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British Geological Survey, Keyworth, Nottingham NG12 5GG, United Kingdom, e-mail: j.riding{at}bgs.ac.uk
Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen NV, Denmark, e-mail: nep{at}geus.dk
BioStrat Services Limited, 1 Chapelstone Cottages, Finstwaite Lane, Backbarrow, Ulverston, Cumbria LA12 8PY, United Kingdom, e-mail: davebailey{at}compuserve.com
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Abstract |
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 TOP Abstract INTRODUCTIONTHE TAXONOMIC POSITION OF...SYSTEMATIC PALEONTOLOGYCONCLUSIONSACKNOWLEDGEMENTSReferences Cited |
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INTRODUCTION |
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TOPAbstractINTRODUCTIONTHE TAXONOMIC POSITION OF...SYSTEMATIC PALEONTOLOGYCONCLUSIONSACKNOWLEDGEMENTSReferences Cited |
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THE TAXONOMIC POSITION OF MUDERONGIA SP. A OF DAVEY (1979) AND MUDERONGIA SIMPLEX SENSU DAVEY (1979) |
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TOPAbstractINTRODUCTIONTHE TAXONOMIC POSITION OF...SYSTEMATIC PALEONTOLOGYCONCLUSIONSACKNOWLEDGEMENTSReferences Cited |
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, 2). Davey (1979) described Muderongia sp. A as differing from Muderongia simplex Alberti 1961 due to its distinctive angular, as opposed to subspherical, endocyst. Davey (1979) further commented that the endocyst of Muderongia sp. A may extend into the proximal part of the antapical horns. In fact, the endocyst of Muderongia sp. A of Davey (1979) often markedly extends into the proximal portion of all the four or five horns (e.g., Riding and Thomas, 1988, pl. 1, fig. 8). This partial extension of the endocyst into the horns formed by the pericyst in Muderongia sp. A engenders a characteristically cornucavate cyst organisation, which contrasts markedly with the typically circumcavate cyst organisation of the Lower Cretaceous forms attributed to Muderongia simplex (see, for example, Davey, 1979, pl. 2, figs 7, 8). No intermediate morphotypes between these two forms have been observed.
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Davey (1979) and Helby (1987) suggested that Muderongia sp. A of Davey (1979) may be related to Senoniasphaera jurassica (Gitmez & Sarjeant 1972) Lentin & Williams 1976 and the genus Senoniasphaera Clarke & Verdier 1967 respectively. However, Muderongia is classified in the Family Ceratiaceae; prior to the publication of Fensome et al. (1993), it was termed an unequivocal ‘psuedoceratioid’ genus (Poulsen and Riding, 1992). By contrast, Senoniasphaera belongs to the Family Areoligeraceae and is a ‘compressed gonyaulacoid form’ (e.g., Bint, 1986). Monteil (1991) appeared to agree with Helby’s (1987) assertion that Muderongia sp. A of Davey (1979) belonged in Senoniasphaera, as he illustrated this morphotype as Senoniasphaera tabulata Backhouse & Helby, in Helby, 1987 (Monteil, 1991, pl.1, figs 3a–3c). This implicit synonymisation is rejected here as Senoniasphaera tabulata differs from Muderongia sp. A of Davey (1979) in that it has relatively small paracingular protrusions (as opposed to lateral horns), the cavation is minimal except at the paired antapical horns, and it has complete and well-expressed paratabulation by parasutural ridges (Helby, 1987, text-figs 21–23).
In summary, therefore, the holotype of Muderongia simplex Alberti 1961 (Alberti, 1961, pl. 2, fig 4) is clearly cornucavate; see Stover et al. (1996, pl. 5, fig. 13). Furthermore, one of us (NEP) has confirmed this by a restudy of the type material in 1994. Therefore, we contend that Muderongia simplex sensu stricto has an angular endocyst and is cornucavate and the circumcavate forms with subspherical endocysts are a new species, herein named as Muderongia endovata sp. nov. The latter forms are largely Lower Cretaceous and have been erroneously and extensively assigned to Muderongia simplex.
