EARLY ORDOVICIAN CONODONTS FROM THE SOUTHERN CUYANIA TERRANE (MENDOZA PROVINCE, ARGENTINA)
OLIVER LEHNERT, MARTIN KELLER , and OSVALDO BORDONARO
Lehnert, D., Keller, M., and Bordonaro, D. 1998. Early Ordovician conodonts from the southern Cuyan ia terrane (Mendoza Province, Argentina). In: H. Szaniawski (ed.), Pro ceedings of the Sixth Europea n Cono dont Symposium (ECDS VI). - Palaeontologia Polonica 58, 47- 65. Lower Ordovician do lomites and limestones of the Ponon Trehue Formation (Mendoza Province, Argentina) have been sampled for conodonts. The documented conodont faunas indicate a Late Tremadoc through Late Arenig age and are comparable with those from the Precordillera to the north . Composition of the faunas and sedim entological feature s show that the two areas were connected and demonstrate that the outcrops of San Rafael and the Precordillera are part of the same terrane. The faunas show a trend from Midcontinent shallow-water conodonts in the lower part of the succession to temperate-water faunas in the middle part. Pandemic faunas, together with elements of the cold-water group are present in the uppermost interval of the Ponon Trehue Formation and mirror a remark able sea-level rise. Key w o r d s : Conodonta, biostratigraphy, paleogeography, Early Ordovician, Cuyania Terrane , western Argentin a. Oliver Lehnert [[email protected], Martin Keller [[email protected], Institut fur Geologie und Mineralogie, Universitiit Erlangen, Schlossgarten 5, D-91054 Erlangen, Germany. Osvaldo Bordon aro, Centra Regional de Investigaciones Cientificas y Tecnicas (CRIC IT) , CC l3I, 5500 Mendoza, Argentina.
Received 2 February 1997. accepted 30 September 1997 48 OLlVER LEHNERT, MARTIN KELLER and OSVALDO BORDONARO
INTRODUCTION
The Precordillera of San Juan, La Rioja, and Mendoza and other outcrops of Early Paleozoic platform carbonates in western Argentina, together with the basement of the western Sierras Pampeanas, represent fragments of a Laurentia-derived "Cuyania Terrane" (RAMOS 1995). In the Precordillera, approx. 2100 m thick tropical carbonate platform deposits (KELLER 1997) were deposited from the late Early Cambrian to the Early Llanvirn in a miogeoclinal setting . This terrane with its Cambro-Ordovician carbonate platform is unique in South America. It has a possible extension of 1000 km by 600 to 800 km (RAMOS 1995; K ELLER 1997).
Geological Provinces of Northwestern Argentina
• Cuyania Terrane D Sierra de Famatina D western Sierras Pampeanas D Paleozoic outcrops undifferentiated
Fig. 1 A. Location of the "Cuyania Terrane" in western Argenti na (modified from K ELLER 1997). B. The study area (Fig. 2), south of the city of San Rafael, is marked by a star. EARLY ORDOVICIAN CONODONTS FROM SOUTHERN CUYANIA TERRANE 49
RAMOS et al. (1986) pointed out strong sedimentological and faunal affinities between the Precordillera and the Appalachians. Con sequently, RAM OS et al. (1986) and RAM OS (1988) interpreted the Precordillera as an exotic terrane of possible Laurentian provenance. Recent investigations suggest that this terrane originated in the Ouachita embayment at the southern margin of Laurentia (DALLA SALDA et al. 1992a, b; DALZI EL et al. 1994; ASTINI et al. 1995, KELLER and DICKERSON 1996). In the study area (Figs 1, 2), cry stalline basement of Grenvillian age (RAMOS personal communication 1996) composed of siliciclastic metasediments, gneisses, and granitoids is exposed. North of the Ponon Trehue Creek, these Prec ambrian rocks (Cerro La Ventana Formation, Fig . 2) are overlain by Lower Ordovician carbonates of the Ponon Trehue Formation. South of the creek, the basal sedimentary succes sion con sists of Middle to Late Ordovician (Llanvirn- Caradoc) deposits dominated by siliciclastic s (Lindero Formation; Fig. 2). WICHM ANN ( 1928) was the first who compared the carbonates of the San Rafael area with Ordovician outcrops in the northern part of the Mendoza Province. Ordovician fos sils from San Rafael have been first described by NUNEZ (1962). BALDIS and BLASCO (1973) reported Llanvirnian to Caradocian? trilobites. LEVY and NULLO (1975) described Llanvirnian to Llandeilian brachiopods. Only one short paper (H ER EDI A 1982) dealt with the occurrence of conodonts iPygodus anserinusi ; however, the sa mple localit y is not given in that paper. Other publications dealing with this area are those of PAD ULA (1951), CRIADO ROQUE and IBANEZ (1979), and NUNEz (1979). The purpose of this study is to document for the first time the conodont faunal success ion of a craton al part of the Cuyania Terrane. Additionally, the data indicate that sea-level changes in the San Rafael area were simultaneous with those known from the miogeoclinal setting to the north. Also, we discuss here the onlap of the carbonates onto the craton and the strong condensation of the carbonate sequence. Finally, the new dat a support the suggestions of various authors that the terrane was derived from Laurentia. In the discussion of faunal affinities we will follow the terminology of BAGNOLl and STOUGE (1991) for the paleogeographical distribution of Arenig conodonts. These authors distinguished five different groups in two major realms (Midcontinent, North Atlanti c): a pandemic group, a cold water group (North Atlantic Province ), a warm water group (Midcontinent province), a temperate water group, and a warm water China group (China and Korea endemics). The specimens figured (IANIGLA PI 710-762) are deposited in the repository "Paleontologfa de Invertebrados del IANIGLA" (lnstituto Argentino de Nivologfa, Glaciologfa y Cienci as Ambientales; Departamento de Geologfa y Paleontologfa) in Mendoza, Argentina. Acknowledgements. - We thank Dr. Jerzy DZIK (Institute of Paleobiology, Poli sh Academy of Sciences) for his careful review and critical comments, which improved the paper significantly. The "Deutsche Forschungsgemeinschaft" is gratefully acknowledged for financing the research on the Cam bro-Ordovician conodonts from the Argentine Precordillera and the San Rafael area by O. LEHN ERT (Le 867/2- 1) and the sedimentologic inve stigations on the Early Paleozoic success ions by M. KELLER (Ke 470/2-2). We also grat efully acknowledg e the logi stic support provided by the Centro de Investiga cion es Cientfficas y Tecni cas (CRICYT,Mendoza) and the "Museo Municipal de Historia Natural de San Rafael ".
