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Systematic palaeontology
Class Coleoidea Bather, 1888
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Order Belemnitida von Zittel, 1895
Suborder Belemnopseina Jeletzky, 1965
Family Belemnitellidae Pavlow, 1914
Genus Belemnella Nowak, 1913
Subgenus Belemnella Nowak, 1913
Subgenus Pachybelemnella Schulz, 1979
Subgenus Neobelemnella Naidin, 1975
Remarks – In all three subgenera, the rostrum cavum is completely calcified, that is, they have a genuine alveolus. In the study area, at least five species can be ascribed to these subgenera. All have irregularly formed, often wavy, dorsolateral double furrows, and the angle between the main vascular imprints and those double furrows is in excess of 30°, while the AA is between 10 and 23°, and the SD between 0 and 4.5 (5) mm. Pachybelemnella (type species: Belemnella obtusa Schulz, 1979, by original designation) is comprised of species with a relatively shorter rostrum solidum than those referred to the subgenus Belemnella (type species: Belemnites lanceolatus von Schlotheim, 1813 [ICZN Opinion 1328 [1985], name no. 2979]), which is moderately slender in species with a clavate profile and stout in those with weakly clavate to weakly conical rostra. The subgenus Neobelemnella (type species: Belemnitella kazimiroviensis Skołozdrówna, 1932, by monotypy), which externally is often difficult to distinguish from Belemnitella junior, is characterised by large values for AA (20-23°) and SD (3-5 mm), well-developed vascular imprints which branch from the dorsolateral double furrows under an angle of < 40°, and a short, conical juvenile stage.
Belemnella (?Belemnella) cf. praearkhangelskii Naidin, 1964
Pl. 3, figs. 1, 2.
Description – Species characterised by a long, slender rostrum (Ls 67.3-74.3 mm), (weakly) lanceolate in ventral and cylindrical to weakly lanceolate in lateral aspect; faintly developed vascular imprints; acute apical end, well-developed mucro; small values for SD (0.5-2.5 mm) and AA (12-16°).
Occurrence – Known exclusively from the Vijlen Member (interval 4) at Altembroeck (‘s-Gravenvoeren, northeast Belgium; Keutgen, 1997, 2011), of middle sumensis Zone age (late early Maastrichtian).
Belemnella (Pachybelemnella) cf. inflata (Arkhangelsky, 1912)
Pl. 1, figs. 1-3.
Description – Species characterised by a moderately long rostrum (Ls 60-72 mm), markedly clavate in ventral and weakly lanceolate in lateral aspect; obtuse apical end; vascular markings relatively weakly developed, but dorsolateral depressions and double furrows marked; small values for SD (1.0-2.5 mm) and AA (12-14°).
Occurrence – Confined to the basal Vijlen Member at Pesaken-Crapoel (southern Limburg) as remanié elements from the Belemnitella minor II Zone, of late late Campanian age (Keutgen et al., 2010; Keutgen, 2011).
Belemnella (Pachybelemnella) ex gr. sumensis/cimbrica
Pl. 3, figs. 5, 6.
Description – Representatives of the sumensis/cimbrica group have a stout, relatively short rostrum solidum (Ls 45-65 mm), generally with rounded apical end and comparatively weakly developed mucro; cylindrical to weakly clavate in ventral, conical to cylindrical in lateral aspect; vascular markings and dorsolateral double furrows mostly weakly developed; larger values for AA (14-17°) and SD (1.5-4 mm).
Discussion – In the middle portion of the Vijlen Member, belemnitellids occur which match the species concept of both Belemnella (P.) sumensis Jeletzky, 1949, and Belemnella (P.) cimbrica Birkelund, 1957, but most samples recorded previously in the literature are now considered reworked. From interval 3 of this member at Aachen-Schurzelterstraße, Keutgen et al. (2010) recorded Belemnella ex gr. sumensis/cimbrica below the first appearance datum (FAD) of Belemnitella junior; the mean values of this sample indicate either a late form of Belemnella sumensis or, alternatively, Belemnella cimbrica, a more precise identification being impossible. Early forms of Belemnella sumensis are common at Altembroeck in interval 4 of the Vijlen Member (Keutgen, 1997, 2011), where they co-occur with Belemnella cf. praearkhangelskii (see above) and the typically late Maastrichtian Belemnitella junior and Belemnitella lwowensis. In northern Germany, Belemnella praearkhangelskii is of middle sumensis Zone age.
Occurrence – Common, but often reworked, in the middle portion of the Vijlen Member (intervals 3 and 4), in the border area between southern Limburg (the Netherlands) and the Voerstreek (Belgium), as well as near Vaals (Schneeberg), Lemiers, and between Vijlen and Aachen.
Belemnella (Pachybelemnella) obtusa Schulz, 1979
Pl. 3, figs. 3, 4.
Description – Species characterised by a stout rostrum solidum (Ls 40-60 mm); in large-sized specimens, apical end obtuse; cylindrical to weakly clavate in ventral, clavate to cylindrical in lateral aspect; vascular markings and dorsolateral double furrows weakly developed; larger values for AA (14-17°) and SD (1.5-4 mm).
Occurrence – Fairly common, albeit exclusively reworked, in some ‘belemnite graveyards’ in the basal Vijlen Member, as at Slenaken and Beutenaken (Schulz, 1979; Keutgen & Van der Tuuk, 1991), of obtusa Zone age.
