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Drepanoistodus svendi sp. nov. urn:lsid:zoobank.org:act: 0921F27A-ECF6-498C-8943-4DEB96CFBB38 Fig. 6I–L Drepanoistodus aff. basiovalis (Sergeeva) - Rasmussen 2001: 73–74, pl. 5 fig. 17.— Mellgren et al. 2012: fig. 5u. Diagnosis A Drepanoistodus species characterised by a geniculate element with a recurved cusp and distinct keels on both the cusp and the upper margin of the base. Weakly curved but distinct carinas are developed on both sides of the cusp, especially well developed on the inner side. Etymology Named after the Danish palaeontologist and conodont specialist Svend S. Stouge, Natural History Museum of Denmark, University of Copenhagen. Material examined Five geniculate elements including three from the Lynna section. Holotype, geniculate element (Fig. 6J–K); LO 12483T. Type locality River bank near the mouth of Lynna River, village of Kolchanovo, St. Petersburg region, Russia (60°00′39″ N, 32°33′49″ E). Type stratum Approximately 40 cm below the local top of the Volkhov Formation, sample LY 12-14, ca 20 cm above the base of the Lenodus variabilis Zone sensu Lindskog et al. (2020). Description Cusp is recurved (bent weakly downward), with distinct keels developed along the anterior (upper) and posterior (lower) margins. A median, longitudinal, weakly curved carina is developed on both sides of the cusp, most distinct on the inner side of the cusp. Cusp is almost twice as long as the upper margin of the cusp; the mean ratio between the length of the free upper margin and the free cusp (Fig. 3) is ca 0.55 with a standard deviation of 0.13. Basal margin varies from rounded (convex) to almost straight. A distinct keel is developed on the upper margin. Anterior margin is rounded or weakly rounded (convex). Angle A (Fig. 3) between the cusp and upper margin of the base varies considerable with a mean of 24° and standard deviation of 6.9 (Fig. 5B). Zone. L. Same specimen as I in outer view. M–O. Drepanoistodus viirae sp. nov. M. LO 12484T, holotype, inner view, sample LY12-31, interzone (“uncertain interval”) between the Lenodus variabilis Zone and the Yangtzeplacognathus crassus Zone sensu Lindskog et al. (2020). N. Same specimen as M in outer view. O. LO 12485t, inner view, sample LY 12-31, interzone (“uncertain interval”) between the Lenodus variabilis Zone and the Yangtzeplacognathus crassus Zone sensu Lindskog et al. (2020). P–Q. Drepanoistodus aff. basiovalis (Sergeeva, 1963), LO 12486t, inner and outer view, respectively, sample LY12-9, L. antivariabilis Zone. R –S. Drepanoistodus stougei Rasmussen, 1991, LO 12487t, inner and outer view, respectively, sample LY12-13, L. variabilis Zone. T. Drepanoistodus cf. suberectus (Branson & Mehl, 1933), LO 12488t, inner view, sample LY14-2, Y. crassus Zone. Scale bar = 200 μm (all specimens illustrated at same scale). Remarks Drepanoistodus svendi sp. nov. is distinguished from all the other Drepanoistodus species in the present study by the recurved cusp and the curved carina on each side of the cusp. Like D. iommii sp. nov., it is characterised by a clearly longer upper margin of the base compared to the cusp length than in D. basiovalis. The D. svendi sp. nov. population is located in the lower, right quadrangle of the PCA plot, far from any other species of Drepanoistodus, and the biplot vectors representing the recurved cusp and the curved carina point in this direction (Fig. 4). The PERMANOVA test on the first seven PCA axis shows that the probability that the D. basiovalis and D. svendi sp. nov. populations are the same, is exceedingly low (p (same) = 1.00E- 04). Occurrence The lower part of the L. variabilis Zone (samples LY12-13, LY12-14). Moreover, D. svendi sp. nov. has been recorded from Steinsodden, Norway, from the top of the B. norrlandicus – D. stougei Zone and the base of the overlying B. medius – H. holodentata Zone, which correlate with the middle part of the L. variabilis Zone (as D. aff. basiovalis sensu Rasmussen 2001), and from the L. pseudoplanus Zone or E. suecicus Zone at the island Osmussaar, Estonia (Mellgren et al. 2012; reported as D. aff. basiovalis).

