Evolution of the Late Ordovician High-Latitude Conodonts an D Dating of Gondwana Glaciations

Bollettino della Società Paleontologica Italiana Modena, Novembre 1999

Evolution of the Late Ordovician high-latitude conodonts an d dating of Gondwana glaciations

Jerzy DziK Instytut Paleobiologii Polska Akademia Nauk, Warszawa

KEYWORDS- Conodonts, Evolution, Late Ordovician, Glaciation.

ABSTRACT- The presence ofthe rapidl.y evolving conodont lineage ofAmorpho1;1narhus in the Middle and Late Ordovician of the Ho!.y Cross Mountains (P olana) enables correlation ofenvironmental events there with those Jrom other areas ofthe world. The fauna! succession ofthe conodonts records especial!.y well the profound climatic changes in the Ashgill. The record can be calibrated climatical!.y on the basis ofperiodic immigrations of species known to be abundant either in the Ordovician subpolar regions (Sagittodonrina, Scabbardella) or subtropics (Rhodesognathus, Icriodella, Birksfeldia). Increased contribution ofScabbardella is general!.y connected with a decrease in taxonomic diversity of the species association. A genera! trend toward cooling, which is partial!.y reversed close to the end of carbonate sedimentation in the area, is shown. The phyletic succession o{Amorphognathus chronospecies is shown stratophenetical!.y. This is used to propose a provisional correlation ofthe events recorded in the Ho!.y Cross Mountains with those within the carbonate sedimentation intervals in areas closer to Gondwana. A late population ofA. tvaerensis, which shows much similarity to the Thuringian Kalkbank A. venrilatus and presumab!.y being ancestral to it, co- occurs in the Ho!.y Cross Mountains with Rhodesognathus. This suggests that the Kalkbank warm event was coeva! with the topmost phosphate- rich part ofthe Mojcza Limestone immediate!.y above, where A. superbus occurs. A. sp. n., which characterizes the lower part ofthe mar!.y strata above the Mojcza Limestone with a lowest diversity assemblage, is known also from latera! equivalents ofthe Kullsberg mud mound limestones of Sweden. lts transition to A. ordovicicus corresponds to the peak ofabundance ofcold-water species. The proposed transition from A. ordovicicus to A. duftonus and a significant increase in contribution o{Dapsilodus at the expense oJScabbardella preceded the cessation of carbonate sedimentation in the area and it seems to be coeva! with similar events in the Carnic Alps.

RIASSUNTO- [Evoluzione dei conodonti ordoviciani delle alte latitudini e datazione delle glaciazioni gondwaniane] -La presenza della linea a rapida evoluzione del genere Amorphognathus nell'Ordoviciano medio e superiore delle Ho!.y Cross Mountains (Polonia) permette di correlare eventi ambientali registrati in quest'area con quelli di altre parti della Terra. La successione delle faune a conodonti testimonia molto bene quali profondi cambiamenti climatici siano avvenuti nell'Ashgill. !dati climatici possono essere calibrati sulla base di periodiche immigrazioni di taxa che nelf'Ordoviciano sono abbondanti nelle regioni subpolari (Sagittodontina, Scabbardella) o subtropicali (Rhodesognathus, Icriodella, Birksfeldia). Un prpessivo aumento di Scabbardella è in genere accompagnato da una diminuzione nella diversità tassonomica. Ne eme;t,e un trend generale di rajjreddamento, che è in parte invertito al termine della seaimentazione carbonatica della fine del periodo. La successione p/etica delle cronospecie di Amorphognathus è illustrata Questo approccio permette di formulare un primo tentativo di correlazione degli eventi registrati nelle Ho!.y Cross Mountains con quelli degli intervalli carbonatici di aree più vicine al Gondwana. Una popolazione tardiva di A. rvaerensis, molto simile ad A. venrilatus del Kalkbank (Turingia) e suo probabile predecessore, èpresente nelle Ho!.y Cross Mountains assieme a Rhodesognathus. Ciò suggerisce che l'evento freddo del Kalkbank sia coevo con la più alta parte ricca in fosfato del Calcare di Moicza, dove è presente A. superbus. Amorphognathus n.sp., che è tipico degli strati marnosi con scarsa diversità specifica al di sopra del Calcare di Mojcza, è noto anche in sedimenti equivalenti ai calcari di scogliera del Kullsberg, in Svezia. La sua evoluzione verso A. ordovicicus avviene in corrispondenza di un picco di abbondanza di forme di acque fredde. La transizione da A. ordovicicus a A. duftonus e un significativo aumento nella presenza di Dapsilodus e un calo di quella di Scabbardella precedono la fine della sedimentazione carbonatica nell'area e sembrano essere coevi con eventi analoghi nelle Alpi Carniche.

