Scolopodus striatus Pander, 1856

Tolmacheva, Tatiana Yu., 2006, Apparatus of the conodont Scolopodus striatus Pander, 1856 and a re-evaluation of Pander’s species of Scolopodus, Acta Palaeontologica Polonica 51 (2), pp. 247-260 : 255-259

Scolopodus striatus Pander, 1856

Figs. 5A, B, D ,?E, F, 6, 7, 8.

1856 Scolopodus striatus sp. nov.; Pander 1856: 26, pl. 2: 8a–d, pl. A: 5f.

1856? Scolopodus costatus sp. nov.; Pander 1856: 26, pl. 2: 7a–d, pl. A: 5e.

1856 Scolopodus semicostatus sp. nov.; Pander 1856: 26, pl. 2: 4a–b, pl. A: 5e.

1856 Scolopodus aequilateralis sp. nov.; Pander 1856: 26, pl. 2: 5a–c, pl. A: 5e.

1856 Scolopodus quadratus sp. nov.; Pander 1856: 26, pl. 2: 6 a–d, pl. A: 5d.

1955 Scolopodus rex sp. nov.; Lindström 1955: 595, 596, pl. 3: 32.

1955 Scolopodus rex sp. nov. var. paltodiformis nov.; Lindström 1955: 596, pl. 3: 33, 34.

1964 Scolopodus rex Lindström ; Lindström 1964: 37, figs. 10H, 47h.

1972 non Scolopodus rex Lindström ; Bergström et al. 1972: pl. 1: b.

1974 Scolopodus rex Lindström ; Viira 1974: pl. 3: 22, 23.

1974 Paltodus scolopodiformis sp. nov.; Sergeeva 1974: pl. 1: 10, 11.

1974 Scolopodus rex Lindström ; van Wamel 1974: 94, pl. 5: 18.

1974 non “ Scolopodus rex ” Lindström ; Serpagli 1974: 86–87, pl. 17: 1a–3b, pl. 28: 10.

1976 Scolopodus rex Lindström ; Dzik 1976: fig. 17h,?k,n, l,?m, non i.

1976 non Scolopodus rex Lindström ; Landing 1976: 640, pl. 4: 14.

1978 Scolopodus rex Lindström ; Löfgren 1978: 109, 110, pl. 1: 38, 39.

1982 Scolopodus quadratus Pander ; Fåhraeus 1982: 21, pl. 2: 1–14, pl. 3: 1–8, 15.

1981 non aff. Scolopodus rex Lindström ; Ethington and Clark 1981: 104, 105, pl. 12: 1, 2.

1982 Scolopodus sublaevis Pander ; Fåhraeus 1982: 21, pl. 1: 1–17, pl. 3: 9–14.

1988 Scolopodus spp. ; Bergström 1988: pl. 3: 43–45. 1990 Scolopodus rex Lindström ; Stouge and Bagnoli 1990: 25, pl. 9: 1–6.

1993 non Scolopodus rex Lindström ; Lehnert 1993: pl. 4: 4. 1994 non Scolopodus rex Lindström ; Seo et al. 1994: pl. 10: 10–12. 1995 Scolopodus? rex Lindström ; Löfgren 1995: fig. 9as–at. 1998 non Scolopodus rex Lindström ; Zhang 1998: pl. 17: 5–8. 2000 non Scolopodus rex Lindström ; Dubinina 2000: pl. 11: 20, 23. 2001 Scolopodus quadratus Pander ; Rasmussen 2001: pl. 17: 12. 2001 Scolopodus sp. ; Tolmacheva et al. 2001: fig. 5: 28.

Topotype: Specimen PMU In 1028 ( Fig. 6A ) .

Topotype horizon: The Billingen Regional Stage, Prioniodus elegans Zone.

Topotype locality: The Popowka River section, the East Baltic .

Material.—190 acontiodiform elements, 123 scandodiform elements, 44 subrounded elements, 95 paltodiform, and 253 compressed paltodiform elements.

