Middle Ordovician (late Dapingian–Darriwilian) conodonts from the Shallow Bay and Green Point formations, Cow Head Group, and the Lower Head Formation are recorded from three sections in Gros Morne National Park. The collection was investigated to clarify local age relationships between the uppermost part of the Cow Head Group and the interbedded to overlying sediments of the Lower Head Formation. Conodonts from St. Pauls Inlet North section indicate a middle Dapingian age for the upper lower Bed 13, latest Dapingian to early Darriwilian age for the upper Bed 13, an early Darriwilian (Dw 1) age for the top beds or Bed 15 of the Shallow Bay Formation at Lower Head, and the Lower Head Formation is referred to the Darriwilian. The uppermost part of the lower Bed 13 contains Periodon hankensis n. sp., Gothodus sp. A, and Diaphorodus delicatus followed by Periodon macrodentatus, Ansella longicuspica, Erraticodon n. sp. A, and Spinodus wardi n. sp. in the lowermost part of upper Bed 13. The fauna with P. macrodentatus is referred to the newly established Periodon macrodentatus conodont (phylo-)Zone, which is used for global correlation. The uppermost fauna in the Cow Head Group, i.e., Bed 15, includes Histiodella holodentata, Nealeodus martinpointensis, Oistodella pulchra, Dzikodus peavyi, and Yangtzeplacognathus n. sp. A , which are included in the Histiodella holodentata conodont (Bio-)Subzone of the Periodon macrodentatus Zone. Nealeodus is a new genus introduced here; Periodon hankensis n. sp. and Spinodus wardi n. sp. are new species described from the beds 13 and 15, respectively, in the Cow Head Group; Drepanodus aff. D. giganteus, Drepanodus aff. D. robustus, Erraticodon n. sp. A, Protopanderodus cf. P. cooperi, P. cf. P. varicostatus, and Yangtzeplacognathus n. sp. A are taxa referred to in open nomenclature.
The Cow Head Group (Middle Cambrian – Middle Ordovician; Kindle and Whittington 1958; James and Stevens 1986) in western Newfoundland (Fig. 1) at first sight looks like a chaotic series of shale, bedded limestone, and not least large to very large scale conglomerates or “megabreccias.” These are mostly composed of a variety of limestone boulders and clasts (James and Stevens 1986). The group is up to ca. 500 m thick and excellently exposed along the coast (James and Stevens 1986), and the main outcrops are within the federal Gros Morne Park (Fig. 2). The Cow Head Group is overlain conformably by the Lower Head Formation, which is composed of clastic sediments.
The Cow Head Group is biostratigraphically important because of the richness of its macrofaunas and microfaunas (e.g., Kindle and Whittington 1958; Erdtmann 1971; Fortey et al. 1982; Ludvigsen et al. 1989; Robson and Pratt 2001; Westrop et al. 1996; Young and Ludvigsen 1989). It represents a thick, nearly complete section of the eastern Ordovician palaeoslope of Laurentia, and the global stratotype section and point (GSSP) for the global Cambrian–Ordovician system boundary is placed within the group (at Green Point; Cooper et al. 2001; Fig. 2).
New conodont collections from the upper Bed 13 and especially Bed 15, which comprises the top strata of the Cow Head Group, and from limestone blocks in the Lower Head Formation provide significant new information on genera and species occurrences and ranges, and necessitate revisions of and additions to the biostratigraphic data provided previously by Pohler (1994) and Johnston and Barnes (1999, 2000). This paper presents description of the latest Dapingian to early Darriwilian part of the conodont sequence and also describes the youngest Middle Ordovician conodont fauna recorded in situ from the Cow Head Group.
The Cow Head Group has attracted much scientific attention since Richardson (in Logan 1863) provided the first information on the spectacular exposures on the Cow Head Peninsula in western Newfoundland. Schuchert and Dunbar (1934) described the Cow Head Group in detail and promoted the idea that the deposits were the result of thrusting and their fieldwork resulted in large collections of fossils. Oxley (1953) mapped the area at St. Pauls and Parsons Pond (Fig. 2), and noted the presence of two facies and found that the Cow Head deposits were sedimentary. Kindle and Whittington (1958) named the complex Cow Head Group and defined it as an orderly succession of sedimentary rocks composed of bedded carbonate and shale deposits and chaotic grainstone and conglomerate. Rodgers and Neale (1963) interpreted the Cow Head Group as coeval to the autochthonous carbonate succession and assumed a long distance transport of the group. Stevens (1970) referred the Cow Head Group, together with other transported rocks, to the Humber Arm Supergroup, which is composed of the more distal Curling Group and Cow Head Group that accumulated close to the continental margin. The source of the Cow Head Group conglomerates should be the edge of the autochthonous carbonate bank (James 1981; James and Stevens 1986).
The Cow Head Group, approximately 500 m thick, consists of deeper to deep-water carbonates, shales, and conglomerates of Middle Cambrian to Middle Ordovician (Whiterockian) age. The strata of the group are widely exposed in central western Newfoundland (Figs. 1, 2), where they are preserved in repeated allochthonous slices. These slices structurally overlie coeval autochthonous to para-autochthonous platformal sediments that are separated by either mélange or faults. The conformably overlying Lower Head Formation is composed of mainly medium- to thick-bedded greywacke and a few breccias composed of carbonate clasts (James and Stevens 1986).
At first, the Cow Head Group was subdivided into beds that were given successive numbers, i.e., Beds 1–14, based on the succession on the Cow Head Peninsula (Kindle and Whittington 1958; Figs. 2, 3). This numbering system has been in use since then because it is simple, practical, and often easy to follow in the field. James and Stevens (1986) recognized an additional unit — Bed 15 — lying conformably on Bed 14 at Lower Head (Figs. 2, 3).
James and Stevens (1986) mapped the whole group in great detail and formally established two formations and seven members (Fig. 3). The two formations reflect both the nature and depositional setting of the Cow Head Group sediments. The Shallow Bay Formation represents the carbonate-dominated proximal slope, whereas the siliciclastic-dominated Green Point Formation accumulated in a distal slope setting.
The 100 to 300 m thick Shallow Bay Formation with its four members is predominantly composed of conglomerate and grainstone with intervals of bedded limestone and shale. Characteristic of the succession within the formation are the very prominent units composed of conglomerates and breccias, termed “Megabreccias” by James and Stevens (1986), as the single blocks may be large to extremely large. In the Ordovician succession of the Cow Head Group the three megabreccia units (i.e., beds 10, 12, and 14) are preserved (Fig. 3). The Shallow Bay Formation is considered, as mentioned earlier in the text, to be composed of mostly proximal deposits representing an upper slope depositional setting.
The Green Point Formation is 400 to 500 m thick. It is composed of mainly green and red, and minor black, shale with minor intervals of bedded limestone, shale and limestone, and conglomerates and breccias. The formation overlies limestone and conglomerates of the Shallow Bay Formation and is conformably overlain by greywacke of the Lower Head Formation. The upper boundary can be gradational with beds of Cow Head lithologies interbedded with thin beds of greywacke in the uppermost part of the Cow Head Group (James and Stevens 1986).
The sediments of the Green Point Formation are considered to represent a lower slope depositional setting (James and Stevens 1986).
Localities used in this paper
The topmost strata of the Middle Cambrian – Middle Ordovician Cow Head Group, western Newfoundland comprise the upper Bed 13, Bed 14, and Bed 15 (Fig. 3). The clastic (greywacke)-dominated Lower Head Formation overlies conformably these beds. The investigated strata are intercepted by the prominent “megabreccia” (Bed 14), which in many places has removed most of the upper part of Bed 13.
For this study, collections from the at St. Pauls Inlet North section, Western Pond South section, and Lower Head section at Shallow Bay are used (Fig. 2).
St. Pauls Inlet North
The St. Pauls Inlet North section (49°51′N, 57°48′W) investigated here is situated in St. Pauls Inlet (Fig. 2). This section was described by Kindle and Whittington (1958) and measured in detail by James and Stevens (1986), who referred the strata to the St. Pauls Member of the Green Point Formation, Cow Head Group (Figs. 3, 4). Johnston and Barnes (1999, 2000) presented the conodont succession mainly from the early (Floian) and early Middle Ordovician (Dapingian) interval, whereas information about the top Dapingian and Darriwilian conodont fauna from the upper Bed 13 is sparse.
The uppermost parted limestone (unit 77) divides Bed 13 into the lower and upper Bed 13 in this section. The lower Bed 13 is composed of shale and prominent parted limestone beds, 18.6 m thick. The outcrops of the lower part of Bed 13 are exposed along the west coast of St. Pauls Inlet, and the succession consists of mainly black shale, grey to dark grey, bedded wackestone–grainstone, and a few conglomerate horizons (Fig. 4). Graptolites are abundant from the lower Bed 13 (James and Stevens 1986; Williams and Stevens 1988; Maletz et al. 2003), and the sub-unit is referable to Isograptus (v.) maximus and I. (v.) maximodivergens graptolite zones (Dapingian global Stage; Middle Ordovician). Eleven samples from the lower Bed 13 have been investigated.
The Dapingian–Darriwilian succession — or the upper Bed 13 — at the St. Pauls Inlet N section is predominantly composed of dark grey, green, and red shales, with minor but important thin interbeds of lime mudstone, grainstone, dolostone, and a few breccias (Fig. 4). Levisograptus austrodentatus is not recorded from this section, but presumably it should be present within the upper Bed 13 according to Williams and Stevens (1988, text-fig. 10).
Ten samples from the upper Bed 13 have been investigated covering the interval from units 78 to 84 of James and Stevens (1986) in the section (= upper Bed 13; Fig. 4). Unfortunately, this interval in the Cow Head Group, mainly developed as siltstone and shale, is largely barren for conodonts or the yield of conodonts is low in this interval (see also Western Brook Pond South). Some of the investigated samples are barren, but a few diagnostic conodonts are recorded (Table 1).