Genus Drepanoistodus Lindström, 1971 Type species Oistodus forceps Lindström, 1955, subsequently designated by Lindström (1971). Remarks Drepanoistodus is here interpreted as quinquemembrate and comprises four nongeniculate coniform elements and one geniculate coniform element that collectively make a curvature-transition series from erect to recurved element types (e.g., Stouge & Bagnoli 1990; Rasmussen 1991). The nongeniculate elements comprise a suberectiform element associated with drepanodontiform type-l, type-2 and type-3 elements. In general, Middle Ordovician nongeniculate Drepanoistodus elements from Baltica can be described as follows: the suberectiform element is characterised by a straight, erect cusp. The drepanodontiform type-1 element has a strongly recurved cusp, which is keeled both anteriorly and posteriorly. The anterior keel is twisted strongly inwards. An extension, sometimes triangular in outline, may occur at the anterobasal corner. The drepanodontiform type-2 element has a recurved cusp which is keeled. It is separated from the drepanodontiform type-l element by the straight or only weakly twisted anterior margin, and by the consistent presence of an anterobasal flare, commonly with a triangular outline. The drepanodontiform type-3 element is typified by a slightly recurved cusp, which is anteriorly and posteriorly keeled and not twisted. As opposed to the drepanodontiform type-1 and type-2 elements, it lacks the anterior triangular flare. For a more comprehensive description, see Rasmussen (1991). Many coniform conodont apparatuses are not easily placed in the locational PMS notation scheme favoured by Sweet (1981, 1988), or the more biologically correct terminology advocated by Purnell et al. (2000), because it is very difficult or even impossible to identify locational homologues with the ozarkodinid notation (Smith et al. 2005). This is primarily a consequence of the lack of natural assemblages in many conodont genera and families, including Drepanoistodus. In most cases, it is extremely difficult to distinguish between individual Middle Ordovician Drepanoistodus species based on the largely homeomorphic nongeniculate elements (van Wamel 1974; Dzik 1983; Stouge 1984; Rasmussen 2001), and this is indeed also the case with respect to the species studied herein. Because our material includes nothing but isolated conodont elements (as opposed to articulated clusters or natural multi-element assemblages), the identification of Drepanoistodus at the species level is solely based on the geniculate element, which are described below. The stratigraphical distribution of the studied specimens of Drepanoistodus is shown in Table 3., Published as part of Rasmussen, Jan Audun, Eriksson, Mats E. & Lindskog, Anders, 2021, Middle Ordovician Drepanoistodus (Vertebrata, Conodonta) from Baltica, with description of three new species, pp. 106-134 in European Journal of Taxonomy 774 on pages 117-118, DOI: 10.5852/ejt.2021.774.1533, http://zenodo.org/record/5557148, {"references":["Lindstrom M. 1971. Lower Ordovician conodonts of Europe. Geological Society of America Memoirs 127: 21 - 61. https: // doi. org / 10.1130 / MEM 127 - p 21","Stouge S. & Bagnoli G. 1990. Lower Ordovician (Volkhovian - Kundan) conodonts from Hagudden, northern Oland, Sweden. Palaeontographica Italica 77: 1 - 54.","Rasmussen J. A. 1991. Conodont stratigraphy of the Lower Ordovician Huk Formation at Slemmestad, southern Norway. Norsk Geologisk Tidsskrift 71: 265 - 88.","Sweet W. C. 1981. Macromorphology of elements and apparatuses. In: Robison R. A. (ed.) Treatise on Invertebrate Paleontology, Part W, Miscellanea, Suppl. 