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SYSTEMATIC PALEONTOLOGY |
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TOPAbstractINTRODUCTIONTHE TAXONOMIC POSITION OF...SYSTEMATIC PALEONTOLOGYCONCLUSIONSACKNOWLEDGEMENTSReferences Cited |
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Class Dinophyceae Pascher 1914
Subclass Peridiniphycidae Fensome et al. 1993
Order Gonyaulacales Taylor 1980
Suborder Ceratiineae Fensome et al. 1993
Family Ceratiaceae Willey & Hickson 1909
Genus Muderongia Cookson & Eisenack 1958 emend. Stover & Evitt 1978
Type.
Muderongia mcwhaei Cookson & Eisenack 1958.
Remarks.
Monteil (1991) deemed Phoberocysta to be a junior synonym of Muderongia as part of a major revision of these Upper Jurassic–Lower Cretaceous genera. Both Muderongia and Phoberocysta are cavate, ceratioid genera with apical archeopyles. The genera differed, prior to Monteil’s (1991) revision, principally in that Muderongia is a proximate cyst with a smooth periphragm and Phoberocysta is proximochorate, its periphragm being surmounted by parasutural and intraparatabular processes. This distinction is a major morphologic feature and intergradation between the genera has not been demonstrated; furthermore, the two genera have different stratigraphic ranges. Muderongia emerged in the latest Jurassic (mid Volgian) and has been reported throughout the Early Cretaceous into the Albian (Costa and Davey, 1992; Riding and Thomas, 1992). The inception of Phoberocysta is in the late Ryazanian and the range top of the longest ranging species, Phoberocysta neocomica (Gocht 1957) Millioud 1969, is early Aptian (Heilmann-Clausen, 1987; Costa and Davey, 1992). Furthermore, the consistent presence or absence of processes is a well established criterion for generic separation. For example, the following pairs of genera are characterised by the respective absence and presence of processes or other major discrete ornamentation: Endoceratium–Pseudoceratium, Mendicodinium–Ctenidodinium, Odontochitina–Xenascus, Pareodinia–Gochteodinia, Subtilisphaera–Palaeohystrichophora and Rhombodinium–Wetzeliella. Endoceratium–Pseudoceratium and Odontochitina–Xenascus are, like Muderongia and Phoberocysta, ceratioid genera. In a recent index of dinoflagellate cyst genera and species, Lentin and Williams (1993) upheld all the taxonomic proposals of Monteil (1991). However, previous and subsequent major studies on dinoflagellate cysts generally and ceratioid cysts specifically have all maintained the separate generic identities of Muderongia and Phoberocysta (e.g., Wall and Evitt, 1975; Stover and Evitt, 1978; Evitt, 1985; Bint, 1986; Helby, 1987; Fensome et al., 1993; Stover et al., 1996; Williams et al., 1998). In this study, we recognise both genera and reject the synonymisation of Muderongia and Phoberocysta proposed by Monteil (1991). We prefer to retain the generic synopsis and modified description of Stover and Evitt (1978, pp. 66, 67), which was considered by Helby (1987, p. 298) to represent an emendation. Furthermore, we also reject the synonymisation by Monteil (1991) of Muderongia extensiva Duxbury 1977 with Muderongia mcwhaei Cookson & Eisenack 1958 as the former consistently has significantly longer horns than the latter. Additionally, these two species are confined to separate provinces; Muderongia extensiva is confined to northwest Europe, whereas Muderongia mcwhaei is restricted to Australasia and the South Atlantic region. We also reject the placing of Phoberocysta tabulata Raynaud 1978 into Muderongia by Monteil (1991) because of the lack of prominent parasutural processes, in this species.