Western Brook Pond South
The Western Brook Pond South section is situated along the shore of the Western Brook Pond (49°47′N, 57°50.5′W; Fig. 2) and was described by James and Stevens (1986) in great detail (Fig. 5). The strata are referred to the St. Pauls Member of the Green Point Formation.
The succession of the Bed 13 (units 33 to 50) at the Western Brook Pond South section (Fig. 5) is mainly composed of thin parted limestone succeeded by red and yellow, dolomitic shale and dolostone with very conglomeratic beds. The thick-bedded greywacke (units 53 to 65) of the Lower Head Formation includes a few horizons with limestone blocks. One such horizon is unit 62 (James and Stevens 1986; Fig. 5), and another level is present within unit 64 (Fig. 5).
Isogratus (v.) maximodivergens Biozone (Castlemanian 4) is recorded from the units 34 to 36 and may range up to include unit 38 (Williams and Stevens 1988; Maletz et al. 2003). Williams and Stevens (1988) reported Levisograptus austrodentatus from unit 50 and from higher beds. Maletz (1998), however, suggested that the graptolite fauna from unit 50 should be younger, i.e., the Levisogaptus dentatus Biozone, and that unit 62 tentatively lies within the Holmograptus lentus Biozone (Maltez 2011, personal communication, 2011), which is clearly Darriwilian (Dw 1).
Three samples from the Isograptus (v.) maximodivergens Biozone have been examined, three samples from unit 42 and two samples, one from unit 62 and another from unit 64, are collected from the limestone blocks preserved in the green sandstone of the Lower Head Formation. The interval from unit 43 to unit 62 proved to be barren for conodonts.
The conodont fauna is relative low diverse, and generally, the yield is low (Table 1). At this locality, some specimens show clearly evidence of transportation, and thus, the collection does include both autochthon and allochthon faunal elements. It has not been possible to distinguish between autochthonous and allochthonous taxa in this investigation.
Lower Head section at Shallow Bay
The Lower Head section is situated about 6 km to the north of Cow Head Peninsula (49°57.9′N, 57°46.2′W; Kindle and Whittington 1958; James and Stevens 1986); it is a coastal exposure in the northernmost part of Shallow Bay (Fig. 2). The outcrops at Lower Head are structurally disturbed and the strata are preserved and exposed in an eastern anticline and western syncline, as it is interpreted by Kindle and Whittington (1958). James and Stevens (1986) suggested that a more complicated setting is possible especially because the exposures of “Bed 14” are not similar in development, and, although the conglomerate beds are considered coeval, the origin or source to the blocks could be different. Pohler (1994, p. 14) reported Paraprioniodus costatus (i.e., Darriwilian) obtained from a clast collected from Bed 14 at Lower Head east.
The section investigated here is the “western syncline” of James and Stevens (1986, p. 115; Fig. 6). The strata are named Bed 15 and referred to the Factory Cove Member (James and Stevens 1986). Bed 15, representing the top of the Shallow Bay Formation of the Cow Head Group, is conformably overlain by sandstone of the Lower Head Formation (James and Stevens 1986, p. 115). The section is crucial for the understanding of the stratigraphy of the Cow Head Group and the depositional relationship to the overlying sandstone of the Lower Head Formation (see James and Stevens 1986, figs. 6, 7 for a detailed review and details about the locality).
At Lower Head, the lower boundary of the succession is developed as a fault, which cuts into Bed 14 (Fig. 6). The top of the section, i.e., the sandstone of the Lower Head, is covered by sand and gravel in the beach and, presumably, it is fault-bounded. The conformable succession is well exposed at low tide, and the strata are mainly preserved in the cores of the syncline and with a gentle tilt towards the east. The exposed succession consists of Bed 14 conglomerate capped by a grainstone, ca. 4 m thick, succeeded by Bed 15, which is 9 m thick, and composed of interbedded green siltstone and shale with minor wackstone and dolostone beds and grainstone beds and lenses that up-section gradually become less frequent to absent, and the upper 4 m consist of siltstone (Fig. 6). These sediments are in turn conformably overlain by ca. 4 m of green, medium- to thick-bedded sandstone of the Lower Head Formation.
Kindle and Whittington (1958) provided a list of macrofossils (trilobites and gastropods) from Bed 14 and referred the fauna to Whiterockian (Middle Ordovician). The same authors also listed graptolites from the black shale situated next to the outcrops of Bed 14, but this graptolite fauna is older, i.e., Floian Stage, than the macrofauna found from Bed 14. James and Stevens (1986) reported Levisograptus austrodentatus (= Undulograptus austrodentatus in James and Stevens), the marker species for the base of global Darriwilian Stage, from a horizon at ca. 2 m above the top of Bed 14 demonstrating the Darriwilian age for Bed 15.
Thirteen samples collected from beds 14 and 15 have been searched for conodonts; two samples collected from the middle and top part of Bed 14 are barren and excluded from Table 1. The conodont fauna (Table 1) is obtained from the wackestone and grainstone horizons in Bed 15, whereas seven samples collected from the very thin-bedded dolomitic limestone, dolostone, and dolomitic shale were barren.
The conodont fauna
The Periodon lineage in Cow Head Group
In the Cow Head Group, the Middle Ordovician conodont assemblage (Fig. 7) is dominated by species referred to Periodon. The genus evolved from Periodon primus Stouge and Bagnoli, 1988, a Tremadocian species, where the P elements are undenticulated, into the early Floian Periodon selenopsis Serpagli, 1974, in which the Pa element carries denticles only on the upper edge of the base, to Periodon flabellum Lindström, 1955, a species with serration on the anterior edge of the base of the Pa element (Serpagli 1974; Löfgren 1978; Stouge and Bagnoli 1988; Rasmussen 2001; Johnston and Barnes 2000).
Periodon cf. P. flabellum follows and is known from the Isograptus (v.) lunatus to I. (v.) victoriae graptolite zones (i.e., top Floian to basal Dapingian stages; Maletz et al. 2003). This species represents the first phase of development, in which the anterior corner of the base of the Pa element begins to be extended to the development of a true anteriorly directed anterior, denticulate process. During gradual evolution, the number of free denticles on the anterior process increases from 1 (small) to 1 (large) (= Periodon aff. P. flabellum) in the Tripodus laevis conodont Zone (= Isograptus (v.) victoriae and Isograptus (v). maximodivergens graptolite biozones (of Maletz et al. 2003). The lowermost part of the upper Bed 13 of the Cow Head Group is characterized by the new species Periodon hankensis n. sp., where the Pa element with one anterior denticle is replaced by the Pa element carrying mainly two anterior denticles. The range of Periodon hankensis matches that of the upper range of the I. (v.) maximodivergens in the Cow Head Group.
The next following species is Periodon macrodentatus (Graves and Ellison 1941; Fig. 7); it carries three anterior, free denticles that gradually decrease in size away from the cusp. Periodon macrodentatus ranges from the upper Bed 13 and through Bed 15 (i.e., to the top of the Cow Head Group) and is recorded from the Lower Head Formation. The even younger Periodon zgierzensis Dzik, 1976 (= Nicholsonograptus fasciculatus graptolite Biozone; Maletz 2009, fig. 4) shows the next development of this evolutionary pattern, in which the Pa element carries four anterior, free denticles on the anterior process (Stouge et al. 2011). This latter species is not known from the Cow Head Group but is recorded from the Table Head Group (Stouge 1984).
The S elements likewise increase the number of denticles on the posterior process, and this system helps to distinguish the species (Löfgren 1978; Stouge and Bagnoli 1988; Rasmussen 2001). Further the development of “inverted basal cavities” of the S elements occurred in the Middle Ordovician. The M element changes from morphs without anterior denticles to morphs with denticles on the anterior edge of the base to forms with an anteriorly extended base, where the number of denticles increases on the anterior process.
Information on the conodont succession in the Cow Head Group was first published by Fåhræus (1970). Fåhræus and Nowlan (1978) presented a detailed geological map of the Cow Head Peninsula and described several new taxa from many beds of the Cow Head Group. Landing (in Fortey et al. 1982), Barnes (1988), and Bagnoli et al. (1987) described several species of Cordylodus Pander, 1856 from the Cow Head Group, whereas Nicoll et al. (1999) focused on description of the conodont genus Iapetognathus Landing, 1982 (see also Terfelt et al. 2011).
Introduction of a formal Ordovician conodont zonation of the Cow Head Group commenced with Beds 9 to 11 on the Cow Head Peninsula (Stouge and Bagnoli 1988). Subsequently Pohler (1994) and Johnston and Barnes (1999) focused on beds 9–14 from additional sections.
The Lower (excluding the Tremadocian) to Middle Ordovician conodont faunal succession in Cow Head Group is distinctive and diverse. However, each bed is characterized and dominated by one genus, whereas other taxa — although present — occur as minor components of the fauna. In Bed 9, the conodont zonation is based on the genus Prioniodus Pander, 1856, and three zones were introduced (Stouge and Bagnoli 1988). Prioniodus gilberti Stouge and Bagnoli, 1988, which is the first representative of the genus, appears in the preceding horizon, i.e., Bed 8 (upper Tremadocian), where it is recorded near the top of the bed. In Bed 9, the Prioniodus lineage (Floian Stage) dominates, but near the top of Bed 9, the first representative of Oepikodus, i.e., Oepikodus communis appears (Stouge and Bagnoli 1988).
Oepikodus evae is present in Bed 11 and totally dominates the fauna, i.e., more than 60% to 70% of the total taxa are Oepikodus evae (Stouge and Bagnoli 1988; Pohler 1994; Johnston and Barnes 1999), and, so far, Bed 11 is only referred to a single biozone. Periodon becomes increasingly more important up through Bed 11, and Periodon selenopsis and P. flabellum are present. In the upper part of Bed 11, Oepikodus intermedius takes over and occurs together with P. flabellum. After the inception of Bed 12, the overlying Bed 13 becomes totally dominated by Periodon. The lower Bed 13 is dominated by Periodon cf. P. flabellum and Periodon aff. flabellum (Fig. 7), whereas the upper Bed 13 and Bed 15 are characterized by Periodon hankensis and Periodon macrodentatus, and it is this uppermost Periodon assemblage that is described in this report.