2, Conodonta: 5 - 20. Geological Society of America and the University of Kansas Press, Lawrence.","Sweet W. C. 1988. The Conodonta: morphology, taxonomy, paleoecology, and evolutionary history of a long-extinct animal phylum. Oxford Monographs on Geology and Geophysics 10: 1 - 212.","Purnell M. A., Donoghue P. C. J. & Aldridge R. J. 2000. Orientation and anatomical notation in conodonts. Journal of Paleontology 74: 113 - 122. https: // doi. org / 10.1666 / 0022 - 3360 (2000) 074 2.0. CO; 2","Smith M. P., Donoghue P. C. J. & Repetski J. E. 2005. The apparatus composition and architecture of Cordylodus Pander - Concepts of homology in primitive conodonts. Bulletin of American Paleontology 369: 19 - 33.","Van Wamel W. A. 1974. Conodont biostratigraphy of the Upper Cambrian and Lower Ordovician of north-western bland, south-eastern Sweden. Utrecht Micropaleontological Bulletins 10: 1 - 126.","Dzik J. 1983. Early Ordovician conodonts from the Barrandian and Bohemian-Baltic faunal relationships. Acta Palaeontologica Polonica 28: 327 - 368.","Stouge S. 1984. Conodonts of the Middle Ordovician Table Head Formation, western Nemoundland. Fossils and Strata 16: 1 - 145.","Rasmussen J. A. 2001. Conodont biostratigraphy and taxonomy of the Ordovician shelf margin deposits in the Scandinavian Caledonides. Fossils and Strata 48: 1 - 180."]}

Drepanoistodus cf. suberectus (Branson & Mehl, 1933) Fig. 6T Drepanoistodus cf. suberectus (Branson & Mehl, 1933) – Löfgren 2003: fig. 7s–u. — Mellgren & Eriksson 2010: fig. 7k (only). — Hints et al. 2012: fig. 6h. Material examined Four geniculate elements including three from the Lynna section. Remarks Drepanoistodus cf. suberectus is included in the present work because it superficially resembles Drepanoistodus viirae sp. nov. Originally, D. suberectus was described as Oistodus suberectus from the Upper Ordovician strata of Missouri, USA, by Branson & Mehl (1933), but it was not until 1966 that conodont specialists included the geniculate element in the apparatus (see Bergström & Sweet 1966 and Webers 1966, for details). The D. suberectus type locality near Ozora, Missouri, was located and restudied by Bergström & Leslie (2010) who documented the conodont fauna and illustrated three different elements of D. suberectus, including the geniculate element. The Upper Ordovician geniculate D. suberectus elements (e.g., Stauffer 1935; Nowlan 2002; Bergström & Leslie 2010) are generally more rounded anteriorly and carry more pronounced keels on the cusp than the three geniculate elements at hand, thus leading us to leave the Lynna River specimens in open nomenclature. Drepanoistodus cf. suberectus occurs only sporadically in the Lynna River section samples. It is characterised by a short upper margin of the base compared to the free cusp (b/c ratio near 0.20 in the three specimens found). Angle A between the upper margin of the cusp and the carina on the cusp (see Fig. 3) varies considerably (41–52°) but it is wider than that of the other Drepanoistodus species described here. Moreover, it is typified by a convex basal margin; weakly rounded anterior margin, and a weakly developed carina on the straight cusp, which is located on the lower half part of the cusp. Superficially, D. cf. suberectus resembles D. viirae sp. nov. because of the relatively short base, but the latter species is distinguished by a narrower angle A (see Fig. 3); wider sides anteriorly on the cusp; laterally compressed