Mammites Laube and Bruder, 1887

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

Genus Mammites Laube and Bruder, 1887

Type species: Ammonites nodosoides Schlüter, 1871 ; lower Turonian of Westphalia, northern Germany; by monotypy .

Mammites nodosoides ( Schlüter, 1871)

Figs. 5 , 6 .

1871 Ammonites nodosoides ; Schlüter 1871: 19, pl. 8: 1–4.

1981 Mammites nodosoides ( Schlüter, 1871) ; Wright and Kennedy 1981: 75, pl. 17: 3; pl. 19: 3; pl. 20: 4; pl. 22: 4; pl. 23: 1–3; pl. 24: 2, 3; text-figs. 19B, 23, 24. [with full synonymy].

2013 Mammites nodosoides ( Schlüter, 1871) ; Wilmsen and Nagm 2013: 666, figs. 17G, H, 18A, B.

2014 Mammites nodosoides ( Schlüter, 1871) ; Wilmsen and Nagm 2014: 218, fig. 10a, b.

2014 Mammites nodosoides ( Schlüter, 1871) ; Amédro and Delvaque 2014: 144, pl. 3: 1, 2.

2016 Mammites nodosoides ( Schlüter, 1871) ; Kennedy and Gale 2016: 278, fig. 18.

2018 Mammites nodosoides ( Schlüter, 1871) ; Matrion 2018: 195, fig. 129A, B.

2019 Mammites nodosoides ( Schlüter, 1871) ; Kennedy and Kaplan 2019: 49, pls. 19–21.

Material.— In total, 194 specimens from the lower Turonian Cretaceous ), Briessnitz Formation, Germany, Dresden, locality: Leubnitz (81 specimens), Leutewitz (three specimens), Lockwitz (107 specimens), and Omsewitz (three specimens), were systematically studied. Due to preservational issues, only 119 specimens could be used for statistical analyses. Repository numbers are provided in SOM 4 .

Measurements.—See SOM 4.

Description.—This large species is very abundant in Saxony; the largest specimen reaches a diameter of 384 mm, but there are also many small individuals with D <50 mm. With a UD of 26.3%, M. nodosoides is moderately involute. The Wb/Wh ratio is 0.8 on average, which defines a slightly compressed, rectangular whorl cross-section. The umbilicus is moderately deep and has a broadly rounded shoulder and a convex wall. The number of umbilical tubercles ranges from seven to eleven per whorl; they are the source for pairs of weak and broad ribs. Those ribs carry prominent rounded inner- and clavate outer ventrolateral tubercles. During ontogeny, the inner ventrolateral tubercles migrate up the venter and merge with the outer ventrolateral ones. The umbilical tubercles bloat during ontogenetic growth. The result of this development is that adult individuals of M. nodosoides show large umbilical and ventrolateral horns. The venter is flat to slightly concave, and the flanks are flat and parallel.

Stratigraphic and geographic range.— Mammites nodosoides is the index ammonite of the eponymous upper lower Turonian standard ammonite zone and was recorded from several European countries, the Middle East, northern Africa, Madagascar and North as well as South America ( Wright and Kennedy 1981).

Statistical analyses.—After the measurement and/or calculation of nine relevant morphological variables, classical clustering and linear discriminant analysis were executed on 119 specimens (see Fig. 6 and SOM). In the classical clustering, two large groups emerged (group 1 and 2). The first group is characterized by large, the second one by medium- and small-sized specimens with respect to maximum diameters. The Cophenetic distance (the smallest distance between two clusters) reaches the high maximum value of 60 at the last junction of all clusters in one big joint cluster. This value might have been caused by the high number of individuals. In the LDA diagram, two scatter plots of the large groups are visible. The values of both groups are broadly distributed; they overlap in the lower part of the diagram.

Figures

Fig. 5. Photographic illustration of typical large (A) and small (B) specimens of the acanthoceratid ammonoid Mammites nodosoides (Schlüter, 1871) from the lower Turonian of the Briessnitz Formation, Leubnitz, Germany. A. MMG: SaK 5200 in lateral (A1) and apertural (A2) views. B. MMG: SaK 5203 in lateral (B1, B3) and apertural (B2) views.

Fig.6. Statistical test of potential dimorphism in Mammites nodosoides (Schlüter, 1871) based on 119 specimens.The repository number of each specimen is given on top of the diagram. A. Classical clustering; the red color characterises particularly small individuals with D = 33–65 mm in between the large group of potential microconchs. 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.