Dendrina belemniticola Mägdefrau, 1937

Wisshak, Max, 2017, Taming an ichnotaxonomical Pandora’s box: revision of dendritic and rosetted microborings (ichnofamily: Dendrinidae), European Journal of Taxonomy 390, pp. 1-99 : 19-21

Dendrina belemniticola Mägdefrau, 1937

Fig. 3

Dendrina belemniticola Mägdefrau, 1937 (partim): 55, pl. IV, fig 1 (top individual = lectotype). Dendrina orbiculata Hofmann, 1996: 73 , pl. 7, figs 1–4 .

Dendrina constans Hofmann, 1996: 76 , pl. 7, figs 5–6, pl. 8, figs 1–2 .

Dendrina – Quenstedt 1849 (partim): 470, pl. 30, figs 36–37 bottom individuals). — Pictet 1857: 535, pl. CX, fig. 2b. — Radwański 1972 (partim): 257, figs 1–4 .

Without name – Quenstedt 1885 (partim): 496, pl. 38, fig. 39 (unlabelled individual above trace labelled “r”). — Dacqué 1921 (partim): 457, fig. 214 (reproduced from Quenstedt 1849).

Dendrina belemniticola – Häntzschel 1962 (partim): W230, fig. 144-2 (reproduced from Mägdefrau 1937); 1975 (partim): W127, fig. 78-7 (reproduced from Mägdefrau 1937). — Nadjin 1969 (partim): 138, fig. 53 (reproduced from Quenstedt 1849), pl. III, fig. 7, pl. IV, figs 1 (top trace, reproduced from Mägdefrau 1937). — Voigt 1972 (partim): 95, pl. 1, figs 3e, 6 (fig. 3e reproduced from Quenstedt 1849), pl. 2, figs 1d , (above trace labelled “T”) ( fig. 1 reproduced from Quenstedt 1849, fig. 6 reproduced from Quenstedt 1885), pl. 5, fig. 4. — Nestler 1975 (partim): 108, fig. 159b (reproduced from Quenstedt 1849). — Schnick 1992 (partim): 112, pl. 3, figs 5–6, pl. 4, figs 1–5 . — Reich & Frenzel 2002: 207, pl. 50, fig. 8. — Schulz 2003: 391, fig. 9.10.71 (top centre). — Košt’ák 2004: 32, fig. 5. — Girod & Rösner 2013 (partim): 280, fig. 12. — Rudolph 2014 (partim): 18, fig. 23. — Buatois et al. 2017: 161, fig. 75A (lectotype). — Wisshak et al. 2017: 131, figs 3/1–3, 4/3.

Rosetten-Form D – Hofmann & Vogel 1992: 56, pl. III, fig. C.

Rosetten-Form E – Hofmann & Vogel 1992: 57, pl. V, figs A–B.

Dendrina orbiculata – Glaub et al. 2007: fig. 21.4/2.

Original diagnosis

n/a

Emended diagnosis

Rosette nearly circular in outline, with densely spaced galleries of relatively constant width and radiating from the centre, bi- and trifurcating at acute angles. Galleries anastomose readily where they meet, or coalesce to produce broad fused sections in the centre of the trace.

Original description

Galleries form rosettes 1.5 to 6 mm in diameter, radiating from the centre of the rosette, thereby multiply branching in irregular intervals. Galleries are 0.08 to 0.25 mm wide, run parallel to the surface of the rostrum, and neither penetrate deeper nor connect to the surface. The diameter of the galleries, measured vertically to the surface of the rostrum, is around 0.05 mm. [Translated from German]

Supplementary description

Plewes (1996) provided the following description: “Cast material of this ichnospecies shows that the rosettes are prostrate and remain the same thickness across the diameter of the trace. As rosettes become larger, the inner portions coalesce to become a single, flattened hole with an intricate outline and occasional open, elongate portions, remnants of the branches within the rosette. The width of the branches is relatively constant where the branches have not fused, with an average width of 187 µm (n = 9, SD = 50.19). Fine tubules from the branches lead to the surface. Diameter of the trace can be up to 3 to 4 mm. Its thickness is approximately 140 µm to 200 µm. Individual borings seem able to avoid other borings.” SEM investigations of epoxy casts by Hoffman (1996), for the junior synonyms D. orbiculata and D. constans , added the observations that the rosette is developed 40 to 80 µm below the substrate surface, is connected to the latter by rhizoidal appendages of 20–40 µm in diameter, and that there is often a radial slit-like incision developed to either side of the centre in many specimens. The proximal end of this slit is where the initial inlet tunnel connects to the trace, as exhibited, unmentioned, in both of Hofmann’s junior ichnospecies holotypes (see also Schnick 1992). The diameter of the rosette ranges from 1.5 to 4 mm ( Plewes 1996; Hofmann 1996, for junior synonyms D. orbiculata and D. constans ); the maximum diameter of 6 mm, as given by Mägdefrau (1937), included specimens of D. dendrina .