INTRODUCTION 30 million years (according to estimates by T ucker & McKerrow, 1995) are represented by only ten meters The present study is based on three exposures in of rock succession, with only one biostratigraphically the Holy Cross Mountains, Poland. All of them have identifìable gap. In fact, the entire Ordovician is been known for a long time and preliminary extremely condensed in the Holy Cross Mountains. descriptions of both their geology an d Jaleontology The Zalesie section, with its 38 m of rock sequence, are available in the literature (reviewe in Dzik & covers the time span from the Late Tremadoc to the Pisera, 1994). Additional conodont samples have been end of the Ashgill. Even the Early Ordovician coarse collected from new trenches dug in the northern wall clastics, dominant in and not represented of the quarry (in 1994), in the Zalesie in Zalesie, add only 38m more to equally condensed ravine (also in 1994), and in the fìeld in front of the Middle and Late Ordovician sections. Such a low rate Mojcza quarry (in 1995). of sediment accumulation requires that the area of The Mojcza Limestone, together with the unnamed deposition of the Mojcza Limestone and Zalesie lower carbonate member of the Zalesie Formation, is Formation carbonates, the Malopolska Massif and the an extreme case of stratigraphic condensation. At least Holy Cross Mountains, was tectonically very quiet. lt 238 ]. DZIK was earlier peneplained in one of the Late Tremadoc (Middle Llandovery) graptolite shales are below eustatic falls, and isolated from any external source of (Tomczyk, 1954). The basal part of the carbonate coarse clastics. Biogeographic and paleomagnetic data succession is not exposed. lt is hidden under Early suggest that the Malopolska microcontinent was Ordovician Buk6wka sandstone debris. As the thickness separated from both Baltica an d Gondwana by oceani c of the limestone units in seems closely areas. lt was located closer to the South Pale than similar to that in M6jcza, i t may be inferred that about Baltica, but farther from it than the African parts of four basal meters of the succession, those below the Gondwana (Dzik, 1990; Lewandowski, 1993). main M6jcza K-bentonite layer, are not available for study. Complexodus and Eoplacognathus elongatus occur Mojcza in the oldest sampled strata. Amorphognathus tvaerensis is documented by its diagnostic ne (M) elements The M6jcza section (Text-fìg. l; Tab. l) provides somewhat above this horizon (sample MG-48). the bes t record of conodont evolution in the Holy Cross Rhodesognathus is represented (Text-fìg. l), although Mountains (Dzik, 1994). In addition to the part of not as abundantly as in M6jcza (samples MG-41 to the section exposed in the quarry, 1.8 m more of MG-37), and is replaced by more abundant Ordovician limestone an d 4 m more of Silurian shales Amorphognathus above. A single ne (M) element with calcareous intercalations have been sampled in a indicates A. superbus. The resulting correlation with trench dug in the fìeld near the quarry. This is mostly respective strata in M6jcza is consistent with the a marly limestone with detritus of ostracodes and presence of phosphatic ooids, which in M6jcza echinoderms, especially in the topmost part. The bed continue to the top of the A. superbus Zone. As at about 20 cm below the top of the limestone series M6jcza, the range of Hamarodus in contains vertically oriented phosphatic tubes of overlaps that of Rhodesognathus. Sphenothallus, and 1.50 m below the top conchs of A level with a strongly weathered dolomitic longiconic orthoceratid nautiloids occur. The Ordovi- mudstone follows and the fìrst bed above it (sample cian limestone is covered by a soft sandy mari, l O cm MG-33) containsAmorphognathus ordovicicus, as shown thick, with mixed Ordovician and Silurian conodonts, by a single ne (M) element. The part of the succession very well preserved bur fragmented, an d a thick bed of corresponding to that of an unnamed species of a plastic K-benronite. There are calcareous concretions Amorphognathus (referred to here asA. sp. n.) in M6jcza in the top part of the K-bentonite and a continuous 1- is thus missing in or is rcpresented by the 2 cm rhick limestone intercalation above it. The mudstone. Some support for such a correlation is limestone contains a typical Pterospathodus celloni Zone provided by the abundance of agglutinating assemblage, which indicates rhat the topmost Ashgill foraminifera (indicative of a supply of fine quartz grains and most of rhe Llandovery strata are missing there. to the area, earlier missing), which at M6jcza are O ne may guess that these were soft shales and that the restricted in occurrence to the uppermost part of the erosion that removed them stopped at the topmost successi o n, with A. ordovicicus s.s. Elements of the same limestone bed of the sequence. morphology, with very elongated cusp, in samples MG- 21 and M G-17 suggest that the carbonates do no t reach Mi?dzygorz the leve! of A. duftonus. The incompleteness of the section may be due to its even stronger The strata exposed in (Text-fìg. l) stratigraphic condensation than at that of M6jcza or originated in a slightly shallower water sedimentation be caused by tectonic dislocations. regime than those a t M6jcza. Both belong to the centrai In the Ordovician-Silurian boundary Kielce facies region, where there was continuous fine clastics are reduced (probably tectonically) to a carbonate sedimentation from the end of the Arenig bed of pale shale a few centimeters thick. The oldest until at least the middle of the Ashgill. The M6jcza Silurian black graptolite shales represent the middle Limestone is exposed there in the middle of the Llandovery Monograptus gregarius Zone (Tomczyk, northern wall of the quarry (see Dzik & P isera, 1994). 1954). The beds lie in overturned position and Silurian

Texr-fig. l - Correlarion of rhe rhree main sections of the Middle and Late Ordovician srrata in the Holy Cross Mounrains, Poland. The and Mojcza sections belong to rhe relarively shallower-water Kielce facies regio n, the Zalesie Nowe section belongs ro rhe deeper-water Lagow facies region. Generai age correlarion and recognition of parricular rime unirs is based on the evolution of conodonrs. Logs of percenrage conrribution of elemenrs of conodonr appararuses represenring particular lineages can be used for fìner correlation referring to climatically conrrolled fauna! successions. Climatic gradienrs are calibrateci by using incursions of exoric, subbpolar and tropical species. Numbers in rh e upper parrs of rhe logs denote episodes of climare cooling idenrified in rhe Mojcza succession. Conrinuous horizonrallines indicate K-bentonite horizons. 3 !:: .(ii" c.

