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Subspecies Hoploscaphites constrictus johnjagti Machalski 2005 | ||||||
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| Diagnosis / Definition: | ||||||
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Machalski (2005): DIAGNOSIS.- Terminal subspecies in the Hoploscaphites con− strictus lineage successive to H. c. crassus, defined by the presence of ribbing throughout the body chamber in macro− conchs. |
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| Discussion / Comments: | ||||||
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Machalski (2005): HOLOTYPE.- MGUH 20220 (Fig. 12D; see also Birkelund 1993: pl. 17: 23a, b) from the indurated part of the Grey Chalk at Stevns Klint. TYPE HORIZON.- Top of the upper upper Maastrichtian Belemnella kazi− miroviensis and the equivalent Argyrotheca stevensis–Magas chitoni− formis zones. TYPE LOCALITY.- Stevns Klint, Denmark. DERIVATION OF THE NAME.- in honour of John W.M. Jagt, a prominent stu− dent of Late Cretaceous faunas, and a friend. UPPER MAASTRICHTIAN MATERIAL.- From Denmark: 86 speci− mens from Stevns Klint (MGUH 20202–20220, 59 unregis− tered or provisionally registeredMGUHspecimens and 8 un− registered specimens in the private collection of Alice Ras− mussen, Fakse), 24 specimens from “Dania” quarry (MGUH 20168–20181, 20187–20193, 20195–197). From Poland: 54 specimens from Me³giew (ZPAL Am. 12/252–305). From Belgium: a single specimen from the former Albertkanaal outcrops (RGM P. 254, Jongmans collection). From the Netherlands: a single specimen from the former Blom quarry (NHMM JJ 11151), two from Vroenhoven (Albertkanaal section) (NHMM JJ 403, JJ 430), six from the Ankerpoort− Curfs quarry, Geulhem (NHMM JJ 5551, JJ 12456, JJ 12735, JJ 12847, JJ 12848, JJ 12903), three from the ENCI quarry, Maastricht (NHMM MK 3585, JJ 11115, JJ 11114). From Sweden: seven specimens from Limhamn (MGUH 20152–20155, 20157–20159). LOWER DANIAN MATERIAL.- A single specimen from Stevns Klint (MGUH 27366). DISCUSSION.- The holotype comes from the indurated portion of the Grey Chalk, c. 30 cm thick, at the top of the upper Maastrichtian in the Stevns Klint succession. A sample of 80 individuals (61 adult macro− and 19 microconchs) from that horizon was studied (see also Machalski 2005). Macroconchs (Fig. 12D) range between 36 and 51 mm and microconchs be− tween 27 and 33 mm in maximum length (Fig. 9F). Body chambers are covered by relatively strong ribs in all adult macroconchs studied; ventrolateral tubercles extend to right up to the aperture in many of these (Birkelund 1993; Ma− chalski 2005). The differences between H. c. johnjagti subsp. nov. and H. c. constrictus are rather subtle (Fig. 8). Ribbing is present on the body chamber in most of the Cotentin macroconchs but is usually weaker in comparison to that seen in material from the indurated Grey Chalk. In addition, the extension of ventrolateral tuberculation to the aperture occurs much more rarely in material from Cotentin than in that from the in− durated chalk at Stevns Klint. Nevertheless, some specimens from Cotentin, e.g., macroconchs assigned to the “crassus” variety by Kennedy (1986: pl. 15: 18–20; 29–31), are virtu− ally indistinguishable from those occurring at the indurated top of the Grey Chalk at Stevns Klint. On this basis, both Kennedy (1986) and Machalski (1996) interpreted the fauna from Cotentin to range very high into the Belemnella kazi− miroviensis Zone, a view proved incorrect by recent studies of inoceramid bivalves from that area (Ireneusz Walaszczyk, personal communication 2005). The sample from the Grey Chalk below the indurated zone, maximum 4 metres thick (Hart et al. 2004, 2005), com− prises six adult macroconchs (Machalski 2005). Four of them belong to the ribbed morphotype, whereas two represent the smooth morphotype which is typical of samples of H. c. crassus. Still lower in the Stevns Klint section, in the pure white chalk, the smooth morphotype prevails. Consequently, the white chalk sample is assigned to H. c. crassus (Ma− chalski 2005; see above). The sample from the “Dania” quarry in Jylland (for loca− tion, see Birkelund 1993: fig. 1) comprises 21 adult macro− and 3 adult microconchs (Machalski 2005). None of these is precisely located within the section exposed, which was a maximum of 16 metres thick (Håkansson and Hansen 1979). Specimens measured range between 35 and 53 mm in maxi− mum diameter. Most of the adult macroconchs from “Dania” represent the ribbed morphotype; only a few specimens have smooth sectors on their body chambers (Birkelund 1993; Machalski 2005). Of special importance are