THE SECTION AND THE CONODONTS
The Ponon Trehue Formation has been recently redefined by BORDONARO et al. (1996). In its type section at Cerro Ai Sol (Fig. 2), the succession was subdivided into 4 informal units. Striatodontus prolificus (PI. 1: 1) has been obtained from a level 3 m above the base of the dolomites of unit I (sample CAS I - see Fig . 2). Unfo rtunately, sample CAS 2 from the thick-bedded dolomites which form the upper part of this basal unit yielded brachiopod fragments only. No data were obtained from unit 2 composed of biolaminites and microbial boundstones. The dolomites and microbial carbonates of the two basal units represent deposits of a peritidal environment. In unit 3 of the Ponon Trehue Formation, different lithologies and open-marine macrofaunas are present. S. prolificus (PI. 1: 2-4, 7, 8), Colaptoconus quadraplicatus, and Eucharodus parallelus (PI. 1: 5) have been recovered from sponge-algal mounds at the base of this unit (sample CAS 3). The se conodonts represent Midcontinent warm-water species, typical of coeval shallow-water deposits in the Precordillera. Grainstones and packstones with cherts, bioclasts, and intraclast s are associated with those mounds. 50 OLlVER LEHNERT, MARTIN KELLER and OSVALDO BORDONARO
Cerro Chinche
," ,,"e> u "" , " , o " c" " ,, ,,0 o 1 km ~ ,,",," ~ ,,0,," g ,,",," g ,,() ,, " " 00" " " ,," ,,(> , '" ,,"" 0 ° 0 "" 0 " 0"0 0 ° ° 0 ° ,,°,, "0 0 0°,,"000 ",, °0 ""0"" ° 0 g ,," ,," ~ ,,'" 0 '" g ,,",," g "" ,,C' g "u ')" + c c ,," c " ,," " " ,, " " " ,, " " " + -+ "" '-=:=''-' _ J o : ~ c o : ': 0::0° :0::0°: 0::00: " + ", + type section D alluVium] Ponon Trehue Formation Quaternary basalts info rma l D units .!.1Q ~.J.g * f\ 75m -.i ~ Permian 7 8 .!. 3 -5! a Carboniferous - 4 3 Middle/Uppe r 50m - D Ordovician (Lindero Fm.) Lower Ordovician 2 (Ponon Trehue Fm.) • Precamb rian 25m - - ~ D (Cerro La Venta na Fm.) - -r- - 1 -r - -r- +- - +- 1 """ f\ * conodonts trilobites crinoids ~ 1 7 C receplaculilids orthoceratids brachiopods sponges ~ ~ ~ Fig. 2 Distribut ion of Ordovician deposits north and south of Ponon Trehue Creek and type section of the Ponon Trehue Formation (Cerro Ai Sol), modified from Bordonaro et al. ( 1996). Sampled horizons (samples CAS 1- 10) are indicated by arrows. Approximately 4 m above the base of this unit, "Drepanodus'' gracilis has been found in a grainstone sample (CAS 4; PI. I: 6). The next two samples (CAS 5 and CAS 6, Fig. 2) from the overlying nodular wackestones yielded the first Early Arenig faunas with elements of the temperate-w ater group (Berg stroemognathus) and the pandemic group tTropodu s. Oepikodusi . Brachiopods, algae, and echinoderm fragments are abundant. In sample CAS 5, Bergstroemognathus extensus (PI. I: 14, 19), Juanognathus jaanussoni (PI. 1: 9), Scolopodus cf. rex (PI. I: 10, 11 ), Tropodu s sweeti (PI. 1: 12,13, IS), Scolopodus krummi (PI. 1: 20; PI. 2: 4, 9), Oepikodus communis (PI. 1: 17), and Drepanodus arcuatus (PI. 1: 18) have been found . Also, sample CAS 6 contained one element of the deeper-water species Paracordylodus gracilis (PI. I: 16). This is the lowermost occurrence of a cold-water group genu s in the section. The upper part of unit 3 consists of thick-bedded wackestones with biostromes of large receptaculitids, EARLY ORDOVICIAN CONODONTS FROM SOUTHERN CUYANIA TERRANE 51 Fischerites camacho (NITECKI and FORNEY) , and sponges. At the top of unit 3 (sample CAS 7), the first elements of Periodon flabellum (PI. 2: 3, 6), another open-marine element of the cold-water group, are present together with the pandemic Oepikodus evae (PI. 2: 1, 5, 7). In addition, the temperate-water genus Bergstro emognathus (B. extensus, PI. 2: 2) has been found. However, Fahraeosodus marathonensis (PI. 2: 8), also occurring at this level, represents a species typical of tropical environments of Laurentia (e.g. , FINN EY and ETHIN GTON 1992). The top of the sequence exposed at Cerro Ai Sol is composed of dark gray nodul ar wackestones and grain stones (unit 4: 6 m thick) that reveal a sea-level rise and remarkable deepening of the environment. Three samples have been taken from these limestones (CAS 8-CAS 10), I m, 3.5 m, and 6 m above the base of unit 4. P. flabellum (PI. 2: 12, 13, 17) and Protopanderodus gradatus (PI. 3: 4, 5) are present in all three samples. Paroistodus originalis (PI. 2: 10; PI. 3: 15) and the hyolithelminthid Phosphannulus universalis (PI. 3: 14) have been found in CAS 8 and CAS 10. Erraticodon? balticus (PI. 2: 14; PI. 3: 3), Drepanoistodus forceps (PI. 3: 13), o. aff. lanceolatus (PI. 2: 11; PI. 3: 2, 9, 16), and Pteracontiodus cryptodens (PI. 2: 15, 16; PI. 3: 10) were obtained from samples CAS 9 and CAS 10. Additionally, O.? tablepointensis (PI. 3: I, 11) and Drepan oistodus basiovalis (PI. 3: 6, 12) are present in sample CAS 10. AGE AND CORRELATION For a detailed discussion of the intercontinental correlation of the assemblage zones established in the coeval sections of the Precordillera (La Silla and San Juan Formations; LEHNERT 1993, 1995) and as applied here, the read er is referred to LEH NERT (1995). HAR RI S and REPETSKI (cited in HARRlS et al. 1995) established a correlation between SWEET'S (19 84) chronozones, which are based on graphic correlation of North American succession s, and BERGSTROMS (1971) biozones described from Balto scandic sediments (Fig. 3). The correlation of the faunas discussed in this