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Zalesie Nowe Hamarodus above that formation. A thin intercalation of a black day separates the The depositional environment in the southern area limestone horizon from the series of dolomite and of the Holy Cross Mountains (the Lag6w regio n) was limestone beds. They contain uncommon and rather relatively off-shore with respect to M6jcza and poorly preserved conodonts, dominated by Scabbardella Mi<';dzyg6rz. The carbonate succession at the Zalesie and Amorphognathus, which are generally similar to Nowe section (Text-fìg. l) is closely similar to that of those from the M6jcza section. Unfortunately, no ne M6jcza despite some diagenetic alteration of the rocks, (M) element ofAmorphognathus has been found, which which are more tectonized than in M6jcza, and show makes a more precise correlation impossible. The two greater weathering. The K-bentonite in the middle of lower dolomite beds are relatively rich in Hamarodus, the succession is the same as in M6jcza, as proven by which is very rare in the third one and a little more an increased contribution of Phragmodus polonicus and common in the topmost bed. This may be interpreted Complexodus pugionifer at that stratigraphic level. as an expression of two warmer epochs separated by a Unlike M6jcza, there are numerous marly intercalations single colder episode, but it has to be kept in mind (but stili with phosphatic ooids) within the upper part that the more calcareous dolomite beds are separated of the organodetrital limestone, corresponding by marly intercalations in which conodonts are presumably to the Nemagraptus gracilis transgression. unknown. lt may appear that each of the four dolomite Close to the end of carbonate sedimentation, Amorpho- beds corresponds to a separate warm episode recorded gnathus disappeared almost completely and the in M6jcza. Possibly, this uni t corresponds to the entire assemblage became dominated by species with Ordovician sequence above the M6jcza Limestone at coniform elements. lnitially this was 'Scolopodus' M6jcza. peselephantis (in sample ZA-25) which corresponds to In Zalesie Nowe, a rather uniform fìne-clastic rock a similar increase in contribution of this species in continues to the top of the Ordovician, with M6jcza (samples MA-86 to MA-88). The topmost Mucronaspis occurring in its lower part (Czarnocki, limestone layer (sample ZA-23) contains Sagittodontina 1928; Kielan, 1956, 1960). Sedimentation was conti- and numerous Strachanognathus, like the horizon nuous across the Silurian-Ordovician boundary. Above immediately preceding the mass occurrence of the pale shales with K-bentonite intercalations of the Rhodesognathus in M6jcza (sample MA-91; Fig. 2) . Zalesie Formation there is an unfossiliferous black, Apparently the immigration of this species to the Holy organic-rich layer, a few centimeters thick, and then a Cross Mountains coincided with the end of carbonate graptolite shale that passes gradually into a radiolarite. sedimentation in Zalesie. Both the latest Ashgill Normalograptus persculptus and Above, there are more than three meters of marls the earliest Llandovery Parakidograptus acuminatus an d shales with thin dolomitic intercalations and a level Zones were reported from the shales (Kielan, 1956) with ooids. There is a thick K-bentonite bed, an d severa! although more recent collecting has failed to provide minor ones (Chlebowski, 1971 identifìed six such any guide graptolite species in the dominantly intercalations), within this series, which ends with normalograptid assemblage. purple-red shales with small ferruginous concretions (oxidized pyrite?). Unfortunately, no conodonts have been recovered from this part of the section and its EVOLUTIONARY CALIBRATION dating remains rather unprecise. lt is tempting to correlate the Zalesie K-bentonites with those of the Although severa! of the conodont species Baltic area (see Bergstrom et al., 1995, 1997), the represented in the M6jcza Limestone and the lower Kinnekulle K-bentonite being especially widely part of the Zalesie Formation have short stratigraphic distributed (Huff et al., 1992) but they seem to be ranges, in most cases this reflects only their ecologica! signifìcantly younger than the Baltic ones. There is also sensitivity and has little to do with evolution or even no Baltic equivalent to the main M6jcza bentonite. with a more geographically uniform succession of lmmediately above there is the only bed of pure faunas. Perhaps the only lineage (possibly two parallel limestone in the entire section. This is a dark brown lineages) that is of some value in an interregional nodular rock with numerous darkly stained worm correlation is that ofAmorphognathus. Even in this case burrows in its basai, muddy part. Conodonts are easily the more or less continuous succession of populations, extracted but rather uncommon an d represented mostly typical of the Middle Ordovician part of the Holy Cross by Hamarodus, specifìcally indeterminate Amorpho- Mountains succession, was punctuated in the Late gnathus (almost certainly A. ordovicicus), an d Ordovician by climatic instability. The fìrst such Scabbardella. This is an assemblage similar to that from ecologica! displacement was expressed by an incursion the topmost M6jcza Limestone at M6jcza and such a of Rhodesognathus (Text-fìg. 3), in fact representing an correlati o n has bee n proposed earlier (Dzik et al., 1994), allopatric lineage closely related to Amorphognathus. although the lack of phosphatic ooids may rather After its disappearance, a morphologically distinct suggest its correlation with one of the horizons rich in species ofAmorphognathus occurred in the area, possibly LATE ORDOVICIAN CONODONTS AND GONDWANA GLACIATIONS 241 of foreign origin (A. ventilatus). The locallineage of invaded the temperate regions during a global cooling. Amorphognathus, at least when present with The paleomological basis for the interregional Rhodesognathus, evolved toward the morphology of A. correlation of particular climatic events recognized in superbus. This was the species that later replaced A. Mojcza is very weak. This results mostly from the rarity venti!atus, which again suggests a migrational event. of small and fragile diagnostic elements of Amorpho- Perhaps the subsequent series of morphologies, gnathus in the studied strata. Unfortunately, there seems represented by an unnamed chronospecies with a ne to be no alternative to this way of reasoning in (M) element small demicle at the external margin of a correlating the events. Despite ali those reservations, a high cusp, then A. ordovicicus, lacking such a denti de, preliminary correlation is here proposed. Problems that and finally A. duftonus, with a newly formed denticle result from poor knowledge of the guide species are at the junction of the processes, is a phyletic series. discussed below. Some uncertainty is introduced, however, by the extremely wide population variability of Amorphognathus AMORPHOGNATHUS VENTILATUS FERRETTI & BARNES, 1997 (see Dzik, 1994) which characterizes especially the population ofA. ventilatus from Thuringia (see Ferretti This species is undoubtedly the most importane in & Barnes, 1997). Among specimens found there, forms the age correlation of the Kalkbank, the only carbonate closely similar to A. ordovicicus occur. This may mean horizon in the Ordovician ofThuringia. The single ne that it was a member of an allopatric lineage that (M) element in Kniipfer's (1967) collection was

Ctl O) Ctl :::: Cl) :.§ -5 Cl) f! -5 -5 .gc: eQl Ctl o .Q e o sample .Q Cl) :::: Ctl "" c: MA m l) 2- ""Clco O) Q Cl)

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Text-fìg. 2 - Changes in relative contribution to samples of the main lineages of coniform conodonts and Sagittodontina in the upper part of the M6jcza succession. Note that generally warm-water Panderodus is restricted to epochs of lowered contribution from the cold-water Scabbardella. The Gondwanan lineage of Sagittodontina ceased ro occur in the area before the peak of the early Ashgill cooling. Ranges of the Amorphognathus species which enable interregional correlation shown o n left. 242 ]. DZ!K

(l) -5e sample

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Text-fìg. 3 - Changes in relative conrribution ro samples of the main lineages of co nodonrs with elaborate appararuses. Note the restricted occurrences of warm-water Welsh immigrane Rhodesognathus and two peaks in abundance of Amorphognathus. classifieci as Amorphognathus superbus Rhocies, 1953 by They introciuceci the new species, A. ventilatus, far Dzik (1989) because ofits similarity to specimens from elements similar to the one illustrateci by Kniipfer the top of the M6jcza Limestone, nameci 'A. superbus (1967) anci associateci elements with a very prominent early form' in Dzik (1990; also Dzik, 1994). This cusp without any cienticles on its sicies were icientifieci interpretation was not accepteci by Ferretti & Barnes asA. ordovicicus Branson & Mehl, 1933. On this basis (1997), who haci at their ciisposal an extremely large anci somewhat arbitrarily, they proposed that the collection of Kalkbank conocionts, incluciing l 02 ne Kalkbank is of early A. ordovicicus Zone age. In fact, a (M) elements of Amorphognathus. Cusp morphology complete transition berween these morphologies can of ne (M) element is extremely variable in their sample. be traceci in their sample, with no evicience of LATE ORDOVICIAN CONODONTS AND GONDWANA GLACIATIONS 243