Muderongia endovata sp. nov. Plate 1, figs. 1, 2
; Text-Figure 3
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; Woollam and Riding, 1983, pl. 8, figs. 7–8; Thusu and Van der Eem, 1985, pl. 53, fig. 4; Williams and Bujak, 1985, text-fig. 33.16; Aarhus et al., 1986, fig. 10o; Davey, 1987, pl. 5, fig. 14; Habib and Drugg, 1987, pl. 4, fig. 1; Heilmann-Clausen, 1987, pl. 1, figs. 9–10; Thusu et al., 1988, pl. 29, figs. 8, 9; ?Barron, 1989, pl. 2, figs. 8, 9; Colin et al., 1992, pl. 4, figs. 11, 12; Costa and Davey, 1992, pl. 3.2, fig. 4; Poulsen, 1996, pp. 57, 58, pl. 23, fig. 5. Muderongia simplex Alberti, 1961, p. 12, pl. 2, fig. 6, pl. 12, fig. 1 (non. pl. 2, figs. 1, 2, 4, 5, pl. 12, fig. 2) subsp. simplex (autonym, now redundant); Schiøler, 1992, pl. 9, fig. 5.
Muderongia sp. cf. M. simplex Alberti, 1961, p. 12, pl. 2, figs. 1, 6, pl.12, fig. 2 (non. pl. 2, figs. 2, 4, pl. 12, fig. 2); McIntyre and Brideaux, 1980, pl. 12, fig. 4.
Muderongia sp. cf. M. mcwhae1i Cookson & Eisenack 1958, p. 41, pl. 6, figs. 1–5; Wiseman, 1980, pl. 1, fig. 3.
Derivation of Name.
The specific epithet refers to the ovoidal shape of the endocyst.
Diagnosis.
A species of Muderongia, the thin periphragm of which forms one apical horn, two equatorial/lateral horns and one antapical horn giving a typical rhomboid to rounded subpentagonal ceratioid amb. The area of the periphragm in the right antapical area, close to the 5'''/6''' parasuture, forms a prominent shoulder or protrusion which is a reduced or incipient right antapical horn. The left antapical horn is close to the 1p/1'''' parasuture and is the longest and most prominent. The horns are subconical, tapering distally and with rounded, closed terminations. The equatorial/lateral horns, however, may be subrhombic with a medial concavity at the distal extremities at the position of the paracingulum. The equatorial/lateral horns are frequently longer posterior to the position of the paracingulum and may point slightly in an antapical direction. The endocyst is ovoidal to longitudinally elongate subspherical; it may have a small antapical boss. The ovoidal/subspherical endocyst engenders a circumcavate cyst organisation. Periphragm continuous, thin, smooth to microscabrate; endophragm continuous, relatively thick, smooth, scabrate or microgranulate. Archeopyle apical, type (4A). Paratabulation corniform gonyaulacacean, indicated, sometimes partially, by low, smooth, discontinuous ridges on the periphragm. Paracingulum indicated by low ridges on the periphragm and frequently a medial concavity on the equatorial/lateral horns. Parasulcus indicated by low ridges on the periphragm and the parasulcal notch, offset to the left.
Holotype.
Specimen MPK 1275, Housed in the palynological collections of the British Geological Survey, Keyworth, Nottingham, UK.
Locality and Horizon.
Haldager No. 1 Borehole, Denmark (Davey, 1979, text-fig. 1b), core depth 863.19m–866.24m.
Paratype.
Specimen figured as Muderongia simplex Alberti, 1961 (pl. 2, fig. 6). Housed in the palynological collections of the Bundesanstalt für Geowissenschaften und Rohstoffe Aussenstelle, Berlin, Germany.
Locality and Horizon.
The Valanginian of the Dabendorf Borehole, Germany (slide 2a/D1 of Alberti, 1961).
Dimensions.
The holotype measures 104.5 µm in overall length and 75.5 µm in overall width; the endocyst is 64.5 µm long and 55.5 µm wide. The paratype is 118.0 µm in overall length and 92.5 µm in overall width; the endocyst measures 76.0 µm in length and 72.5 µm in width.
Assemblage of 35 specimens measured (µm):
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Remarks.
The periphragm of Muderongia endovata sp. nov. is normally psilate and the pericoel is typically narrow. The horns are usually relatively short in comparison to other representatives of the genus, however the length of these may vary significantly within the species.