Thus, the conodont fauna in Cow Head Group and from the base of the Floian Stage extending into the Darriwilian Stage is developed as three acmes and each one is characterized by three conodont genera: first Prioniodus (Floian Stage — Stage slice Fl 1 of Bergström et al. 2009), then Oepikodus (Floian Stage — Stage slice Fl 2 of Bergström et al. 2009), and finally Periodon (Dapingian and Darriwilian — Stage slices Dp 1 to Dw 2 of Bergström et al. 2009) that dominates the top part of the Cow Head Group.
Lower Bed 13: The conodont faunal succession from the lower Bed 13 is characterized by Periodon aff. P. flabellum; associated species include Tripodus laevis, Jumodontus gananda, Oistodus multicorrugatus, Paroistodus originalis, Protoprioniodus aranda, Pteracontiodus cryptodens, and Apteracontiodus sinuosus. Johnston and Barnes (1999) introduced the Tripodus laevis Zone for this interval. It is characteristic for the whole of this interval that Drepanodus Pander, 1856 is represented by two species and these two species, i.e., Drepanodus aff. D. giganteus (Sweet and Bergström) and Drepanodus aff. D. robustus Hadding, occur in large to very large specimens and range in size among the largest conodont elements recorded in the material. The first species is characterized by elements carrying multiple costae, whereas the elements of the latter species are smooth and the arcuatiform one only possesses two, posteriorly located, costae.
The top of the Lower Bed 13 records the change from Periodon aff. flabellum to Periodon hankensis n. sp., which is the species where the Pa element carries two free denticles on the anterior process; this species is associated with the first appearance of Spinodus wardi n. sp. and Ansella longicuspica (Table 1). Other characteristic species in this interval of the Cow Head Group include the first appearance of some very simple platform elements.
Upper Bed 13: Periodon macrodentatus fauna replaces the conodont fauna from the lower part of the upper Bed 13 (Table 1). Other species that are new to the Cow Head Group appearing in the upper Bed 13 include Ansella longicuspica and Spinodus wardi n. sp. followed by Nealeodus martinpointensis, which is recorded just below the Lower Head Formation in the St. Pauls Inlet North section (Fig. 4; Table 1; see also Johnston and Barnes 1999, table 2). The Drepanodus species from lower Bed 13 range through upper Bed 13 and into Bed 15, where they are relatively frequent. Paroistodus originalis from below continues through the upper Bed 13 and extends to the top of the overlying Bed 15. This latter species is followed by Paroistodus horridus (i.e., Stouge 1984; Albanesi and Barnes 2000), but this species has not been recorded from the investigated sections.
Bed 15: The conodont fauna from Bed 15 above the Bed 14 megabreccia has not been described before. This assemblage is unique and is found together with graptolites that constrain the youngest strata of the Cow Head Group to the mid Darriwilian (Dw 2) (Williams and Stevens 1988; J. Maletz, personal communication, 2011). Periodon macrodentatus continues from the lower part of the upper Bed 13 and dominates the conodont assemblage in Bed 15, whereas Nealeodus martinpointensis, Paroistodus originalis, and the large Drepanodus species extend into Bed 15 from below. Protopanderodus becomes frequent and both Protopanderodus cf. P. cooperi and P. cf. P. varicostatus are relatively common in the interval. Taxa with their first appearance in Bed 15 include Histiodella holodentata, Dzikodus peavyi, Oistodella pulchra, Protopanderodus strigatus, Yangtzeplacognathus n. sp. A, and Tripodus combsi (Bradshaw, 1969) (= Acodus combsi Stouge, 1984).
As mentioned earlier in the text, current knowledge of the Ordovician conodont zones in the Cow Head Group is the sum of the efforts by several authors commencing with Fåhræus and Nowlan (1978) and followed by Stouge and Bagnoli (1988), Pohler et al. (1987), Pohler (1994), and Johnston and Barnes (1999, 2000). Johnston and Barnes (1999) defined the Tripodus laevis conodont Zone from the lower Bed 13 in the St Pauls Inlet North section, and the zone comprises the interval immediately below the succession of the upper Bed 13 (Fig. 3), which is investigated here.
The Tripodus laevis conodont (bio-)Zone corresponds to the Isograptus (v.) victoriae, Isograptus (v.) maximus, and (v.) maximodivergens (pars) graptolite biozones (Johnston and Barnes 1999; Maletz et al. 2003), belonging to the Dapingian global Stage (Middle Ordovician; Cooper and Sadler 2004; Bergström et al. 2009). Tripodus laevis is known from the base of the Whiterockian Series in the Utah sections (Ethington and Clark 1982), and its appearance has been proposed as a marker for the top of the Ibexian Series (Early Ordovician) of North America (Ross et al. 1997).
Here two new (bio-)zones and one new (bio-)subzone are added to the existing scheme; the new zones follow the Middle Ordovician (Dapingian) Tripodus laevis conodont Biozone of Johnston and Barnes (1999, 2000). The new zones, named Periodon hankensis and Periodon macrodentatus zones, are established on the succession in Bed 13 and based on data from the St. Pauls Inlet North section and the Western Brook Pond South section (Figs. 4, 5; Table 1); the Histiodella holodentata Subzone of the Periodon macrodentatus Zone is introduced for Bed 15 (i.e., the top beds of the Cow Head Group at Lower Head; Fig. 4).
Periodon hankensis conodont Zone (new zone)
First appearance datum (FAD) of Periodon hankensis to FAD of Periodon macrodentatus.
The zone is dominated by Periodon hankensis. The associated fauna (Table 1) includes Costiconus flexuosus, Drepanodus spp., Drepanoistodus spp., Paroistodus originalis, and Protopanderodus spp., which all range from below and extend through the whole zone. Newcomers to the zone include Ansella longicuspica and Spinodus wardi; Oepikodus sp. (cf. evae) and Protopriniodus aranda from below extends to the top of the zone.
Sample SPIN 12 (unit 78 of James and Stevens 1986; upper Bed 13), St. Pauls Member of the Green Point Formation at the St. Pauls Inlet North section.
Dapingian Stage (probably Stage slice Dp 2 of Bergström et al. 2009).
This zone largely matches the upper Isograptus (v.) maximodivergens graptolite Biozone in the Cow Head Group (Williams and Stevens 1988; Maletz 2009, 2011; J. Maletz, personal communication, 2011) but apparently is extending beyond the graptolite biozone.
Periodon macrodentatus conodont Zone (new zone)
FAD of Periodon macrodentatus to FAD of Periodon zgierzensis.
The zone is dominated by Periodon macrodentatus. The associated fauna (Table 1) includes Costiconus mysticus, Drepanodus spp., Drepanoistodus spp., Paroistodus originalis, and Protopanderodus spp., which all range from below and extend through the whole zone. Newcomers to the zone include Dzikodus peavyi, Erraticodon n. sp. A, Histiodella holodentata, Kellidontus sp., Nealeodus martinpointensis, Oistodella pulchra, Periodon gladysi, and Yangtzeplacognathus n. sp. A, all of which are confined to the upper part of the zone in the Cow Head Group.
Sample SPIN-14 (unit 82 of James and Stevens 1986; upper Bed 13), St. Pauls Member of the Green Point Formation at the St. Pauls Inlet North section.
Darriwilian Stage (Stage slices Dw1 – Dw2 of Bergström et al. 2009).
This zone largely matches and overlaps the range of the Levisograptus austrodentatus, L. dentatus and Holmograptus lentus biozones in the Cow Head Group (Williams and Stevens 1988; Maletz 2009, 2011; J. Maletz, personal communication, 2011).
The assemblage characteristic of the lower P. macrodentatus Zone is succeeded by the first appearance of Dzikodus hunanensis, Histiodella cf. holodentata (= an intermediate form between Histiodella holodentata and Histiodella kristinae; see Stouge 2001; Du et al. 2005; Stouge and Zhao 2006; Stouge et al. 2011), Paroistodus horridus and Periodon zgierensis. This transition is not recorded from Bed 15 at the Lower Head section presented in this paper but is recognized in the younger Table Head Group (i.e., Stouge 1984).
Histiodella holodentata Sub(bio-)zone
FAD of Histiodella holodentata to FAD of Histiodella cf. holodentata.
The subzone is characterized by the appearance of Histiodella holodentata, which is fairly common. Other species are the same as mentioned for the Periodon macrodentatus Zone.
The Lower Head section in Shallow Bay, western Newfoundland, Canada (Fig. 2).
Darriwilian Stage (Stage slice Dw 1 of Bergström et al. 2009).
Cow Head Group
Cow Head Peninsula, Bed 14
James and Stevens (1986) noted that the strata of the upper Bed 13 are practically missing in many sections representing the proximal setting (i.e., Cow Head Peninsula and sections in Shallow Bay) as a result of the deep excavation by the Bed 14 megabreccia. Fåhræus and Nowlan (1978) and Pohler (1994) recorded Periodon hankensis (= Periodon flabellum sensu Fåhræus and Nowlan, 1978) and Periodon macrodentatus (= Periodon aculeatus Hadding sensu Pohler), as well as older species of Periodon, from Bed 14. Pohler (1994) mentioned the presence of the Midcontinent taxon Paraprioniodus costatus recorded from Bed 14 at Lower Head. The same or the closely similar species is recorded from the Spring Inlet Member of the Table Point Formation (Stouge 1984; Darriwilian) where it occurs just below the first appearance of Histiodella holodentata. The presence of both Periodon hankensis and P. macrodentatus in Bed 14 demonstrates that Bed 14 indeed “cannabilized” upper Bed 13 strata — and older strata — and the blocks were deposited farther downslope.