Sample MA 150 151 190 191 152 153 154 155 156 157 158 159 160 161 162 Scolopodus 11 7 20 3 2 Walliserodus 4 47 273 122 4 10 47 64 50 15 3 3 3 51 2 Scabbardella 753 1862 435 190 39 5 327 318 100 203 1685 812 384 279 257 Dapsilodus 3 25 8 3 4 4 2 33 43 7 18 16 6 Panderodus 29 26 152 65 8 5 15 29 14 87 27 6 1 1 Cornuodus 54 111 17 2 3 2 23 9 7 3 2 1 Strachanognathus 9 1 Staufferella 1 3 Protopanderodus 1 3 2 1 Paltodus 2 3 49 47 2 Orepanoistodus 31 12 143 42 7 44 48 4 8 4 1 Pseudooneotodus 3 Phragmodus 2 Baltoniodus 32 13 179 104 31 5 1? Sagittodontina 10 17 Rhodesognathus 1056 500 51 14 5 1 9 Amorphognathus 224 122 523 414 101 21 18 20 10 43 343 139 69 118 71 lcriodella 6 10 4 1 10 Birksfeldia 1 Hamarodus 4 1 51 35 195 112 96 150 50 Spinodus 1 3?

Sample MA 163 164 165 166 167 168 169 170 171 172a 172b 173 174 175 Scolopodus 5 3 2 3 2 5 Walliserodus 24 42 203 108 7 2 13 48 3 37 67 24 75 Scabbardella 71 130 756 393 281 313 460 509 94 317 736 318 832 4 Dapsilodus 3 124 36 118 143 102 551 51 51 168 375 553 5 Panderodus 1 17 35 28 64 79 40 14 38 75 33 61 Cornuodus 2 21 16 26 31 16 26 11 4 33 56 17 Protopanderodus 9 19 16 23 4 1 1 12 15 2 5 2 Paltodus 1 1? 8 1 Drepanoistodus 2 3 Pseudooneotodus 2 4 8 6 10 2 1 4 5 6 15 Amorphognathus 29 43 338 254 215 142 156 122 48 63 127 148 225 11 Ieri ode/la 1 Birksfeldia 1 5 10 1 Distomodus 31 Pterospathodus 7 Hamarodus 12 27 246 181 15 17 6 15 1 18 85 17 28 Plectodina 3 Gen. indet. 1 1 Drepanodus 1

T ab. l - Numerica! contribution of particular conodont genera ro samples taken from the upper part of the Mojcza section. bimodality in the frequency distribution. Moreover, denticles (the second one usually rudimentary, tips one element with a denticle on the outer side of the the merging point of internai and posterior processes) cusp (thus of a morphology typical of A. superbus) include 14 specimens. Specimens without additional points to a complex pattern of developmental contro! denticles on the cusp (thus closely resembling elements of the morphology. In the Kalkbank assemblage the in the A. ordovicicus s.s. populations, although with a dominating morphology of ne (M) elements is that somewhat wider an d shorter cusp) are equally common with one large denticle emerging obliquely from the (13 specimens), the distribution seems thus almost inner side of the cusp (53 specimens in Ferretti & Gaussian. Thus i t is proposed that only one species of Barnes, 1995 collection). Elements with two such Amorphognathus is represented in the Kalkbank 244 JDZIK assemblage. A direct relationship ofA. ventilatus to A. ordovicicus The unusually large number of ne (M) elements is unlikely because of the primitively long external extracted from the Kalkbank sample by Ferretti & ('anterior') process in ne (M) element of A. ventilatus Barnes (1995) cannot alone explain the extraordinary (induding specimens dassified as A. ordovicicus by diversity of their morphologies in the assemblage. No Ferretti & Barnes, 1997). This process was relatively doubt that they were much more variable than in any long and some specimens from the Kalkbank show a other described Late Ordovician population of small dentide on it. A gradua! reduction of the entire Amorphognathus. A possible solution to this puzzle may process can be seen in the successi o n from A. superbus be provided by the apparent immigrational nature of through A. sp. n. to A. ordovicicus in the Mojcza section. the whole Kalkbank fauna. This can be matched with An independent origin of A. ordovicicus from A. similar cases of invasion by warm-water conodont ventilatus would require that in each of the two separate assemblages into environments that were ecologically lineages the reduction proceeded in parallel. different earlier, which used to be connected with an The arched internai process, which is shared by the increase in the population variability. In the Devonian ne (M) element of all the Ashgill species of Amorpho- an d Carboniferous this pattern of a disparate variability gnathus, apparently developed already in the late has been explained as an effect of the character population of A. tvaerensis. Perhaps A. ventilatus displacement that follows complication of a community originated directly from A . tvaerensis by an almost after its establishment (Dzik, 1997, p. 70). An intere- complete reduction of the external denticulation in the sting feature of the associateci Sagittodontina population ne (M) elements. The Mojcza specimens from samples is that some ne (M) elements also developed additional MA-96 and MA-97, previously named 'A. superbus early oblique dentides dose to the ti p of the cusp. Sometimes form' (Dzik, 1994, text-fig. 22, pl. 23, fig. 3), share it is difficult to distinguish between the elements of with those from Kalkbank the very characteristic fan- Sagittodontina andAmorphognathus. This refers also to like arrangement of dentides in the ne (M) elements. the oz (Pb) elements, which are extremelyvariable, and Additional sampling at the same level (samples MA- range from morphologies dose to those typical of 190 and MA-191; Pl. l, figs. 1-21) yielded 116 ne Rhodesognathus (and erroneously identified as such by (M) specimens. Among 42 specimens from sample Dzik, 1990) to those with wide, short processes, similar MA-190 preserved well enough to show the position to specimens that occur much lower in the Polish of the cusp, 27 have the cusp in a marginai position, sections (see Dzik, 1994). 13 bear a single external dentide an d in two specimens