Stratigraphical and Geographical Distribution.
Muderongia endovata sp. nov. is a geographically extremely widespread species which has been reported from the Early Cretaceous of arctic Canada, Australia, Europe, Greenland, the Middle East, offshore North Africa, the North and South Atlantic, Norway, and Spitsbergen (see synonymy listing, above). It is present, in significant proportions, (attributed to Muderongia simplex) from the late Ryazanian (Stenomphalus zone) to the late Hauterivian (Marginatus/Variabilis zones) in northwest Europe (Text-Figure 1; Duxbury, 1978; Davey, 1979; 1982; Woollam and Riding, 1983; Costa and Davey, 1992). Duxbury (1977) and Heilmann-Clausen (1987) stated that this form extends into the early–mid Barremian. It is possible that either the species is present sporadically and in low numbers in Lower Barremian strata or that these Barremian records represent reworking. Schiøler (1992) illustrated a specimen of this species (as Muderongia simplex subsp. simplex) from the Upper Cretaceous (Coniacian) of Bornholm, Denmark, which is intepreted as representing stratigraphical recycling from the late Ryazanian to late Hauterivian.
Barron (1989, pl. 2, figs. 8, 9) illustrated a single specimen which he attributed to Muderongia simplex (i.e. Muderongia endovata) from the Middle Volgian of northeast Scotland. This specimen differs from typical Lower Cretaceous specimens of Muderongia endovata in that it has relatively long equatorial/lateral and antapical horns. It is therefore questionably attributed to Muderongia endovata and is most likely to be an aberrant specimen. Poulsen (1996, pl. 23, fig. 5) also illustrated a rather squat specimen of Muderongia endovata (as Muderongia simplex) from ammonite-bearing strata from the Middle Volgian of Poland. This record is from the Scythicus Subzone of the Scythicus Zone, which is equivalent to the Albani Zone. Thus it appears that Muderongia endovata may be extremely rare in the mid Volgian of Europe, absent during the late Volgian–early-earliest late Ryazanian and reappearing in large numbers in the late Ryazanian (Stenomphalus Zone).
Comparison.
Muderongia endovata sp. nov. differs from all other species of this genus in having relatively short, straight and blunt apical, lateral and antapical horns and an ovoidal to subspherical endocyst, giving a circumcavate cyst organisation. The lateral horns are of the Axial type L I of Monteil (1991), meaning that they are aligned with the paracingulum, indented and show equal development of precingular and postcingular extensions (Monteil, 1991, table 3). Thus all species with ‘bent’ and ‘curved’ lateral horns (types L II and L IV of Monteil (1991) respectively) differ profoundly from Muderongia endovata in both lateral horn morphology and general shape. These taxa comprise Muderongia australis, M. asymmetrica, M. crucis, M. extensiva, M. macwhaei, M. staurota, M. testudinaria and M. tetracantha. Furthermore, although Muderongia endovata has a single antapical horn, it is not axial (i.e. type ATP I of Monteil, 1991) as the horn is distinctly offset to the left and there is a reduced or incipient horn in the right antapical area. Hence, Muderongia endovata is deemed to have ‘joined’ (type ATP II) antapical horns of Monteil (1991, table 4). This means that Muderongia aequicornus, M. pariata and M. tomaszowensis differ from M. endovata as they have ‘not joined’ (type ATP III) and axial antapical horn types (Monteil, 1991). Additionally, Muderongia longicorna has two long, subequal antapical horns, which may be pointed distally. Microperforate periphragm is a characteristic feature of Muderongia microperforata, M. perforate and M. siciliana. Furthermore, M. siciliana is a small species with unequally developed lateral horns (Torricelli, 1996). Muderongia simplex differs from M. endovata in having a rounded rectangular to subpentagonal endocyst, engendering a cornucavate cyst organisation.
Muderongia perforata Alberti 1961 emend. nov. Plate 1, fig. 3; Text-Figure 4
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Emended Diagnosis.