Martin Point South
At Martin Point South, the conodont fauna reported by Johnston and Barnes (1999, 2000) from redeposited limestone blocks, was found within massive sandstone beds of the Lower Head Formation. At that time, this fauna was new and the source to the limestone blocks was unknown. It comprises most of the species recorded here from the Histiodella holodentata Subzone of the Periodon macrodentatus Zone at the Lower Head section suggesting a common source of the fauna in the Lower Head limestone blocks and the Cow Head Group and that the reworking process occurred at or shortly after deposition and consolidation of the Bed 15 strata. The fauna from the limestone blocks at Martin Point South also includes other and older taxa and these additional species are considered as reworked elements that were exhumed from older strata and incorporated in the conglomerate in the Lower Head Formation at Martin Point.
Western Brook Pond South section
The conodont fauna recorded from unit 62 and unit 64 of the Lower Head Formation includes Periodon macrodentatus, Histodella holodentata, and Ansella longicuspica (Table 1), which demonstrate that this fauna is largely coeval with those from the Lower Head Formation and recorded from the other localities. The record and yield, however, is poor compared with the yield and diversity of the microfauna recorded from the re-deposited limestone conglomerates at Martin Point South and St. Pauls Inlet North sections.
Table Head Group
Table Point section
The top of the Periodon macrodentatus Zone is not recorded within the Cow Head Group. The upper boundary of the zone, however, is present within the top of the Table Point Formation of the Table Head Group, where Periodon zgierzensis appears and occurs together with Paroistodus horridus and Histiodella kristinae (= Nicholsonograptus fasciculatus graptolite Biozone; Darriwilian Stage, Stage slice Dw 2; Stouge 1984; Maletz 2009).
The Histiodella holodentata Subzone covers the portion of the Histiodella tableheadensis Zone defined in the lower part of the Table Point Formation of the Table Head Group at Table Point (Stouge 1984). Currently, it is accepted that H. holodentata (s.s.) Ethington and Clark, 1982 is a senior objective synonym of the older examples of H. tableheadensis Stouge, 1984 and that it includes the holotype of the latter (e.g., Stouge 2001; Du et al. 2005; Bauer 2010; Mellgren and Eriksson 2010, p. 361; Stouge et al. 2011). In western Newfoundland, the range of Histiodella holodentata s.s. is confined to the Little Spring Inlet Member of Ross and James (1987) (= units A1 and A2 sensu Stouge 1984) of the Table Point Formation, which otherwise is characterized by Midcontinent Province taxa (Stouge 1984). The same interval is referred to the Uromystrum validum trilobite Zone (Rohr et al. 2004). However, Histiodella holodentata s.s. is succeeded — as mentioned earlier — by another fully denticulate species, here referred to as Histiodella cf. holodentata (see Stouge 2001; Du et al. 2005; Stouge et al. 2011) and appears together with Paroistodus horridus (i.e., the successor of Paroistodus originalis). Histiodella cf. holodentata was replaced by Histiodella kristinae Stouge, 1984 — a transition that is recorded in the top part of the Table Point Formation (Stouge 1984) and in China (Zhang 1998; Stouge 2001; Du et al. 2005; Chen et al. 2006; Stouge et al. 2011).
This discussion is restricted to exposures situated along the (present) eastern Laurentian margin of Canada and USA. The conodont scheme introduced here and in Stouge et al. (2011) is used as reference (Fig. 8).
The Lévis Formation of the Quebec Group at the Cóte Fréchette section yields Middle Ordovician conodonts (Uyeno and Barnes 1970) from the interval of the Lévis Formation, which is known as the Shumardia Limestone (see Maletz 2009); the macrofauna is referred to zone D1 of Raymond (1914).
The conodont fauna of the Lévis Formation shares several genera and species with beds 13 and 15 and typically the large Drepanodus spp., but also Spinodus wardi, are present. Paroistodus originalis and Periodon macrodentatus occur together with Histiodella holodentata in the lowermost investigated beds at the Cóte Fréchette section, and apparently Periodon zgierzensis appears in the top strata of the section. The lower Lévis conodont fauna also includes Paraprioniodus neocostatus Bauer, 2010, a taxon characteristic of the lowermost Spring Inlet Member of the Table Point Formation at Table Point (Stouge 1984; see Bauer 2010), which is referred to the Histiodella holodentata Sub-biozone.
Direct association between conodonts and graptolites occurs in the Lévis Formation. The Shumardia Limestone comprises the Isograptus (v.) maximodivergens, Levisograptus austrodentatus (with two subzones; Dw 1), Levisograptus dentatus (with two subzones), and Holmograptus lentus graptolite biozones (Dw 2; Maletz 1997, 2011). The conodont fauna described by Uyeno and Barnes (1970) derived from the part of the Shumardia Limestone, is referred to the Levisograptus dentatus graptolite Biozone (Mitchell and Maletz 1995; Maletz 1997, 2011). The presence of both Periodon macrodentatus and Histiodella holodentata in the lower part of the middle Shumardia Limestone suggests that the Histiodella holodentata Subzone of the Periodon macrodentatus Zone is correlative (pars) with the Levisograptus dentatus graptolite Zone (Dw 2). The top strata with Periodon zgierensis are subsequently younger and may correspond to the upper part of the Levisograptus dentatus Biozone and (or) the Holmograptus lentus Biozone.
The Mystic Formation unconformably overlies Lower Ordovician deposits and is itself overlain by graptolitic shale referred to the comprehensive Paraglossograptus tentaculatus (= previously the P. etheridgei) Zone (Mitchell and Maletz 1995). Barnes and Poplawski (1973) obtained conodonts from limestone boulders of the Mystic Formation, southern Quebec, and identified two distinct conodont faunas: one is early Floian and the other is Darriwilian in age. Many taxa from the Darriwilian blocks are shared with Bed 15 of the Cow Head Group, i.e., Ansella longicuspica, Histiodella holodentata, and Periodon macrodentatus, but also some species that are younger than those recorded from Bed 15 are present. Hence, Periodon cf. P. zgierzensis, Dzikodus hunanensis, possibly Histiodella kristinae, as well Paroistodus horridus have been found in some boulders from the Mystic Formation. These species are the direct successors of, respectively, Periodon macrodentatus, Dzikodus peavyei, Histiodella holodentata, and Paroistodus originalis. This suggests that the fauna from these boulders in the Mystic Formation is younger than the Bed 15 fauna at Lower Head and that the younger Mystic assemblage is coeval with the Table Head fauna.
Anse au Crapaud Formation
The Anse au Crapaus Formation exposed at the Méchins section in Quebec (Bernstein et al. 1992) is composed of mainly shale, siltstone, limestone, and minor conglomerates. The investigation of the graptolite fauna from the Méchin section (Maletz 2009) shows that the succession comprises the Darriwilian Levisograptus austrodentatus and Holmograptus spinosus graptolite biozones.
The graptolites of the Levisograptus spinosus graptolite Biozone occur in direct association with conodonts. The small but characteristic conodont fauna includes the species: Histiodella cf. holodentata (= Histiodella sp. in Maletz 2009), Paroistodus horridus and Periodon macrodentatus (Maletz 2009 and own observation). All the listed species of this small conodont fauna derived only from the Holmograptus spinosus graptolite Biozone. The conodont assemblage is part of the comprehensive Periodon macrodentatus Biozone, but it is younger than the Histiodella holodentata Subbiozone recorded from Bed 15 of the Cow Head Group and from the Springs Inlet Member of the Table Head Group (Stouge 1984). Histiodella cf. holodentata succeeds Histiodella holodentata in the Table Head Group, and it is the characteristic species of the Table Point Formation, western Newfoundland (Stouge 2001; Stouge and Zhao 2006; Stouge et al. 2011).
New York State
The type section of the Deep Kill Shale investigated by Landing (1976) is composed of graptolitic shale with limestone interbeds; the upper Deep Kill Shale yields Zone 9 graptolites or the comprehensive Paraglossograptus tentaculatus Zone. The conodont fauna from this zone is similar in composition to the Bed 15 conodont fauna and their mutual correlation is proposed. Higher in the section Histiodella cf. holodentata and Dzikodus cf. D. hunanensis are recorded from limestone blocks in the shale, and this fauna is younger than that investigated here. In addition, Paroistodus horridus has been found in the Stuyvesant Falls Formation (Landing 1976), and this level is also younger than that dealt with here from Bed 15 at the Lower Head locality.
The conodont fauna from the Oil Creek Formation of the Simpson Group, Arbuckle Mountains, south-central Oklahoma is of Midcontinent Province affinity (Bauer 2010). In general, it is not similar to the fauna recorded from the Cow Head Group, although a few species are shared. These are Ansella longicuspica (= Ansella jemtlandica sensu Bauer), Dischidognathus primus, Fahraeusodus marathonensis, Pteracontiodus cryptodens, Tripodus combsi, and Histiodella holodentata.
Pteracontiodus cryptodens is present in the lower Bed 13, where it occurs together with Periodon aff. flabellum in the Tripodus laevis conodont Biozone corresponding to the Isograptus (v.) victoriae and I. (v.) maximodivergens graptolite biozones. All the other species, aside from Ansella and Histodella, in common, are rarely represented in the Cow Head Group; however, confidant correlation with Bed 15 is based on the presence of Histiodella holodentata, which appears in the upper part of the Oil Creek Formation (Bauer 2010). The Oil Creek Formation also includes Histiodella labiosa (= Histiodella sp. A of Sweet et al. 1971), which is characteristic of Midcontinent Fauna 4 (Sweet et al. 1971).
Marathon basin, Texas
Graves and Ellison (1941) and Bradshaw (1969) described the fauna elements from the Fort Peña Formation in Texas, USA, and the similarity with the Cow Head fauna is obvious. Several species are indeed identical with those of the Cow Head fauna, especially those from Bed 15. The Fort Peña Formation shares Drepanodus spp., Protopanderodus spp., and Periodon macrodentatus (Graves and Ellison, 1941), but the current available information from the Fort Peña Formation (Graves and Ellison 1941; Bradshaw 1969) does not permit any more detailed correlation.