specimens show− ing a morphology intermediate between the ribbed and smooth morphotypes (e.g., Birkelund 1993: pl. 15: 10, 12). Because ribbed macroconchs predominate, the entire sample from “Dania” is assigned to H. c. johnjagti subsp. nov. (= Hoploscaphites constrictus subsp. B ofMachalski 2005). The morphologically transitional individuals between the smooth and ribbed morphotypes attest to the in situ evolution of the subspecies from its precursor H. c. crassus (= Hoploscaphites constrictus subsp. A of Machalski 2005). In summary, the Danish record allows to interpret H. c. johnjagti subsp. nov. as the terminal stage in the evolution of the lineage in Europe. The sample from Meùgiew comes from the topmost metre of the upper Maastrichtian succession there and includes 11 adult macroconchs (Fig. 12B; see also Machalski 2005: fig. 9G) and 23 adult microconchs (Fig. 7C; see also Machalski 2005: fig. 9F); the remainder of the specimens are spires and fragments of adults, which cannot be classified in terms of the dimorphism (Machalski 2005). The maximum length of macro− and microconchs ranges between 31 and 36 mm and between 21 and 27 mm, respectively (Fig. 9E). All macro− conchs fromMeùgiew belong to the ribbed morphotype which allows them to be considered con(sub)specific with the sample from the indurated portion of the Grey Chalk at Stevns Klint. This would then provide a time correlation of scaphitid−bear− ing levels at Stevns Klint and Meùgiew (Machalski 2005). The sample studied from the Limhamn quarry, southern Sweden, is composed of seven adult macroconchs of the ribbed type (Birkelund 1993: pl. 14: 1–4, 6–7, 12). The sample from the Maastricht area studied comprises six adultmacroconchs (Fig. 12C; see also Jagt 1995: pl. 5: 15, 16) and six microconchs. These specimens come from the ENCI, Ankerpoort−Curfs and Blom quarries, and all stem from the upper part of the Meerssen Member of the Maastricht Forma− tion, from subunits IVf−4 to −6 in local terminology (Jagt et al. 1996). These subunits represent the last 5–10 metres of the up− perMaastrichtian succession in the area, depending on the lo− cality (Jagt et al. 1996). Adult macroconchs from the Maas− tricht area range between 32 and 51 mm in maximum length, whereas adult microconchs reach between 31 and 35 mm. Of the five better−preserved adult macroconchs in this lot there are three ribbed individuals: two from the top of IVf−6 and a single one from IVf−4. Body chambers in the two other speci− mens from subunits IVf−4 and IVf−5/6 are smooth. Although the number of well−localised specimens avail− able fromtheMaastricht area is rather limited, it appears likely that the distribution of Hoploscaphites constrictus in the upper part of the Meerssen Member is similar to that in the Grey Chalk of the Stevns Klint succession. Populations from lower levels within the upper part of this unit are characterised by the co−occurrence of smooth and ribbed specimens. In contrast, those from its top seem to be composed exclusively of the ribbed variant. The latter assumption finds support in Jagt (2002: 519), who stated that: “Stout specimens with coarse or− nament and ventrolateral tubercles extending to (near) the ap− erture (forma crassus of authors) are best known from the top of the unit (IVf−6)”. In the present paper, the whole sample from the upper part of the Meerssen Member is provisionally attributed to H. constrictus johnjagti subsp. nov. However, it cannot be excluded that additional bed−by−bed collecting may show that material from levels below the top of the subunit IVf−6 should actually be assigned to H. c. crassus. All adult macroconchs of Hoploscaphites constrictus il− lustrated by Kennedy et al. (1986: pl. 3: 1, 9–12; pl. 5: 1–17, 21–26) from the upper Maastrichtian of Petites−Pyrénées (France) bear distinct ribs on the flanks and, consequently, are here assigned to H. c. johnjagti subsp. nov. The subspe− cies seems to occur also in the uppermost Maastrichtian, just below the boundary clays, in Mangyshlak, Kazakhstan (re− ported as Hoploscaphites constrictus crassus by Naidin et al. 1990; see also Jolkichev and Naidin 2000: fig. 4: 11), al− though this needs to be checked during further study. A single, well−preserved mould of Hoploscaphites con− strictus from the lowermost Danian Cerithium Limestone at Stevns Klint (Machalski and Heinberg in press: figs. 3, 4, 6; Fig. 12A1– A4), interpreted as the earliest Danian survivor by Machalski and Heinberg (in press), reveals distinct ribs on the body chamber and is assigned herein to H. c. johnjagti subsp. nov. This conclusion is based on the assumption that even a single individual can be assigned