Belemnella (Neobelemnella) gr. kazimiroviensis (Skołozdrówna, 1932)
Pl. 2, figs. 4-6.
Description – Characteristic of this group are relatively small to medium-sized, slender rostra (Ls 40-70 mm; mean 55 mm); acute apical end, barely developed mucro; lanceolate in ventral, lanceolate to subcylindrical in lateral aspect; vascular imprints, dorsolateral depressions and double furrows, and longitudinal striae well developed; bottom of ventral fissure curved downwards, generally S-shaped; large values for SD (3-4.5 mm) and AA (c. 20°).
Discussion – Van der Tuuk & Bor (1980, p. 128) noted that ‘populations’ of this species (or species group) appeared to comprise juvenile and subadult individuals only. This observation has been corroborated subsequently (J.W.M. Jagt, unpublished data). In fact, mature guards such as the one illustrated herein (Pl. 2, figs. 2, 3) are very rare. Birkelund (1957) was first to record this form from the Maastrichtian type area; to date, we know that representatives of this group (for which also the names archangelskyi Naidin, 1952, and skolozdrownae Kongiel, 1962, are available) are confined to the highest part of the Meerssen Member (Maastricht Formation), and possibly even indigenous at the base of the early Paleocene Geulhem Member in the Geulhem area, although most specimens from that level are abraded, fragmentary or have episkeletozoans. Others, however, appear to be (par)authochtonous.
Occurrence – Restricted to the upper Meerssen Member, the first representatives having been recorded from the top of subunit IVf-3/base of IVf-4 (J.W.M. Jagt, unpublished data). To date, I have seen material from the St. Pietersberg (ENCI HeidelbergCement Group quarry), the Geulhem-Berg en Terblijt area (former Ankerpoort-Curfs and Blom quarries; Geulhemmerberg subterranean galleries), and the Albert Canal between Vroenhoven and Veldwezelt (Belgium).
Genus Belemnitella d’Orbigny, 1840
Belemnitella junior Nowak, 1913
Pl. 2, figs. 1-3.
Description – Species characterised by large, but relatively slender rostra (Ls 51.8 mean, Dp 11.9 mm mean); generally subcylindrical in ventral and subconical in lateral aspect; slightly flattened over entire length; apical end obtuse or acute with well-developed mucro; dorsolateral depressions, double furrows and vascular imprints usually well developed; ‘pseudogranulation’ ventrally and longitudinal striae dorsally; mean values of Qp, BI, SD, FA and AA are 0.94, 4.3, 6.9 mm, 29.7° and 18.7°, respectively
Discussion – As noted by Keutgen et al. (2010), this is a typical representative of the Belemnitella mucronata group, which co-occurs through most of its range with Belemnitella lwowensis of the Belemnitella langei group (see below).
Occurrence – Ranging from interval 4 of the Vijlen Member to the very top of the Maastricht Formation (Meerssen Member, subunit IVf-6) throughout the study area. Common in the Lanaye Member (Gulpen Formation), the basal Valkenburg Member, and at some intervals within the Emael and Nekum members (Maastricht Formation).
Belemnitella lwowensis Naidin, 1952
Pl. 1, figs. 4-6.
Description – Species characterised by fairly large and very slender rostra (Ls 49.2 mm mean; Dp 9 mm mean), weakly lanceolate to subcylindrical in ventral and subcyl-indrical in lateral view; flattened over entire length; apical end acute or slightly obtuse with well-defined mucro; dorsolateral depressions, double furrows and vascular markings usually well developed; ‘pseudogranulation’ ventrally, and longitudinal striae both ventrally and dorsally. Mean values for Qp, BI, SD, FA and AA are 0.91, 5.5, 6.3 mm, 55.6° and 18.7°, respectively.
Occurrence – Co-occurring with Belemnitella junior throughout its entire range, from the Vijlen Member (interval 4) up to the Emael Member (Maastricht Formation); in the Maastricht Formation, the ratio lwowensis/junior being around one to ten (Christensen et al., 2004; Keutgen et al., 2010).
Belemnitella cf. minor II Christensen, 1995
Pl. 1, figs. 7, 8.
Description – Species characterised by large-sized rostra (Ls 46.4 mean, DP 12.9 mm mean), stout, yet slightly more slender than typical B. minor II (mean BI c. 3.7); cylindrical or slightly conical in ventral and high conical in lateral aspect; juvenile guards more conical in both ventral and lateral views; slightly flattened over entire length; apical end acute or obtuse with mucro; vascular imprints well developed both laterally and ventrally, dorsolateral depressions and double furrows prominent; some specimens have ‘pseudogranulation’ ventrally and longitudinal striae on posterior dorsal side; mean values of Qp, SD, FA and AA of a ‘population’ from the basal Vijlen Member (Keutgen et al., 2010) are 0.98, 11.7 mm, 23.4° and 19.3°, respectively.
Discussion – This is stouter and with a larger SD than Belemnitella minor I, yet slightly more slender than the real Belemnitella minor II from the Paramoudra and Sidestrand Chalk members in Norwich, England (Christensen, 1995), with a mean BI value of 3.7.
Occurrence – Confined to the basal Vijlen Member at Pesaken-Crapoel (reworked; see Belemnella cf. inflata above), the Bovenste Bos quarry and the Beutenaken area (southern Limburg), ranging from late late Campanian to earliest Maastrichtian (see Keutgen et al., 2010; Keutgen, 2011).