Some Trans-Lapetus Conodont Faunal Connections in the Tremadocian

Bollettino della Società Paleontologica Italiana 37 (2-3), 1998 ISSN 0375-7633 Modena, Novembre 1999

Some trans-lapetus conodont faunal connections in the Tremadocian

Anita LbFGREN John E. REPETSKI Raymond L. ETHINGTON Department of Geology U. S. Geologica! Survey Department of Geologica! Sciences Lund Universiry Reston, Virginia Universiry ofMissouri-Columbia

KEYWORDS- Conodonts, Variabiloconus, Paleobiogeography, Ordovician, Tremadocian, Baltoscandia, Laurentia.

ABSTRACT- Paleobiogeographical barriers within the Iapetus Ocean ejfectively restricted conodont faunas in Baltica ftom contact with those in Laurentia during Tremadocian time. Only species ofCordyfodus, Paltodus, Drepanodus, Paroistodus and l:;P.etognathus have been reported to occur on both sides ojthe lapetus Ocean. Continued studies offaunas ftom deeper platjorm and slope settings ojNorth America (Laurentia) and generally deeperwa_ter faunas o[Scandinavia (Baltica) reveal that these faunas share a jèw more species. One o{these taxa was first described as Oneotodus vanabi11s LmdstriJm, 1955, ftom upper TremadoCian beds ofsouth-central Sweden. !t now has been recovered ftom Nevada and Pennsylvania as well. lts apparatus appears to be seximembrate, with only minor geographic variation ofelements between Baltica and Laurentia. Comparison with species oj the Laurentian genus Variabiloconus Landing, Barnes & Stevens, 1986, has convinced us that "0. "variabilis should be transferred to Variabiloconus. A closely related taxon, Variabiloconus transiapeticus n. sp., is reported ftom south-central Sweden, Nevada and Colorado, strengthening the connection between conodont faunas in the two paleocontinents in the Tremadocian. Moreover, a jèw specimens o{the North American zona! index species Rossodus manitouensis Repetski & Ethington, 1983, have been found in samples {rom the Paltodus defrifer Zone in Scandinavia, confirming previous correlations and demonstrating that even the strictest paleobiogeographical clelimitations ca n sometimes be overcome.

RIASSUNTO- [Relazioni tra le faune a conodonti tremadociane attraverso l'oceano Giapeto] -Barriere paleogeografiche nell'oceano Giapeto hanno limitato i contatti tra le faune a conodonti del Baltica e quelle del Laurentia durante il Tremadociano. Solo alcune specie di Cordylodus, Paltodus, Drepanodus, Paroistodus e Iapetognathus sono state segnalate in entrambe le sponde dell'oceano Giapeto. Nuovi studi condotti su faune di piattaforma profonda e di scarpata del Nord America (Laurentia) e di acque generalmente profonde della Scandinavia (Baltica) mostrano che queste faune contengono altre specie comuni. Uno di questi taxa, che era stato descritto come Oneotodus variabilis Lindstrom negli strati del Tremadociano sup. della Svezia centro-meridionale, viene segnalato anche in Nevada e in Pennsylvania. Il suo apparato sembra essere seximembrato e la sua composizione presenta solo qualche differenza, poco significativa, tra le popolazioni di Baltica e di Laurentia. Un conftonto con specie nord-americane del genere Variabiloconus Landing, Barnes & Stevens suggerisce che "0. "variabilis debba essere riftrito a questo genere. Un altro taxon, strettamente collegato, Variabiloconus transiapeticus n. sp. , viene segnalato in Svezia centro-meridionale, Nevada e Colorado, aumentando così le relazioni tra le faune a conodonti tremadociani dei due paleocontinenti. Inoltre, alcuni esemplari della specie indice nord-americana Rossodus manitouensis Repetski & Ethington sono stati trovati in Scandinavia in campioni della biozona a Paltodus deltifer: questi ritrovamenti conformano le precedenti relazioni e dimostrano come anche le più restrittive limitazioni paleogeografiche possano a volte essere superate.

INTRODUCTION dosely related one, Variabiloconus transiapeticus n. sp., both seem to have a seximembrate apparatus. The North American Midcontinent (Laurentia) W e also have found the North American zonal index with its shallow, tropical sea had few conodont taxa in species Rossodus manitouensis in very low abundance in common with the colder, generally deeper sea that a few samples from the Paltodus deltifer Zone in covered Baltica in the late Tremadocian (see e.g. Baltoscandia. This discovery confirms previous Bergstrom, 1990). In uppermost Cambrian to mid- correlations and emphasizes the importance of long- Tremadocian strata, more or less cosmopolitan species distance faunal connections in stratigraphy. of Cordylodus provi de a fìrm framework for correlation (Bagnoli et al., 1987; Kaljo et al., 1988), whereas most correlations of the upper Tremadocian between LOCALITIES AND MATERIAL Laurentia and Baltica have been inferred indirecdy. The new information provided here allows direct Variabiloconus variabilis (Lindstrom) has been comparison of faunas from either side of the Iapetus recovered from the southwestern part of the Ocean and reveals additional faunal connections. One allochthonous Hamburg klippe near Jonestown, eastern taxon was described fìrst as Oneotodus variabilis by Pennsylvania, (JR, unpublished USGS collection Lindstrom (1955) from upper Tremadocian beds of 11546-CO; Fredericksburg 7 -l /2 minute topographic south-central Sweden. It has now been compared with quadrangle, Lebanon County); see Epstein et al. (1972) well known Laurentian taxa such as Teridontus and for a general description of the Hamburg klippe and Variabiloconus, and we are convinced that "O. "variabilis discussion of faunas ca. 45 km to the east-northeast of belongs to Variabiloconus. This species, and a new and Jonestown; see also Bergstrom et al. (1972) and Faill 160 A. LOFGREN,j.E. REPETSKJ, R.L. ETHIN GTON