Type material, locality and horizon

Until recently, all three belemnites of the original type material of D. belemniticola were considered lost and only the original plate negatives remained deposited in the collections of the Institut für Geowissenschaften und Geographie in Halle, Germany ( MLU. Mäg1937. IV.1, 6 and 8). Plewes (1996) consequently considered the individuals on Quenstedt’s original ( Quenstedt 1849: pl. 30, fig. 36) as holotypes (e.g., Fig. 3C ) – an invalid “ neotype ” designation in an unpublished thesis. Fortunately, two of the types (corresponding to Mägdefrau’s pl. IV, figs 1 and 6) were rediscovered hidden among other belemnites in the systematic collection at Halle, making a neotype designation unnecessary. However, because Mägdefrau’s material comprised specimens of both D. belemniticola and D. dendrina , and owing to the circumstance that he did not specify a holotype, the upper specimen on his plate IV, figure 1 ( MLU. Mäg1937. IV.1) is hereby formally designated as the lectotype ( Fig. 3D ). The other specimen on this figure, as well as the specimens figured on Mägdefrau’s plate IV, figures 6 and 8, are within the morphological range of D. dendrina . The lectotype is preserved in an upper Senonian belemnite from Rosenthal near Peine, Germany.

Remarks

The original description actually represents an amalgam of D. dendrina and D. belemniticola , as Mägdefrau (1937) did not have the methods at hand to study the minute connections to the substrate surface.

In comparison to D. dendrina , the rosette of D. belemniticola is always nearly circular in outline, and the more densely spaced galleries are less wide and have acute branching points, thus being more radially oriented. In addition, the fusion of galleries is very common, as are the resulting anastomoses, both rarely exhibited characters in D. dendrina . The trace is commonly solitary and tiers are rarely developed. Distinction is complicated in the case of juvenile specimens or mature specimens with a relatively loose and unfused branching.

Figures

Fig. 3. Dendrina belemniticola Mägdefrau, 1937. A. Original illustration of belemnite with various traces including D. belemniticola (arrow; reproduced from Quenstedt 1849: pl. 30, fig. 36); provenance unresolved. B. Original amalgam, including D. belemniticola (arrow; reproduced from Quenstedt 1885: pl. 38, fig. 39). C. Re-illustration of original Quenstedt Dendrina (reproduced from Plewes 1996: pl. 22, fig. 3); inlet tunnel roughly at 11h in this and the following four sub-figures. D. Lectotype of D. belemniticola in an upper Senonian belemnite from Rosenthal near Peine, Germany (compare to Mägdefrau 1937: pl. IV, fig. 1). E. Holotype of junior synonym D. orbiculata Hofmann, 1996. SEM of epoxy cast of an upper Campanian belemnite from Lüneburg, Germany. F. Paratype of junior synonym D. constans Hofmann, 1996. SEM of epoxy cast of a lower Maastrichtian belemnite from Lüneburg, Germany. G. Holotype of junior synonym D. constans. SEM of epoxy cast of a lower Maastrichtian belemnite from Lüneburg, Germany. E–G illustrate the morphological range of D. belemniticola from almost completely fused radiating galleries, to partially fused galleries forming anastomoses, to rarely fused radiating galleries. H. Detail of partly obscured inlet tunnel connecting to centre of a paratype of junior synonym D. orbiculata. SEM of epoxy cast of an Upper Cretaceous belemnite from Lüneburg, Germany. I. Rarely observed overlap of D. belemniticola in a lower Maastrichtian belemnite from Rügen, Germany. J. Specimen of D. belemniticola (left) next to a D. dendrina (right) at the very tip of a lower Campanian belemnite from Höver, Germany.

Fig. 1 (page 7). Morphological characters of dendrinid microborings with respect to overall shape and symmetry of the trace, its vertical profile, openings to the substrate surface, orientation of entrance tunnel (where present), branching pattern and surface texture (in order of decreasing relevance as ichnotaxobase).