However, some older species and especially Histiodella sinuosa representing the Histiodella sinuosa Biozone (Sweet 1984) of the Midcontinent Province is present in the Fort Peña Formation (Bradshaw 1969), and it occurs together with Periodon macrodentatus. Histiodella sinuosa is absent from the Cow Head Group, and so far it is not known from western Newfoundland. Presumably, the Histiodella sinuosa Biozone (of Sweet 1984) is coeval to the lowest interval of the Periodon macrodentatus Zone, i.e., corresponding to the lower nearly barren strata of the upper Bed 13 in the Cow Head Group (Table 1).
A second taxon, i.e., Paroistodus horridus — as the Table Head Group, Mystic and Anse au Crapaud formations, Quebec, and in the strata in New York — is also present in the Fort Peña Formation (Bradshaw 1969), which suggests that the Fort Peña Formation is extending into younger levels than Bed 15 at Lower Head and, so far, have not been observed from the Cow Head Group.
Of “local” palaeobiographical interest is the presence of Oistodella pulchra in the Fort Peña Formation. This taxon is constrained to the Fort Peña Formation, and the record from Bed 15 of Cow Head Group is the second locality in North America where this species has been recorded (Johnston and Barnes 2000 and this paper).
Global biostratigraphical significance
Some of the described conodont species offer great potential for global correlation as they are recorded from elsewhere in North America, North Europe (Scandinavia) and China (Chen et al. 2006; Stouge et al. 2011). The stratigraphical first appearance of, respectively, Periodon macrodentatus and Histiodella holodentata in the Cow Head Group (and Table Head Group) is largely similar to their distribution in the Darriwilian (Middle Ordovician) of China (Zhang 1998; Du et al. 2005; Chen et al. 2006; Stouge et al. 2011) and in Scandinavia (Rasmussen 2001; Stouge and Nielsen 2003; Mellgren and Eriksson 2010).
In China, at the global stratotype section of the Darriwilian stage at Huangnitang, Chengshan, Zhejiang, the Yangtzeplacognathus crassus, “Histiodella holodentata”, and the Histiodella kristinae conodont biozones are established (Chen et al. 2006). The record of the conodonts in the lower Middle Ordovician interval is poor in the section and a closer correlation for this level is not possible.
Periodon macrodentatus appears together with Yangtzeplacognathus crassus and Paroistodus horridus in the section, and it ranges to the Histiodella kristinae conodont Biozone in the Huangnitang section. Thus, the Periodon macrodentatus Zone as defined here in this paper also comprises the Y. crassus and the following “Histiodella holodentata” conodont biozones. This upper range of Periodon macrodentatus matches the one recorded from the Table Head Group, where P. zgierensis succeeds Periodon macrodentatus in or at the base of the H. kristinae conodont Biozone. The Y. crassus conodont Biozone, however, is younger than the Histiodella holodentata Subbiozone established here from Bed 15 in the Cow Head Group; hence, the interval tentatively referred to as “Histiodella holodentata” conodont Biozone following above the Yangtzeplacognathus crassus Biozone and before the Histiodella kristinae Biozone (Chen et al. 2006) probably represents Histiodella cf. holodentata of this paper, and hence, it correlates with the main part of the Table Point Formation at Table Point, western Newfoundland (Stouge 1984, 2001).
Chen et al. (2006) referred the interval with Histiodella cf. holodentata to the Nicholsonograptus fasciculatus graptolite Biozone, a match, however, that is younger than promoted in this paper (i.e., Homograptus spinosus; Fig. 8) and needs to be confirmed (see also Maletz 2009, p. 744).
Periodon macrodentatus and Histiodella holodentata are recorded from the Guniatan Formation of central and south China (Zhang 1998); the same faunal succession is also characteristic in the Dawangou Formation, Tarim Region, Xinjiang, western China where also Histiodella sinuosa and the younger Histiodella species, i.e., H. kristinae and H. bellburnensis, are present (Du et al. 2005; Stouge and Zhao 2006; Stouge et al. 2011).
In northeastern Europe (i.e., Scandinavia), the two taxa are less frequently represented, but the recognized faunal succession is identical to that of the Cow Head Group (i.e., Rasmussen 2001; Stein formation, Norway); Stouge and Bagnoli (1999, S. Öland, Sweden); Stouge and Nielsen (2003, Fågelsång, Sweden), and Mellgren and Eriksson (2010, Hällekis, Sweden), allowing for a precise trans-Iapetus correlation (Rasmussen and Stouge 1995). The Periodon macrodentatus Zone is recognized and the Histiodella holodentata Subzone is recorded below the Y. crassus Biozone.
Other areas may be included when the two species are becoming better recognized.
The Periodon hankensis Zone has (yet) not been recognized, but the species has been positively identified from Scandinavia, where it occurs in the Baltoniodus norrlandicus conodont Zone (Dapingian Stage; stage slice Dp 2; Bagnoli and Stouge 1996).
Ansella brevicauda, Paroistodus originalis, and the taxa described here in open nomenclature (Erraticodon sp. nov. A, Drepanodus spp., and Protopanderodus spp.) may prove to be additional aids in correlation when more and (or) better preserved material becomes available. The conodont species Dzikodus peavyi and Yangtzeplacognathus sp. A revised herein are not at a stage or do not have much potential for wider biostratigraphical correlation, as they are only known from the Cow Head Group.
The Cow Head Group conodont fauna is largely of North Atlantic Provincial affinity but shows some generic and species-level similarity to the Midcontinent Province (palaeocontinent Laurentia). The association of Periodon and Histiodella is of low to temperate latitudinal distribution. The lower Bed 13 is referred to the Tripodus laevis conodont Biozone (Johnston and Barnes 1999), but the new species: Periodon hankensis may be a taxon with potential for global correlation as its distribution largely coincides with (pars) the Isograptus (v.) maximodivergens graptolite Biozone (Castlemanian (Ca 4) – Dapingian global Stage (Dp 2); Fig. 8).
Upper Bed 13 and Bed 15, the two stratigraphic youngest shale–limestone units of the Cow Head Group, or the lowest units of Lower Head Formation, western Newfoundland produce an exceptional conodont fauna that include species that are not well known elsewhere. However, the Periodon-dominated conodont fauna can be linked into associated graptolite ranges in the Darriwilian, and the Periodon macrodentatus Zone and Histiodella holodentata Subzone offer potential for both local and wider biostratigraphical correlation (see Stouge et al. 2011).
Within the Cow Head Group, Bed 14 includes species that are only known from the lower member of the Table Head Group. The striking faunal similarity between the fauna from Bed 15 at the Lower Head section and the transported fauna from Martin Point South and western Brook Pond South also demonstrates that the source for the Martin Point South conodont fauna (i.e., Johnston and Barnes 2000), St. Pauls Inlet South, and Western Brook Pond South specimens was probably “local” and from the same origin (Table 1), i.e., derived from the marginal to uppermost slope deposits that shortly after deposition were transported down slope and re-deposited into a deeper to distal slope setting in the greywacke of the Lower Head Formation.
In beds 13 and 15 of the Cow Head Group, the Middle Ordovician Periodon lineage that evolved from the Lower Ordovician Periodon primus Stouge and Bagnoli, 1988 – Periodon flabellum Lindström, 1955 lineage has reached the evolutionary level, where the number of free denticles on the anterior process of the Pa element is first two and later three. These evolutionary stages are referred, respectively, to Periodon hankensis n. sp. and Periodon macrodentatus (Graves and Ellison, 1941) the latter first by Rasmussen (2001) and followed in this paper with minor revisions; the two taxa are the nominate species of the newly established Periodon hankensis Phylozone and the international Periodon macrodentatus Phylozone. The two conodont phylozones and the Histiodella holodentata Sub-biozone are established in the Cow Head Group and have correlative potential for all the North American (Laurentia) continental marginal deposits, as well as on the global scale (Stouge et al. 2011).
Figured specimens are housed in the Provincial Museum of Newfoundland and Labrador, Canada (NFM) at the Rooms, St. John’s, NL. Additional specimens are housed in the Micropalaeontological collections of the Geological Museum, University of Copenhagen, Denmark.
Conodont species are listed alphabetically in Table 1. The present systematic descriptions are not intended to be the “complete” description with full synonymy, but the synonymy given here indicates the concept of the species as it is interpreted herein. Also, it is only selected groups of species and far from all recorded species (Table 1) that are included in the descriptions. Many species recorded here are considered fully described by previous authors and (or) the material at hand is sparse and, thus, does not add substantial news to the current understanding of the species.
Genus Ansella Fåhræus and Hunter, 1985
Belodella jemtlandica Löfgren, 1978.
Ansella longicuspica Zhang, 1998
1973 Belodella erecta (Rhodes & Dineley) s.f. Barnes and Poplawski, 1973, p. 759, pl. 4, figs. 19–20.
1973 Belodella n. sp. s.f. Barnes and Poplawski, pp. 769–770, pl. 4, figs. 5, 9–10, 18, 18a; text-fig. 2F.
1978 Belodella sp. A Fåhræus, 1970 s.f.; Fåhræus and Nowlan, p. 461, pl. 3, fig. 21.
1998 Ansella longicuspica n. sp. Zhang, pp. 48–50, pl. 1, figs. 1–4.
2010 Ansella jemtlandica Bauer, p. 6, pl. 1, figs. 1–2, 4–5.
The species has been fully described by Zhang (1998).
Ansella longicuspica is common and a characteristic element of the early Darriwilian conodont assemblages preserved in Bed 14 (Fåhræus and Nowlan 1978) and Bed 15 of the Cow Head Group, in Quebec, Canada and in South China (see Zhang 1998).
Upper Bed 13, Bed 15, and limestone blocks in the Lower Head Formation at Martin Point South and Western Brook Pond South. Specimens belonging to the species have also been recorded from Bed 14 (Fåhræus and Nowlan 1978).