paper with the standard zonations in the Baltic area and North America is shown in Fig. 3. A discu ssion of the age of the lowermost part of the Ponon Trehue Formation is based on the presence of Striatodontus prolificus. This species is first found in the Glyptoconus flowerilGlypto conus bolites shallow-water zone and is an index fossil of the overlying S. prolificus/S. lanceolatus shallow-water zone of JI and BARN ES (1994) in western Newfoundland . The latter zone approximately correlates with the lower Acodus deltatu s-M. diana e interval of ETHI NGTON and CLARK ( 1982) and the M. diana e Zone of Ross et al. (1993). In North Ameri can sections, S. prolificus is first present in the Low Diversity Interval and ranges up into the Acodus deltatu s-Oneotodus costatus Zone. At the top of this zone, there are transitional forms to Parapanderodus striatus (J.E.REPETSKl, written communication). According to REP ETSKI (personal communication), the earliest occurrence of typical elements of P. striatus can be dated for the 0. communis Zone. Based on the presence of S. prolificus , we conclude that carbonate sedimen tation at Cerro Ai Sol did not start before the Low Diversity Interval (Fig. 3). Unit 1 to basal unit 3 correlate with strata of the upper La Silla Formation and lowermost San Juan Formation in the Precordillera tParapanderodus striatusiColaptoconus quadraplicatu s assemblage zone). The contact between unit 2 and unit 3 marks a first deepening which corresponds to the change in sedimentology from the La Silla Formation to San Juan Formation in the Precordillera. The abrupt change from restricted-marine facies to lime stones with open-marine and diverse faunas (KELLER et al. 1994), that can be observed at the contact, also refle cts a deepening event. Unfortunately, C. quadraplicatu s and Eucharodus parallelus, together with S. prolificus in the reef mounds at the base of unit 3, represent long-ranging taxa (Low Diversity Interval-Reutterodu s andinus Zone; Ro ss et al. 1993) and do not permit a more precise assignment. "Drepanodus " gracilis , found in a grainstone 2 m higher up in the section, is also known from North America where it is first present in the upper Fauna D of ETHINGTON and CLARK (197 1), the Acodus? deltatus-Oneotodus costatus interval of ETHINGTON and CLARK (1982), or the Acodus deltatus-Oneotodus costatus Zone of Ross et al. (1993). Thus, the grainstones from 2 m up to 5 m above the base of unit 3 may roughly be correlated with those zones. Thi s part of the succession correponds to the A. ? deltatus-P. proteus assemblage zone of LEHNERT (1995). The overlying strata of the Ponon Trehue Formation are coeval with the time-interval of the O. communisir. elegans assemblage zone. In correlative strata of the San Juan Formation, B. extensus, O. communis, and Scolopodus krummi have been found. 52 OLIVER LEHNERT, MARTIN KELLER and OSVALDO BORDONARO (/J SERIES t'5 ro :2: Balto- North Argentine ~ - W ~ scandia Precordillera I a> ca> I- J::. America a>= ro~ ...: Zone! ~.- Cl) l/) J::. Asse mblages (f)ro :;:; t ID Subzone Faun a Zone Zones o.."E >- 'C 0 E 0::: Cl) m Z « o Z ° Fig . 3 Corre lation of the Early Ordovician Ponon Trehue Formation with coeval strata in the Precordillera to the north (La Silla and San Juan formation s). Sources of conodont zonat ions: Baltoscandia - LINDSTROM (1971), BERGSTROM ( 1971), LOFGREN (1978) ; North America - ETHINGTON and CLARK (1971, 1982). Sweet et al. (197 1), SWEET (1984) . Ross et al. (1993); Precordi llera - LEIINERT (1993 , 1995). Other species obtained from unit 3 such as P. gra cilis, Scolopodus cf. rex, D. arcuatus, and T. sweeti are already present in older beds at Cerro La Silla. The biostromal horizons at the top of unit 3 formed during the O. evae chron, as indicate d by the presence of the zonal index fossil. In these horizon s, the abundance of the large receptac ulitid Fischerites cama cho is interesting . In the Precordillera, this receptaculitid is present in the upp er O. evae Zone in the Niquivil section (approx . 10 km SSW' of Cerro La Silla). EARLY ORDOV ICIAN CONODONTS FROM SOUTHERN CUYANIA TERRANE 53 The age determination for the top of the Pon on Trehue Formation (unit 4) is hampered by the lack of zona l index fossil s. Therefore, the San Rafael faunas have to be ind irectly corre lated mainly by co mparison with coeval stra ta in the Precordillera, from where the index foss ils have previou sly been descr ibed . The presence of P. originalis indi cates that this fauna is not older than the P. origina lis Zo ne. In the Precord illera, however, the associatio n of P. cryptodens, P. originalis, and D. basiovalis is only present in the Amorphognathus variabilis Zon e and the ove rly ing E. suecicus Zo ne (LEHN ERT 1995 ; ORTEGA et al. 1995 ). In the E. sueeieus Zo ne, this assemblage is associated with H. kristi nae and E. suecicus. Because P. flabellum, whic h is present at the top of the Ponon Trehue Formation, is replaced by Periodon aculeatus within the A. variabilis Zo ne, the top of the successio n ca nnot be younger than the lower part of the A. variabi lis Zo ne. Another line of evi de nce althoug h suggests a correlation with the lower A. variabilis Zo ne. P. cryptodens is a typi cal species of the following un its: ( I) Histiodella altifrons Zo ne; (2) the M. fla bellum/T. laevis and P. cryptodenslliistiode lla altifro nslMultioistodus auritus inte rva