A species of Muderongia, with a distinctly ceratioid outline and which is dorsoventrally compressed. The thin periphragm forms five prominent horns which comprise a single apical horn (axial, type AP I), two indented lateral horns (axial, type L I) and two antapical joined horns (type ATP I). The left antapical horn is well developed and normally is over double the size of the right antapical horn. The horns are typically conical, proximally wide and rounded distally; the distal extremities may be closed or perforate. The endocyst is oval, giving rise to a circumcavate cyst organisation. The periphragm is thin, psilate to scrabrate; the endophragm is continuous, relatively thick and psilate, scabrate or granulate. Archeopyle apical, type (4A), the principal suture of which indicates a distinctly left-offset parasulcal notch. Operculum free. Paratabulation is indicated by the archeopyle, the paracingulum which is frequently marked by low ridges and/or indentations of the lateral horns, and the parasulcus which may be indicated by the offset parasulcal notch.
Neotype.
Plate 2, figure 9 of Alberti (1961), housed in the palynological collections of the Bundesanstalt für Geowissenschaften und Rohstoffe Aussenstelle, Berlin, Germany. The holotype (pl. 2, fig. 8 of Alberti, 1961) is lost (Dr. J. Strahl, written comm.).
Locality and Horizon of the Neotype.
Turonian of the Pirna Borehole, Sachen, Germany, slide 2a of Alberti (1961). The latter author considered that the specimens of Muderongia perforata from the Turonian of the Pirna Borehole may have been reworked.
Dimensions.
Holotype, 144 µm in length (width not measured); range 123 µm to 166 µm in length and 108 µm to 116 µm in width according to Alberti (1961). Neotype, 191 µm in length and 165 µm in width; endocyst 109 µm in length and 83 µm in width. Paratype, 148 µm in length and 109 µm in width; endocyst 83 µm in length and 67 µm in width.
Remarks.
The emendation of this species is largely related to the establishment of a neotype because the holotype cannot been located. We agree with Monteil (1991) that this species should be considered separate from Muderongia pariata Duxbury 1983 (see comparison), contrary to a synonymisation by Aarhus et al. (1990).
Stratigraphical and Geographical Distribution.
Valanginian of the Dabendorf Borehole, Germany (personal observation, NEP) and Turonian (possibly reworked, Alberti 1961) of the Pirna borehole, Germany.
Comparison.
Muderongia perforata differs from most other species of Muderongia in having distally perforate horns; Muderongia microperforata has a microperforate periphragm; M. pariata has only one antapical horn.
Muderongia simplex Alberti 1961 emend. nov. Plate 1, figs. 4–6; Text-Figure 5
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Muderongia cf. simplex, Alberti, 1961, p. 12, pl. 2, figs. 1–2, 4–6, pl. 12, figs. 1–2; Raynaud, 1978, p. 398, pl. 1, fig. 12.
Muderongia sp., Habib, 1978, pl. 1, fig. 4.
Muderongia sp. A, Davey, 1979, p. 64, pl. II, figs. 4–5; Davey and Riley, 1978, pl. 3, fig. 3; Davey, 1982, p. 30, pl. 9, figs. 1–3; Riding, 1984, pl. 5, fig. 1; Thusu and Vigran, 1985, pl. 52, fig. 5; Van Helden, 1986, p. 196, pl. 5, fig. 3; Riding and Thomas, 1988, p. 78, 80, pl. 1, fig. 8, pl. 2, fig. 8; Barron, 1989, p. 200, pl. 2, fig. 5; Riding and Thomas, 1992, pl. 2.18, fig. 6; Fensome et al., 1996, pl. 2, fig 1.
Senoniasphaera tabulata, Backhouse and Helby in Helby 1987, p. 317–319, text-figs 21–23; Monteil, 1991, pl. 1, figs. 3a–3c (non. pl. 1, figs. 1a–c, 2a–c).
Emended Diagnosis.