( 1997). A richer collection of V. variabilis was found age and Laurentian origin ever had been prepared, so in USGS collection 11545-CO (A. G. Harris, collector; the presence in it of R. manitouensis cannot be unpublished) from the base of the limestone member attributed to contamination. of the Goodwin Formation in Ninemile Canyon, Rossodus manitouensis also was recovered from a Antelope Range, Eureka County, Nevada (Merriam, sample taken at the same leve! as Lindstrom's (1955) 1963). This sample also yielded Variabiloconus sample 5 from Stora Backor, Vastergodand, and from transiapeticus n. sp. The latter taxon has been obtained a sample from the lower part of the Ceratopyge in Colorado from the Manitou Formation; in Williams Limestone (Bj0rkasholmen Formation) at Canyon in the Rampart Range near Manitou Springs Bjerkasholmen, just outside the city of Osio, Norway and in Missouri Gulch north ofWoodland Park. Both (Bockelie, 1982, p. 115). Both of these samples carne localities are in the frontal ranges of the Rocky from the Paltodus deltifer Zone. As with the sample Mountains (Maher, 1950; Berg & Ross, 1959). from Brattefors, these specimens are perfecdy consistent Another Manitou locality that has yielded this form is with their associateci faunas in terms of CAI an d details at Horseshoe Mountain in the Mosquito Range about of preservation and appearance. Paleogeographic 11 km southeast of Leadville, Colorado (Ethington locations of these samples is shown in Text-fìg.l. collections; see Maher, 1950, for detailed descriptions of the Williams Canyon and Missouri Gulch localities; Preservation and repository- The material generally see Myrow et al., 1995, for location of Horseshoe is well to verywell preserved, enabling us to study details Mountain). of surface striation, distribution of white matter, etc. The largest collection of V. variabilis elements (1533 The figured specimens are deposited in the type specimens) was retrieved from Scandinavia, from collections of the Department of Paleobiology, U.S. sample Vg84-26, upper Paltodus deltifer Zone at National Museum of Natura! Hisrory (USNM), Brattefors, Sweden (Lofgren, 1997a). A few other Washington, D.C. samples from this locality and interval yielded this taxon, as did samples from Orreholmen which is 45 km south-southeast of Brattefors (Lofgren, 1996; see FAUNAL CONNECTIO S Tjernvik, 1956, for description of the Stenbrottet/ Orreholmen locality). This is the same stratigraphic Studies of faunas from deeper platform and slope interval and the same generai area from which settings ofNorth America and generally deeper water Lindstrom's (1955) type material of this taxon carne. faunas of Scandinavia have thus revealed that these Additional specimens were recovered from a sample faunas share a few more species than had been assumed the upper P. deltifer Zone at Ottenby, southern before. Oland, Sweden (see Tjernvik, 1956, for description of Three localities in western Baltica (two in this locality). Vastergodand, Sweden, and one near Osio, Norway, Variabiloconus transiapeticus n. sp. is f'resent in a see Text-fìg. l) have yielded extremely rare specimens stratigraphically slighdy higher sample (LH6) from of the North American zonal index species Rossodus Brattefors (reported as "Laurentian taxa'' by Lofgren, manitouensis Repetski & Ethington, 1983, in beds 1997a). Brattefors is a unique locality, located at the referred to the upper part of the Baltic Paltodus deltifer foot of the hill Kinnekulle in the Province of Zone. The Scandinavian specimens represent slighdy Vastergodand, sourh-central Sweden. The conodont asymmetrical coniform element types (perhaps Sb samples collected at Brattefors carne from an upper elements; Pl. 3, fìgs. 13, 15, 21) and fall within the Tremadocian sequence that was deposited and limits of variation for North American populations of preserved inside conical collapse structures that formed the species. How these specimens carne to be dispersed in mid-Tremadocian time. Teves & Lindstrom (1988) to an area so far from the tropical main area of described the formation of and general stratigraphy distribution of the species (Repetski & Ethington, within these structures. The stratigraphic sequence 1983; Ethington & Repetski, 1984; Chen & Gong, within the Brattefors "plugs" probably is more complete 1986 [ref.orted therein as "Acodus" oneotensis]; Shergold and less condensed than that in any other area in & Nicol , 1992) is conjectural. Chance dispersa! of the Sweden with beds of similar age. Lofgren ( 1977a) gave animals by abnormal current conditions or through particulars about the rest of the conodont faunas in ocean-crossing predators is possible. the Brattefors samples discussed here. Suffìce it here Rossodus manitouensis was a rare visitor to Baltica, to note that conodonts are particularly abundant in but two species of Variabiloconus seem to have been one of these samples (Vg84-26; 10,464 elements per established as normal parts of the fauna in the upper kg of rock). One of the specimens of Rossodus Tremadocian ofBaltoscandia. Formerly Variabiloconus manitouensis (Pl. 3, fig. 21) was found in that sample; was believed to have been restricted to circumequatorial the abundance of this species thus is less than 0.006% areas (e.g., Landing et al., 1986; Ji & Barnes, 1994). of the elements from this sample. The sample was The two species, Variabiloconus variabilis and V. processed in a laboratory where no sample of similar transiapeticus n. sp., have been found to be part offaunas TRANS-IAPETUS CONODONTS 161

