, fig. 9E). This taxon differs from P. zeravshanicus, which possesses a thin pointed end, by having a relatively rounded posterior end bearing three rows of nodes. Distribution. According to Bardashev & Ziegler (1992) and Talent & Mawson (1999), this species is recorded in the Polygnathus pireneae Zone. However, in the figure given by Yolkin et al. (2011), this species ranges from the upper part of the Eognathodus kindlei Zone to the lower part of the P. pireneae Zone. The taxon occurs in Australia and Asia (Tajikistan, South China).

Origin of Polygnathus Over the past 40 years, the origin of Polygnathus has been discussed extensively and two strikingly different opinions have been summarized by several authors (Sweet 1988, Mawson 1995, 1998, Bardashev et al. 2002, Martínez-Pérez & Valenzuela-Ríos 2014). Klapper & Philip (1972), Cooper (1973) and Klapper & Johnson (1975) suggested that Polygnathus evolved from Eognathodus, whereas Lane & Ormiston (1979) and Sweet (1988) argued that Polygnathus derived from ‘Ozarkodina Branson & Mehl, 1933’, which has a spathognathodontan Pa element. Recently, it has become more accepted that the Polygnathus lineage evolved during the Pragian from the Eognathodus lineage rather than from ‘Ozarkodina’ (Mawson 1995, 1998, Bardashev et al. 2002, Martínez-Pérez & Valenzuela-Ríos 2014). Polygnathus pireneae has long been descrbed as the oldest member of this genus, which thereafter greatly diversified and gave rise to many cosmopolitan and endemic species. However, Mawson et al. (1992) and Mawson (1998) attributed two Pragian eognathodid species characterized by three rows of nodes on the upper platform surface, Eognathodus trilinearis zeravshanicus and E. trilinearis trilinearis, to Polygnathus (P. zeravshanicus and P. trilinearis respectively). Initially, Mawson et al. (1992, p. 51) suggested that P. trilinearis gave rise to P. pireneae. Later, Mawson (1998) altered her previous opinion and proposed two lineages to explain the derivation of Polygnathus: E. sulcatus secus Philip, 1965–P. trilinearis–P. hindei Mashkova & Apekina, 1980 and E. sulcatus sulcatus–E. sulcatus kindlei– P. zeravshanicus–P. pireneae. Subsequently, Bardashev et al. (2002) reviewed the previous opinions regarding the origin of Polygnathus and distinguished two lineages: E. sulcatus–E. zeravshanicus–P. pireneae and E. secus–E. trilinearis–P. kitabicus/P. sokolovi. They modified the diagnosis of Eognathodus and attributed P. zer-

ALCHERINGA avshanicus and P. trilinearis back to Eognathodus. Moreover, they even assigned those early eognathodids with a medial trough to a new genus, Gondwania, which they considered to be the precursor of Eognathodus. However, that genus is treated as a junior synonym of Eognathodus herein based on the original definition of Eognathodus (see below). Later, after having studied the Devonian sequences of the Kitab State Geological Reserve, Uzbekistan, Yolkin et al. (2011) suggested the following lineages to show the phylogenetic relationships of eognathodids and the earliest polygnathids: G. juliae (Lane & Ormiston 1979) (=E. sulcatus juliae)–E. jurii Apekina in Apekin & Apekina, 1992 (=E. sucatus nu morph Mawson & Talent, 1994)–P. trilinearis–P. pireneae. As discussed above, although the opinions on the derivation of P. pireneae have been controversial, P. zeravshanicus and P. trilinearis are widely accepted as the earliest polygnathids, and both are interpreted to derive from Eognathodus. At the Liujing section, two markedly different Pragian species with a capacious basal cavity protruding beyond the platform margins and a laterally extended platform whose upper surface is flat and smooth are recognized below the first appearance of Polygnathus trilinearis from the Nahkaoling Formation and tentatively assigned to Eognathodus kuangi (Fig. 3A–F) and E. nagaolingensis (Fig. 3G–K). Representative Pa elements of Eognathodus are characterized by a carminiscaphate outline (Clark et al. 1981, W162–W164) with double rows of nodes on the upper platform surface, whereas representative Pa elements of the earliest species of Polygnathus are also carminiscaphate with three rows of nodes. Those carminiscaphate Pa elements have a platform with lateral extensions and a capacious, commonly cup-like basal cavity on the lower side. According to Sweet (1988, p. 95), polygnathids can be easily distinguished from eognathodids by the introduction of a third row of nodes on the platform, a novel feature accepted by Mawson et al. (1992) and Mawson (1998) as the main basis for attributing E. trilinearis zeravshanicus and E. trilinearis trilinearis to Polygnathus. Thus, according to the definition given by Clark et al. (1981), it seems plausible to assign these two species from the Nahkaoling Formation to Eognathodus. Eognathodus kuangi and E. nagaolingensis are both carminiscaphate just like eognathodids and earliest polygnathids. They resemble representative species of Eognathodus in having two rows of nodes throughout the platform or restricted to the posterior part of the platform, but differ by the flat and smooth upper platform surface lacking the characteristic sulcus (Fig. 3A, D, G, I). This feature makes E. kuangi and E. nagaolingensis readily distinguishable from the earliest polygnathids, which are very similar to these two species in outline but commonly have a carina (the third row of nodes) running from the anterior end to the posterior end of the platform. Apparently, E. kuangi and E. nagaolingensis have remarkably different upper