A species of Muderongia, the thin periphragm of which forms one apical, two equatorial/lateral and two antapical horns, giving a typically rhomboid to rounded subpentagonal ceratioid amb. The apical, equatorial/lateral and the left antapical horns are highly variable in length, however all may be relatively prominent. The right antapical horn is close to the 5'''/6''' parasutural boundary and is consistently significantly reduced in size. The left antapical horn is close to the 1p/1'''' parasuture. The horns are normally conical, tapering slightly distally and with blunt, rounded, closed terminations. The equatorial/lateral horns, however, may be parallel-sided with a slight medial concavity at the distal extremities at the position of the paracingulum (i.e. indented or ‘notched’). The endocyst is rounded rectangular to subpentagonal; it approaches the shape of the pericyst in that the endophragm extends slightly into the horns. The relatively small size of the right antapical horn means that the endocyst frequently does not penetrate into this incipient horn or protuberance. The rounded/subangular endocyst engenders a cornucavate cyst organisation; the two cyst layers are normally in contact in the areas between the horns. Periphragm continuous, thin, smooth to microscabrate; endophragm continuous, relatively thick, smooth, scabrate, occasionally having low discontinuous anastomosing crests. Archeopyle apical, type (4A), operculum free. Paratabulation generally not indicated, presumably corniform gonyaulacacean; rarely it may be faintly indicated by low, discontinuous ridges on the periphragm. Paracingulum frequently indicated by low ridges on the periphragm and/or a medial concavity on the equatorial/lateral horns. Parasulcus may be indicated by the parasulcal notch, offset to the left.
Holotype.
The original holotype, Plate 2, figure 4 of Alberti (1961), is lost (J. Strahl, written comm.). We therefore must nomimate a neotype specimen and hereby nominate the best specimen of Muderongia sp. A of Davey (1979). This is considered to be figure 5 on Plate 2 of Davey (1979). This specimen was illustated by Monteil as Senoniasphaera tabulata (Monteil, 1991, pl. 1, figs. 3a–3c). The specimen is British Geological Survey (BGS) figured specimen MPK 1271 and is curated in the palynological collections of the Basin Analysis and Stratigraphy Group, BGS, Nottingham, UK.
Locality and horizon.
The original holotype, which is now lost, was from the Valanginian of the Dabendorf Borehole, near Berlin, Germany (Alberti, 1961, p. 12). The neotype is from the BGS Warlingham Borehole, Surrey (NGR TQ 3476 5719; Worssam and Ivimey-Cook, 1971). The core sample at 696.65m is from the Upper Kimmeridge Clay (Rotunda zone).
Dimensions.
Holotype, 151 µm in length and 121 µm in width according to Alberti 1961, p. 12). The specimen of Alberti (1961, pl. 2, fig. 1) measures 198 µm in length and 148 µm in width; its endocyst is 99 µm in length and 82 µm in width. The material of Alberti (1961) thus appears to be significantly larger than the material below, which is largely from England.
Assemblage of 30 specimens measured (µm):
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Remarks.
The main expression of intraspecific variation within Muderongia simplex is the length of the horns. Some morphotypes, particularly those from the uppermost Kimmeridgian, frequently have relatively short apical, paracingular and antapical horns (e.g., Davey, 1979, pl. 2, fig. 4; Riding and Thomas, 1988, pl. 1, fig. 8). However, these features, aside of the right antapical horn, may be prominent (e.g., Fisher and Riley, 1980, pl. 4, fig. 3; Riding and Thomas, 1988, pl. 2, fig. 8). The majority of Volgian representatives have relatively long horns(e.g.,Bailey etal., 1997,text-fig. 4i). This morphostratigraphical aspect requires further detailed study. The periphragm is readily folded, reflecting its thinness. Note that the neotype was illustated by Monteil as Senoniasphaera tabulata (Monteil, 1991, pl. 1, figs. 3a–3c).
Stratigraphical and Geographical Distribution.
