Lotharingibelus subgiganteus (Branco, 1879) n. comb.

(Figs 5 A-C; 6A-E)

Belemnites subgiganteus Branco, 1879: 101, pl. 6, figs 2, 2 a-e. — de Roebe 1881: 549. — Benecke 1905: 292, pl. 27, figs 1-4. — Hof 1994: pl. 2, fig. 3 (specimen to the right).

Belemnites sp. – Benecke 1898: 48-49, pl. 4, figs 10-13 (orthorostra).

Mesoteuthis subgiganteus – Schirardin 1961: 115.

Megateuthis subgigantea – Riegraf 1995: 54. — Weis 1999: 232, figs 11, 39-40. — Neige et al. 2021: Appendix S3 (taxonomical dataset).

Dactyloteuthis crossotela (Blake) – Weis 1999: 219, figs 33-34 (orthorostra).

TYPE MATERIAL. — Neotype. Luxembourg • Paris Basin, Differdange, Oberkorn, Kiemerchen; 49°30’16”N, 5°53’07”E; “couche grise” (Pseudoradiosa Zone); upper Toarcian; MNHNL TO265 (Fig. 5A).

ADDITIONAL MATERIAL. — France • 3 specimens; Paris Basin, Meurthe-et-Moselle, Thil; upper Toarcian; MNHNL DOT505 a, DOT505b, DOT505c (Fig. 5C) • 1 specimen (with epirostrum); Paris Basin, Meurthe-et-Moselle, south of Nancy, Ludres; upper Toarcian; MAN 2023.0.166 (Fig. 6A) • 1 specimen (orthorostrum); Paris Basin, Meurthe-et-Moselle, Maxéville near Nancy; upper Toarcian; MAN 2023.0.163 (Fig. 6C) .

Luxembourg • 2 specimens; Paris Basin, Differdange, Oberkorn, Kiemerchen; “couche grise”; Pseudoradiosa Zone, upper Toarcian; MNHNL DOT511 a, DOT511b (Figs 5B; 6E) • 1 specimen (orthorostrum); Paris Basin, Niederkorn; upper Toarcian; MNHNL DOU997 • 1 specimen (orthorostrum); Paris Basin, Rumelange; “couche grise”; upper Toarcian; MNHNL LG101 (Fig. 6B) • 4 specimens (with epirostrum); Paris Basin, Esch-sur-Alzette; “couche noire”; upper Toarcian; MNHNL DOU514, DOU559 a-c • 1 specimen (orthorostrum); Paris Basin, Differdange; upper Toarcian; MNHNL DOT470 (Fig. 6D) • 1 specimen (with incomplete epirostrum); Paris Basin, Differdange; “base du calcaire supérieur” (Mactra subzone); upper Toarcian; MNHNL DOT499 .

TYPE HORIZON. — “Couche grise de Differdange”, Minette ironstone formation (Pseudoradiosa Zone) (Maubeuge 1947; Di Cencio & Weis 2020).

TYPE LOCALITY. — Luxembourg, Paris Basin, Differdange, Oberkorn, Kiemerchen, a former mining site, nowadays a protected area (Weis 2022).

OCCURRENCE. — Paris Basin (France, Luxembourg, and Belgium), upperToarcian (Dispansum Zone to Mactra subzone, Aalensis Zone).

DESCRIPTION

Large to very large sized, elongate-conical rostrum with epirostral development. The profile and the outline of the orthorostrum are symmetrical and conical. The profile of the epirostrum is slightly asymmetrical, conical to cylindriconical, its outline is symmetrical and cylindriconical. The apex of the orthorostrum is striated but bears no grooves. The epirostrum bears two long and incised dorsolateral grooves and several, irregular dorsal and ventral striae. The cross section is elliptical, compressed (compression index between 1.16 and 1.24; Table 2). The alveolus occupies one third to one fifth of the total rostrum length and one half of the sole orthostrum length. The alveolus is slightly displaced towards the venter. The apical line is goniolineate. Alveolar angle 28-30°.

REMARKS

Branco (1879) reported the species from his “Oberregion der Schichten mit Trigonia navis”, currently uppermost Toarcian, Pseudoradiosa Zone (Maubeuge 1947; Di Cencio & Weis 2020) from three localities: Ars, St.-Quentin near Metz, and Villerupt. The type material (syntypes) described by Branco (1879), originally housed in the collections of the Geologische Landessammlung von Elsass-Lothringen in Strasbourg, was destroyed in a fire in 1967 (Jean-Claude Gall, pers. comm. 1998) and has to be considered as definitely lost (Kévin Janneau, pers. comm. 2022). We herein select as the neotype specimen MNHNL TO265 from the “Couche grise de Differdange” of the Minette ironstone formation in the Kiemerchen section (southwest of Oberkorn, Luxembourg) (Fig. 5A). This locality, a former mining site, nowadays a protected area (Weis 2022), is situated 4 km away from the town of Villerupt and is located in the same geological sub-basin of DifferdangeLongwy (Fig. 1); the neotype is from the same geological horizon and formation of the syntypes. The designation of a neotype is considered necessary in order to clarify the taxonomic status of Belemnites subgiganteus and in particular its differential characters in respect to Belemnites meta .