Genus Drepanodus Pander, 1856
Drepanodus arcuatus Pander, 1856.
Dzik (1994), Stouge and Bagnoli (1988), Rasmussen (2001), and Löfgren and Tolmacheva (2003) reconstructed the apparatus of Drepanodus and at least six morphological elements can be recognized. Löfgren and Tolmacheva (2003) assigned the elements of Drepanodus to P, M, and S positions, but this approach is here considered “speculative” because the natural apparatus of Drepanodus is unknown — thus, a “conservative” nomenclature for the elements is maintained here.
Drepanodus cf. D. giganteus (Sweet and Bergström, 1962)
1941 Acontiodus sp. Graves and Ellison, p. 4, pl. 2, fig. 24.
1941 Acontiodus reclinatus Lindström; Bradshaw, p. 1148, pl. 131, figs. 6, 9.
1969 Acontiodus robustus (Hadding); Bradshaw, p. 1148, pl. 131, fig. 13 only.
1969 Distacodus sp. Bradshaw, 1969, pl. 131, figs. 3–4.
1969 Scolopodus giganteus Sweet and Bergström; Bradshaw, pp. 1162–1163, pl. 132, fig. 7.
1970 Acontiodus sp. 1 Uyeno and Barnes, p. 104, pl. 21, figs. 1–2, 7H.
1970 Acontiodus sp. 2 Uyeno and Barnes, p. 104, pl. 21, figs. 4–5, 7I.
1970 Scolopodus n. sp. 1 Uyeno and Barnes, p. 116, pl. 22, figs. 1–2, 7B.
1970 Scolopodus n. sp. 2 Uyeno and Barnes, pp. 116–117, pl. 22, figs. 3–5, 7A.
1973 Protopanderodus cooperi (Sweet and Bergström); Barnes and Poplawski, p. 782 (pars), pl. 3, figs. 4–5 (only).
1973 Protopanderodus reclinatus (Lindström); Barnes and Poplawski, p. 782, figs. 2, 3?.
1973 Protopanderodus cf. P. giganteus (Sweet and Bergström); Barnes and Poplawski, p. 782, pl. 1, fig. 4.
1976 Scolopodus giganteus Sweet and Bergström; Landing, pp. 639–640, pl. 4, fig. 13.
1994 Drepanodus? planus (Pander); Pohler, pl. 2, figs. 3, 7.
Most of the individual elements have been described by previous workers and need no further comment. The assemblage represents an early variety of Drepanodus giganteus (Sweet and Bergström, 1962) from the Upper Ordovician.
Bed 13, Bed 15, and limestone blocks in the Lower Head Formation at Martin Point South and Western Brook Pond South.
Drepanodus cf. D. robustus Hadding, 1913
1941 Oistodus pandus Branson and Mehl; Graves and Ellison, p. 5, pl. 2, fig. 34.
1969 Acontiodus robustus (Hadding); Bradshaw, p. 1148 (pars), pl. 131, figs. 8, 10, 14.
1969 Drepanodus homocurvatus Lindström, Bradshaw, p. 1150, pl. 135, fig. 8.
1969 Scandodus cf. S. pipa Lindström; Bradshaw, p. 1161, pl. 135, figs. 3, 4.
1970 Acontiodus sp. 3 Uyeno and Barnes, p. 105, pl. 21, figs. 10, 11, 7D.
1970 Acontiodus robustus (Hadding); Uyeno and Barnes, p. 104, pl. 21, figs. 18, 19, 7G.
1970 Drepanodus homocurvatus Lindström; Uyeno and Barnes, p. 107, pl. 21, fig. 9.
1970 Oistodus? sp. Uyeno and Barnes, p. 110, pl. 22, figs. 19, 20.
1970 Scandodus pipa Lindström; Uyeno and Barnes, pp. 115–116, pl. 22, figs. 6, 7, 7C.
1973 Acontiodus robustus (Hadding) s.f. ; Barnes and Poplawski, pp. 768–769, pl. 2, fig. 15.
1973 Protopanderodus cooperi (Sweet and Bergström); Barnes and Poplawski, p. 782 (pars), pl. 3, fig. 1 only.
1976 Acontiodus robustus (Hadding); Landing, pp. 629–630, pl. 1, fig. 8.
1976 Protopanderodus cooperi (Sweet and Bergstrom); Landing, pp. 638–639 (pars), pl. 4, fig. 7.
1994 Drepanodus arcuatus (Pander); Pohler, pl. 2, figs. 1, 2, 4–6.
All the forms of the genus (arcuatiform, sculponeaform, graciliform, notched arcuatiform, and pipaform) are present. The arcuatiform is present as long-based type with a curved and keeled cusp with two posterior located costae (Fig. 7J), the sculponeaform (Fig. 6K) is usually smooth, the graciliform is strongly reclined and keeled, and the pipaform is recurved with a short base.
Bed 13, Bed 15 and limestone blocks in the Lower Head Formation at Martin Point South and Western Brook Pond South.
Genus Dzikodus Zhang, 1998
Polonodus tablepointensis Stouge, 1984.
The genus is characterized by species having paired, similar, but not identical, pastiniscaphate Pa elements and dissimilar stelliplanate Pb elements; a geniculate M element; and a series of S elements are also included in the apparatus.
Dzikodus peavyi (Johnston and Barnes, 2000)
2000 Polonodus? peavyi n. sp. Johnston and Barnes, pp. 35–36 (pars), pl. 14, figs. 9, 15 only.
Johnston and Barnes (2000, pl. 14, fig. 15) described the dextral Pa element of this species, and it was chosen as holotype for the species. The sinistral Pa element was not described by Johnston and Barnes and has only been recorded here as fragments. Based on the fragments, the dextral Pb element is 4-lobed, forming an X. The sinistral Pb element is elongated with a posterior extended process. The anterior process is bent to the left, and the anterior lateral process is in a straight line with the main denticle row of the posterior process.
The elements have ornamented surfaces; they are here allocated to the genus Dzikodus because M and S elements also belong to the apparatus (see also Johnston and Barnes 2000, p. 36). Here the species is only recorded from Bed 15 and, hence, considered typical for Bed 15, but it is not very abundantly represented, and the elements are often incomplete.
Some elements that Johnston and Barnes (2000) placed in the same apparatus have been allocated herein to Yangtzeplacognathus n. sp. A.
So far, this species is the oldest recorded representative of Dzikodus.
Bed 15 of the Cow Head Group at Lower Head and in limestone blocks in Lower Head Formation at Martin Point South.
Genus Erraticodon Dzik, 1976
Erraticodon n. sp. A
1985 Erraticodon sp. Löfgren, p. 124, figs. 4AT–4AY.
2000 Erraticodon cf. E. balticus Dzik, 1978; Johnston and Barnes, p. 19, pl. 4, figs. 18, 20, 23, 24, 29.
The apparatus is here interpreted to be septimembrate. One P element is extensiform digyrate with denculate processes. The second P element has not been recorded here. The M element is dolabrate with a recurved cusp; the anterior edge of the base meets the aboral margin at an angle of about 90°, but curves upward towards the posterior; the upper margin of the base and the posterior process are denticulate. The Sa element is alate with one, tall denticle on each side of the cusp. The posterior process is denticulate, and the unit is arched when seen in lateral view. The denticles are free and become increasingly larger towards the middle of the posterior process. The Sb element is bipennate, and the lateral process is strongly curved and points towards the posterior; the posterior process has one denticle that is much taller than the others. The Sc element is denticulate bipennate. The Sd element is tertiopedate with posterior, outer lateral and anterior processes; the outer lateral and the posterior process are nearly of equal length, whereas the anterior process is shortest. All processes are denticulate.
Erraticodon n. sp. A differs from E. alternans (Hadding, 1913) in that the Sa and Sc elements do not possess a very large, tall denticle on the posterior process. In Erraticodon alternans (Hadding, 1913), the development towards more denticles is obvious; a very large denticle on the posterior process of S element is prominent on the Sa, Sb, and Sc elements.
In Newfoundland, E. alternans is present in the Table Cove Formation of the Table Head Group (= E. balticus in Stouge 1984).
Bed 13 (rare) and Bed 15 (present).
Genus Histiodella Harris, 1962
Bryantodina sinuosa Graves and Ellison, 1941.
The multi-elemental apparatus of Histiodella Harris, 1962 consists of a carminate P element, geniculate M element and a series of S elements, which include alate (Sa), digyrate (Sb), bipennate (Sc), and Sd element.
McHargue (1982) presented the first interpretation of the multielemental apparatus of the multielement genus Histiodella. The P element evolved from simple and non-denticulated elements to types with serrated edges, followed by P elements with denticles. Along with this development the P element increased in length relative to the height of the element. The evolutionary trend of the S elements is that the number of denticles increased and the elements became relatively more frequent. The small geniculate M element remains conservative and so far is not known to change morphologic from one species to another.
Histiodella altifrons is the first true representative of the genus and elements are adenticulated. This species is succeeded by Histiodella minutiserrata, in which the P elements become serrated. The stratigraphically younger Histiodella sinuosa is with fully serrated P elements, and in Histiodella serrata, it is denticulated. The P element of Histiodella holodenta is fully denticulated, and the cusp is the highest of these. Stouge (1984) described the younger or middle Darriwilian species Histiodella kristinae and Histiodella bellburnensis, where the length/height ratio of the P element is increased, the anterior denticles become increasingly higher, the posterior part of the element becomes gradually longer, and the cusp reaches a nearly median position.
McHargue (1982), Ethington and Clark (1982), and Stouge (1984) demonstrated that denticulated S and a geniculate M element are indeed present in the apparatus of Histiodella. The same authors also noted that these additional elements both were small and not frequently found.
In the Cow Head collection, the carminate P elements are associated with small elements similar to those illustrated by Ethington and Clark (1982) and Stouge (1984), and are herein referred to S and M elements.