recovered the lower to middle Tremadocian (Assemblage 2) graptoliteAnisograptus richardsoni from a level probably no more than 2 m stratigraphically separated from sample 11545-CO at this same locality. The collections from the latter locality also produced specimens of Variabiloconus transiapeticus n. sp. Samples yielding V. transiapeticus n. sp. have been obtained in Colorado from the Manitou Formation in Williams Canyon near Manitou Springs, and in Missouri Gulch north of Woodland Park. Variabiloconus transiapeticus n. sp. occurs at a slighdy higher stratigraphic level than V. variabilis a t Brattefors in Sweden (sample LH6 ofLofgren, 1997a). Thus far Variabiloconus has no t been found elsewhere in Sweden, perhaps because beds of equal age have not been preserved outside the unique "plugs" of Brattefors (Teves & Lindstrom, 1988; Lofgren, 1997a). Variabiloconus is represenred by other species in more typical, shallow water Midcontinent settings, but none of them is known to be represented in Baltica. lt thus is highly probable that V. variabilis and V. transiapeticus n. sp. belonged to a Variabiloconus stock that had slighdy different environmental preferences (e.g., col der water) and also wider geographical dispersa! Text-fìg. l - Sketch map of the Tremadocian showing the locations than species belonging to the main part of the lineage. of fìnds of Rossodus manitouemis in Scandinavia/Baltica (fìlled circles) and of Variabiloconus transiapeticus n. S(J. The stratigraphic interval representing times when and/or V. variabilis in NorthAmerica/Laurentia (stars). conditions o n the Baltic si de of lapetus were suitable Base map from McKerrow et al. (1991) . for Variabiloconus must have been very limited, fori t is restricted to the upper part of the Paltodus deltifer Zone. The N orth American ranges of Variabiloconus variabilis and V. transiapeticus n. sp. start in the R. manitouensis in Baltica as well as in faunas from deeper platform Zone (Missouri Gulch locality in Colorado and and slope settings in North America. Variabiloconus probably the Ninemile Canyon locality in N evada) and variabiliswas described for the fìrst rime from the upper probably extend into the Macerodus dianae Zone Paltodus deltifer Zone ofSweden by Lindstrom (1955), (Hamburg klippe sample). The minor morphological and most subsequent reports of it from outside differences berween North American and European Balroscandia are dubious (see synonymy list). One specimens observed may be due to slight difference in exception is Landing's (1983) report of its occurrence their ages, bur more likely they can be explained as an in a deep shelf to continental slope setting in Vermont. instance of geographical separation of populations. We have found this species at two other localities with similar settings; one is the allochthonous Hamburg klippe in eastern Pennsylvania. The origina! si te of these SYSTEMATIC PALEONTOLOGY strata is uncertain; they could represent peri-Laurentian slope facies or slope deposits of an intra-lapetus Genus VAR!ABILOCONUS Landing, Barnes & Stevens, microcontinent that subsequendy was amalgamateci 1986 onto Laurenria (e .g., Faill, 1997). The other localiry where V. variabilis has been found is the Goodwin TJpe species - Paltodus bassleri Furnish, 1938. Formation in Eureka Counry, N evada, as part of a fauna (in sample 11545-CO) most likely correlatable with Remarks - Landing et al. (1986) diagnosed the Rossodus manitouensis Zone, but dominateci by Variabiloconus as having a multimembrate apparatus species more typical of the Paltodus deltifer Zone of of variously costate an d sulcate, microstriated elements Baltoscandia. Ethington ( 1981) reported faunas of the with albid cusps and inrergradational symmetries, and Rossodus manitouensis Zone from the underlying their Table 3 lists up to seven different element types. Caryocaris shale member of the Goodwin Formation All of the specimens of Oneotodus variabilis illlustrated at this section, and JR has recovered faunas assignable by Lindstrom (1955) in the origina! description of the ro the Low Diversity lnrerval and Macerodus dianae species were derived from the same sample, Stora Zone beginning at more than 20 m above this collection Backor 5, from the upper Paltodus deltifer Zone, and inrerval. Additionally, Erdtmann & Comeau (1980) are part of the same apparatus. Ethingron & Brand 162 A. LOFGREN, ]E. REPETSKJ, R.L. ETHINGTON