l of ETIIIN GTON and CLARK 1982; and (3) Midcontinent faunas I and 2 (SWEET et al. 1971 ). All these units are corre lated with the lower A. variabilis Zo ne. In co ncl usio n, the faunas in the uppermost hori zon s of un it 4 discu ssed so far represe nt elements which are typical of the upp er Sa n Ju an Fo rmatio n. In the Precordillera, these fau nas are attribute d to the Late Arenig (LEIINERT 1995). By co mparison with the strata in the Precord illera, we attr ibute the sedi me nts at the top of the Ponon Trehue Fo rmatio n also to the Late Are nig . Critical to thi s assignme nt is the presence of Oistodus'l tablepointensis. This species has been reported so far only from Late Wh iterockian/E arl y Llanvirnian strata in Newfoundland (STOUGE 1984), where it has only a short range from the lower Histiodella tab leheadensis phylozon e (= Histiodell a holodentatai to the lower part of the Histiodella kristinae ph ylozon e of STOUG E (1984: fig . 18). Th is inter val correlates with the upp er A. variabilis to lower E. suecicus Zo ne in the Baltoscand ic area (Fig. 3). Th e presence of Oistodus'l tab lepointe nsis indi cates either that the strata at the very top of the Ponon Trehue are yo unge r than we ass ume fro m the accompa nying faunas or that the taxon appea red slightly ea rlier in the Cuyania Terrane than in Newfound land . An assig nme nt to the Late Are nig is also corroborated by the pre sence of Protopanderodus gra dat us and Paroistodus origina lis which are rep laced by the ir successo rs duri ng the A. variabilis Zo ne. DI SC USSI ON Biostratigraphi c correlations of the Upper Trem adoc to Upper Arenig stra ta near San Rafael with coeval miogeoclinal stra ta in the Precordillera (Cerro La Si lla section) permit a co mpar iso n of fauna l co mposi tions and sedi mentology between bot h successions. In both successions, there is a tren d in compositio n of co nodont faunas of the war m-water gro up in the lower part to pandemic and temperate-water faunas in the younger strata. In the Ponon Tre hue Formation. this trend is reflected in the sediments of unit I to basal unit 3. In the Precordillera, this trend is present from the upper part of the La Silla For mation to the lower par t of the San Juan Form ation . Additionally, in both areas representatives of the cold-water group come in with the global transgression of O. evae Zone (upper unit 3 of the Ponon Trehu e Formation). Th is eustatic eve nt represents the most extensive sea-leve l rise during Early Ordov ician times (e.g., BAGNOLl 1994). The lower biostromal succession (base of unit 3) corresponds to the lower reef mou nd horizon at Cerro La Si lla as described by CANAS and CARR ER A (1993) . The upper biostrom al co mplex (top of unit 3) tentatively is co mpared with the upper reef mound horizon in the San Juan Formatio n. Both form ed during an initia l relative sea-level rise. Th e pronounced sea-level rise (nodular limestones of unit 4) in the upper part of the Ponon Trehu e For mation is reflected by the common occ urrence of ope n-mar ine elements such as Periodon fl abellum. The same eve nt is also observed in the sec tio ns of the Precordill era (KELLER 1997). Thi s deepening during the Late Arenig finally led to the drownin g of the Precordilleran car bonate platfo rm during Ear ly Llanvim times . Wh en co mpared with the sec tio ns of the ca rbonate platfo rm in the Precordillera (BORDONARO et al. 1996), the carbo nate s ex posed in the San Rafael area represent a strongly reduce d succession. Abo ut 80 m of carbo nates near San Rafael correspond to more than 300 m of limeston es in the miogeocl inal succession (Fig. 4). Furthermo re, more than 1500 m of Ca mbrian and Early Ordovician sedime nts were deposited on this carbo nate platform (La Laja Forma tio n, Zo nda Fo rmation, La Flech a Formatio n, and the lower part of the La Sill a Formation) unt il the first carbonates onlapped the basem ent in the Ponon Trehu e area (F ig. 4) . Stro ng ly redu ced sediment thick nesses, togeth er with the Ordovician onlap onto the basem ent , indicate that the outcrops at Pon on Trehu e rep rese nt a cratonal setting, the only crato nal sec tio n known fro m the Cu yania terrane so far. 54 OLlV ER LEII ERT. MARTI N KELLER and OSVALDO BORDONARO Precordillera San Rafael (miogeoclinal setting) (cratonal setting) formation lithology and depositional formation lithology environment -- - - - . ~ Gualcamayo - - graptolitic > - - - black shales not preserved c: - - ra - -- ::i - - drownina of platform I- - c: . ~ Cl 0- E ~;~;~ .- c: 1 t 0 open marine > Ql Sa n Juan to -E~ (") limestones Ponon E ~ ~ 0 _ oco ~Y'·- Trehue . - o - 0 - ..