Dictyoporus nodosus 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 : 44-46

Dictyoporus nodosus Mägdefrau, 1937

Fig. 15

Dictyoporus nodosus Mägdefrau, 1937: 55 , pl. IV, fig. 10.

Cliona fenestralis Elias, 1957: 383 , pl. 40, fig. 2.

Cicatricula retiformis Palmer & Palmer, 1977: 185 , fig. 6.

Dictyoporus garsonensis Elias, 1980: 273 , figs 1–3 .

Dictyoporus nodosus – Häntzschel 1962: W230, fig. 144-5 (reproduced from Mägdefrau 1937); 1975: W127, fig. 78-5 (reproduced from Mägdefrau 1937). — (?) Pugaczewska 1965: 75, pl. I, fig. 1 ; 1970: 427, pl. I, fig. 1 . — Nadjin 1969: 155, pl. IV, fig. 10 (reproduced from Mägdefrau 1937). — Plewes 1996: 191, pl. 36, figs 1–7 . — Buatois et al. 2017: 161, fig. 75D (holotype). — Breton et al. 2017: 46, fig. 3D.

Without name – Lindström 1979: 154, fig. 2A–C. — Girod & Rösner 2013: 282, fig. 15c.

Calcideletrix breviramosa – Ghare 1982: 132, pl. 1, fig. 6. — (?) Košt’ák 2004: 32, fig. 12 (poor illustration).

Calcidelatrix flexuosa – Plewes 1996 (partim): 186, pl. 33, figs 3, 5, pl. 34, figs 5–6. — (?) Košt’ák 2004: 32, fig. 11 (poor illustration).

Dendroid-Form A – Bundschuh 2000: 63, pl. 8, figs 5–8.

Dendroid-Form C – Bundschuh 2000: 66, pl. 9, figs 3–5.

Original diagnosis

n/a

Emended diagnosis

Overall shape as well as gallery diameter and mesh-size varies but generally decreases towards the periphery of the trace. Branching points flattened parallel to the substrate surface and with rounded outline. Peripheral branches taper to pointed ends and have a jagged appearance. Galleries either developed as open channels and/or prostrate tunnels with few rhizoidal connections to the substrate surface.

Original description

Channels 0.06–0.08 mm in diameter, with swellings at branching or crossing points. [Translated from German]

Supplementary description

The morphology of this ichnospecies is quite variable and partly dependent on the ontogeny of the trace or the type of substrate. All of this variability is evident in the Upper Cretaceous material alone and concerns the overall shape of the traces, ranging from radial symmetrical and circular to oval specimens ( Fig. 15C ) to more irregular outlines with little discernible centre ( Fig. 15 A–B, D–F). It also concerns the degree and the mesh size of the anastomoses, with a general trend towards smaller size at the periphery of the trace, which often goes along with a decrease in gallery diameter ( Fig. 15 C–F). Most conspicuously, the variability is expressed in the preservation of the galleries as open surficial etchings vs true endolithic tunnels, including the combination of both orientations within one and the same trace, either laterally grading into each other ( Fig. 15D ) or developed as multiple tiers ( Fig. 15 E–F). Published data on the diameter of the trace range from 0.5 to 14 mm ( Elias 1957, for junior synonym Cliona fenestralis ; Palmer & Palmer 1977, for junior synonym Cicatricula retiformis ; Bundschuh 2000 for synonyms ‘Dendroid-Form A’ and ‘Dendroid-Form D’), and tunnel diameters were specified to range from 60 to 80 µm ( Mägdefrau 1937; Plewes 1996).

Type material, locality and horizon

The holotype ( Fig. 15 A–B) is preserved in a Belemnitella mucronata (Schlotheim, 1813) rostrum from the Upper Cretaceous of Misburg near Hannover, Germany, deposited in the collections of the Institut für Geowissenschaften und Geographie, Halle , Germany ( MLU.Mäg1937.IV.10 ).