L. subgiganteus n. comb. bears some resemblance with the epirostrum-bearing specimens of Dactyloteuthis crossotela . However, the orthorostrum of L. subgiganteus n. comb. differs from that of D. crossotela by the stronger conical profile of the former. Moreover, the epirostrum of L. subgiganteus n. comb. bears two strongly incised dorsolateral grooves. Due to this feature, L. subgiganteus n. comb. has been formerly attributed to the genus Megateuthis . However, L. subgiganteus n. comb. differs from Megateuthis by the shape and features of its orthorostrum, which bears no grooves. The similarity of the orthorostra of L. meta n. comb. and L. subgiganteus n. comb. demonstrates their close affinities and their inclusion into a single genus.

A POSSIBLE SEXUAL DIMORPHISM

IN LOTHARINGIBELUS N. GEN.

Belemnites are supposed to show some degree of sexual dimorphism given that dimorphic traits are well documented in other cephalopods, such as ammonites and living coleoids (Davis et al. 1996; Wilkin 2022). An example of a possible sexual dimorphism in belemnites has been described by Doyle (1985) from the Toarcian of Yorkshire. In that case the presence of an epirostrum has been interpreted as a sexual adaptation. This idea had already been advanced by earlier workers (d’Orbigny 1842-1851; Lissajous 1925). Schlegelmilch (1998) comments that it is “tempting to interpret these results as a sexual dimorphism but not necessarily so” and suggests studying further potentially dimorphic pairs, such as Dactyloteuthis similis and D. semistriata . Stevens et al. (2017) studied in detail the Cretaceous epirostrum-bearing belemnite Neohibolites minimus (Miller, 1826) (see also Spaeth 1971) and concluded that the interpretation of the epirostrum as a sexually selected character remains plausible. In a recent paper about the anatomy of the giant belemnite genus Megateuthis, Klug et al. (2024) conclude that “there is no hard evidence for sexual dimorphism in belemnites yet. Concerning the two large forms Megateuthis suevica and M. elliptica, their widely overlapping occurrence and their similar morphologies are remarkable. Such species pairs evoke the question for sexual dimorphism, which has been discussed for belemnites a few times […]”.

On the other hand, dimorphism in belemnites could also have been expressed in other ways than solely by differences in rostrum size and shape. For example, biometric methods were used by Delattre (1956) in Toarcian Odontobelus Naef, 1922 and Ippolitov (2006) in Middle and Late Jurassic Hibolithes Montfort, 1808, in which the epirostrum is seldom present (e.g., H. duperroni Combémorel, 1988). Geochemical methods were used by McArthur et al. (2007), who showed significant differences within two types of rostra attributed to a single species. In Recent squids, Arkhipkin et al. (2015) evidenced an elongate structure, the “tail”, which facilitates the development of a more mobile adult phase in these coleoids; by analogy, the elongate epirostrum in extinct coleoids like the belemnites could have played a similar role. However, in some groups like Onykia spp., the elongation of the body occurs within both males and females, but in other groups, Lycoteuthis Pfeffer, 1900 for instance, it occurs only amongst males. The dimorphic vs. adaptive nature of the epirostrum remains therefore still a question open to debate (see also Bandel & Spaeth 1988; Stevens et al. 2017). Another hypothesis was advanced based on well preserved soft-part belemnites from the German Posidonia shale; one specimen shows an enlarged (> 5 mm) hook (mega-onychites) at the base of the arm crown which was interpreted as sexual dimorphism (Hauff 1985; Schlegelmilch 1998; Wilkin 2022). This hypothesis has been discarded by some workers (Riegraf 1996), who argued that in recent coleoids large hooks would occur in both the females and the males. Opposed to this view, Stevens (2010) reported that in modern squids large hooks are developed during maturity and that their presence in males only hints at a reproductive rather predatory function, so it seems likely that fossil mega-hooks fulfilled a similar role. It is important, however, to note that such mega-hooks are known only in Jurassic belemnites (Klug et al. 2024).

Doyle (1992)

Regarding Lotharingibelus meta n. comb. and L. subgiganteus n. comb., we are undoubtedly in presence of a “dimorphic pair” similar to the one identified by Doyle (1985) for the genus Youngibelus (synonym of Cuspiteuthis). Similar pairs have since then been identified in Early and early Middle Jurassic belemnites (Pliensbachian to Bajocian) (Table 3). In none of those pairs was a sexual dimorphism proven, though the possibility cannot be ruled out. In the case of Lotharingibelus n. gen., it can further be noted that the ratio of rostra of L. meta n. comb. to L. subgiganteus n. comb. is c. 10 to 1. These data are based on the rostra that are currently present in public collections and need to be taken with great care as it is likely that there is a collection bias. For Cuspiteuthis, Doyle (1985) gave ratios of 1.1 and 1.2 for two localities. Given the data at hand, it is therefore difficult to draw a conclusion about the sexual dimorphism in Lotharingibelus n. gen. Further studies on the “dimorphic pairs” known so far (Table 3) are needed to corroborate the hypothesis of sexual dimorphism, either linked with the development of an epirostrum or reflected by differences in size and form of the rostrum (Ippolitov 2006).