cusp with distinct keels, and a median, as opposed to a lower, carina. Occurrence The Yangtzeplacognathus crassus Zone at Lynna River (samples LY12-34, LY14-2 and LY14-5). Drepanoistodus cf. suberectus has also been documented from the L. variabilis Zone of Hällekis, Sweden (Mellgren & Eriksson 2010)., Published as part of Rasmussen, Jan Audun, Eriksson, Mats E. & Lindskog, Anders, 2021, Middle Ordovician Drepanoistodus (Vertebrata, Conodonta) from Baltica, with description of three new species, pp. 106-134 in European Journal of Taxonomy 774 on page 127, DOI: 10.5852/ejt.2021.774.1533, http://zenodo.org/record/5557148, {"references":["Branson E. B. & Mehl M. G. 1933. Conodont studies no. 2; conodonts from Joachim (Middle Ordovician) of Missouri; from the Plattin (Middle Ordovician) of Missouri; from the Maquoketa-Thebes (Upper Ordovician) of Missouri; a study of Hinde's types of conodonts preserved in the British Museum. Missouri University Studies 8: 77 - 167.","Lofgren A. 2003. Conodont faunas with Lenodus variabilis in the upper Arenigian to lower Llanvirnian of Sweden. Acta Palaeontologica Polonica 48: 417 - 436.","Hints O., Viira V. & Nolvak J. 2012. Darriwilian (Middle Ordovician) conodont biostratigraphy in NW Estonia. Estonian Journal of Earth Sciences 61: 210 - 226. https: // doi. org / 10.3176 / earth. 2012.4.03","Bergstrom S. M. & Sweet W. C. 1966. Conodonts from the Lexington Limestone (Middle Ordovician) of Kentucky and its lateral equivalents in Ohio and Indiana. Bulletin of American Paleontology 50: 269 - 441.","Webers G. F. 1966. The Middle and Upper Ordovician Conodont Faunas of Minnesota. Minnesota Geological Survey, Special Publication 4: 1 - 123.","Bergstrom S. M. & Leslie S. A. 2010. The Ordovician zone index conodont Amorphognathus ordovicicus Branson & Mehl, 1933 from its type locality and the evolution of the genus Amorphognathus Branson & Mehl, 1933. Journal of Paleontology 29: 73 - 80. https: // doi. org / 10.1144 / jm. 29.1.73","Stauffer C. R. 1935. Conodonts of the Glenwood beds. Geological Society of America Bulletin 46: 125 - 168. https: // doi. org / 10.1130 / GSAB- 46 - 125","Nowlan G. S. 2002. Stratigraphy and conodont biostratigraphy of Upper Ordovician strata in the subsurface of Alberta, Canada. Special Papers in Palaeontology 67: 185 - 203."]}

Drepanoistodus iommii sp. nov. urn:lsid:zoobank.org:act: 0E2832F5-672E-4FAE-B5A5-CBA5DE1A4824 Fig. 6E–H partim Drepanoistodus aff. basiovalis – Mellgren & Eriksson 2010: fig. 7m (only). Drepanoistodus cf. basiovalis – Mellgren et al. 2012: fig. 5e. Diagnosis A Drepanoistodus species characterised by a geniculate element with distinct keels on the cusp and upper margin of the base; a straight basal margin; a straight to weakly rounded (convex) anterior margin and cusp which is approximately twice the length of the upper margin of the base. Etymology Named in honour of legendary guitarist Tony Iommi, founding member of heavy metal band Black Sabbath. Material examined Ten geniculate elements including eight from the Lynna section. Holotype, geniculate element (Fig. 6E–F); LO 12479T. Type locality River bank near the mouth of Lynna River, village of Kolchanovo, St. Petersburg region, Russia (60°00′39″ N, 32°33′49″ E). Type stratum Approximately 10 cm above the local base of the Lynna Formation, sample LY 12-16. Lower part of the Lenodus variabilis Zone. Description Cusp reclined and straight with distinct keels developed on the anterior (upper) and posterior (lower) margins. A median, longitudinal carina is developed on both sides