Emended diagnosis.—A species of Scolopodus consisting of five element morphotypes: acontiodiform, subrounded, compressed paltodiform, paltodiform and scandodiform. All elements are nongeniculate, finely costate and dominantly hyaline. Acontiodiform elements are symmetrical and nearly symmetrical elements with a low, slightly bloated base; symmetrical subrounded elements are characterised by high base with round to triangular cross−section and almost straight reclined cusp. Compressed paltodiform elements are asymmetrical with variable height of the base. Asymmetrical paltodiform and scandodiform elements have smooth outer sides, costate inner sides and twisted cusps.

Description.—Acontiodiform elements ( Figs. 6H, B , 8A–C ) are symmetrical and nearly symmetrical with low base and reclined cusp. The base is bloated and slightly expanded posteriorly. The lateral sides of elements are costate and usually carry from 1 to 5 prominent costae. Anterior and posterior sides of the elements are usually smooth but occasionally costate with the costae confined to the basal region. Basal margin is rounded, circular or oval in cross−section: basal cavity is shallow. These elements are considered to be the P elements.

Subrounded elements ( Fig. 8H, I ) are symmetrical with a high base, a deep basal cavity and a reclined, cusp that is strongly recurved above the base and rounded in cross−section. Most large adult specimens have four or five costae on the lateral sides as well as costae on the posterior side. Anterior side of the elements is usually smooth, or rarely costate. Basal margin is flat with triangular cross−section. These elements are considered to be Sa elements.

Compressed paltodiform elements ( Figs. 6A, C, E, J, K , 7D–I ) are slightly asymmetrical, laterally compressed elements with reclined cusp and base of variable height. Both lateral and posterior sides bear prominent costae. Anterior is smooth, or rarely costate. Two morphological variants can be recognised: short−based ( Figs. 6A, C , 7E, F, H, I ) and long−based ( Figs. 6E , 7D, G ). Short−based elements are more numerous whereas long−based forms are relatively less common in the collections as are elements with short, posteriorly extended base ( Fig. 7F ). Long−based elements are usually less asymmetrical and smaller than other compressed paltodiform elements. Basal margin is usually flat with oval or rounded cross−section.

Paltodiform elements ( Figs. 6D , 7A–C ) are asymmetrical with a curved cusp and base of variable height. Inner side is costate whereas the outer side is usually smooth, but occasionally with fine costae. Rare specimens have prominent costae in the posterior part of the outer side. Two variants of paltodiform elements can be recognised: moderate−based with a deep basal cavity and short based with a shallow basal cavity. Base is elongated or suboval in cross−section and slightly bloated posteriorly, forming a broad basal rim. Paltodiform and compressed paltodiform elements are considered to be the transition series of S elements.

Scandodiform elements ( Figs. 6F, G , 8D–F ) are strongly asymmetrical with a very low base and a laterally compressed, keeled cusp that is strongly recurved above the base and twisted. The inner side of elements carries prominent costae, whereas the outer side is usually smooth. Some large specimens have fine costae that are confined to the base and lower part of cusp. Base is slightly expanded posteriorly and suboval in cross section. Basal cavity is shallow. Scandodiform elements are considered to be M elements.

The number of costae on elements of all morphotype groups is different and varies from one to six, or even seven, but is not strongly influenced by the overall size of the elements. Small juvenile elements usually have fewer costae. The main and most prominent costae are often associated with short additional costae that are confined to the basal region. The edge of the basal margin of all elements is smooth with a low rim on the basal margin; all costae begin a short distance from the basal margin. The surface of elements of all morphotypes groups is usually smooth but occasionally fine longitudinal striation is present in addition to the costae; juvenile elements are more often striated.