Histiodella holodentata Ethington and Clark, 1982
1982 Histiodella holodentata n. sp. Ethington and Clark, pp. 47–48, pl. 4, figs. 1, 3, 4, 16.
1984 Histiodella tableheadensis n. sp. Stouge, pp. 87–88 (pars), pl. 18, figs. 8, 13, 14, not fig. 12 (= Histiodella cf. holodentata).
1998 Histiodella tableheadensis Stouge; Zhylkaidarov, p. 60, fig. 2.
2005 Histiodella holodentata Ethington and Clark, 1981; Du et al. p. 365, pl. 1, figs. 22–26, 28.
2005 Histiodella holodentata Ethington et Clark, 1981; Du et al. p. 365 (pars), pl. 1, figs. ?22 (= broken element), 24, 25, not figs. 22, 28 (= Histiodella cf. holodentata).
2010 Histiodella holodentata; Bauer, pp. 8–9, pl. 2, fig. 9.
The Pa element is carminate and fully denticulate. The cusp is prominent and the tallest point on the element; it occupies a posterior but not posteriormost position. M element is a small and geniticulate with a narrow base. The Sa element has four edges, where the anterior and the two lateral ones are denticulated. The posterior edge is a prominent keel that runs from the tip of the cusp to the base. The base is small without a posterior extension. The Sc element is bipennate and with denticulated processes.
The carminate P element of Histiodella holodentata Ethington and Clark, 1982 is identical to the specimens from the Table Head Group and named Histiodella tableheadensis by Stouge in 1984 (the Table Head manuscript was submitted before the appearance of Ethington and Clark (1982) in 1982) and H. tableheadensis is the junior synonymy of H. holodentata (see also Du et al. 2005; Bauer 2010, p. 8; Mellgren and Eriksson 2010, p. 361).
A potential Sd element has not been recorded.
All the elements are striated on the cusp, and the edges along the basal region are crimped and with swollen ledge above the crimped region.
The Sc element resembles the Sc element of H. sinuosa. It differs by being denticulated on the posterior extension, whereas in the same element of H. sinuosa, the posterior edge is a sharp keel (see Bauer 2010, pl. 2, fig. 21). Perhaps this is an additional distinctive character on the species level.
All elements of Histiodella holodentata recorded here have characteristic microstriae on the cusp and an edge along the aboral margin, which demonstrate that the elements derived from the same organism.
Genus Nealeodus n. gen.
Lenodus? martinpointensis Johnston and Barnes, 2000.
Johnston and Barnes (2000) tentatively referred elements of this new genus to Lenodus Sergeeva, 1963. However, the Nealeodus apparatus is composed of hyaline elements, which are large, nongeniculate, but denticulate simple cones (Pa, Pb), a complete series of S elements and a geniculate M element. Platform and ramiform elements typical of Lenodus are not hyaline and present in this genus.
Pteracontiodus Ethington and Clark, 1982 resembles the present genus, but the hyaline elements of the former are not denticulate.
N. martinpointensis is the only known species of the genus.
Derivation of name
Ward Neale, former Head of Geology Department, Memorial University of Newfoundland, St. John’s, NL, Canada.
A septimembrate apparatus composed of fairly large hyaline conodont elements. The base is high and triangular in profile and elements have fused but distally free denticles on one or both edges of the base and cusp; the elements have a serrate to minutely denticulate appearance.
Nealeodus martinpointensis (Johnston and Barnes, 2000)
2000 Lenodus? martinpointensis n. sp. Johnston and Barnes, pp. 22–23, pl. 3, figs. 16–31, text-fig. 1.
Each individual element of the species has been fully described by Johnston and Barnes (2000).
Top of the upper Bed 13 and Bed 15 of the Cow Head Group and limestone clast in Lower Head Formation at Martin Point S.
Genus Oistodella Bradshaw, 1969
Oistodella pulchra Bradshaw, 1969.
Multielement apparatus of composed of denticulated and keeled dolobrate element (P) and geniticulate (M), alate (Sa), tertiopedate (Sb), dolabrate (Sc), and quadriramate (Sd) elements. The elements are keeled on the cusp, except for the Sa element, which has two lateral costa. The upper arched margin of the base of the P and S elements is denticulated. The M element is denticulated on the posterior margin of the cusp. All elements are hyaline.
The Oistodella apparatus is similar to, if not identical with, that of Triangulodus van Wamel, 1974 and emended by Bagnoli and Stouge (1996); it is composed of keeled, hyaline simple cone elements. The genus Triangulodus comprises only undenticulate or simple cone elements, but the obvious morphological similarity, the hyaline aspect and apparatus configuration, demonstrates that Oistodella was derived from Triangulodus.
Oistodella pulchra Bradshaw, 1969
1969 Oistodella pulchra n. sp. Bradshaw, pp. 1155–1156, pl. 136, figs. 10–11.
? 1994 Paraprioniodus costatus (Mound); Pohler, pl. 4, fig. 13 (only).
2000 Oistodella cf. O. pulchra Bradshaw, 1969; Johnston and Barnes, pp. 25–26, text-fig. 3.
The P elements are dolabrate with a curved but sub-erect cusp (Pa) and recurved to reclined cusp (Pb), strongly developed anterior keels and denticles on the upper edge of the base. The P elements have open base and a bulge on the base and just beneath the cusp. The Pa element has a large keel on the anterior edge of the cusp and base and is extended to the anterior at the basal corner. The Pb element has a triangular base and reclined cusp without antero-basal extension.
The dolabrate M element is characterized by having inclined denticles on the posterior edge of the recurved to reclined cusp. The number of denticles varies from three to six.
The Sa element is alate, with short lateral processes that continue on the cusp as narrow costae. The upper edge of the base and the short posterior process are denticulate.
The Sb element is tertiopedate. The anterior and lateral edges are adenticulate, whereas the upper edge of the base and the posterior process carry denticles.
The Sc element is dolabrate, nearly flat on the inner side, and with convex outer side; the anterior edge of the base is irregular, indicating development of incipient denticles. The upper edge of the base and the posterior process are denticulate.
Sd element is dolabrate and with denticles on the upper edge of the base and the posterior process.
Pohler (1994) illustrated a “cordylodiform” referred to Paraprioniodus costatus (Mound). The illustrated specimen, however, may well be the Pa element of Oistodella seen from the outer side, but the specimen is not easy to identify.
Johnston and Barnes (2000) indicated that the Cow Head specimens could possibly be different from the Fort Peña species; however, the present (and larger) material shows that the specimens display great variability in the number of denticles. The variability in the present material covers the elements from both the Fort Peña Formation and the Cow Head Group; hence, the genus is — so far — represented by one species only.
Bed 15 and limestone blocks in Lower Head Formation at Martin Point South.
Genus Periodon Hadding, 1913
Periodon aculeatus Hadding, 1913.
Periodon hankensis n. sp.
1978 Periodon aculeatus Hadding; Fåhræus and Nowlan, p. 462, pl. 3, figs. 1, 7-1, 13, (not 12 = ? Periodon macrodentatus); text-fig. 5, figs G–L.
1994 Periodon aculeatus Hadding; Pohler, p. 33 (pars), pl. 4, figs. 25–27 only.
1997 Periodon sp. C Bagnoli and Stouge, pp. 152–153, pl. 6, figs. 19–20.
2000 Periodon aculeatus Hadding, 1913; Johnston and Barnes, pp. 32–35 (pars), pl. 13, figs. 12, 17, 20, 23, 24, 28, 31; (?)text-fig. 4, figs. 22–28.
2001 Periodon zgierzensis Dzik; Rasmussen, pp. 116–118, pl. 14, figs. 6–18.
Pa element, NFM F-870 (Fig. 11M).
Type locality and stratum
St. Pauls Inlet North, western Newfoundland, Canada; sample SPIN 20, xxx Formation, Dapingian Stage, Middle Ordovician.
Derivation of name
After Hank Williams, the former Professor of geology at Memorial University, St. John’s, NL, Canada.
The bipennate Pa element of this species has two free denticles on the anterior process; the S elements are fully denticulate and have four denticles between the cusp and the largest denticle on the posterior process, and a fairly well-developed zone of recessive basal margin; the M element is bipennate geniculate with one to three denticles on the anterior edge of the base.
The Pa element is bipennate. The anterior process carries normally two anterior and free denticles and four to five posterior denticles; advanced Pa elements may carry one additional distal and small “satelite” denticle. The cusp is tall, keeled, and reclined, and the element is gently convex to the outer side. The base is excavated below the cusp and has well-developed smooth bulge on the inner side.
The Pb element is digyrate with a strongly twisted anterior process. The anterior process is slightly thickened at the lateral surfaces.
The geniculate M element has up to two anterior denticles. The element is reclined and cusp is inwardly bent.
The Sa element is alate with three denticulated processes. The lateral processes are posteriorly directed.
Sb element is tertiopedate — or nearly so — with one short lateral process without denticles. The posterior denticulated process is twisted.
The Sc element is dolobrate with denticles on the base and the posterior process, with normally four denticles between the cusp and the larger denticle on the posterior process. The anterior margin of the base or short anterior process bears two denticles.
The Sd element is tertiopedate. All processes are denticulated. The posterior process is twisted, the outer lateral process bent downwards and slightly backward.
Periodon hankensis n. sp. differs from Periodon macrodentatus in that the number of denticles on the anterior process of Pa element is two to two and a half, whereas at Periodon macrodentatus, it is three to three and a half. The prominent edge on the process and below the denticles typical of Pa elements of Periodon macrodentatus is not developed on P elements of Periodon hankensis n. sp.
Fåhræus and Nowlan (1978) illustrated a Pa element similar to those recorded from St. Pauls Inlet. The Pa element is advanced and apparently has two large and one small anterior process.
Pohler (1994) distinguished Periodon elements in Bed 14 and named one group Periodon aculeatus “intermediate forms.” These specimens are identical to Periodon hankensis n. sp. and undoubtly were derived from Bed 13 strata.