of the cusp, but it is especially distinct on the inner side. Base is characterised by a straight or almost straight basal margin and a distinct keel on the upper margin. Whereas this keel is slightly convex, the upper margin below the keel is straight. Anterior margin is usually straight or weakly rounded (convex), but occasionally, it is strongly rounded. Angle A between the cusp and upper margin of the base is ca 30° (mean) with a standard deviation at 4.2 (Fig. 5B), and the mean ratio between length of the free upper margin (b) and the free cusp (c) is 0.54 (standard deviation 0.10). Remarks In the PCA plot (Fig. 4), the population of D. iommii sp. nov. is situated in the upper right corner, separated from the D. basiovalis population as well as the other two new species populations described herein. The vectors in the biplot demonstrate that this is mainly due to the straight basal margin, the relatively long upper margin (high b/c values), and the usually straight anterior margin in D. iommii sp. nov., which is in accordance with the characters diagnosed above. The hypothesis that the population of D. iommii sp. nov. is morphologically different from the D. basiovalis population is supported by the PERMANOVA test (Fig. 5A), which shows that the probability that the two populations are the same is exceedingly low (p (same) = 1.00E- 04). Occurrence The L. antivariabilis Zone (sample LY12-9) to the L. variabilis Zone (sample LY12-21b). Outside the St. Petersburg region, D. iommii sp. nov. has been recorded from the L. variabilis Zone at the Hällekis quarry in Västergötland, Sweden (Mellgren & Eriksson 2010; referred to as D. aff. basiovalis) and from the L. pseudoplanus Zone or E. suecicus Zone of the island Osmussaar, Estonia (Mellgren et al. 2012; reported as D. cf. basiovalis)., Published as part of Rasmussen, Jan Audun, Eriksson, Mats E. & Lindskog, Anders, 2021, Middle Ordovician Drepanoistodus (Vertebrata, Conodonta) from Baltica, with description of three new species, pp. 106-134 in European Journal of Taxonomy 774 on pages 119-120, DOI: 10.5852/ejt.2021.774.1533, http://zenodo.org/record/5557148, {"references":["Mellgren J. I. S., Schmitz B., Ainsaar L., Kirsimae K. & Eriksson M. E. 2012. Conodont dating of the Middle Ordovician breccia cap-rock limestone on Osmussaar Island, northwestern Estonia. Estonian Journal of Earth Sciences 61: 133 - 148. https: // doi. org / 10.3176 / earth. 2012.3.01"]}

Drepanoistodus viirae sp. nov. urn:lsid:zoobank.org:act: AD10D9B3-9802-4DAC-97C0-B44EB8DE195D Fig. 6M–O Drepanoistodus basiovalis (Sergeeva, 1963) – Löfgren 2000b: fig. 4p; 2003: fig. 7aa. — Lindskog et al. 2020: fig. 7v–w. partim Drepanoistodus cf. basiovalis – Rasmussen 2001: 73, pl. 5 fig. 16 (only). Drepanoistodus cf. stougei Rasmussen, 1991 – Rasmussen 2001: 76, pl. 6 fig. 12. Drepanoistodus aff. suberectus (Branson & Mehl, 1933) – Mellgren & Eriksson 2010: fig. 7f. aff. Drepanoistodus basiovalis – Feltes & Albanesi 2013: fig. 3.12. ? partim Drepanoistodus basiovalis – Zhen 2020: 18–19, fig. 7b (only). Diagnosis A Drepanoistodus species characterised by a geniculate element with a wide, straight, compressed cusp and a very short base, where the free cusp typically is ca 4 times longer than the upper margin of the base. Etymology Named after the Estonian palaeontologist and conodont specialist Viive Viira, Tallinn University of Technology, Estonia. Material examined Nine geniculate elements including five from the Lynna section. Holotype, geniculate element (Fig. 6M–N); LO 12484T. Type locality