All elements are characterised by the basal cavity tips that are situated close to the anterior margin of the elements

( Fig. 3 ). Remarks.— Fåhraeus (1982) divided S. striatus between two

Pander species, mainly on the basis of the presence of fine striations on the surface of S. sublaevis elements and their absence in S. quadratus . Examination of a large number of elements from the Popowka River locality as well as from the Harku section shows the rare occurrence of striations on the surface of all morphotypes of elements. Moreover, elements may be smooth ( Fig. 7B 4 ) or striated ( Fig. 8G ) or with intermediate structures ( Fig. 7G 1 ). Juvenile elements are more often striated than adult or gerontic ones. Therefore, it is likely that striations and other surface microstructures were formed, or are preserved, as a result of biological or taphonomic processes and do not represent features of systematic value.

Some symmetrical and slightly asymmetrical elements of Scolopodus reported outside Baltoscandia ( Dubinina 2000; Lehnert 1993; Ji and Barnes 1994; Zhang 1998) are morphologically very similar to S. striatus . The difference between Baltoscandian and North American forms was discussed by Ethington and Clark (1981) and later by Ji and Barnes (1994) who assigned the North American Scolopodus to Scolopodus subrex Ji and Barnes, 1994 based on the higher number of costae, its greater height and sometimes costate anterior margin of the base. Ethington and Clark (1981) noted that small additional costae are not typical for the North American Scolopodus rex −like forms. However, the S. striatus elements in the available collections from Baltoscandia demonstrate wide variability in the morphological characters listed above. Some rare varieties of paltodiform and scandodiform elements bear costae on the outer side, and also the anterior side of some large compressed paltodiform elements can be costate. Moreover, the number of costae varies significantly from sample to sample. The earliest representatives of S. striatus from the clays of the Hunneberg Stage are characterised by relatively fewer costae whereas the elements from the Billingen Stage (at the Ottenby section, Sweden) bear more numerous and high costae. However, all scandodiform Scolopodus elements from Baltoscandia are nongeniculate. Scolopodus with geniculate scandodiform elements in the apparatuses like those reported from China by Zhang (1998: pl. 17: 8) seem to belong to another species of Scolopodus .

Stratigraphic and geographic range.—From the upper part of the Paroistodus proteus Zone up to the Baltoniodus norrlandicus Zone in the St. Petersburg district (Pander 1986; Sergeeva 1974; Tolmacheva et al. 2001), Estonia ( Viira 1974), Sweden ( Lindström 1955, 1964; Fåhraeus 1982; van Wamel 1974; Löfgren 1978; Stouge and Bagnoli 1990), Norway ( Rasmussen 2001), and Poland ( Dzik 1976).

Figures

Fig. 5. Scolopodus species originally described by Pander. A. Scolopodus striatus Pander, 1856, in lateral (A1, A4), posterior (A2), and anterior (A3) views; A5, cross section of the base (Pander 1856: table 2, fig. 8a–d, table A, fig. 5f). B. Scolopodus semicostatus Pander, 1856, in lateral views (B1, B2); B3, cross section of the base (Pander 1856: table 2, fig. 4a, b, table A, fig. 5e). C. Scolopodus sublaevis Pander, 1856, in lateral (C1) and posterior (C2) views; C3, cross section of the base (Pander 1856: table 2, fig. 3a, b, table A, fig.5e). D. Scolopodus quadratus Pander, 1856, in lateral (D1, D2), posterior (D3), and lower (D4) views; D5, cross section of the base (Pander 1856: table 2, fig. 6a–c, table A, fig. 5e). E. Scolopodus costatus Pander, 1856, in lateral (E1, E4), posterior (E2), and anterior (E3) views; E5, cross section of the base (Pander 1856: table 2, fig. 7a–d, table A, fig. 5e). F. Scolopodus aequilateralis Pander, 1856, in lateral (F1, posterior (F2), and anterior (F3) views; F4, cross section of the base (Pander 1856: table 2, fig. 5a–c, table A, fig. 5e).