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platform surfaces from all species of Polygnathus and Eognathodus described and illustrated previously, thus increasing the biodiversity of Eognathodus. They probably signify a close phylogenetic relationship between Polygnathus and Eognathodus. As pointed out above, Polygnathus is considered to have evolved from the Eognathodus lineage by the development of a third row of nodes; however, the platform ornamentation of phylogenetically late eognathodids is quite varied. According to Mawson & Talent (1994, p. 55), the platform ornamentation in the E. sulcatus nu morph ranges ‘from parallel rows of variably sized nodes, a ladder-like arrangement of horizontal ridges, an irregular arrangement of nodes on either side of a sulcus, or an irregular arrangement of nodes without a sulcus but commonly with nodes in addition to the normal two rows’. Consequently, the specimens covered with three longitudinal rows of nodes and illustrated as E. jurii by Yolkin et al. (2011, pl. 2, figs 11– 12) in fact belong to one of the various morphs depicted by Mawson & Talent (1994). Additionally, in one specimen (Yolkin et al. 2011, pl. 2, fig. 11) the third row of denticles is linear, whereas in the other specimen (Yolkin et al. 2011, pl. 2, fig. 12) it is irregularly arranged. A similar phenomenon is evident in the holotype of E. nagaolingensis (see remarks under this species). Therefore, it is demonstrated that the platform ornamentation in E. jurii and E. nagaolingensis is an inconsistant feature and the development of a third row of nodes probably should be explained as ontogenetic or infraspecific variability. Moreover, apart from the development of a third row of nodes on the platform, previous researchers have always ignored or overlooked another important morphological change of the platform in the evolution from Eognathodus to Polygnathus, which is the degeneration of the sulcus or the flattening of the upper platform surface. Phylogenetically early eognathodids, such as E. sulcatus sulcatus, E. sulcatus kindlei and E. sulcatus juliae, have a narrow platform ornamented with a medial trough between two marginal rows of nodes. The earliest polygnathids, such as P. trilinearis, P. zeravshanicus, P. sokolovi and P. pireneae possess a wide and flat platform, which is ornamented by three rows of nodes, whereas phylogenetically late eognathodids including E. secus and E. jurii usually have a weakly developed sulcus or even lack a sulcus on the upper platform surface. This morphological change is clearly demonstrated by E. kuangi and E. nagaolingensis, whose upper platforms are smooth and flat, and only ornamented with two rows of nodes. In addition, specimens illustrated as the E. sulcatus nu morph by Mawson & Talent (1994, figs 8I–P, 9A–C) also develop a relatively wide, and more or less flat platform. Yolkin et al. (2011) pointed out that the slender platform of E. jurii (in fact, compared with early eognathodids, the platfrom is quite wide) was flat. As a result, the degeneration of the sulcus or the flattening of the upper

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platform surface should be regarded as one of the most important morphological changes in the evolution from Eognathodus to Polygnathus, especially in the eognathodid evolutionary stage. Considering the stratigraphical succession of E. kuangi, E. nagaolingensis and P. trilinearis at the Liujing section, the first two were probably contemporaneous with E. jurii and E. secus, and represent an intermediate evolutionary stage, probably the latest eognathodids, in the evolution from Eognathodus to Polygnathus. However, the direct precursors and immediate descendants of these two species are unclear.