River bank near the mouth of Lynna River, village of Kolchanovo, St. Petersburg region, Russia (60°00′39″ N, 32°33′49″ E). Type stratum Approximately 15 cm above the local base of the Sillaoru Formation, sample LY 12-31. Lower part of the 90 cm thick interzone (“uncertain interval”) between the Lenodus variabilis Zone and the Yangtzeplacognathus crassus Zone sensu Lindskog et al. (2020). Description Cusp is reclined, wide (from upper to lower margin) and straight, with keels developed along the anterior (upper) and posterior (lower) margins. A weak, median, longitudinal carina is developed on the inner side of the cusp. Occasionally, the carina may be distinct. Basal margin is weakly rounded or straight. A distinct keel is developed on the upper margin. Anterior margin is rounded or weakly rounded (convex). Angle A (Fig. 3) between the cusp and upper margin of the base is ca 30° (mean) with a standard deviation of 4.3 (Fig. 5B), and mean ratio between length of the free upper margin and the free cusp is ca 0.25 with a standard deviation of 0.05. Remarks Drepanoistodus viirae sp. nov. is situated in the lower left quadrangle of the PCA plot (Fig. 4). Like D. basiovalis, it is clearly separated from D. iommii sp. nov. and D. svendi sp. nov., whereas it partly overlaps with the D. basiovalis population, when only the PC 1 (x) and PC 2 (y) axis is plotted. The vectors in the biplot reinforce that D. viirae sp. nov. is characterised by a convex basal margin, a weakly developed carina and a short upper margin on the base (= low b/c value), the latter because it is situated in the opposite direction of the b/c vector, as seen in Fig. 4. The partial overlap with D. basiovalis occurs because the two species share some characters. A significant difference, however, is that D. viirae sp. nov. has a relatively shorter upper margin of the base, where the mean b/c ratio is 0.40 in D. basiovalis but only 0.25 in D. viirae sp. nov. (Fig. 5B). Moreover, D. viirae sp. nov. is characterised by a wider cusp when viewed from the side and, typically, a less developed carina on the cusp. The hypothesis that the D. viirae sp. nov. population is morphologically separate from the D. basiovalis population is supported by the PERMANOVA test (Fig. 5A), which shows that the probability that the two populations are the same is low (p (same) = 8.00E- 03). Drepanoistodus viirae sp. nov. is distinguished from the stratigraphically older Drepanoistodus contractus on the relatively wider and more compressed cusp and the usually less distinct longitudinal carina, and from D. cf. suberectus on the markedly smaller angle between the cusp and the upper margin of the base (mean angle = 46° in D. cf. suberectus, 30° in D. viirae sp. nov.). Occurrence The lower part of the L. variabilis Zone (sample LY12-13) to the lower part of the interzone (“uncertain interval”) between the L. variabilis Zone and the Y. crassus Zone (sample LY12-31) sensu Lindskog et al. (2020). In addition, D. viirae sp. nov. has been recorded from the B. norrlandicus and basal Y. crassus zones at Gillberga, Sweden (Löfgren 2000b, 2003); the uppermost part of the P. rectus – M. parva Zone at Steinsodden, Norway, which correlates with the uppermost P. originalis Zone (as D. cf. stougei sensu Rasmussen 2001); the lower part of the B. medius – H. holodentata Zone at Andersön, Sweden, correlating with the uppermost part of the L. variabilis Zone (as D. cf. basiovalis sensu Rasmussen 2001), and the L. variabilis Zone at Hällekis, Sweden (as D. aff. suberectus sensu Mellgren & Eriksson 