- "U ra E restrictive limestones - / ~ 0 - ---l onlap f~ - La Silla co (Bahamian type) I- (") - - non-deposition peritidal shallowing- ~ La Flecha upward cycles E or c. c:J erosionally I1l / peritidal dolomites ~ c ~ / removed /I EQl 11l"U ,-,:0 E open marine E La Laja 0 -.:: to limestone-siliciclastics Ql to ~ t/ alternations 0 Fig. 4 Strati graphy and de positi onal enviro nments of the Ca mbro-Ordov ician carbonate platform successio n in the Precordill era (modified from KEl.I.ER et al. 1994: thicknesses acco rding to KEI.I.ER 1997). ote that more than 1500 m of platform sediments arc prese rved in the miogeocl inal setting until the onlap onto the craton is recogn ized near San Rafael. Ordovician conodont paleobiogeography and provincialism have been discussed and docum ented in various papers. Aspects of the Early Ordo vician have been stresse d by ETlII NGTON and REI' ETSK I ( 1984), MII .I.ER ( 1984), BER GSTROr-.l (1990), and BAGNOI.I and STO UGE ( 1991, 1996). The conodont s from unit I to basal unit 3 as well as the faunas from the La Silla Formation and the lower San Juan Formation (LEH ERT 1997) are typical of the North American Midcontinent Faunal Province. The presence of these conodo nts toge ther with almost identic al, coe val reef structures from the San Juan Formation (CA-AS and CARR ERA 1993; CA-AS and KEI.LER 1993) agrees with the interpretation that the San Rafael region is a part of the Cuyania Terrane. Fauna l composition and sedimentology of the Ponon Trehu e Form ation are in agreement with a derivation of the terran e from the southern margin of Laurentia (e.g.. DALLA SALDA et al. 1992a, b; DALZIE L et al. 1994; ASTINI et al. 1995; DALZI EL 1997; KELL ER 1997). TAXON OMIC AN D BIOSTRATI GRAPHIC REM ARKS The conodonts from San Rafael show a high thermal maturation. The conodont elements exhibit a high Color Alteration Index (CAI of EI'STEI N et al. 1977) of about 6. Accordin g to REJEBI A et al. ( 1987), this suggests a thermal heatin g between 360 and 550°C. Unfortun ately, the conodonts are partly recrystallized and fragm ented, but the faunal elements can be well compared with those described from the Argentin e Precord illera (La Silla Formati on and San Juan Formation ). EARLY ORDOVICIAN CONODONTS FROM SOUTHERN CUYAN IA TERRAN E 55 The species mention ed in the text are well known from many other areas including the Precordillera proper. Therefore, they are listed only with reference to their original descriptions and to descriptions in the scope of multielement taxonomy or detailed synonymy lists. The occurrences in the Precordillera are not specifically discu ssed in this paper, but are added only for stratigraphic information. Unless otherwise stated, we always refer to the standard Cerro La Silla section, the type section for both the La Silla Formation and the San Juan Formation as defined by KELL ER et al. (1994). Bergstroemognathus extensus (GRAvES et ELLlSON, 1941). - Oistodus extensus sp. n. - GRAVES and ELLl SON 1941: p. 13, pI. I: 16, 28 (M element); Bergstroemognathus extensus (GRAV ES et ELLISON, 1941) - SER PAGLI 1974: pp. 40- 43, pI. 9: la- Se; pI. 21: 1-7 ; text-fig. 7 (synonymy of multielement species until 1974), STOUGE and BAGNOLl 1988: p. 113, pI. I: 6-13 (synonymy until 1988), LEH NERT 1995: p. 75, pI. 5: 20, 21; pI. 20A: 6; pI. 20B: 2 (synonymy until 1994). The species is present in samples CAS 5 to CAS 7 (unit 3). In the Precordillera, it is common in the lower part of the San Juan Formation where it first appears in the P. elegans/O. communis assemblage zone. Colaptoconus quadraplicatus (BRANSON et MEIIL, 1933). - Scolopodus quadraplicatus sp. n. BRANSON and MEHL 1933: p. 63, pI. 4: 14, IS; Glyptoconus quadraplicatus (BRANSON et MEHL) KENNEDY 1980: pp. 61-63, pI. I: 39-45 (detailed description and synonymy), STOUGE and BAGNOLl 1988: p. 120, pI. 3: 20, 21 (synonymy until 1988); LEH NERT 1995: pp. 89-90, pI. I: 10, 12, pI. 2: 15-16, 18 (synonymy until 1994). The species was found in sample CAS 3 (reef mound s, basal unit 3). In the Precordillera, it is observed from the upper La Silla Formation to the P. elegans/O. communis assembl age zone of the San Juan Formation. Drepanodus arcuatus PANDER, 1856. -LOFGR EN 1978: pp. 51-53, pI. 2: I, 2, 4-8, non 3 (D. planus] (description and synonymy until 1978), STOUGE and BAGNOLI 1988: pp. 115-116, pI. 2: 1-6 (detailed synonymy until 1988), STO UGE and BAGNOLI 1990: p. 14, pI. 9: 7-10 (synonymy until 1990), LEH NERT 1995: p. 82, pI. 3: IS, 16 (synonymy until 1994). The species is present in sample CAS 5 (unit 3). In the Precordill era, it is common in the San Juan Formation first occurrin g in the A. ?deltatus/P. p roteus asse mblage zone. "Drepanodus" gracilis (BRANSON et MEIIL, 1933) sensu LINDSTROl\I, 1955 s.f. - Drepanodus'l gracilis BRANSON et MEIIL - L1 ND STR OM 1955: pp. 562-563, pI. 4: 44, pI. 5: 6, 7; Drepanodus gracilis (BRA NSO N and MEHL 1933) sensu L1 ND STR OM 1955 - ETHI NGTON and CLARK 1982: pp. 37-38, pI. 3: 7, text-fig. 10 (description and synonymy until 1981). Drepanoistodus basiovalis (SER(;I<:EVA, 1963). - Oistodus baslovalis sp. n. - SERGEEVA 1963: pp. 96-98, pI. 7: 6, 7; text-fig. 3; STOUGE and BAG NOLl 1990: p. IS, pI. 5: 18-24 (synon ymy until 1990); LEH NERT 1995: pp. 85-86, pI. 9: 9; pI. 10: 5, 12 (synonymy until 1994). The species was found in sample CAS 10 (unit 4, top of Ponon Trehue Formation) and in the Precordillera in the uppermost part of the San Juan Formation where it replaces its precursor D. forceps in strata which are correlated with the A. variabilis Zone. Drepanoistodus forceps (LINI>STROl\I, 1955). - Oistodus fo rceps sp. n. - L1 NDSTROM : p. 574, pI. 4: 9-13, text-fig. 3M; Drepan oistodusforceps (LI DSTROl\I) - LOFGREN 1978: pp. 53-55, pI. I: 1-6; text-fig. 26A (detailed descripti on and synonymy until 1978), STO UGE and BAGNOLl 1990: p. 16-17, pI. 5: 6-9 (synonymy until 1990), LEII NERT 1995: p. 86, pI. 3: 20; pI. 6: 2 (synonymy until 1994). The species was obtained from samples CAS 9 and CAS 10 (unit 4). In the Precordill era, it is present from the O. el'lle Zone up to the top of the San Juan Formation (A. var iabilis Zone). Erraticodon'l balticus DZIK, 1978. - Tlirraticodon balticus sp. n.