to a horizontally defined taxon as it is most probable that it represents the predominant morphology in its population (Dzik 1985). More well−pre− served specimens are needed to substantiate this assumption. Other specimens reported by Machalski and Heinberg (in press) from the Cerithium Limestone at Stevns Klint (MGUH 27368, 27359, 27360) are too fragmentary for the style of ribbing on their flanks to be clearly established. The same concerns four specimens of Hoploscaphites constrictus from the lowest Danian (Meerssen Member, subunit IVf−7) at the Ankerpoort−Curfs quarry. These (NHMM 2001 180/1, 2, 2002 006, 2002 053A–D, 2002 057), regarded as earliest Danian survivors by Jagt et al. (2003), are preserved as spires retaining small portions of body chamber; these cannot be as− cribed to either of the dimorphs. According to Machalski (2005), the smaller size of adult macroconchs is an additional character which distinguishes populations of H.c. johnjagti subsp. nov. from those of H. c. crassus in Poland and Denmark (Machalski 2005; compare Fig. 9C, D and Fig. 9E, F). This may still hold true in a more general geographic perspective as adult macroconchs of the subspecies from the Netherlands and France are of a size comparable to specimens from the top of the Maastrichtian succession at Stevns Klint and Mełgiew. However, samples of H. c. crassus from lower levels in the upper Maastrichtian, e.g., from Rejowiec (Fig. 9B), do not differ significantly from samples of H. c. johnjagti subsp. nov., as far as size is concerned. Microconchs in all samples of H.c. johnjagti subsp. nov. studied generally match the style of ribbing of macroconchs (compare Figs. 7C and 12B; see also Fig. 8). Microconchs seem to dominate the record of the subspecies in the Maas− tricht area (Kennedy 1987; John W.M. Jagt, personal com− munication 2005) and at Mełgiew (Machalski 2005; Fig. 9E). It is not clear whether this results from ecological or preservational bias. STRATIGRAPHIC AND GEROGRAPHIC RANGE.- Top of the upper up− per Maastrichtian in Denmark (top of the Belemnella kazimi− roviensis Zone and its equivalent Argyrotheca stevensis– Magas chitoniformis Zone), Sweden (top of Belemnella kazi− miroviensis Zone), Poland (top of Belemnella kazimirovien− sis Zone), the Netherlands and Belgium (top of Belemnella kazimiroviensis Zone), France, and possibly Kazakhstan (top of Belemnella kazimiroviensis Zone). Possibly lowermost Danian at Stevns Klint, Denmark. |
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| Systematics: | ||||||
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51 Familia Scaphitidae Genus Hoploscaphites Species Hoploscaphites constrictus Species Hoploscaphites schmidi Subspecies Hoploscaphites constrictus johnjagti |
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| Synonym list: | ||||||
| Machalski (2005): 1861 Scaphites constrictus d'Orbigny. - Binkhorst : p.38 pl. 5d; fig. 6a-h
1986 Hoploscaphites constrictus Sowerby. - Kennedy et al. : p.1019 pl. 3, fig. 1, 9-12;
pl. 4, fig. 1-19;
pl. 5, fig. 1-17, 21-26
1987 Hoploscaphites constrictus Sowerby. - Kennedy : p.197 pl. 31, fig. 1, 8-26;
pl. 32, fig. 1-12, 18-21
sic! 1987 Hoploscaphites constrictus constrictus Sowerby. - Tuuk : p.73 fig. 5-7, 11, 20-23
1987 Hoploscaphites constrictus niedzwiedzkii Uhlig. - Tuuk : p.76 fig. 9, 10, 24
1987 Hoploscaphites indet. constrictus ssp. . - Tuuk : p.77 fig. 8, 25
p 1993 Hoploscaphites constrictus Sowerby. - BIRKELUND : p.57 pl. 14, fig. 1-4, 6, 7, 12;
pl. 15, fig. 1-14;
pl. 16, fig. 6-16;
pl. 17, fig. 5-9, 11-23 [non pl. 14, fig. 5; pl. 17, fig. 10 =
Holposcaphites constrictus crassus]
p 1995 Hoploscaphites constrictus Sowerby. - Jagt : p.30 pl. 5, fig. 15, 16;
pl. 7, fig. 13-19 [non pl. 7, fig. 7 = Hoploscaphites constrictus
subsp. indet.]
? 2000 Hoploscaphites constrictus crassus Lopuski. - Jolkichev & Naidin : fig. 4:11
2005 Hoploscaphites n spp. constrictus johnjagti Machalski. - Machalski : p. 665, 670 fig. 7c, 12
2005 Hoploscaphites ssp. constrictus B . - Machalski : p.667 fig. 9A-H
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| Stratigraphy - relative ages: | ||||||
| upper Maastrichtian ? lower Danian: Machalski (2005) |
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| References: | ||||||
Binkhorst,J.T.. (1861): Kennedy,W.J..; Bilotte,M..; Lepicard,B.. and Segura,F.. (1986): Kennedy,W.J.. (1987): Tuuk,V.V.L.. (1987): BIRKELUND,T.. (1993): Jagt,J.W.M.. (1995): Jolkichev,N.A.. and Naidin,D.P.. (2000): Machalski,M.. (2005): |
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| Anonymous: Unedited TaxonConcept data | ||||||
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