Remarks

As noted above, the considerable morphological range of D. nodosus questions the validity of a number of other ichnotaxa characterised by strongly anastomosing networks of channels or shallow tunnels. As a consequence, a number of ichnospecies are herein lumped within D. nodosus as subjective junior synonyms. This concerns Cliona fenestralis , established by Elias (1957) as a sponge biotaxon, based on a single natural cast in a Carboniferous brachiopod. The holotype is currently lost but the morphological resemblance to D. nodosus is evident from the original illustration alone (reproduced in Fig. 15G ). The second junior synonym is Cicatricula retiformis , reported by Palmer & Palmer (1977) from an Ordovician hardground ( Fig. 15H ). Its preservation as an anastomosing network of open channels does not merit retaining a separate ichnospecies, let alone ichnogenus. The third junior synonym is Dictyoporus garsonensis , established by Elias (1980) based on traces in an Upper Ordovician rugose solitary coral and characterised as a combination of larger, surficial to epilithic anastomoses grading into smaller, endolithic tunnels in the periphery of the trace ( Fig. 15I ). Reinvestigation of the holotype showed that the diagenetic alteration and state of preservation render such a distinction problematic, and the body fossil preservation of epilithic algae thalli (according to Elias the part of the trace shown at the top of Fig. 15I ) is herein questioned. These features more likely present mineralised infills of either shallow etched channels or exposed parts of endolithic tunnels, and both of these features are well within the morphological range of D. nodosus . The trace also appears to be very common in Silurian skeletal carbonates, such as reported by Bundschuh (2000) under the informal names Dendroid-Form A and C, with the two forms again illustrating the morphological variability of D. nodosus , which agrees with the appearance of this trace in epoxy casts of Cretaceous specimens.

Figures

Fig. 15. Dictyoporus nodosus Mägdefrau, 1937. A–B. Overview and close-up of the holotype in an Upper Cretaceous belemnite from Misburg, Germany. C. Specimen with lower degree of anastomosis, but better defined centre; same belemnite as holotype of Calcideletrix flexuosa Mägdefrau, 1937. D. Large specimen in a shell of the bivalve Inoceramus Sowerby, 1814 from the upper Campanian of Kronsmoor, Germany, showing a combination of open channels and endolithic tunnels. E–F. Incipient and transmission light micrographs of a pyritised specimen in an aptychus from the lower Campanian of Höver, Germany, showing surficial channels, a deeper tier of endolithic tunnels and variability in tunnel diameter. G. Holotype of junior synonym Cliona fenestralis Elias, 1957, preserved as natural cast in a Late Mississippian brachiopod (currently lost; reproduced from Elias 1967: pl. 40, fig. 2; scale bar derived from original description). H. Holotype of junior synonym Cicatricula retiformis Palmer & Palmer, 1977 on a slab of Ordovician hardground, displaying readily anastomosing channels with a decrease in mesh size towards the periphery. I. Holotype of junior synonym Dictyoporus garsonensis Elias, 1980, preserved in an Upper Ordovician rugose coral.

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).

Fig. 2. Dendrina dendrina (Morris, 1851) comb. nov. A. Original illustration of belemnite with various traces, including D. dendrina (arrows; reproduced from Quenstedt 1849: pl. 30, fig. 36); provenance unresolved. B. Original amalgam, including D. dendrina (arrows and label “d”; reproduced from Quenstedt 1885: pl. 38, fig. 39). C. Re-illustration of original Quenstedt Dendrina (reproduced from Plewes 1996: pl. 22, fig. 5). D. Original illustrations of Talpina dendrina (= D. dendrina; reproduced from Morris 1851: pl. IV, figs 4–7; 5 = Talpina ramosa; 6a = Trypanites solitarius). E. Morris’ original belemnite from the Upper Cretaceous of Norfolk, UK, including the lectotype of D. dendrina (encircled). F–G. Close-up of lectotype under incipient and transparent light; the inlet canal is clearly visible. H–I. Three paralectotypes in the same belemnite. J–K. Planar and oblique views of the holotype of junior synonym D. fluensis Hofmann, 1996, illustrating the typical multi-tier occurrence, irregular branching, and meandering galleries; SEM of epoxy cast of a belemnite from the lower Maastrichtian at Kronsmoor, Germany. L. Holotype of junior synonym D. crassa Hofmann, 1996, within the morphological range of D. dendrina; SEM of epoxy cast of a belemnite from the lower Maastrichtian at Kronsmoor, Germany.

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.