- DZIK 1978: p. 66, pI. IS: 1-3 ,5, 6: text-fig. 6 (description); ?Erraticodoll balticus DZI K- LEH NERT 1995: pp. 87- 88, pI. 9: 13. 16 (synony my until 1994). The Erraticodon elements present in samples CAS 9 and CAS 10 (unit 4) most probably correspond to Erraticodon balticus. However, the preservation of the fragmented material does not permit an unequi vocal determination. One M element of an Erraticodon with a long process is not typical of this specie s (DZIK personal communication). This element is figured as Erraticodon sp. (PI. 2: 14). E. balticus is found in the uppermost part of the San Juan Formation (SARMI ENTO 1990). 56 OLl VER LEHN ERT, MARTI N KELLER and OSVALDO BORDONARO Eucharodus parallelus (BRANSON et MEHL, 1933). - Drepanodus parallelus sp. n. -BRANSON and MEH L 1933: p. 59, pI. 4: 17; Eucha rodus pa rallelus (BRANSO Net MEHL) -KENNEDY 1980: pp. 58-60, pI. 1: 35-38 (detailed descripti on and synonymy until 1980), STO UGE and BAGNOLl 1988: p. 11 8, pI. 3: 14 (synonymy until 1988), SMITH 1991: pp. 33-34, text-fig. 19d- f (detailed synonymy until 1991), LEH NERT 1995: p. 88, pI. 2: 15, 16, 18 (synonymy until 1995). The species was obtained from sample CAS 3 (unit 3). It is also present in the lowermost part of the San Juan Formation (G. quadraplicatusl R striatus to basal P. elegans/O . communis assemblage zone). Fahraeosodus marathonensis (BRA DSHAW, 1969). - Gothodus marathonensis sp. n. -BRADSH AW 1969: p. 1151 , pI. 137: 13-15, text-fig. 3S-U; "Mikrozarkodina " marathonensis (BRADS HAW) - ETHI NGTON and CLAR K 1982: pp. 55-56, Taf. 5: 14, 19, 20, 23, 24, 27 (detailed description of multielement species and synonymy until 1981); Fahraeosodus marathonensis (BR ADS HAW) - STOUGE and BAGNOLl : p. 119, pI. 4: 15-17 (synonymy until 1988), LEH NERT 1995: p. 89, pI. 7: 19, pI. 8: I (synonymy until 1994). The species is present in sample CAS 7. It represents a rare element of the San Juan faunas (0. evae zone to Assemblage VI in the upper part of the Niquivil section; LEH NERT 1993). Iuanognathus jaanussoni SERI'AGLI, 1974. - Juanognathus jaanussoni sp. n.- SERPAGLI 1974: pp. 50,51 , pI. 11 : 8a-1 2c; pI. 23: la-5b; text-fig. 9 (detailed description and synonymy until 1974), LEH NERT 1995: p. 92, pI. 3: 2, 3 (synonymy until 1994). The species is found in sample CAS 5 (unit 3). It is common in the middle and upper part of the San Juan Formation. Oepikodus communis (ETIIINGTON et CLARK, 1964). - Gothodus communis sp. n. - ETHI NGTONand CLARK 1964: pp. 690, 692, pI. 11 4: 6, 14; text-fig. 2F; Oepikodus communis (ETHINGTON and CLARK) STO UGE and BAGNOLl 1988: p. 121, pI. 5: 8-12 (synonymy until 1988), LEH NERT 1995: pp. 98-99, pI. 5: 22, 27- 29; pI. 8: 19- 24 (syno nymy until 1995). The species was obtained from sample CAS 5 (unit 3). In the San Juan Formation, it is present from the upper P. elegans/O. communis to the O. evae Zone. Oepikodus evae (L1 'DSTRC)I\I , 1955). - Prioniodus evae sp. n. - LINDSTROM 1955: p. 589, pI. 6: 4-10; Prioniodus (Oepikodus) evae L1 N D S T R O ~I- SERPAGLI 1974: pp. 67-69, pI. 15: 9a-13; pI. 26: 1-10; pI. 31: I (description and synonymy until 1974), LOFGREN 1978: pp. 79, 80, pI. 9: 7-1 1, 17A, B (synonymy until 1978); Oepikodus evae (L1 ND STRC)M) - STO UGE and BAGNOLl 1988: pp. 121, 122, pI. 5: 1- 7 (synonymy until 1988), LEH NERT 1995: pp. 99- 100, pI. 20B: 1 (synonymy until 1994). The pandemic species was obtained from sample CAS 7 (top of unit 3). It is abundant in the O. evae Zone in the Precordill era (references compiled by SARM IENTO and GARCI A-LoPEZ 1993). Oistodus aff.lanceolatus PANDER, 1856.- TOistodus eii.lanceolatu s PANDER- STOUGEand BAGNOLl 1988: p. 123, pI. 6: 1-8; LEH NERT 1995: p. 101. pI. 8: 6-8; pI. 20B: 12 (description and synonymy). The species was found in samples CAS 9 and CAS 10 (unit 4) and is mainly assoc iated with other shallow-water species in the reef mound horizons of the upper San Juan Formation (assemblages V and VI of LEH NERT 1993). Oistodus't tablepointensis STO UG E, 1984. - Oistodus'l tablepointensis sp. n. - STOUGE 1984: pp. 75-76, pI. 14: 2-12 (description and synonymy). Paracordylodus gracilis LINDSTRO l\I, 1955. - Paracordylodu s gracilis sp. n. - L1 NDSTR OM 1955 : p. 584, pI. 6: 11-12 (S element); LOI'GREN 1978: pp. 67-68, pI. 9: 15A-1 6B (synonymy of the multielement species until 1978); LEH NERT 1995: p. 105, pI. 4: 3 (synonymy until 1994). The species was found in sample CAS 6 (unit 3). P. gracilis is always represe nted by a few individuals only. However, this species is widely distributed on the San Juan platform. This distribution was discussed by SARM IENTO and GARCI A-LoPEZ (1993). P. gracilis is observed in the P. elegans/O. communis assemb lage zone at Cerro La Silla and in the P. elegans and O. evae assemblage zones in Niquivil (LEH NERT 1993). Paroistodus originalis (SERGEE YA , 1963).