2010). Moreover, it shares some characteristics with the geniculate element from strata correlated with the L. pseudoplanus Zone of the Canning Basin, Australia, which was included in D. basiovalis (Zhen 2020: fig. 7b), but this identification is questionable., Published as part of Rasmussen, Jan Audun, Eriksson, Mats E. & Lindskog, Anders, 2021, Middle Ordovician Drepanoistodus (Vertebrata, Conodonta) from Baltica, with description of three new species, pp. 106-134 in European Journal of Taxonomy 774 on pages 123-124, DOI: 10.5852/ejt.2021.774.1533, http://zenodo.org/record/5557148, {"references":["Sergeeva S. P. 1963. [Conodonts from the Lower Ordovician in the Leningrad region.] Paleontologicheshij Zhurnal 1963 (2): 93 - 108. [In Russian.]","Lofgren A. 2000 b. Early to early Middle Ordovician conodont biostratigraphy of the Gillberga quarry, northern Oland, Sweden. GFF 122: 321 - 338. https: // doi. org / 10.1080 / 11035890001224321","Lindskog A., Eriksson M. E., Rasmussen J. A., Dronov A. & Rasmussen C. M. O. 2020. Middle Ordovician carbonate facies development, conodont biostratigraphy and faunal diversity patterns at the Lynna River, northwestern Russia. Estonian Journal of Earth Sciences 69: 37 - 61. https: // doi. org / 10.3176 / earth. 2020.1.03","Rasmussen J. A. 2001. Conodont biostratigraphy and taxonomy of the Ordovician shelf margin deposits in the Scandinavian Caledonides. Fossils and Strata 48: 1 - 180.","Rasmussen J. A. 1991. Conodont stratigraphy of the Lower Ordovician Huk Formation at Slemmestad, southern Norway. Norsk Geologisk Tidsskrift 71: 265 - 88.","Branson E. B. & Mehl M. G. 1933. Conodont studies no. 2; conodonts from Joachim (Middle Ordovician) of Missouri; from the Plattin (Middle Ordovician) of Missouri; from the Maquoketa-Thebes (Upper Ordovician) of Missouri; a study of Hinde's types of conodonts preserved in the British Museum. Missouri University Studies 8: 77 - 167.","Feltes N. A. & Albanesi G. L. 2013. The Periodon and Paroistodus conodont biofacies in the lower member of the Las Aguaditas Formation (Middle Ordovician), Central Precordillera, Argentina. In: Albanesi G. L. & Ortega G. (eds) Conodonts from the Andes International Conodont Symposium: 17 - 23. Asociacion Paleontologica Argentina, Buenos Aires 3.","Zhen Y. Y. 2020. Revision of the Darriwilian (Middle Ordovician) conodonts documented by Watson (1988) from subsurface Canning Basin, Western Australia. Alcheringa 44: 217 - 252. https: // doi. org / 10.1080 / 03115518.2020.1737227","Lofgren A. 2003. Conodont faunas with Lenodus variabilis in the upper Arenigian to lower Llanvirnian of Sweden. Acta Palaeontologica Polonica 48: 417 - 436."]}

Drepanoistodus basiovalis (Sergeeva, 1963) Fig. 6A–D Oistodus basiovalis Sergeeva, 1963: 96, pl. 7 figs 6–7, text-fig. 3. Drepanoistodus basiovalis – Lindström 1971: 43, text-figs 6, 8. — Stouge & Bagnoli 1990: 15, pl. 5 figs 18–24. — Dzik 1990: fig. 12; 1994: 78, pl. 16 figs. 16–20, text-fig. 12a; 2020: fig. 7A–E. — Rasmussen 1991: 277, fig. 6l; 2001: 71–73, pl. 5: 9 (cum. syn.). — Löfgren 1994: fig. 6.30; 2000a: fig. 4w; 2006: figs 3n, 3ab. — Viira et al. 2001: fig. 5z. — Zhen & Percival 2004: 93, fig. 11a–j. — Tolmacheva et al. 2013: pl. 3, fig. 24. partim Drepanoistodus basiovalis – Löfgren 1978: 55–56, pl. 1 figs 11–16 (only), non 17 (= D. contractus (Lindström, 1955)). — Olgun 1987: 49, pl. 6w (only). — Landing et al. 2003: fig. 4e (only). — Zhen et al. 2011: 222–227, fig. 12a?, b–n, p–q (only). cf. Drepanoistodus basiovalis – Zhang 1998: 61–62, pl. 5 figs 5–12 (unusually short upper margin of the base). ? Drepanoistodus basiovalis – Lehnert et al. 1998: 55, pl. 3 figs 6, 12 (12 may belong to Paroistodus originalis (Sergeeva, 1963)). — Boncheva et al. 2009: text-fig. 3.8 (broken element). — Albanesi & Ortega 2016: fig. 7(6) (shares characters with D. basiovalis and D. cf. balticus). — Feltes et al. 2016: fig. 3ac. — Wu et al. 2018: fig. 5e (unusually long base compared to the cusp). non Drepanoistodus basiovalis – Gutiérrez-Marco et al. 2008: 153, figs 3.29–3.31 (may be Drepanoistodus cf. basiovalis or Drepanoistodus cf. suberectus (Branson & Mehl, 1933). — Hints et al. 2012: fig. 6h (= Drepanoistodus cf. suberectus). — Wu et al. 2017: fig. 7u (= Drepanoistodus contractus (Lindström)). — Lindskog et al. 2020: fig. 7v–w (= Drepanoistodus viirae sp. nov.). Original diagnosis (translated from Sergeeva, 1963 [in Russian]) Inclined conodonts, almost symmetrical, with a wide shortened base, the edge of which is rounded. Material examined 33 geniculate elements including 24 from the Lynna section. Original description, slightly shortened (translated from Sergeeva, 1963 [in Russian]) Medium-sized conodonts (0.52–0.92 mm), inclined; the degree of inclination of the cusp is 45–60°, sometimes up to 80°. Base high, not very long, elongated along the CD; base length 2.5–3 times its height (comment by the authors: “ we find the meaning of the latter measure ambiguous ”). Base wall slightly transparent near the edge, rounded. The angle between the sides AC is more than 90°; angle between AD 40–45°; corners are smoothly obtuse. Transverse in cross section, the base is oval, elongated along CD and compressed along L1L2. From the C side, the base is compressed, sometimes with a thin keel near the tip, with a small keel on side D. The sides of the base L1 and L2 are smooth and flat. Basal cavity is not always visible, it is wide, but not deep, without visible tops. The cusp is long, straight or slightly curved towards L1, sharply tapering towards the tip; compressed. The sides of the cusp are almost flat, with a welldeveloped longitudinal, wide carina on L1 and less developed carina on the side L2. The carinae usually run from the base to the tip of the cusp. Thin keels occur on the lower (D) and upper (C) parts of the cusp. Remarks In her original diagnosis, Sergeeva (1963) only included geniculate elements with a rounded basal margin in “ Oistodus ” basiovalis, which is also evident from the species epithet: basiovalis (meaning oval base). This interpretation of the geniculate element in Drepanoistodus basiovalis is followed here. Additional typical characters that may be added to the original species description include: anterior margin and upper anterior corner rounded or weakly rounded; cusp usually straight; a median or median to lower, longitudinal carina present on the inner (sometimes slightly concave) side of the element. Carina is more distinct in Darriwilian specimens than in Dapingian ones. Whereas angle A (Fig. 3) between the cusp and the upper margin is 29.6° with a standard deviation at 5.6, the mean ratio between the length of the free upper margin and free cusp (b/c ratio) reaches 0.40 with a standard deviation of 0.1 (Fig. 5B). Occurrence Drepanoistodus basiovalis occurs from the L. antivariabilis Zone (sample LY12-9) to the interzone (“uncertain interval”) between the L. variabilis Zone and the Y. crassus Zone sensu Lindskog et al. (2020) in the Lynna River section (sample LY12-21b; between LY12-21 and LY12-22). 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