Spathites (Jeanrogericeras) reveliereanus ( Courtiller, 1860 )

Wondrejz, Constanze, Nagm, Emad & Wilmsen, Markus, 2023, Dimorphism in Late Cretaceous ammonites- evidence from early Turonian ammonite faunas of the Briessnitz Formation in Saxony, Germany, Acta Palaeontologica Polonica 68 (4), pp. 639-657 : 646-651

Spathites (Jeanrogericeras) reveliereanus ( Courtiller, 1860)

Figs. 7–10 .

1860 Ammonites reveliereanus ; Courtiller 1860: 249, pl. 2: 5–8.

1980 Spathites (Jeanrogericeras) reveliereanus (Courtiller) ; Kennedy et al. 1980: 826, pls. 105: 1–12; pl. 106: 1–2; text-figs. 3, 5, 6. [with synonymy]

2013 Spathites (Jeanrogericeras) reveliereanus ( Courtiller, 1860) ; Wilmsen and Nagm 2013: 664, figs. 15, 16, 17A–F.

2014 Spathites (Jeanrogericeras) reveliereanus ( Courtiller, 1860) ; Wilmsen and Nagm 2014: 216, fig. 9a.

2014 Spathites (Jeanrogericeras) reveliereanus ( Courtiller, 1860) ; Amédro and Delvaque 2014: 143, pl. 13: 2.

2015 Spathites (Jeanrogericeras) revelieranus ( Courtiller, 1860) ; Kennedy et al. 2015: 465, fig. 21A–C.

2016 Spathites (Jeanrogericeras) revelerianus ( Courtiller, 1860) ; Kennedy and Gale 2016: 273, figs. 9–11.

2018 Spathites (Jeanrogericeras) reveliereanus ( Courtiller, 1860) ; Matrion 2018: 195, figs. 132C, D, 136B, 138A, B, 139A, B, 140A.

Material.— In total, an assemblage of 61 specimens from the lower Turonian (Cretaceous), Briessnitz Formation, Germany, Dresden, locality: Leubnitz (35 specimens), Lockwitz (25 specimens), Omsewitz (1 specimen). Due to imperfect preservation, only 38 could be used for the statistical analysis (see SOM). Repository numbers are provided in SOM 5 .

Measurements.—See SOM 5.

Description.—Medium-sized to large species, which is moderately involute coiled (UD ≈ 24.7%). There are many relatively large specimens with diameters> 100 mm and also many smaller specimens with D ≈ 50 mm. Large specimens have a broader quadrate apertural cross-section with broadly rounded venter, reflecting higher Wb/Wh ratios, while in smaller individuals, the Wb/Wh ratio is lower, and their cross-section is more rectangular. The flanks are weakly convex in intercostal section. The ventrolateral shoulders are narrowly rounded, and the venter is slightly convex. The strong and straight primary ribs develop in pairs at commonly eight umbilical tubercles per whorl. Approximately at mid-flank, intercalated secondary ribs appear. Each rib carries strong outer ventrolateral bullae. The umbilicus is very deep, the umbilical wall is steep, and the umbilical shoulder is rounded.

Stratigraphic and geographic range.— Spathites (Jeanrogericeras) reveliereanus is known from the lower Turonian Mammites nodosoides Zone and the middle Turonian Collignoniceras woollgari Zone of Europe ( France, Spain, Germany, Romania), India and Morocco (see Wilmsen and Nagm 2013 and Kennedy and Gale 2016 for further details).

Statistical analyses.—Based on the measurement and/or calculation of eight relevant morphological variables, classical clustering and linear discriminant analysis were conducted on the 38 relevant specimens (see Fig. 8 and SOM). In the classical clustering analysis, two groups are clearly separated from each other. The Cophenetic distance is not quite high with 30, but that can be explained by the relatively low number of individuals in comparison to the other two studied species. In the LDA, the two groups are again conspicuously apart from each other and not as scattered as in the other species, i.e., they appear to be more coherent.

Figures

Fig. 7. Photographic illustration of typical large (A) and small (B) specimens of the acanthoceratid ammonoid Spathites (Jeanrogericeras) reveliereanus (Courtiller, 1860) from the lower Turonian of the Briessnitz Formation, Leubnitz, Germany. A. MMG: SaK 5230 in lateral (A1) and apertural (A2) views. B. MMG: SaK 5256 in lateral (B1, B3) and ventral (B2) views.

Fig.8. Statistical test of potential dimorphism in Spathites (Jeanrogericeras) reveliereanus (Courtiller, 1860) based on 38 specimens.The repository number of each specimen is given on top of the diagram. A. Classical clustering; inferred macro- and microconchs are marked by blue and red colors, respectively. B. Linear discriminant analysis (LDA); the color code follows the assignment of the classical clustering above. The dark blue lines are biplots of all variables, an overlaying of a score plot and a loadings plot in a single graph, which enables to visualise high-dimensional data by using a two-dimensional graph.

Fig.9.Acanthoceratid ammonoid Spathites (Jeanrogericeras) reveliereanus (Courtiller,1860) MMG:SaK 16896 from the lower Turonian of the Briessnitz Formation, Leubnitz, Germany. A. Outer whorl in ventral (A1), lateral (A2), and apertural (A3) views; the fracture at which the outer whorl separates from the inner whorl (arrow) and an umbilical tubercle (UT) are marked. B. Inner whorl in lateral (B1, B3) and apertural (B2) views; the umbilical tubercle (UT) and the position of the fracture shown in A2 are marked by arrow.

Fig. 10. Representative antidimorphs: [m] = microconch, [M] = macroconch of the acanthoceratid ammonoid Spathites (Jeanrogericeras) reveliereanus Courtiller, 1860); based on (A) MMG:SaK 5256 in lateral (A1) and apertural (A2) views and (B) MMG: SaK 5230 in lateral (B1) and apertural (B2) views. Key features of both antidimorphs are listed (see text for further explanation).