EXPLANATION OF PLATE l

Figs. 1-21 - Amorphognathus aff. ventilatus Ferretti & Barnes, 1997. Late Caradoc of the M6jcza section, Holy Cross Moumains, Poland. l) sp (Pa) elemem ZPAL cVI/819, sample MA-190. 2) oz (Pb) elemenr ZPAL cVI/821, sample MA-190. 3) sp (Pa) elemem ZPAL cVI/820, sample MA-190. 4) sp (Pa) elemenr ZPAL cVI/805, sample MA-191. 5) sp (Pa) elemem ZPAL cVI/804, sample MA-191. 6) ne (M) elemem ZPAL cVI/826, sample MA-190. 7) ne (M) elemem ZPAL cVI/830, sample MA-190. 8) ne (M) elemenr ZPAL cVI/828, sample MA-190. 9) ne (M) elemem ZPAL cVI/829, sample MA-190. 10) ne (M) elemenr ZPAL cVI/827, sample MA-190. 11) rr (Sa) elemenr ZPAL cVI/824, sample MA-190. 12) ke (Se) elemem ZPAL cVI/822, sample MA-190. 13) hi (Se) element ZPAL cVI/825, sample MA-190. 14) ne (M) elemem ZPAL cVI/799, sample MA-191. 15) ne (M) elemem ZPAL cVI/801, sample MA-191. 16) ne (M) elemem ZPAL cVI/800, sample MA- 191. 17) ne (M) elemem ZPAL cVI/797, sample MA-191. 18) ne (M) elemem ZPAL cVI/798, sample MA-191. 19) ne (M) elemem ZPAL cVI/802, sample MA-191. 20) ne (M) elemem ZPAL cVI/803, sample MA-191. 21) pl (Sb) elemem ZPAL cVI/823, sample MA-190. Figs. 22-26 - Amorphognathus tvaerensis Bergsrriim, 1962 late form rransirional ro A. superbus Rhodes, 1953. Late Caradoc of rhe M6jcza section, Holy Cross Mounrains, Poland. 22) sp (Pa) elemem ZPAL cVI/759, sample MA-152. 23) oz (Pb) elemem ZPAL cVI/761, sample MA-152. 24) sp (Pa) elemem ZPAL cVI/760, sample MA-152. 25) ne (M) elemem ZPAL cVI/765, sample MA-152. 26) ne (M) element ZPAL cVI/764, sample MA-152. Figs. 27-30 - Amorphognathus superbus Rhodes, 1953. Late Caradoc of the M6jcza section, Holy Cross Moumains, Poland. 27) sp (Pa) element ZPAL cVI/758, sample MA-156. 28) oz (Pa) elemenr ZPAL cVI/756, sample MA-156. 29) tr (Sa) elemem ZPAL cVI/762, sample MA-156. 30) ne (M) elemenr ZPAL cVI/767, sample MA-154. Fig. 31 - Pseudooneotodus mitratus (Moskalenko, 1973). Ashgill of rhe M6jcza section, Holy Cross Moumains, Poland. 31) elemem ZPAL cVI/784 in occlusa! view, sample MA-172A. Fig. 32 - Gen et sp. indet. Ashgill of the M6jcza section, Holy Cross Mountains, Poland. 32) elemem ZPAL cVI/783 in occlusa! view, sample MA-172B. Figs. 33-36 - 'Plectodina' alpina Serpagli, 1967. Ashgill of the M6jcza section, Holy Cross Moumains, Poland. 33) sp (Pa) elemem ZPAL cVI/781, sample MA-172A. 34) oz (Pb) elemem ZPAL cVI/780, sample MA-172A. 35) tr (Sa) elemem ZPAL cVI/714, sample MA-115. 36) ne (M) element ZPAL cVI/782, sample MA-172A. Figs. 37-39 - Birksfeldia selli Serpagli, 1967. Ashgill of the M6jcza section, Holy Cross Moumains, Poland. 37) oz (Pb) elemenr ZPAL cVI/778, sample MA-172B. 38) ke (Se) elemem ZPAL cVI/777, sample MA-161.39) ne (M) elemem ZPAL cVI/779, sample MA-172B.

(Ali specimens x 70) ]. DZIK, LATE ORDOVICIAN CONODONTS AND GONDWANA GLACIATIONS P!. l 246 ]. DZIK

13 bear a single external denticle and in two specimens there are two such denti cles (they are then AMORPHOGNATHUS SUPERBUS RHODES, 1953 eirher ofA. superbus or A. tvaerensis morphology). The main difference between the M6jcza and Kalkbank In the topmost part of the M6jcza Limestone cono- populations is that the modal number of denticles donts are rare an d the contriburion ofAmorphognathus (including cusp) in sample MA-190 is three (21 to the assemblage is very low. Two ne (M) elements in specimens) while in Thuringia most of the specimens samples MA-154 and MA-100 (Dzik, 1994, text-fìg. bear only two or even one denticle (cusp alone). 22) show that A. superbus was represented rh ere. They Moreover, sinistra! sp (Pa) elements in the M6jcza are characterized by a relatively short straight cusp sample stili bear a rudimentary lobe at the internai associated with parailel strong denticles (Pl. l, fìg. 30). process, which disappeared somewhat higher in rhe section, wheareas in the Kalkbank this lobe is AMORPHOGNATHUS SP. N. completely missing (Ferretti & Barnes, 1997). However, the M6jcza population may be ancestrai to A series of populations following A. superbus in A. ventilatus. Such a taxonomic decision results in a M6jcza (P l. 2, fìgs. 1-12) show a graduai transformation fundamentally different age correlation. Instead of towards a rather different morphology of the ne (M) belonging to the early A. ordovicicus Zone, the Kaikbank elements. The cusp is much longer and only one event would be dose in age to the A. superbus Zone. denticle is presento n the externai process. In the early The presence of similar specimens in the Nabala stage population from samples MA-l 09 an d MA-l the of Estonia may suggest that A. ventilatus ranged up to external process was relatively long, only somewhat the level of Amorphognathus sp. n. shorter than in A. superbus. Large specimens may have Its origin, ifbetter documented, may appear useful developed an additionai smail denticle (Dzik, 1994, as a marker of at least a regional importance. An Pl. 3, fìg. 6a). In samples somewhat above in the section emendati o n to the originai diagnosis ofA. ventilatus is the external process was much shorter, aithough stili here proposed, as an Amorphognathus species chara- pointed, the cusp was even longer and the external cterized by ne (M) elements with a sharp-edged, wide denticle attached closer to it. cusp without any external denticularion but with an This segment of the phyletic evolution of the Ashgill additional single, obliquely emerging denticle (or two Amorphognathus was classifìed earlier (Dzik, 1994) denticles) on its inner margin and a long external withinA. ordovicicus buti t defìnitely deserves separation process, sometimes bearing a rudimentary denticle. at the chronospecies level.