(1981) demonstrated that none of Lindstri:im's 1996 "Oneotodus" variabilis Lindstriim- LOFGREN, fìg. 8L. specimens could be congeneric with the type species non 1998 Oneotodus variabilis Lindstriim -ALBANES I, p. 127, of Oneotodus, O. simplex (Furnish, 1938). Generai pl. 5, fìgs. 31-32. shape, microstriation and white matter distribution in the type species of Variabiloconus, V. bassleri, are similar Description- The cusp is albid and the base hyaline, to those in "0. " variabilis, a fact already commented and the boundary between these regions typically is on by Landing et al. (1986, p. 1946), who tentatively fairly sharp, making an angle of about 30 degrees with assigned "O. "variabilis to Variabiloconus. W e agree with the posterior margin of the cusp. This distribution of these authors that elements of V. variabilis have more white matter resembles that found in the older species reclined cusps and weaker costae than those of V. Teridontus nakamurai (Nogami) as described by Nicoll bassleri. (1994). In that species the line delimiting white an d As reconstructed here, the apparatus of V. variabilis hyaline matter makes a greater angle with the posterior consists of six element types, the ones fìgured by edge of the cusp than in any of the V. variabilis Lindstri:im (1955) in his text-fìgure 6 as a and b (=Sb), specimens investigated by us. as c (=Sa), and as d (=Sd), respectively, one type with a lntertwining, rather coarse striations (each c. l rm rounded anterior and sharp posterior margin (=Se), a wide) can be observed on well-preserved elements of short-based type represented by the specimens V. variabilis, particularly on the posterior face of Sa illustrateci by Lindstri:im's Pl. 5, fìgs. 4 and 5 (=Pa), elements. LandinR et al. (1986) described elements of and a short-based concavo-convex type, often with a V. bassleri as being 'longitudinally microstriated," while latera! costa a t the base-cusp transiti o n ( =Pb). Ji & Barnes (1994) found V. bassleri elements "covered Severa! of the element types also can be recognized by faint striations." Buggisch & Repetski (1988, pl. 2, in apparatus reconstructions of Variabiloconus bassleri fig. 19) and Nicoll (1994, fig. 4:2e) found striations of (Furnish) by Landing & Barnes (19 81), Landing et al. the same size as or slightly coarser than those of V. (1986), Fa.lmeus & Roy (1993) and, butto a !esser bassleri in Teridontus nakamurai (Nogami). extent, by Ji & Barnes (1994). Teridontus nakamurai (Nogami) also seems to include very similar element Sa element (Text-fig. 2A-D, Pl. 2, figs. 10-17) - types according to Nicoll's (1994) reconstruction. Some (Lindstri:im, 1955, pl. 2, figs. 14, 17, text-fig. 6c). The of these element types were recognized in the originai cusp is erect to reclined; its cross-section is round description of that species (Nogami, 1967), an d they distally. The basai cross-section of this symmetrical may be basic to a larger group of conodonts. element is triangular, but the oral margin as well as the antero-lateral corners are rounded aff. The latera! sides of the base carry broadly rounded carinae that end at V ARIABILOCONUS VARIABILIS (Lindstri:im, 1955) the antera-basai corners. The carina is delimited Pls. l, 2; Text-fìg. 2 posteriorly by a groove that fades aut about half way up the cusp in most specimens. The carinae an d grooves 1955 Oneotodus variabilis n. sp. - LINDSTROM, p. 582, pl. are symmetrically placed. The posteri or margin of the 2, fìgs. 14-18, 47, pl. 5, fìgs. 4-5, text-fìg. 6. cusp is not sharp, except far a short segment where it 1968 Oneotodus variabilis Lindstriim - MoUND, pp. 414- 415, pl. 3, fìgs. 42-57, pl. 4, fìgs. 1-8. meets the oral margin in a few elements. This probably non 1970 Oneotodus variabilis Lindstriim - BARNES & TuKE, p. is the same type of element as the type specimen of 90, pl. 18, fìg. 3. Paltodus bassleri Furnish, 1938. American Sa elements non 1971 Oneotodus variabilis Lindstriim- JoNES, p. 60, pl. 4, of V. variabilis often have deeper posterior grooves than fìg. lOa-c. the Swedish ones, and the grooves also begin closer to non 1971 Oneotodus variabilis Lindstriim - DRUCE & J ONES, p. 84, pl. 13, fìg. 5a-c, text-fìg. 26m. the aboral margin. The slight differences may be due non 1971 Oneotodus variabilis Lindstriim - GREGGS & BoNo, to the geographical restriction of respective populations. pp. 1467-1468, pl. l, fìgs. 10, 11, 13-16a. 1974 Drepanoistodus acuminatus (Pander) - VAN W AMEL, p. Sb element (Text-fig. 2E-L, Pl. l, figs. 1-3, 7-10, 62-63 (pars), pl. 2, fìgs. 4, ?5 (only). 1974 Oneotodus variabilis Lindstriim- VuRA, p. 97, pl. l, 12, Pl. 2, figs. 1-3, 6, 9)- (Lindstri:im, 1955, pl. 2, fig. fìgs. 14, 15, text-fìg. 118. 47, text-fig. 6b [= the holotype], p l. 2, fig. 15, text-fig. 1975 Oneotodus variabilis Lindstriim - ABAIMOVA, pp. 84, 6a). The posterior margin of the cusp and the oral 85, pl. 7, fìgs. 11, 13, text-fìg. 7 (19, 20). margin of the base are rounded, but the anterior margin non 1977 Oneotodus variabilis Lindstriim - ABAIMOVA & MAR- of the base is smoothly keeled; the keel is flexed to the KOV, p. 93, p l. 14, fìg. 11, p l. 15, fìg. 4. 1978 Oneotodus variabilis Lindstriim - FAHRA':US & inner side, thereby making the elements asymmetrical. NoWLAN, p. 460, pl. l, fìg. 20. Scarce elements have up to a few posteri or costae where 1983 Oneotodus? variabilis Lindstriim, s.f. - LANDING, p. the cusp and base meet. The posterior surface in the 1179, text-fìg. 105, U. region of strongest curvature can be scooped-out or 1983 "Scolopodus" gracilis Erhington & Clark - LANDING, text-fìg. l OV. recessed. Some Sb element have a more reclined cusp 1988 "Oneotodus" variabilis Lindstriim - BAGNOLI et al., p. than the Sa elements, but others, like the holotype, are 212, pl. 40, fìgs. 5, 6. more erect. Some elements (see Pl. l, figs. 8, 9, Pl. 2, TRANS-IAPETUS CONODONTS 163