The specimens of this species represent the “late forms” that Johnston and Barnes (2000) referred to Periodon aculeatus Hadding, 1913. The photographed specimens (Johnston and Barnes 2000, pl. 13) and given in the synonymy earlier in the text, most likely belong to this species; however, the line drawings (text-fig. 4, pp. 22–28) are not easy to identify to species level. Apparently the diagnostic anterior process on the Pa element is broken, so these elements are only tentatively placed in synonymy of Periodon hankensis n. sp.
Periodon macrodentatus (Graves and Ellison, 1941)
1941 Loxodus flabellata n. sp. Graves and Ellison, p. 12, pl. 2, figs. 29, 32.
1941 Oistodus prodentatus n. sp. Graves and Ellison, pp. 13–14 (pars), pl. 2, figs. 6, 22–23, 28.
1969 Prioniodina macrodentata (Graves and Ellison); Bradshaw, p. 1160, pl. 137, fig. 19.
1969 Falodus prodentatus (Graves and Ellison); Bradshaw, p. 1151, pl. 135, figs. 16–17.
1970 Periodon aculeatus Hadding; Uyeno and Barnes, p. 112 (pars), pl. 23, fig. 7 (only).
1970 Prioniodina macrodentata (Graves and Ellison); Uyeno and Barnes, p. 113, pl. 23, figs. 12, 16.
1994 Periodon aculeatus Hadding, 1913; Pohler, p. 33 (pars), pl. 4, figs. 30–32.
2000 Periodon aculeatus Hadding, 1913; Johnston and Barnes, pp. 32–35 (pars), (?)pl. 13, fig. 30, pl. 14, figs. 1–7.
2001 Periodon macrodentata (Graves and Ellison 1941); Rasmussen, pp. 114–116 (pars), pl. 14, figs. 1, 2, 4–8, 3?.
2010 Periodon macrodentata (Graves and Ellison, 1949); Mellgren and Eriksson, p. 359, fig. 6A, 6B.
The bipennate Pa element of this species has three (rarely four) free denticles on the anterior process; the S elements are fully denticulate, and normally they have five to six denticles between the cusp and the largest denticle on the posterior process and a well-developed zone of recessive basal margin; the M element is bipennate geniculate with a short anterior denticulate process.
The Pa element is bipennate. The anterior process carries three anterior denticles, which are free, and normally five posterior denticles. The cusp is tall, keeled, and reclined. On the inner side the element is slightly swollen near the base of the denticles (Fig. 8M), and the surface striation on the cusp does not reach the aboral margin.
The Pb element is bipennate; the anterior process is strongly outwardly bent. The anterior process carries normally three to four denticles and up to six on the posterior process.
The M element is bipennate, geniculate, i.e., with a short anteriorly extended and denticulate process. This anterior process carries up to three small denticles. The reclined cusp forms an angle with the upper edge of the base of about 50°.
The S elements are referred to as Sa, Sb, Sc, and Sd; all the S elements have a well-developed zone of recessive basal margin (or “inverted basal cavity”).
The alate Sa element has two well-developed lateral and denticulate processes.
The Sb element is nearly tertiopedate with a (very) short adenticulate pointed anterolateral keel or process and an outer anterior denticulate process. The aboral margin and the lower edge of the process meet at an angle of ca. 90° when observed in lateral view.
The Sc element is bipennate with denticulate processes. The aboral margin and the lower margin of the posterior process form an angle of ca. 90°. The anterior process is much shorter than the posterior one and is slightly deflected laterally. In this element, the largest denticle is not clearly defined as the denticles increase gradually in size towards the posterior.
The Sd element is tertiopedate with one posterior, one anterior and out outer lateral process. The long anterolateral process carries at least five denticles. The number of denticles between the cusp and the largest posterior denticle is six.
The Pa element of this species differs from the stratigraphically younger Periodon zgierzensis by having three free denticles on the anterior process in contrast to four to five denticles on the latter. It differs from the immediately older Periodon hankensis n. sp., which carries up to two free denticles on the anterior process of the Pa element, and the zone of recessive basal margin on the S elements is little developed on the latter species.
The elements of P. macrodentatus are similar to the elements obtained from the limestone blocks in the Lower Head Formation at the Martin Point South section. Johnston and Barnes (2000) referred the elements of this species to Periodon aculeatus Hadding; however, Periodon aculeatus s.s. is a late Darriwilian species (Dw 3), and it is not present in the Cow Head Group.
Bed 13 at St. Paul’s Inlet North and Bed 15 at Lower Head; also recorded from limestone blocks in Bed 14 and in Lower Head Formation at Martin Point South (Johnston and Barnes 2000) and at Western Brook Pond South.
Genus Spinodus Dzik, 1976
Polygnathus spinatus Hadding, 1913.
Spinodus wardi sp. nov.
1969 Ambalodus? sp. Bradshaw, p. 1148, pl. 137, figs. 10, 11.
1969 Cordylodus sp. Bradshaw, pp. 1148–1149, pl. 135, fig. 14.
1969 Cordylodus? sp. Bradshaw, p. 1149, pl. 135, fig. 13.
1969 Falodus cf. F. extensus (Graves & Ellison); Bradshaw, p. 1151, pl. 135, fig. 15.
1969 Oulodus sp. Bradshaw, pp. 1158–1159, pl. 137, figs. 7–9.
1970 Cordylodus spinatus (Hadding); Uyeno and Barnes, pp. 106–107, figs. 7–11.
1973 Cordylodus ramosus Hadding; Barnes and Poplawski, p. 772, pl. 4, fig. 6.
1976 Cordylodus sp. aff. C. spinatus (Hadding); Landing, p. 631, pl. 1, fig. 14.
1994 Spinodus ramosus Hadding; Pohler, pl. 8, fig. 2.
1998 Spinodus spinatus (Hadding); Zhang, pp. 91–93, pl. 17, figs. 11–13, ?14.
2000 Spinodus cf. S. spinatus (Hadding); Johnston and Barnes, pp. 44–45, pl. 4, figs. 1, 2, 5–7, 11, 13, 14.
NFM F-858 (Fig. 11A); Pa element.
Derivation of name
After Ward Neale, former head of Department of Geology at Memorial University of Newfoundland, St. John’s, NL, Canada.
Type locality and STRATUM
Lower Head section, Shallow Bay, western Newfoundland, Canada, sample LH 2.
All elements robust and denticulate; denticles are free and curved inwardly. Pa element gently arched with few, stout, broad denticles. M element with distinct cusp and large base with denticles on the anterior edge.
Several of the single elements of the species have been described by Bradshaw (1969); Falodus cf. F. extensus (Graves and Ellison) of Bradshaw (1969) is the M element and Ambalodus? sp. is the Sb element.
All the other elements of the species were fully described by Johnston and Barnes (2000).
The specimens have not developed a zone of recessive basal margin (“inverted basal cavity” of Lindström 1964), which is characteristic of Spinodus spinatus (Hadding). The denticles of Spinodus spinatus are widely separated in contrast with the denticles of Spinodus wardi, in which the denticles are proximally close but distally free.
Zhang (1998) showed that the genus is characteristic of deep water deposits.
Genus Yangtzeplacognathus Zhang, 1998
Polyplacognathus juanyeensis An and Ding, 1982.
This multielement genus was established by Zhang (1997), who defined the genus with an apparatus composed of two pairs of pastinate P elements, which are not mirror images of each other. Löfgren and Zhang (2003) changed the apparatus reconstruction of Yangtzeplacognathus to a septimembrate apparatus, i.e., including both M and S elements, which however would suggest reference to the genus Lenodus Sergeeva, 1963 (see Stouge and Bagnoli 1999).
Yangtzeplacognathus elements, however, are unique; they have widely open basal cavities and the pastinate Pa elements may have very strong L- or S-shaped outline, when observed from above. The pastinate Pb elements are more or less Y shaped. The elements are well ornamented with a polygonal micropattern and a pitted surface.
No additional elements were found that could be associated with the paired P elements of Yangtzeplacognathus suggesting that the original definition of Yangtzeplacognathus sensu Zhang (1998) may indeed be valid.
Yangtzeplacognathus sp. nov. A
2000 Polonodus? peavyi n. sp. Johnston and Barnes, pp. 35–36 (pars), pl. 14, figs. 10, 12, 13, 16.
The pastinate Pa elements are best described when observed from above; the elements are developed as sinistral and dextral dissimilar elements. The dextral Pa element has a straight, relatively wide posterior process; the straight main denticle row divides the posterior process into two nearly identical parts; the denticle row turns sharply 90° to the right just in front of the cusp, and the anterolateral process is nearly in a straight line with the denticle row on the posterior process. The sinistral Pa element has a strongly curved outline; the posterior process is very large and wide, and the denticles are placed on the right side of the platform. The denticle row turns sharply to the left in front of the cusp and with the short anterior lateral process pointing forward.
The sinistral and dextral Pb elements are nearly mirror images of each other but differ in that the dextral element is more curved, giving it a Y shape, whereas the left element is more straight giving it a skewed Y-shape.
All elements are deeply excavated and with prominent surface microstructure.
Yangtzeplacognathus n. sp. A differs from Y. crassus in that the dextral Pa element has a very wide posterior inner platform. The anterior process on Yangtzeplacognathus crassus elements is distally bifurcated, a feature that is not seen in this species.
Bed 15 at Lower Head, Shallow Bay and from limestone blocks at Martin Point South section.
Stig M. Bergström (Ohio State University, USA) and John Repetski (US. Geological Survey) are thanked for constructive criticism and comments, which improved the manuscript. Thanks also to the Chief Editor John Greenough for many helpful suggestions. This paper is dedicated to the late Professor Ward Neale, former head of the Department at Memorial University of Newfoundland, and I thank the editors for letting me participate in this Special Issue.
↵1 This article is one of a series of papers published in CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.
- Received October 15, 2010.
- Accepted September 1, 2011.
- Published on the NRC Research Press Web site at http://cjes.nrc.ca on January 30, 2012.
- Published by NRC Research Press