Fig. 6. A–I. Scolopodus striatus Pander, 1856 from the Popowka River locality, St. Petersburg region, Russia. All elements are from the uppermost Prioniodus elegans Zone (Early Ordovician). A. Compressed paltodiform element (S), short−based variant, neotype specimen PMU In 1030. B. Acontiodiform element (P), PMU In 1007. C. Compressed paltodiform element (S), short−based variant, PMU In 1003. D. Paltodiform element (S), inner view, PMU In 1006. E. Compressed paltodiform element (S), long−based variant, PMU In 1008. F. Scandodiform elements (M), inner view, PMU In 1004. G. Scandodiform elements (M), anterior view, PMU In 1005. H. Acontiodiform element (P), detail of the cusp, PMU In 1001. I. Compressed paltodiform element (S), detail of the cusp, PMU In 1002. J, K. Scolopodus striatus Pander, 1856 from the presumably Pander’s collection of conodonts from the Mining Institute, St. Petersburg region, Russia. J. Compressed paltodiform element (S), short−based variant, paratype specimen PMU In 1028. K. Compressed paltodiform element (S), short−based variant, PMU In 1029. Scale bars 200 µm, except H, I for which are 50 µm.

Fig. 8. Scolopodus striatus Pander, 1856 from the Harku section, Estonia. All elements are from the sample H−5, the lower part of the Baltoniodus navis Zone (Early Ordovician). A–C. Acontiodiform elements (Sa). A. PMU In 1019 in inner (A1), posterior (A2), and outer (A3) views; detail of the cusp (A4), note the absence of striation. B. PMU In 1020 in inner (B1) and posterior (B2) views. C. PMU In 1021 in posterior view. D–F. Scandodiform elements (M). D. PMU In 1022 in posterior (D1) and inner (D2) views. E. PMU In 1023 in inner (E1) and outer (E2) views. F. PMU In 1024 in outer (F1), posterior (F2), and inner (F3) views. G. Detail of the cusp, PMU In 1025, note the striation. H, I. Subrounded elements (Sa). H. PMU In 1026 in lateral (H1), posterior (H2), and lateral (H3) views. I. PMU In 1027 in lateral (I1), posterior (I2), and lateral (I3) views. Scale bars 200 µm, except A4 and G for which are 50 µm.

Fig. 7. Scolopodus striatus Pander, 1856 from the Harku section, Estonia. All elements are from the sample H−5, the lower part of the Baltoniodus navis Zone (Early Ordovician). A–C. Paltodiform elements (S). A. Short−based variant, PMU In 1009 in inner (A1) and posterior (A2), and outer (A3) views. B. Medium−based variant, PMU In 1011 in inner (B1), posterior (B2), and outer (B3) views; detail of the cusp (B4). C. Medium−based variant, PMU In 1012 in inner (C1), posterior (C2), and outer (C3) views. D, E. Compressed paltodiform elements (S). D. Long−based variant, PMU In 1013 in lateral (D1) and posterior (D2) views. E. Short−based variant, PMU In 1014 in lateral (E1), posterior (E2), and lateral (E3) views. F. Short−based variant, PMU In 1015 in lateral (F1) and posterior (F2) views. G. Long−based variant, PMU In 1016 in lateral (G2) view; detail of the cusp (G1). H. Short−based variant, PMU In 1017 in lateral (H1) and posterior (H2) views. I. Short−based variant, PMU In 1018 1017 in lateral (I1) and posterior (I2) views. Scale bars 200 µm, except A4 and G1 for which are 50 µm.

Fig. 3. Schematic drawings of Scolopodus striatus Pander, 1856 element morphotypes. A. Acontiodiform element (P). B. Scandodiform element (M). C, D. Paltodiform elements (S). C. Medium−based variant. D. Shortbased variant. E–G. Compressed paltodiform elements (S). E. Long−based variant. F, G. Short−based variant. H. Subrounded element (Sa).

Fig. 4. Scatter diagram showing the ratio between base length and depth of the basal cavity for element morphotypes.

Fig. 1. Location of the Harku section in Estonia and the Popowka River section in Russia. Legend: 1, the Popowka section; 2, the Harku section; dash line marks the Baltic−Ladoga Klint.