M Q R

Text-fig. 2- Camera lucida drawings of Variabiloconus variabilis (Lindstrom, 1955) from sample Vg84-26, upper Paltodus deltijèr Zone, Brattefors. Ali X65. A-D= Sa elements: A) same specimen as Pl. 2, fig. 15; B) same as Pl. 2, fig. 11; C) same as Pl. 2, fig. 12; D) same as Pl. 2, fig. 16. E-L= Sb elements: E) same specimen as Pl. l, fig. l; F) same as Pl. l, fig. 2; G) same as Pl. l , fig. 3; H) same as Pl. l, fig. 7; I) same as Pl. l, fig. 8; J) same as Pl. l, fig. 12; K) same as Pl. l , fig. 9; L) same as Pl. l , fig. 10. M-P= Se element: M) same specimen as Pl. l, fig. 4; N) same as Pl.l, fig. 13; O) same as Pl.l, fig. 18. Q= Sd element: same specimen as Pl. l, fig. 20. R= Pa element, same specimen as Pl. l, fig. 16. S= Pb element, same specimen as Pl. l , fig. 14. 164 A. LOFGREN, ].E. REPETSKJ, R.L. ETHINGTON figs. 2-3 herein; Lindstrom, 1955, pl. 2, fig. 15) Pb element (Text-fig. 2S, P l. l, figs. 5-6, 14-15, display a slightly shorter base but otherwise are closely 19, Pl. 2, fig. 5)- (Not figured by Lindstrom, 1955). similar to other Sb elements. The reclined cusp has rounded anterior and posterior margins; the ora! edge is short and faintly keeled. The Scelement(Text-fig. 2M-P, Pl. l, figs. 4, 13, 18, Pl. anterior margin is smoothly carina te basally an d turned 2, fig. 8)- (Not figured by Lindstrom, 1955). The inwards. An inner, often faint, posterior costa is found cusp is slightly recurved with a rather sharp posterior where the cusp and base meet in many elements. edge, which continues on to the ora! margin. The anterior margin of the cusp and base are rounded. A Element ratios - The ratio berween the different smoothly rounded anterolateral carina is present on element types was calculated for Vg84-26, the sample each si de. The element is slightly concavo-convex with yielding most of the V variabilis specimens. That sample the basal cavity opening to the inner side rather than provided 273 Sa, 750 Sb, 121 Se, 154 Sd, 103 Pa and posteriorly. 121 Pb elements and 11 indeterminate specimens belonging to this taxon. The ratio which agrees most Sd element (Text-fig. 2Q, Pl. l, figs. 17, 20, Pl. 2, closely to these proportions is: 2 Sa: 6 Sb: l Se: l Sd: l fig. 7)- (Lindstrom, 1955, pl. 2, fig. 18, text-figure Pa: lPb. 6d). The cusp is recurved. These elements h ave a subtrapezoidal basal cross-section whose corners are Remarks- No tempia te has been suggested for these rounded off as in Sa elements. In contrast with the Sa kinds of apparatuses. Nicoll's (1994) reconstruction of element, part of the ora! margin and the posterior Teridontus nakamurai had 794 S and 272 P elements margin o n the lower part of the cusp have a sharp edge. which agrees better with six pairs of S elements and One or rwo rather sharp, posteriorly directed latera! rwo pairs of P elements. lt is unusual to have more costae are present on each side of the base; they are than o ne kind ofsymmetrical (Sa) elements. Ji & Barnes placed so that the elements are distinctly asymmetrical. (1994), however, found rwo symmetrical element types (a and c) in Teridontus and Variabiloconus, which Pa element (Text-fig. 2R, P l. l, figs. 11, 16, ?P l. 2, suggests that the symmetrical elements may have had fig. 4) - (Lindstrom, 1955, pl. 5, figs. 4, 5). This a different function or position than in other types of asymmetrical element with a reclined or recurved cusp coniform apparatuses. The similarity of symmetrical typically has a notch at the opening of the basai cavity elements of V variabilis with those of two other so that i t resembles Pa elements of other species of the coniform taxa, Drepanodus arcuatus and Paroistodus genus. A rounded carina continues from this notch up numarcuatus (cf Lofgren, 1997b), makes it improbable the inner side of the base and fades out on the cusp. that these elements should have had radically different The cusp has a rounded cross-section. The basal cavity functions. flares widely, particularly to the ourer side

EXPLANATION OF PLATE l

Figs. 1-20- Variabiloconus variabilis (Lindstrom, 1955) from sample Vg84-26, upper Paltodus deltifer Zone, Brattefors, Vastergorland, Sweden. l) Sb element, inner side, USNM 501091; x80; 2) Sb elemenr, outer side, USNM 501102; x90; 3) Sb elemenr, ourer side, USNM 501103; xl03; 4) Se elemenr USNM 501092; xlOO; 5) Pb elemenr, inner side, USNM 501093; xl20; 6) Pb elemenr, posterior side, USNM 501094; xl03; 7) Sb elemenr, inner side, USNM 501104; xl03; 8) Sb element, costate inner side, USNM 501095; x90; 9) Sb elemenr, costate inner side, USNM 501096; x90; lO) Sb elemenr, costate inner side, USNM 501105; xlOO; 11) Pa elemenr, USNM 501097; xlOO; 12) Sb element, smooth inner side, USNM 501098; x90; 13) Se elemenr, USNM 501099; x90; 14) Pb elemenr, inner side, USNM501100; xl03; 15) Pb elemenr, inner side, USNM 501114; x85; 16) Pa elemenr, USNM 501101; xl20; 17) Sd elemenr, USNM 501106; xl33; 18) Se elemenr, USNM 501107; xlOO; 19) Pb element, inner side, USNM 50 1115; x90; 20) Sd elemenr, USNM 501108; xl20. A. LOFGREN, JE. REPETSKJ, R. L. ETHINGTON, TRANS-IAPETUS CONODONTS P!. l 166 A. LOFGREN, j.E. REPETSKJ, R.L. ETHINGTON

Geographic distribution-The taxon has been found Repetski, 1988), the Rocky Mountains of Canada previously in Sweden (Lindstri:im, 1955; van Wamel, (Ethington & Clark, 1965, p. 197) and from Siberia 1974; Li:ifgren, 1996) an d Estonia (Viira, 1974). (Abaimova, 1975; Abaimova & Markov, 1977) are Previous non illustrateci reports of the taxon from equivocai; most probably they represent some other Baltoscandia by Viira (1966, from Estonia) and taxa. Sergeeva (1966, from western Russia) probably are The specimens figured by Bagnoli et al. (1988) Materia!- About 2000 specimens. from Oland, Sweden, are not typical and could belong t.? other taxa. Nevertheless, V. variabilis is present on Oland (van Wamel, 1974, and undescribed collections from Ottenby, southern Oland). V ARIABILOCONUS TRANSIAPETICUS n. sp. Variabiloconus variabilis also is present in deep shelf Pl. 3, figs. 1-12, 14, 16-20, 22, Text-fig. 3 to continental slope settings in Vermont (Landing, 1983), and is reported herein from the slope deposits Derivation ofname- Referring to the distribution in both the Hamburg klippe in Pennsylvania and from of the species on both sides of the lapetus Ocean. Ninemile Canyon in N evada. Of the previous reports of V. variabilis from outside Baltoscandia, those from TJpe locality- Ninemile Canyon, Antelope Range, Australia (Jones, 1971; Druce & Jones, 1971) clearly Eureka County, Nevada, U. S. A. (Merriam, 1963). concern other Midcontinent taxa (as discussed by Landing, 1983, and Landing et al., 1986) as do those TJpe stratum-Approximately 2.5m above the base from Ontario, Canada (Greggs & Bond, 1971) and of limestone member of the Goodwin Formation, Argentina (Albanesi, 1998). The reported occurrences USGS Collection 11545-CO (A. G. Harris, collector). in the Arbuckle Group of southern Oklahoma (Mound, 1968) are too poorly illustrateci to enable a definite Holotype- USNM 501146 (Pl. 3, fig. 20), an Se identification, and no specimens have been found in element. subsequent studies of faunas from these rocks (undescribed collections of Repetski and ofEthington); Diagnosis-The apparatus of V. transiapeticus consists the location makes an attribution of the specimens to of six element types; an Sa element with sharply a Midcontinent taxon probable, though. Of the reports delimited latera! "wings" and a costate posterior side, from Newfoundland, that by Barnes & Tuke (1970) an Sb element with an inwards-flexed anterior keel on definitely and that by Fahneus & Nowlan (1978) the base and often with a costate inner side, an Se probably concerns Midcontinent taxa. In the latter element with a flexed, slightly concavo-convex shape case the shape of the illustrateci element is similar to and costae on its base, an Sd element which is twisted that of an Sb element of V. variabilis, but the cusp and has up to four costae, and Pa and Pb elements appears to be hyaline, which would exclude it from with widely flaring bases. Ali elements have an erect to that taxon. The records from Antarctica (Buggisch & proclined cusp.