EXPLANATION OF PLATE 2

Figs. 1-12 - Amorphognathus sp. n. Earliest Ashgill(?) of rhe Mojeza seerion, Holy Cross Mounrains, Poland. l) sp (Pa) elemenr ZPAL eVI/766, sample MA-158. 2) sp (Pa) elemenr ZPAL eVI/767, sample MA-158. 3) ne (M) elemenr ZPAL eVI/774, sample MA-158. 4) ne (M) elemem ZPAL eVI/773, sample MA-158. 5) ne (M) elemem ZPAL eVI/775, sample MA-158. 6) tr (Sa) elemenr ZPAL eVI/769, sample MA-158. 7) pl (Sb) elemem ZPAL eVI/770, sample MA-158. 8) ke (Se) elemem ZPAL eVI/771, sample MA-158. 9) hi (Se) elemem ZPAL eVI/772, sample MA-158. 10) oz (Pb) elemem ZPAL eVI/768, sample MA-158. 11) ne (M) elemem ZPAL eVI/359, sample MA-l. 12) ne (M) elemenr ZPAL eVI/460, sample MA-109. Figs. 13-37 - Amorphognathus ordovicicus Branson & Mehl, 1933. Ashgill of rhe Mojeza seerion, Holy Cross Mounrains, Poland. 13) sp (Pa) elemenr ZPAL eVI/785, sample MA-163. 14) sp (Pa) elemem ZPAL eVI/786, sample MA-163. 15) sp (Pa) elemem ZPAL eVI/788, sample MA-165. 16) ne (M) elemenr ZPAL eVI/776, sample MA-161. 17) oz (Pa) elemem ZPAL eVI/808, sample MA-165. 18) sp (Pa) elemem ZPAL eVI/806, sample MA-165. 19) sp (Pa) elemenr ZPAL eVI/807 sample MA-165. 20) sp (Pa) elemenr ZPAL eVI/787, sample MA-165. 21) ne (M) elemem ZPAL eVI/790, sample MA-166. 22) pl (Sb) elemem ZPAL eVI/811, sample MA-165. 23) pl (Sb) elemem ZPAL eVI/810, sample MA-165. 24) ke (Se) elemem ZPAL eVI/812, sample MA-165. 25) tr (Sa) elemem ZPAL eVI/809, sample MA-165. 26) hi (Se) elemem ZPAL eVI/813, sample MA-165. 27) ne (M) elemem ZPAL eVI/815, sample MA-165. 28) ne (M) elemem ZPAL eVI/817, sample MA- 165. 29) ne (M) elemem ZPAL eVI/816, sample MA-165. 30) ne (M) elemem ZPAL eVI/789, sample MA-165. 31) ne (M) elemenr ZPAL eVI/814, sample MA-165. 32) ne (M) elemem ZPAL eVI/818, sample MA-165. 33) ne (M) elemem ZPAL eVI/796, sample MA-173. 34) ne (M) elemem ZPAL eVI/793, sample MA-173. 35) ne (M) element ZPAL eVI/794, sample MA-173. 36) ne (M) elemem ZPAL eVI/792, sample MA-173. 37) ne (M) elemem ZPAL eVI/795, sample MA- 173. Figs. 38-47 - Amorphognathus ordovicicus Branson & Mehl, 1933 transitional to A. dufionus Rhodes, 1955. Late Ashgill of the Mojeza seetion, Holy Cross Moumains, Poland. 38) sp (Pa) element ZPAL eVI/944, sample MA-174. 39) sp (Pa) elemem ZPAL eVI/943, sample MA-174. 40) oz (Pb) elemem ZPAL cVI/945, sample MA-174. 41) oz (Pb) elemem ZPAL eVI/946, sample MA-174. 42) pl (Sb) elemem ZPAL eVI/948, sample MA-174. 43) ke (Se) elemem ZPAL eVI/949, sample MA-174. 44) tr (Sa) elemem ZPAL eVI/947, sample MA-174. 45) hi (Se) elemem ZPAL eVI/950, sample MA-174. 46) ne (M) elemenr ZPAL eVI/951, sample MA-174. 47) ne (M) element ZPAL eVI/952, sample MA-174.

(Ali speeimens x 70) j DZIK, LATE ORDOVICIAN CONODONTS AND GONDWANA GLACIATIONS Pl. 2 248 ]. DZIK