Early diversification of Polygnathus across the Pragian–Emsian boundary The early diversification of Polygnathus across the Pragian–Emsian boundary has been discussed in detail by Yolkin et al. (1994) in the stratotype section (GSSP) of the lower Emsian boundary in Kitab State Geological Reserve, Uzbekistan. Three lineages were recognized from the P. pireneae Zone to the P. kitabicus Zone: P. pireneae–P. kitabicus, P. pireneae–P. pannonicus Mashkova & Apekina, 1980 and P. pireneae–P. sokolovi–P. hindei–P. tamarae Apekina, 1989. Later, Yolkin et al. (2008) distinguished three morphs of P. pireneae from the Kitab Reserve sequences: the kitabiformis morph, the sokoloviformis morph and the pannonicoformis morph, which are closely similar to and gave rise to P. kitabicus, P. sokolovi and P. pannonicus respectively. Recently, Izokh et al. (2011) modified the existing lineages of Yolkin et al. (2008), arguing that the pannonicoformis morph is not phylogenetically related to P. pireneae but should be treated as a separate lineage: P. pannonicoformis Izokh et al., 2011–P. pannonicus. They also suggested that both P. pireneae and P. pannonicoformis are the direct descendants of P. trilinearis. The mode of early diversification of Polygnathus across the Pragian–Emsian boundary has only been demonstrated in Kitab State Geological Reserve, Uzbekistan. The Pragian–Emsian conodonts from the Liujing section provide new insights into the early diversification of Polygnathus across the Pragian–Emsian boundary. Polygnathus trilinearis is recorded from the upper part of the Gaoling Member of the Nahkaoling Formation. This species was known previously only from northeastern Gondwana (Australia) and south TienShan. All three localities hosting P. trilinearis, one of the supposedly earliest polygnathids, were situated in tropical or subtropical areas during the Early Devonian (Fig. 1D herein; Torsvik & Cocks 2004, 2013), indicating that Polygnathus evolved from Eognathodus probably in a tropical or subtropical region. In addition, P. pireneae and P. sokolovi derive from the basal part of the Shizhou Member of the Yukiang Formation and they are even collected from the same level in samples AGP-LJ-78 and AGP-LJ-83. Polygnathus pireneae is


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widespread in Laurasia, northern Gondwana (Spanish Pyrenees) and south Tien-Shan, whereas P. sokolovi has been recored and illustrated only from Gondwana (Spanish Pyrenees? and Australia) and south Tien-Shan. However, the single specimen from the Spanish Pyrenees (Martínez-Pérez & Valenzuela-Ríos, 2014) is fragmentary only with the anterior half of the platform preserved. The contemporaneous appearance of these two species in a section has been reported previously in south Tian-Shan (Yolkin et al. 1994, 2008, 2011) and the Spanish Pyrenees (Martínez-Pérez & ValenzuelaRíos 2014). Thus, the discoveries of P. pireneae and P. sokolovi at the Liujing section partially confirm the early diversification of Polygnathus across the Pragian– Emsian boundary. Moreover, the Liujing record also shows the morphological variability of P. pireneae and evidence of the phylogenetic affinity between as well as P. pireneae and P. kitabicus, as well as P. sokolovi. The kitabiformis morph and the sokoloviformis morph of P. pireneae have never been reported outside Cental Asia before. These two morphs of P. pireneae are recognized together for the first time from the basal part of the Shizhou Member. The contemporaneous occurrences of the kitabiformis and sokoloviformis morphs of P. pireneae with P. sokolovi and their respective similarities to P. kitabicus and P. sokolovi suggest that the latter two species are phylogenetically related to P. pireneae. Apart from the those species discussed above, other early polygnathids recorded from the Kitab State Geological Reserve during the latest Pragian to earliest Emsian, such as Polygnathus pannonicoformis, P. pannonicus, P. hindei and P. tamarae, have not yet been found at the Liujing section.

Acknowledgements We thank Jiang-si Liu [China University of Geosciences (Wuhan)] for his assistance in the field. We are grateful to Cheng-yuan Wang [Nanjing Institute of Geology and Palaeontology], José Ignacio Valenzuela-Ríos and Jauchyn Liao [University of Valencia] for meaningful discussions. Carlos Martínez-Pérez and Nadyezhda Izokh critically read this paper and provided many important suggestions and comments from which we have benefited greatly. We sincerely thank the editor Stephen McLoughlin for his linguistic assistance. This study was funded by the National Natural Science Foundation of China (Grants 40872009, 41272009, 41290260 and 41303001).

Disclosure statement No potential conflict of interest was reported by the authors.

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