EXPLANATION OF PLATE 2

Figs. 1-17- Variabiloconus variabilis (Lindstrom, 1955). Figs. 1-9, 13-14 from sample USGS collection 11545-CO from the base ofthe limestone member of the Goodwin Formation, Ninemile Canyon, Antelope Range, Eureka County, N evada. Figs. l 0-12, 15- 17 from sample Vg84-26, upper Paltodus deltifer Zone, Brattefors, Vastergodand, Sweden. l) Sb element, inner side, USNM 501128; xl02; 2) Sb element, inner side, USNM 501129; x87; 3) Sb element, outer side, USNM 501130; x87; 4) Pa 1 element, USNM 501131 ; x85 ; 5) Pb element, USNM 501132; xl02; 6) Sb element, inner side, USNM 501133; xl02; 7) Sd element, USNM 501134; xll2; 8) Se element, USNM 501135; xll2; 9) Sb element, inner side, USNM 501136; x85; lO) Sa element, posterior view, USNM 501109; xlOO; 11) Sa element, latera! side, USNM 501110; x90; 12) Sa element, latera! side, USNM 501111; xlOO; 13) Sa element, oblique side view, USNM 501137, xl07; 14) Sa element, posterior view, USNM 501138; x107; 15) Sa element, latera! side, USNM 501112, x75; 16) Sa element, latera! side, USNM 501113; x90; 17) Detail of right side of l O, x800. A. LOFGREN, ].E. REPETSKJ, R.L. ETHINGTON, TRANS-IAPETUS CONODONTS P!. 2 168 A. LQFGREN, ].E. REPETSKJ, R.L. ETHINGTON

Generai remarks - Six different kinds of elements the opening to the basai cavity as is its continuation are described here. The basai cavity in ali of them is o n the posterior surface of the cusp. Severa! specimens triangular as seen from the side, with the tip dose to have a costa o n the inner si de an d dose to the posterior the anterior margin (Text-fig. 3A-H). The cusp is albid margin; it begins on the upper part of the base and above a rather sharply delimited triangular area of continues upward on the cusp and parallel to rhe hyaiine materiai along the oral margin and the lower posterior edge. The posterior face of the cusp is flat or part of the posterior margin of the cusp. All elements concave between these edges. Minor costae are present have a more prodined cusp than the corresponding o n the outer sides of the bases and lowermost parts of elements of V. variabilis whose cusp is erect to redined. the cusps of a few specimens. The basai cavity resembles an isosceles triangle in latera! view, with the shortest Sa element(Pl. 3, figs. 10-12)-The cusp is erect to side at the basai cavity opening. The Sb element differs slighdy prodined. lts anterior side is weli rounded, its from the corresponding element of V. variabilis mainly posterior surface is costate. One deep longitudinal in its more prodined to erect cusp. furrow extends along the cusp and base on each side, delimiting the laterai "wings" from the centrai posteri or Se (Text-fig. 3F, G, Pl. 3, figs. 19-20, 22)- part with its two symmetricaliy placed costae. The The cusp is prodined and has keeled orai and posterior element thus is similar to a symmetrical element of margins. The anterior margin is well rounded. The e.g. Semiacontiodus. The element differs from the entire element is slighdy concavo-convex due to flexing, corresponding element in V. variabilis by its more and almost invariably displays asymmetrically sharply delimited latera! "wings" and the costate distributed costae o n the base. The element differs from posterior. the corresponding element of V. variabilis in having less distinctive anterolateral carinae. Sb element (Text-fig. 3C-D, Pl. 3, figs. 7-9, 14)- The cusp is erect to redined with the distai end broken Sd element (Text-fig. 3E, Pl. 3, figs. 16?, 17-18)- in ali available specimens. Its length is not known, but The cusp is erect and the base can have up to four the cusp appears to have been longer than in the costae, two on each side, that continue on the cusp in corresponding element of V. variabilis. The anterior keel some elements. The distribution of the costae gives the of the base is flexed inward and fades to a rather blunt element a concavo-convex an d twisted appearance. The costa on the cusp. The oral edge is sharp except near ora! margin is not keeled, and the oudine of the basai

EXPLANATION OF PLATE 3

Conodont elements from che upper Paltodus deltifer Zone, Brarrefors and Ninemile Canyon.