AMORPHOGNATHUS ORDOVICICUS BRANSON & MEHL, 1933 idemifìed in strata of the uppermost Rawtheyan (berween shelly zones 7 and 8) Cystoid Limestone of In samples above MA-119 and MA-159 ali the Yorkshire by Orchard (1980) as Amorphognathus aff. found ne (M) elements ofAmorphognathus have a very lindstroemi. A conspecifìc population seems to be short external process without any denticles (P l. 2, fìgs. represented also in the 2 m thick limestone sequence 13-37). The elements found are invariably of a small of the Rifugio Nordio section in the Carni c Alps. Three size and their adult morphology remains unknown. ne (M) elements ofAmorphognathuswith smooth cusp Stili, they are easily distinguishable from the preceding margins have been found there by Serpagli (1967) and chronospecies at comparable histogenetic stages. one with an incipient inner denticle. The only ne (M) Although the materia! is too sparse to prove this element of Amorphognathus found by Ferretti ( 1998) biometrically, there seems to be a progressive reduction in the Kralov Dvor Formation immediately below of the external process in the lineage, which fìnally Mucronaspis is also Amorphognathus aff. lindstroemi, resulted in the complete disappearance of external which inaicates that such a form occurs in strata that denticulation. In this respect the ori gin ofA. ordovicicus immediately precedestrata of Hirnantian age. was parallel to the much earlier development of the A. In the 3.5 m thick, possibly more complete Monte ventilatus morphology, which preceded the evolutionary Zermula Carnic Alps section, three elements with a elongation of the cusp and reduction of the external prominent denticle in this position have been found. process. This is the type population of Amorphognathus A complete set of element types of this species has lindstroemi Serpagli, 1967. Severa! ne (M) elements of been illustrateci by Nowlan & Barnes (1981) from the this kind have been reported (one of them illustrateci) Vauréal Formation of the Anticasti lsland, Canada. by Orchard (1980; also Bergstrom & Orchard, 1985), Both the apparatus reconstruction ofA. ordovicicus by in the upper part of the Keisley Limestone of northern Armstrong et al. ( 1996) an d their identifìcation of the England. The Keisley Limestone is covered by shales ne (M) elementare incorrect. Their oz (Pb) element is with Hirnantia (Wright, 1985), similarly as the topmost actually an incomplete sp (Pa). The specimen identifìed Ordovician limestone units in the Holy Cross Moun- as ne (M) is roo poorly preserved to be identifìed, it tains and the Carnic Alps. Bergstrom & Orchard may be a hi element of something else. lnstead, their (1985) poimed out its conspecifìcity with Amorpho- Sb l element resembles more closely ne elements of gnathus duftonus. Amorphognathus. lf so, its long external process is Although the evidence is obviously very limited, a suggestive of a proximity to A. superbus. progressive evolution towards the larger and larger latera! denticle seems likely. The Rifugio Nordio Carnic AMoRPHOGNATHus DUFTONus RHooEs, 1955 Alps population, with only an incipient latera! denticle present in some elements, may then be coeva! with The topmost limestone layer in M6jcza yielded rwo that from the topmost limestone bed in M6jcza and ne (M) elements ofAmorphognathus, o ne of which has the Cystoid Limestone ofYorkshire, but slightly older a rather short cusp with a transversely oriented denti de than that of the Monte Zermula and the uppermost(?) at the merging point of ribs of the internai and posteri or Keisley Limestone of northern England. The origin of processes (Pl. 2, fìgs. 38-42). Such a denticle develops A. duftonus (populations earlier classifìed as A . aff. commonly in specimens from populations of lindstroemi being transitional) may be of some Amorphognathus of various ages. Those, which can be correlative value. In ali the samples of late Amorpho- founa among specimens of A. ordovicicus, for instance gnathus from M6jcza elements ne (M) with the in sample MA-163 where they seem to be especially transverse denticle co-occur with elements lacking is, common, differ from geologically older ones in that and this is clearly a matter of within-population the denticle does not belong to any of the processes variability. The main evolutionary change at the but is located in the middle of the flat area spanning emergence of A. duftonus was probably a relative berween the internai process and its posterior bifur- reduction in length of the cusp in respect to this cation. This apparenly resulted from the evolutionary denti de. increase of the angle of ramifìcation of the internai process, which was initially rather small (although variable), becoming wider and wider, and fìnally loosing ROOTS OF THE SILURIAN CONODONT FAUNAS its connection with the transverse denticle. The denticle probably developed earlier in the histogeny of the In alllocalities of the world where the Ordovician- element than bifurcation of the processes. Silurian transition is well documented by conodonts, Both the ne (M) elements ofAmorphognathus from there is drastic faunal change at the boundary. Only the topmost bed of the M6jcza Ordovician differ from the lineages of coniform conodonts Dapsilodus, specimens found in older strata (even those bearing Panderodus, and Pseudooneotodus occur on both sides the transverse denticle) in having shorter and more of the boundary but their morf,hological simplicity robust cusp. Closely similar specimens have been makes i t uncertain if there is tru y a continuity a t the LATE ORDOVICIAN CONODONTS AND GONDWANA GLACIATIONS 249 species leve!. Possibly, these were extremely post-Ordovician ozarkodinid 'neoprioniodus' element opportunistic species, able to withstand even major (e.g. Dzik, 1994, pl. 24, fig. 20). changes in the environment. Other coniform members One may thus wonder, whether this similarity in of the Ashgill assemblages (thin-crown Scabbardella, the morphology of the anteriormost element in the bizarre Strachanognathus), as well as conodonts with apparatus, as well as the generai tendency to molarize complex apparatuses but of the platform seri es elements the posteriormost elements by developing an elaborate with thin crowns (Hamarodus, Anse/la), probably did platform, does not express an ecologica! proximity of not become extinct immediately. Rather they moved Amorphognathus to the post-Ordovician ozarkodinids. to cold water refugia and disappeared somewhat later, lf so, the main faunistic change at the Ordovician- together with those shrinking environments. The Silurian boundary would not correspond to any extreme case is the Lazarus-type reappearance of the significant difference in the ecology of conodont typically Ordovician Anse/la in the early Wenlock in communities but rather a competitive replacement of Australia (Bischoff, 1997). The lineage of Icriodella re- one taxonomic group by another. invaded the earlier occupied areas already in the Only o ne ozarkodinid species occurs in the Ashgill Llandovery, and only slighdy later the Pterospa- of the Holy Cross Mountains. Due to time proximity thodontidae initiated their rapid evolution. The oldest to the earliest Silurian ozarkodinids its taxonomic pterospathodontid with known apparatus structure is identity deserves some comments, similarly as the two Complexodus (Dzik, 1994), which is not known from other poorly known late Ordovician prioniodontids of strata younger than the early Caradoc. Rare robust restricted paleogeographic distribution, Sagittodontina elements of a pterospathodontid resembling the and Birksjeldia. Silurian Distomodus occur in the Late Caradoc of the Holy Cross Mountains, which supports the Ordovician 'PLECTOD!NA 'ALPINA SERPAGLI, 1967 origin of the family. The earliest Silurian Ozarkodina and Aspelundia, A few additional elements found in Mojcza in the from which probably ali the remaining post-Ordovician carbonate equivalent of the Zalesie Formation have ozarkodinid branches of the Spathognathodontidae and helped to darifY relationships of the single specimen Prioniodinidae developed, show a biramous symme- dassified earlier as a hi (Se) element Yaoxianognathus? trical tr (Sa) element. The biramosity of this element sp. (Dzik, 1994, p l. 24, fig. 21). lts surface is obliterated in the Late Ordovician Yaoxianognathus, as well as by a cover of an acid resistant