- Oistodus originalis - SERGEEVA 1963: p. 98, pI. 7: 8, 9; text-fig. 4; Paro istodus originalis (SERGE EYA) - LbFGR EN 1978: pp. 69-71 , pI. I: 22-25; text-fig. 28 (desc ription and synonymy until 1978), STOUGE and BAGNOLl 1990 : p. 22, pI. 7: 5-10 (synonymy until 1990), LEH NERT 1995: pp. 109, 110, pI. 7: 2, 3; pI. 13: 5 (synonymy until 1994). EARLY ORDOVICIAN CONODONTS FROM SOUTHERN CUYANIATERRANE 57 Periodon flabellum (LINDSTROM, 1955). - Periodon flabellum (LINDSTROM) - LOFGR EN 1978: pp. 72-74, pI. 11: 1-11 , text-fig. 29 (pars) (description and discussion, synonymy until 1978), LEH NERT 1995: p. 112, pI. 7: 8,10,11 (synon ymy until 1994). The species is present in samples CAS 8 to CAS 10 (unit 4). P. flabellum is common in the San Juan Formation, ranging from the O. evae Zone to the top of the San Juan Formation (approx . M . parva Zone - first transitional forms into P. aculeatus zgierzensis DZIK , typical elements of P. aculeatu s HADDING are found at the top of the San Juan Formation). Protopanderodus gradatus SERI'AGLI, 1974. - Protopanderodus gradatus sp. n. - SERPAGLI 1974: pp. 75-77, pI. 15: 5a-8b; pI. 26: 11-15 ; pI. 30: la, b; text-fig. 17 (description and synonymy until 1974), LEH NERT: p. 117, pI. 3: 11 , 12 (synonymy until 1994). The species was obtained from samples CAS 8 to CAS 10 (unit 4). It ranges from the lower part of the San Juan Formation (P. elegans 10. communis assemblage zone) to the A. variabilis Zone (top of the formation at Cerro Potrerillo, north of the Rio Jachal, ORTEGA et al. 1995). Pteracontiodus cryptodens MOUND, 1965. - Pteracontiodus cryptodens sp. n. -MOUND 1965: pp. 197-198, text-figs 1-2, 12, 13, ETHI NGTONand CLARK 1981: pp. 88-89, pI. 14: 1-4,6-10 (synonymy of multielement species to 1981), LEH NERT: pp. 119-120, pI. 7: 7; pI. 13: 13. The species is present in samples CAS 9 and CAS 10 (unit 4). It is a typical species of the M . parva and A. variabilis zones in the Precordillera (ORTEGA et al. 1995). Reutterodus andinus SERPAGLI, 1974. - Reutterodus andinus sp. n.- SERPAGU 1974: pp. 79-81, pI. 17: 9a-d; pI. 28: 1-9b ; text-figs 19-20 (detailed description of multielement species); Reutterodus andinus SERPAGLI -LEH NERT 1995: p. 122, pI. 7: 9-13 (synonymy until 1994). The species was obtained from sample CAS 5 (unit 3). In the Precordillera, the species is first observed in the P. eleganslO. communis assemblage zone. It is an important representative of the O. evae Zone . Scolopodus cf. rex LINDSTROM, 1955. - cf. Scolopodus rex sp. n. - LIND STR OM 1955: p. 595, pI. 3: 32; cf.1978; cf. Sco lopodus rex LINDSTR OM - LbFGREN: p. 109, pI. I : 38-39 (detailed synonymy until 1978); Scolopodus cf. rex L1 ND STROM -LEH NERT: pp. 124-125, pI. 5: 5-6. The species is present in samples CAS 5 and CAS 6 (unit 3). In the Precordillera, it is first observed in the A. ? deltatus IP. proteus assembl age zone and ranges up into the upper O. evae Zone . Scolopodus? krummi (LEHNERT, 1995).- Tropodu s'l krummi sp. n.- LEH NERT 1995: pp. 130-131 , pI. 5: 18, 19 (detailed description). The species is present in samples CAS 6 and CAS 7 (unit 3) and in the lower part of the San Juan Formation which corre sponds to the O. communis/P. elegans assemblage zone. Spinodus sp . - broken fragments of Spinodus have been found in sample CAS 10 (top of unit 4). In the Precordillera, the oldest Spinodus elements [Spinodus spinatus (HADDI NG, 1913)], have been found in the upper part of the San Juan Form ation correlated with the M. parva and A. variabilis zones (e.g., SARMI ENTO 1990; ORTEGA et al. 1995). Striatodontus prolificus (JI et BARN ES, 1994). - Striatodontus prolificus - JI and BAR NES 1994: pp. 61-62, pI. 20: 1-26; text-fig. 36A (detailed description and synonymy). Element s of S. prolificus from the uppermost La Silla Formation and lowermost San Juan Formation have been identified by LEH NERT (1995 : pI. I : 15) and LEH NERT et al. (in press: pI. 2: 22, 23) as Parapanderodus striatus (GRAVES et ELLlSON, 1941). However, as discussed by LEII NERT( 1995: p. 107), the element s from the Precordillera are more robust and shorter than typical elements of P. striatus. In addition , they show a high content of white matter in the cusp instead of being hyaline . Similar elements have been assigned to P. striatus by ETHI NGTON and CLARK (1982), REPETSKI (1982), and Ross et al. (1993) and therefore it should be noticed that in published charts the range of this species includes that of S. prolificus. The species was found in samples CAS I and CAS 3 (unit I and basal unit 3). In the Precordillera, S. prolificus is present in the upper part of the La Silla Formation and in the basal San Juan Formation. Tropodus sweeti (SERPAGLI, 1974). - "Paltodus" Tsweeti sp. n. - SERPAGLI 1974: pp. 58-59, pI. 14: 13a-14b; pI. 24: 8-10; text-fig. 12 (P element); Tropodus swe eti (SERPAGU) - STOUGEand BAGNOLl 1988: p. 142, pI. 16: 10-15 (synonymy of multielement species), LEH NERT 1995: pp. 131-132, pI. 3: 17-19 (synonymy until 1994). 58 OLl VER LEHNERT. MARTI N KELLER and OSVALDO BORDONARO The species was found in sample CAS 5 (unit 3). 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Brut on (ed.), Aspects of the Ordovician System .- Paleontological Con tribut ions of the Univers ity of Oslo 295, 23-35. SWEET, W .e., ETIIINGTO N, R.L. , and BARNES, CR. 1971 . Nor th American Middle and Upper Ordovician co nodont fa un as. In : W. e. Sweet and S.M. Be rgs tro m (eds) , Sy mpos ium on Conodo nt Biostra tigrap hy . - Geo logical Society ofAmerica, Memoir 127 , 163-1 93. WICH MANN, R. 1928. Datos geol6g icos sobre la reg i6n compre ndida entre el Ce rro Nevado y Cerro Nihuil (Provincia de Mendoza ). Unpublished report, Direccion Nac iona l de Mineria. Geologfa e Hid rol ogfa. 60 OLIVER LEHNERT. MARTIN KELLER and OSVALDO BORDONA RO EARLY ORDOV ICIAN CONODONTS FROM THE SOUTH ERN CUYANIA TERRANE (MENDOZA PROVINCE. ARGENTINA) PLATE I Striatodontus prolificus 11et B ARNES, 1995 57 I. Postero-lateral view, IANIGLA PI 7 10. sample CAS I. x 230. 