Muderongia simplex has been recorded from the Upper Jurassic (Middle Volgian) and Lower Cretaceous (Valanginian–Hauterivian) of Europe (e.g., Davey, 1979), North Africa (Thusu and Vigran, 1985) and the western Atlantic (Habib, 1978; Van Helden, 1986). It is present consistently in the Middle Volgian from the Rotunda to the Okusensis/ Kerberus zones (Text-Figure 1; Riding, 1984; Riley et al., 1989; Riding and Thomas, 1992). In the North Sea Basin and adjacent regions, there is an acme of Muderongia simplex between the Rotunda and the Albani zones (Text-Figure 1; Riley et al., 1989; Riding et al., 1993). In Denmark, Muderongia simplex has been recorded from the Albani Zone from the Aars-1 borehole, side track 3. Records from the Lower Cretaceous are extremely scarce and include those of the holotype from the Valanginian of the Berlin area, Germany (Alberti, 1961), material from the Berriasian to lowermost Valanginian from offshore eastern Florida (Habib, 1978) and questionable specimens from the Valanginian–Hauterivian of Spitsbergen (Thusu, 1978, pl.2, fig. 6) and the Barremian of eastern England (Duxbury, 1980, pl. 11, fig. 3). The range top of consistent Muderongia simplex as defined herein in the Okusensis/Kerberus zones is considered to be a reliable biostratigraphic marker. This means that it is possible that the holotype, the material of Habib (1978) and the possible specimens of Thusu (1978) and Duxbury (1980) represent reworked material.
Comparison.
Muderongia simplex differs from all other species of this genus in having a cornucavate cyst organisation with significant incursion of the endocyst into the pericystal horns. Muderongia tomaszowensis Alberti 1961 is typically mildly cornucavate and may be delphicavate or circumcavate (Monteil, 1991). Furthermore, this species has relatively short horns and a characteristically rounded, four-sided endocyst. The endocysts of Muderongia crucis Neale & Sarjeant 1962, Muderongia extensiva Duxbury 1977, Muderongia longicorna Monteil 1991, Muderongia macwhaei Cookson & Eisenack 1958 and Muderongia tetracantha (Gocht 1957) Alberti 1961 may be subangular and extend slightly into the proximal parts of the four horns of these species. However, these forms are readily distinguished from Muderongia simplex by their characteristic long and slender horns. Furthermore, the paracingular horns of these species are consistently indented and bent, the distal portion pointing in an antapical direction, i.e. are of type LII of Monteil (1991).Muderongia aequicornus Århus in Århus et al. 1990 has axial (straight) lateral horns like Muderongia simplex. There may, however, be antapical protrusions in the epicyst of Muderongia aequicornus, but these do not extend into the antapical pericystal horns (Monteil, 1991, pl. 2, fig. 9). Muderongia asymmetrica Brideaux 1977 and Muderongia testudinaria Burger 1980 have two long, tapering, distally pointed antapical horns and Muderongia microperforata (Davey 1982) Monteil 1991 is characterised by microperforate periphragm. Muderongia australis Helby1987, Muderongia endovata sp. nov., Muderongia pariata Duxbury 1983, Muderongia perforata Alberti 1961 and Muderongia staurota Sarjeant 1966 all have ovoidal or subspherical endocysts.
Muderongia tomaszowensis Alberti 1961 emend. nov. Plate 1, figs. 7–9; Text-Figure 6
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Muderongia simplex, Alberti, 1961, pl. 2, fig. 5.
Emended Diagnosis.
A species of Muderongia, the thin periphragm of which forms four prominent horns and one minor protuberance. There are a single apical horn, two lateral-equatorials and one left antapical horn; the minor protuberance is in a right antapical position close to the 5'''/ 6''' parasutural boundary. The shape is ceratioid, compressed dorsoventrally, giving an angular, cruciform appearance. The horns are normally conical with closed, rounded, distal terminations. Thus, M. tomaszowensis has axial lateral horns (type L I) and an axial antapical horn (type ATP I) (Monteil, 1991). The endocyst is subcircular to rhombic in dorsoventral outline; it extends moderately into the lateral horns. The endocyst is rounded antapically. Or, it may extend towards the prominent antapical horn, without penetrating into the horn, thereby giving rise to an apically and antapically circumcavate or hypocavate cyst organisation. The species is cornucavate; the two cyst layers are normally in contact in the areas between the horns. The periphragm is thin, psilate to scabrate and the endophragm is continuous, relatively thick, psilate, scabrate or granulate. Archeopyle apical, type (4A), with the margin indicating a distinct left offset of the parasulcal notch, operculum free. Paratabulation indicated by archeopyle, paracingulum (marked by low ridges and indentation of the lateral horns) and the parasulcus which may be delimited by the parasulcal notch and a narrow, sinuous depression.