Figs. 1-12, 14, 16-20, 22 Variabiloconus transiapeticus n. sp. Figs. 1-2, 7, 9, l O, 12, 16, 20 from USGS eolleecion 11545-CO from che base of che limesrone member of che Goodwin Formacion, Ninemile Canyon, Antelope Range, Eureka Counry, N evada; Figs. 3-6, 8, 11, 14, 17-19,22 from sample LH6, Brattefors, Sweden. l) Pa element, inner side, USNM 501139; x68; 2) Pa element, iner si de, USNM 50 1140; x68; 3) Pa elemenc, poscerior side, USNM 501116; x105; 4) Pa element, outer side, USNM 501117; x105; 5) Pb element, ourer side, USNM 501118; x105; 6) Pb element, inner side, USNM 501119; x105; 7) Sb? elemenc, inner side, USNM 501141; x102; 8) Sb element, oucer side, USNM 501120; x105; 9) Sb element, inner side, USNM 501142; xll2; lO) Sa element, poscerior view, USNM 501143; x107; 11) Sa elemenc poscerior view, USNM 501121; x85; 12) Sa element, poscerior view, USNM 501144; x107; 14) Sb element, inner side, USNM 501122; x105; 16) Sd? element, side view, USNM 501145; x102; 17) Sd elemenc, poscerior view, USNM 501123; xl lO; 18) Sd element, oblique side view, USNM 501124; xl lO; 19) Se element, ourer side, USNM 501125; xl lO; 20) Se element, inner side, USNM 501146; x112 (holorype); 22) Se element, inner side, USNM 501126; xl lO. Figs. 13, 15,21- Rossodus manitouensis Repecski & Echingron, 1983. 13) From Stora Baekor, Vascergodand, Sweden, Lindsrrom's (1955) bed 5, USNM 501147, x185; 15) From Bjerkasholmen, Asker, near Osio, Norway, USNM 501148, x500; 21) From sample Vg84-26, Brattefors; USNM 501127, x135. A. LOFGREN, ]E. REPETSKI, R.L. ETHINGTON, TRANS-IAPETUS CONODONTS P!. 3 170 A. LOFGREN, ].E. REPETSKJ, R.L. ETHINGTON cavity opening approximates a square. The Sd element slightly resemble Sa elements by having two differs from the corresponding element in V. variabilis posterolateral grooves. These are asymmetrically placed, primarily by having a shorter and wider base. however, and the entire element is concavo-convex and slightly twisted. The base flares widely. The Pa element Pa element (Text-fig. 3H, P l. 3, figs. 1-4)-The cusp differs from the corresponding element in V. variabilis is erect. Seen from the posterior side, a few elements e.g. by having a wider basa! cavity.

Pb element (Text-fig. 3A, B, Pl. 3, figs. 5, 6)- The cusp is erect to slightly proclined. This asymmetrical element has a much less flared basa! cavity than the Pa A element. The anterior edge is flexed far to the inner side, which also has a costa. The oral margin is short and only faintly keeled. The element differs from the corresponding element in V. variabilis mainly by its wider angle between the cusp and oral margin.

Pb Remarks-The Sa element of V. transiapeticus n. sp. is less compressed antero-posteriorly than the type specimen ofAcontiodus staujferi Furnish, 1938, which has a hyaline cusp (cf. Landing & Barnes, 1981, p. 1615), and probably represents the same element type of another species. Similar elements with albid cusps were referred to "Acontiodus" iowensis Furnish by Landing & Barnes (1981). Their taxon is of the same age as our V. transiapeticus n. sp., bur its Sa elements seem to be more proclined and to have sharper costate. This taxon may prove to be closely related to, or even conspecific with V. transiapeticus n. sp., but its associated elements have no t been reported as yet. Landing et al. (1986) combined i t with Oistodus meh li Furnish, 1938, and referred to it as Semiacontiodus iowensis.

Occurrence and range-The range of V. transiapeticus n. sp. at the Ninemile Canyon, Nevada, section is poorly constrained at present. We recognize it unequivocally only in sample 11545-CO, taken at approximately 2.5 m above the base of the limestone member of the Goodwin Formation along this traverse. That sample is dominated by an unnamed, probably new, species of Drepanoistodus an d a Drepanodus species that may be a very early representative of D. arcuatus. A late form of Rossodus manitouensis occurs at about 30 m below this sample. Samples from intervening strata have either few specimens or taxa that are not zonally diagnostic. Laurentoscandodus aff. triangularis (Furnish) and "Acanthodus" lineatus (Furnish) occur in this interval and both extend upwards for at least 25m above sample 11545-CO; because both of these species extend only a short way imo the Low Diversity Interval (e.g., see Ethington et al., 1987), it is most likely that the sample containing V. transiapeticus n. sp. is within Texr-fig. 3- Camera lucida drawings of Variabi!oconus transiapeticus the R. manitouensis Zone. Further support is given to n. sp. from sample LH6, upper Pa!todus de!tifer Zone, this assignment by the occurrence of the Assemblage 2 Brarrefors. Ali X90. A-B= Pb elemenrs: A) same graptolite species Anisograptus richardsoni at approx- specimen as P!. 3, fig. 5; B) same as P!. 3, fig. 6. C-D= imately the same horizon (Erdtmann & Comeau, Sb elemenrs: C) same as P!. 3, fig. 14; D) same as P!. 3, fig. 8. E= Sd elemenr, same as P!. 3, fig. 18. F- G= Se 1980). elemenrs: F) same as P!. 3, fig. 22; G) same as P!. 3, fig. Variabiloconus transiapeticus n. sp. is present in an 19. H= Pa elemenr, same as P!. 3, fig. 4. interval of approximately 30 meters in the section in TRANS-IAPETUS CONODONTS 171