2. Postero-lateral view. IAN IGL A PI 711. sample CAS 3. x IR2. 3. Postero-Iateral view. IAN IGLA PI 712 . sample CA S 3. x 202. 4. Postero-Iateral view. IANIGLA PI 7 13. sample CAS 3. x 150. 7. Postero-lateral view. IANIGLA PI 7 14. sample CAS 3. x 166. R. Postero-latera l view. IANIGLA PI 7 15. sample CAS 3. x 2 16. Eucharodus parallelus (BRANSO N et MEHL, 1933) ...... 56 5. Lateral view. IANIGLA PI 7 16. sample CAS 3. x 174. " Drepanodus" grac ilis ( BRANSO N et M EIIL ) sensu LI NDST RO M, 1955 s.f. 55 6. Late ral view. IANIGLA PI 7 17. sample CAS 4. x 170. Iuanognathus jaanussoni S ERPAGLI , 1974 56 9. Posterior view. IANIGLA PI 7 1R. sample CAS 5. x 93 . Scolopodus cf. rex LI NDSTR OM , 1955 57 10. Postero-l ateral view. frag men t. IANIG LA PI 7 19. sample CA S 5. x 121.5. 11 . Lateral view. fragment. IANI GL A PI 720 . sample CAS 6. x I() I) . Tropodus sweeti LI NDSTROM , 1955 . 57 12. Lateral view. fivecostate S element. IAN IGLA PI 72 1. sample CAS 5. x 130. 13. Posterior view. fivecostate S element. IANIGLA PI 72 2. sa mple CA S 5. x 113. 15. Lateral view. P element. IAN IGLA PI 723. sample CA S 5. x 97. Bergstroemognathu s extensus S ERPAGLI , 1974 55 14. Posterior view. Sa element . IANIGLA PI 724 . samp le CAS 5. x 117. 19. Latera l view. S eleme nt, IANIG LA PI 725 . sample CAS 5. x 154. Paracordylodus gracilis LI NDSTROM, 1955 . 56 16. Lateral view. paracord ylodiform element. IANIGLA PI 726. sa mple CAS 6. x 170 . Oepikodus communis ( E THINGTON et C1 .ARK . 1'J64 ) 56 17. Lateral view. P element. IANIGLA PI 727. sample CAS 5. x 170. Drepanodus arcuatus P ANDER, 1856 55 IR. Lateral view, P element, IANIGLA PI 728, sample CAS 5. x 69. Scolopodus'l krummi ( LEHNERT, 1995) 57 20. Posterior view. IANIGLA PI 729 . sample CAS 6. x 130. Palaeontologia Polonica. No. 58. 1998 PI. I 62 OLIVE R LEIINERT. MARTI N KELL ER and OS VALDO BORDONARO EA RLY ORDOVICIAN CON ODON TS FROM THE SO UT HE RN CU YANIA TE RRANE (MEN DOZA PROVINCE. ARGENTINA) PL AT E 2 Oepikodu s eme ( L INDSTROi\1. 1955). .. . . 56 I. Lat eral view. P element . IA NIG LA PI 730. sample CAS 7. x 150. 5. Lateral vie w. S ele me nt. IA NIGLA 1'1 73 1. sample CAS 7. x 2 16. 7. Later al view . S element. IA NIG LA 1'1 732. sample CAS 7. x 154. Bergstroemogna thus exte nsus Serpa gli. 1974 55 2. Lat eral view. M eleme nt. IA NIGLAPI 733. sa mple CAS 7. x 77. Periodonjlabellu m ( LI NDSTR OI\I. 1955 ) . . . 57 3. La ter al view. S elemen t. IA NIG LA PI 734. sa mple CAS 7. x I 13. 6. Lateral view. M e leme nt. IA NI G LAPI 735. sample C AS 7. x 109. 12. La ter al view. S ele me nt. IA NIG LA PI 736. sa mple CAS 9. x 11 7. 13. Posteri or view . S eleme nt. IANI G LA PI 737. sample C AS 9. x 170. 17. Lateral view. P ele me nt. IA NIG LA PI 73H. sample CAS 9. x 130. Scolopodus'l krummi L EIINERT, 1995 57 4. Poster ior view. IANI G LA PI 739. sam ple CAS 7. x 146. 9. Posterior view. IANIGLA PI 740. sa m ple CAS 7. x 77. Fahra eosodus marath on ensis ( BRAD SIIAW, 1969) 56 X. Lateral view. P ele ment. IANIGLA PI 74 1. samp le CAS 7. x 146. Paroistodus originalis S ERGEEVA. 1963 . 56 10. La tera l vie w. o istodiform e leme nt. IANI G LA PI 742. sample CAS 9. x 138. Oistodus aff. lanceolatu s P ANDER . 1856 54 11. Lateral view . IA NI GLA PI 743. sam ple C AS 9 . x 97. Errat icodo n sp...... 55 14. Inn er lateral view. M ele me nt. IA NIG LA 1'1 744. samp le C AS 9. x 73. Pteracont iodus cryptodens M OUND, 1965 57 15. Lateral vie w. IANI G LA PI 745. sa mple CAS 9. x X9 . 16. Lat era l view . IANI G LA PI 746. sa mple CAS 9. x 73. Palaeontologia Polonica, No. 58, 1998 PI. 2 64 OLlVER LEHNERT. MARTIN KELLER and OSVALDO BORDONARO EARLY ORDOVICIAN CONODONTS FROM THE SOUTHERN CUYANIA TERRANE (MENDOZA PROVINCE, ARGENTINA) PLATE 3 Oistodus? tablepointensis S TOUGE, 1984 56 1. Postero-Iateral view, IANIG LA PI 747. sample CAS 10, x 97. 11 . Postero-lateral view, IANIG LA PI 748. sample CAS 10, x 89. Oistodus aff. lanceolatus P ANDER, 1856 56 2. Lateral view, IANIGLA PI 749, sample CA S 9, x 97. 9. Lateral view, Sb element, IANIGLA PI 750, sample CAS 10, x 89. 16. Posteri or view, Sa element , IANIGLA PI 751, sample CAS 9, x 97. Erraticodon'l balticus D ZIK, 1978 .. 55 3. Poster ior view, IANIGL A PI 752, sample CA S 9, x 146. Protopanderodus gradatus S ERPAGLI, 1974 ...... 57 4. Lateral view, IANIGLA PI 753, sample CAS 10, x 134. 5. Lateral view, IANI GLA PI 754, sa mple CAS 10, x 150. Drepanoistodus basiovalis (SERGEEVA, 1963) . 55 6. Lateral view, suberectiform element, IANIGLA PI 755, sample CAS 10, x 125. 12. Lateral view, ois todi form ele ment, IANIGL A PI 756. sample CAS 10, x 11 3. Periodon flabellum ( LINDSTRbM, 1955) ... 57 7. Lateral view, S element, IANI GLA PI 757. sample CAS 10, x 97. Spinodu s sp...... 57 8. Lateral view. frag ment, IANIGLA PI 758, sample CAS 10, x 130. Pteracontiodus cryptodens M OUND, 1965 57 10. Lateral view, IANI GLA PI 759, sample CAS 10, x 11 7. Drepan oistodus forceps LI NDSTROM, 1955 . 55 13. Lateral view, oistodifo rm element, IANIGLA PI 760. sample CAS 10, x 125. Phosphannulus universalis M ULLER, N OGAMI et L ENZ, 1974 ...... 51 14. IANIGLA PI 76 1, sa mple CAS 8, x 154. Paroistodu s originalis (S ERGEEVA, 1963) . 56 15. Lateral view, oistodifo rm element, IANI GLA PI 762, sample CAS 10, x 125. Palaeontologia Polonica, No. 58, 1998 PI. 3