day but it seems now denticulation of the external process in the hi (Se) that this is almost certainly a symmetrical tr (Sa) element and parallel to the cusp arrangement of element with o ne process broken. Such elements occur dentides in the ne (M) element, makes i t a likely relative in the Uqua Limestone population of'Plectodina' alpina of the ancestor of the post-Ordovician ozarkodinids (Prioniodus ethingtoni in Serpagli, 1967). The main (Nowlan et al., 1997). difference between 'Plectodina' alpina and species of The only important evolutionary change needed Yaoxianognathus is thus its primitive, triramous tr (Sa) to produce a typical Silurian ozarkodinid would then element. Whether the mediai process disappeared in be the arching of the internai process of the ne (M) the evolution from the common ancestor of both element, with a parallel to the cusp arrangement of lineages at the origin of Yaoxianognathus or the latter dentides. From some reason this was perhaps the most originated direcdy from a Microzarkodina-like ancestor, conservative feature of the post-Ordovician Ozarko- remains unknown. Two more oz (Pb) elements and dinida, which persisted unchanged in most lineages one ne (M) element have been found, which enables until the late Triassic extinction of conodonts (Dzik, reliable taxonomic identification of the species (P l. l, 1992). In this respect it is ofinterest to notice that in figs. 33-36). the evolution of the ne (M) element of the late 'Plectodina' alpina belongs to an evolutionary branch Ordovician Amorphognathus a closely similar derived from Plectodina but different in lacking a transformation took piace. In the Early and Middle rudimentary process in the oz (Pb) elements and thus Ordovician segment of the lineage, despite basic similar in this respect to Aphelognathus, although changes in the shape of the whole element, its internai differing from it in the morphology of the ne (M) process remained relatively short and straight, which elements, which in Aphelognathus have both processes is the primitive feature ofboth the Prioniodontida and denticulated. 'Ozarkodina' rhodesi Lindstrom, 1959 and early Ozarkodinida (Dzik, 1992, 1994). This changed 'Ctenognathus' pseudofissilis Lindstrom, 1959 from the in the late Caradoc, when the dentides dose to the Crug Limestone ofWales (Lindstrom, 1959; Orchard, cusp developed an orientation parallel to i t (A. superbus 1980) of an early Ashgill age, the first known also from morphology). The internai process elongated the Oanduan (late Caradoc) of the Baltic regio n (Viira, significandy and arched, its denticulation becoming 1974; Dzik, 1983), are among the oldest occurrences prominent with dentide tips pointing in the same of such morphology (Savage & Bassett, 1985). The ne direction as the cusp (A. ordovicicus morphology). In (M) element of'Prioniodina' alpina does not show the effect, a shape developed which dosely matches the specialization typical for related Yaoxianognathus but 250 ]. DZIK both show much similarity ro the Silurian prioniodinid any occurring in the Thuringian Kalkbank assemblage Aspelundia (see McCracken, 1991), perhaps the most and resembles rather Rhodesognathus from M6jcza. primitive in this respect among the Silurian Ozarko- dinida. BIRKSFELDIA SELLI (SERPAGLI, 1967) The Yaoxianognathus lineage seems to be rooted in Y abruptus from the Lexingron Limesrone of Ohio of According to McCracken ( 1987) Birksfeldia circum- the Late Caradoc (Sweet, 1979; Bergstrom, 1990a), plicata Orchard, 1980 differs from Gamachignathus which still did not have developed the characteristic ensifèr McCracken et al., 1980 (as well as G. hastatus external ('anterior') denticle in the hi (Se) element bur McCracken et al., 1980) in having a shorrer additional its ne (M) element had straight and elongated internai (posterior) process in the sp (Pa) element. Bergstrom ('posterior') process. Yaoxianognathus wrighti from the (1990) 'it is unclear if the differences are enough to Clifden Caves Limesrone of Australia, dateci on the j ustify separati o n a t the generi c level'. Moreover, basis of a rather circumstantial evidence as late Caradoc Birks{eldia complicata may be a junior synonym of (Savage, 1990), is probably the next in age member of 'Gothodus' selli Serpagli, 1967 from the Uqua Limestone its lineage. In its almost straight base of the ne (M) of Refugio Nordio in the Carnic Alps. The M6jcza element and single external denticle in the hi (Se) materia! is roo incomplete to support any taxonomic elementi t clearly shows features of the Yaoxianognathus decision (Pl. l, figs. 37-39). In fact, the few fragmentary lineage. Even more advanced in these respects was sp (Pa) or oz (Pb) elements are not diagnostic even at 'Ozarkodina' sesquipedalis Nowlan & McCracken, 1988 the generic level; that these are elements of Birksfeldia from the Whittaker Formation of Canada oflate Ashgill is shown by associateci ke elements. age (Nowlan et al., 1988). It seems identica! with Gamachignathus occurrences in America are gener- Yaoxianognathus yaoxianensis An, 1985 from South ally younger in age than those of Birksfeldia in Europe China, the type species of its genus (An, 1987). (McCracken et al., 1980), an d species originally Most interestingly, the latest Ordovician assemblage attributed ro these genera may rhus represent the with Yaoxianognathus from northern Canada does not subsequent stages in the evolution of the lineage. In contain Amorphognathus an d Gamachignathus (Nowlan Canada Gamachignathus appears in low numbers in et al., 1988), which indicates that Yaoxianognathus is a the late Ashgill (Richmondian) Vauréal Formation an d truly exotic species in respect to the well known Ashgill dramatically increases its contriburion ro the conodont conodont faunas. The Australian Yaoxianognathus was assemblages with the base of the Ellis Bay Formation a member of a probably relatively shallow-water (Gamachian). lt replaces Plectodina, which does not assemblage with robust Aphelognathus species and reach the top of the Vauréal Formation, as well as other warm-water panderodontids. Midcontinent conodonts (McCracken & Nowlan, 1988). According to those aurhors 'Gamachignathus 5AGITTODON T!NA SP. probably favored cool-water environments, and immigrateci to areas marginai to Laurentia in the later The last occurrences of Sagittodontina in rhe Holy Ordovician in response to glacial cooling'. In the Cross Mountains (Text-fig. 2) are still of an older age Malopolska microcontinent, rare appearances of than its type species rype horizon. McCracken (1987) Birksjeldia are connected with increases in contriburion discussed Bergstrom's (1983) suggestion that the Norrh of Scabbardella, which may also indicate association American Midcontinent Noixodontus girardeauensis with cooling events. Satterfield, 1971 (Thompson & Satterfield, 1975; McCracken & Barnes, 1982, Lenz & McCracken, 1982) is separate from Sagittodontina but it remains poorly known. If rh e proposed above correlation of rh e ACKNOWLEDGMENTS Kalkbank is correct, it would be much younger than Sampling in the Carni c Alps in 1991 was possible owing to a the findings of Sagittodontina in Europe and probably support from the Alexander von Humboldr Foundation and also in Libya. Lenz & McCracken (1982) reported guidance by Hans-Perer Schiinlaub (Ausrrian Geologica! Survey). Prioniodus? girardeauensis from sample 7217 at the Field work in rhe Holy Cross Mounrains were fìnanced by rhe Blacksrone River (49.7 m), taken from the top of a Institute of Paleobiology of rhe Polish Academy of Sciences. limestone unir (abour 10 m thick) located between Technical assisrance from Miss Ewa Hara is gratefully acknowledged. Some part of this work was clone in connection calcareous shale below and a shale with graptolites of with the cooperarion program berween rhe Polish Academy of the Glyptograptus persculptus Zone (index species being Sciences (PAN) and rhe Italian Narional Research Council (CNR). absent) above. lt was associateci there with Amorpho- I am very rhankful to Annalisa Ferretti (Univerity of Modena) for gnathus (no ne (M) element found), Plectodina tenuis, showing me her unpublished marerials from rhe Ordovician localiries of southern Europe. Gamachignathus ensifèr, and Oulodus rohneri. I wish also to express my rhanks to Walter C. 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