Williams Canyon near Manitou Springs, Colorado. in the centrai Colorado sections in which it has been lts lowest occurrence there is in a dolostone unit that found. The known range is from the upper part of the Maher (1950) placed in the upper part of the Sawatch Skullrockian Stage through much of the Stairsian Stage Quartzite for which he assumed Late Cambrian age. of the North American Ibexian Series (Ross et al., The species ranges upward through the interval that 1997). he identifìed as the Ute Pass Dolomite, also assumed The range in Sweden of V. transiapeticus n. sp. is by Maher to be of Late Cambrian age, and through diffìcult to assess at present, as it has only been found the lowest 23 meters of dolomites and limestones that in o ne sample in the upper P. deltifèr Zone a t Brattefors Maher identifìed as the Manitou Formation (Lower (Lofgren, 1997a), where it occurs together with, e.g., Ordovician) at this locality. Maher (1950) reported Drepanodus arcuatus. "Orthoceras-type cephalopods" from just above the base of the sequence he identifìed as Manitou, but he did Materia!- More than l 00 specimens. not record any fossils from lower in the section. The discovery of conodonts in the purported upper Sawatch and Ute Pass demonstrates that this interval in Williams Canyon also is of Early Ordovician age. The lowest ACKNOWLEDGEMENTS sample that produced conodonts (ca 0.5 meter below Sample preparation, SEM work an d travel costS for Anita Lofgren the top ofMaher's Sawatch) has V. transiapeticus n. sp. were paid through grants from che Swedish Natura! Science together with Rossodus manitouensis, "Acanthodus" Research Council (NFR). Britt Nyberg, Lund University, drew lineatus, and Chosonodina herfurthi. In its highest Text-fìgs. 1-3. Mike Dunford helped JR with some of che occurrence in the Manitou Formation in Williams phorography. R. L. Ethingron's collections from che Manitou Formation carne from samples obtained by Pau! Myrow, James Canyon, V. transiapeticus n. sp. is associateci with Loch, and himself. ]. F. Miller, ]. Pojeta, ]r. and an anonymous Macerodus dianae H.hrxus & Nowlan. referee provided help fu! reviews of che ms. Variabiloconus transiapeticus n. sp. is present throughout all but the lowest meter of the section of Manitou Formation in Missouri Gulch north of Woodland Park, Colorado. This locality includes the REFERENCES stratum typicum of Rossodus manitouensis Repetski & ABAIMOVA, G., 1975, Ranneordovikskie konodonty srednego Ethington. The Manitou is unconformable beneath the techeniya r. Leny: Trudy Sibirskogo Nauchno-Issledovatelskoto Williams Canyon Formation (?Devonian) at this Institut Geologii, Geofiziki i Mineralogie Syrya locality and does not include equivalents of the upper (SNIGGFIMS) 207: 1-129, Novosibirsk. part of the range shown by V. transiapeticus n. sp. in ABAJMOVA, G. & MARKov, Y.P., 1977, Pervyenakhodki konodonrov nizhneordovikskoy zony Cordyfodus proavus na yuge Sibirskoy the Manitou Springs area to the east. Another Platformy. In Sokolov, V S. & Kanygin, A. V (eds.) , Problemy unconformity (Paul Myrow, personal communication, stratigrafìi Ordovika i Silura Sibiri: 86-94, Trudy Institut 1998) separates the Manitou in Missouri Gulch from Geologii i Geofìziki, Akademii Nauk SSSR, Sibirskoe the shaly underlying rocks which may be of Cambrian Otdelenie. Novosibirsk. age. The evidence presented h ere is consistent with the ALBANESI, G.L., 1998, Taxonomia de conodontes de las secuencias ordovicicas del Cerro Potrerillo, Precordillera Centra! de San biostratigraphic correlation of the Ordovician sections Juan, R. Argentina: Actas de laAcademia Nacional de Ciencias, in this part of the Colorado Front Range provided by 12: 101-252, Cordoba, Argentina. Berg & Ross (1959). BAGNOLI, G., BARNES, C.R. & STEVENS, R.K., 1987, Lower This species is present through 11.4 meters of Ordovician (Tremadocian) conodonts from Broom Point and Green Point, western Newfoundland: Bollettino della Società Manitou Formation at Horseshoe Mountain near Paleonrologica Italiana, 25: 145-158. Leadville, Colorado, The lowest known occurrence BAGNOLI, G., STOUGE, S. &ToNGIORGI, M., 1988, Acritarchs and there is in association with conodonts of the R. conodonts from che Cambro-Ordvician Furuhall manitouensis Zone but the three three stratigraphically (Kopingsklint) section (Oland, Sweden): Rivista Italiana di higher samples from which it was recovered probably Paleontologia e Stratigrafìa, 94: 163-248. BARNES, C. R. &TUKE, M.F., 1970, Conodonts from che St. George represent the Low Diversity lnterval. V. transiapeticus Formati o n (Ordovician), northern Newfoundland: Geological n. sp. is not present in stili higher samples from this Survey of Canada Bulletin, 187: 79-87. locality that contain abundant specimens of Histiodella BERG, R. R. & Ross, R.]., ]R., 1959, Trilobites from che Peerless donnae Repetski, a species typical of the M. dianae and Manirou Formations, Colorado: Journal ofPaleontology 33: 106-119. Zone. BERGSTROM, S.M., 1990, Relations between · conodont The occurrence in Missouri Gulch together with provincialism and che changing palaeogeography during che that in Williams Canyon indicate that V transiapeticus early Palaeozoic. In McKerrow, W. S. & Scotese, C. R. (eds.), n. sp. ranges in the Manitou from a level within the R. Palaeozoic palaeogeography and biogeography: Geologica! manitouensis Zone through the Lower Diversity lnterval Society Memoir 12: 105-121. BERGSTROM, S.M., EPSTEIN, A.G. & EPSTEIN, J.B., 1972, Early into the M. dianae Zone, Because of unconformity or Ordovician Norrh Adantic province condonts in eastern unproductive lithologies, the lower limi t of the range Pennsylvania: U. S. Geological Survey Professional Paper, 800- of this species cannot be established with confìdence D: D37-D44. 172 A. LDFGREN, j.E. REPETSKJ, R.L. ETHINGTON

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