Neotype.
Pl. 2, fig. 13 of Alberti (1961), housed in the palynological collections of the Bundesanstalt für Geowissenschaften und Rohstoffe Aussenstelle, Berlin, Germany. The holotype (pl. 2, fig. 12 of Alberti, 1961) is lost (Dr. J. Strahl, written comm.).
Paratype.
Specimen assigned to Muderongia simplex by Alberti (1961, pl. 2, fig. 5) and housed in the palynological collections of the Bundesanstalt für Geowissenschaften und Rohstoffe Aussenstelle, Berlin, Germany.
Locality and Horizon.
The neotype is from the Valanginian of the Tomaszow Borehole, Poland, slide 8/Val. of Alberti (1961). The paratype is from the Lower Hauterivian of the Werle-3 Borehole, Mecklenburg, Germany, slide 2a/ 14 of Alberti (1961).
Dimensions.
Holotype, 140 µm in overall length and 112 µm in overall width; range 135–175 µm in length and 104–140 µm in width (Alberti, 1961). The neotype is 191 µm in length and 165 µm in width (endocyst 109 µm in length and 83 µm in width). The paratype is 148 µm in length and 109 µm in width (endocyst 83 µm in length and 67 µm in width). The length of this species varies significantly and ranges from large specimens c.190 µm long to smaller specimens c.135 µm in length.
Remarks.
Monteil (1991, p. 477) emended Muderongia tomaszowensis to include specimens with processes, i.e. species belonging to Phoberocysta. This is not followed in this study and our emendation herein excludes proximochorate forms (see also the generic remarks above and Poulsen, 1996). This species is here confined to proximate specimens and is characterised by four prominenthorns; the right antapical horn is significantly reduced to a protuberance.
Stratigraphic and Geographical Distribution.
Muderongia tomaszowensis is confined to the Valanginian to Lower Hauterivian (Lower Cretaceous) of France, Germany and Poland (Alberti, 1961; Monteil, 1991). The holotype and neotype of Muderongia tomaszowensis are from the Valanginian of the Dabendorf borehole, Berlin, Germany and the Tomaszow borehole, Poland, respectively. The paratype is from the Lower Hauterivian of the Werle-3 Borehole, Mecklenburg, Germany.
Comparison.
Muderongia tomaszowensis differs from the majority of the other species of the genus in having only four prominent horns, i.e. one apical horn, two lateral horns (axial type L I) and a single antapical horn (axial type ATP I). Muderongia crucis and Muderongia staurota both have bent lateral horns, and Muderongia tetracantha has curved, antapically tapering lateral horns (Monteil, 1991). Furthermore, Muderongia pariata has finely perforated periphragm in the distal ends of the horns. The principal difference between M. tomaszowensis and Muderongia simplex is that the latter has five horns and a rounded rectangular to subpentagonal endocyst which is strongly extended into the horns. Joined antapical horns typify Muderongia endovata; of these the left horn is small and the right horn is a reduced or incipient structure. Muderongia australis is distinguished by a slightly larger right antapical horn (joined antapical horns, type ATP II) and bent lateral horns (type L II) with short extension posts and Mudeongia macwhaei has bent lateral horns with long posterior distal extensions.
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TOPAbstractINTRODUCTIONTHE TAXONOMIC POSITION OF...SYSTEMATIC PALEONTOLOGYCONCLUSIONSACKNOWLEDGEMENTSReferences Cited |
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