Dendrina Quenstedt, 1849

Type ichnospecies

Talpina dendrina Morris, 1851 (now Dendrina dendrina (Morris, 1851) comb. nov.) by subsequent designation by Häntzschel (1962).

Original diagnosis

n/a

Emended diagnosis

Rosetted boring system, developed closely parallel to surface of calcareous skeletal substrates, with a circular to irregular outline, originating from a single point at the end of a tubular inlet tunnel. Individual galleries vary in width at constant height, ramify and may anastomose or fuse to form a flat central cavity. Fine galleries connect the rosette with the substrate surface, preferentially towards the rounded distal terminations.

Original description

The other group, one may call it Dendrina […], based on its dendritic ramifications, is even more enigmatic, since an entrance can certainly not be found. They are not quite tubes, but merely flattened ramifications, located closely below the surface, not rarely penetrated by Talpinians, and here and there unroofed, in the latter case leaving a rough shallow depression. The figured specimen […] stems from the chalk of Antrim, and shows circular, more ramified, as well as unspecified patchy individuals. [Translated from German]

Remarks

Friedrich von Hagenow (1840) was the first who tackled the conspicuous bioerosion trace fossils in the Upper Cretaceous belemnite rostra from the Isle of Rügen, Germany, by establishing the ichnogenus Talpina with two ichnospecies, T. ramosa and T. solitaria. He also recognised the two most common dendrinids and named them T. foliacea and T. sentiformis. Unfortunately, it appears that he never formally published and figured these two latter ichnospecies, rendering them nomina nuda (Wisshak et al. 2017). The two names only made their way into the literature via citation as “in litt.” (= personal communication) in Geinitz (1849: 108–109) and by indirect reference in Müller (1851: 59–60). Recently, Wisshak et al. (2017) rediscovered syntypes of all four of von Hagenow’s Talpina ichnospecies in collections of the Museum für Naturkunde Berlin and the Naturhistorische Sammlungen Dresden (both Germany), allowing identification of T. foliacea as Dendrina belemniticola and T. sentiformis as Calcideletrix flexuosa, both formally established by Mägdefrau (1937).

The first description and illustrations of Dendrina were provided by Quenstedt (1849: pl. 30, figs 36– 37) whose figures show one belemnite guard (Belemnites mucronatus Schlotheim, 1813) with multiple bioerosion traces specified as Talpina ramosa and Dendrina (Figs 2A, 3A), and another belemnite with T. pungens Quenstedt, 1849, T. solitaria and T. ramosa. The traces are not labelled, thus complicating a correct assignation. Both figures show two morphotypes of dendrinids, the forms later considered by Morris (1851) to be Talpina dendrina and by Mägdefrau (1937) as Dendrina belemniticola (see below). Decades later, Quenstedt (1885: pl. 39, fig. 39) figured another belemnite rostrum (Terebella) with T. pungens, T. solitaria and T. ramosa, as well as Dendrina, this time being clearly labelled (Figs 2B, 3B). The trace labelled as Dendrina is reminiscent of T. dendrina in Morris (1851: pl. IV, figs 6b, 7) (Fig. 2 D–I), whereas the trace corresponding to D. belemniticola in Mägdefrau (1937: pl. IV, figs 1, 6, 8) (Fig. 3D) in turn was not labelled by Quenstedt, albeit interpreted as such by subsequent workers (Nadjin 1969; Voigt 1972; Nestler 1975). The provenance of Quenstedt’s belemnites (Quenstedt 1849) is dubious, and according to the discussion in Voigt (1972) probably neither Antrim (N Ireland), as stated in the figure legend of one of the specimens (Quenstedt 1849: fig. 36) as well as in the original description (see above) and on the label of the material that used to be reposited in the Tübingen collection, nor Rügen (Germany), as stated in the figure explanation of the other specimen (Quenstedt 1849: fig. 37). Instead, it probably originates from some other chalk outcrop, possibly in England. Equally uncertain, but according to Voigt (1972) most likely, is the question of whether or not the original belemnite (Voigt 1972: pl. 2, figs 2–3) is the specimen depicted – with some artistic freedom – by Quenstedt (1849: pl. 30, fig. 37). Both Voigt (1972: pl. 1–2) and Plewes (1996: pl. 22) reinvestigated the original Quenstedt material and provided close-up photographs of the various Dendrina and Talpina specimens (Figs 2C, 3C). Despite an extensive query for the original material in the collections in Tübingen, Munich, Berlin, Frankfurt, Hamburg, London and Aberystwyth (Plewes’ affiliation in 1996, where the specimens were studied last), the whereabouts of the Quenstedt material could not be tracked down and the material has to be regarded currently as lost. Quenstedt neither designated a type ichnospecies, nor provided a diagnosis, both not legal requirements for taxa established prior to 1931 (ICZN 1999). Morris (1851: 87, pl. IV, figs 6b, 7) consequently adopted Quenstedt’s ichnogenus name as a new ichnospecies name under the ichnogenus Talpina von Hagenow, 1840, thereby addressing it as “ Talpina dendrina Quenstedt ”. Based on the practical monotypy of this first nominal species referred to Quenstedt’s bare genus, and by principle of virtual tautonymy, D. dendrina is the type ichnospecies of Dendrina, as previously specified by Häntzschel (1962). However, according to Treatise format, it was therein given in its original ichnogenus combination as Talpina dendrina Morris, 1851 and its assignment as Dendrina dendrina (Morris, 1851) is hereby formally introduced as a new combination.

A related ichnotaxon and potential nomen oblitum (never addressed after 1899) is Talpina rotunda, mentioned without proper description or illustration by Müller (1851: 60) as having a circular shape. However, this very vague morphological description applies to many traces in Cretaceous belemnites and thus does not provide reasonable grounds to seriously consider it a senior synonym of Dendrina belemniticola or D. lacerata, both traces with a quite circular outline. Without a clearly established synonymy, however, it cannot be considered a nomen oblitum either, since this nomenclatural act would require naming a nomen protectum, hence leaving T. rotunda in the nimbus of a nomen dubium.

Between 1859 and 1864, Étallon (Étallon 1859 a, 1859 b, 1864; Thurmann & Étallon 1864) established a total of nine ichnospecies of Dendrina, none of which was adopted by subsequent workers. This is because all of Étallon’s ichnospecies were based on rudimentary descriptions only and with or without only an inadequate illustration. Hence, they have to be regarded as nomina dubia. One of these ichnospecies, i.e., D. elongata, Étallon himself (Étallon 1959 b) assigned to Talpina, and another, i.e., D. stellata, he synonymised with D. dendrina. Likewise of dubious status are the related ichnogenera Cobalia (comprising two ichnospecies) and Haguenowia (four ichnospecies) described by Étallon (1859 a), both also entirely based on nomina dubia. In an attempt to locate the original type material, the collections in Paris, Lyon, Gray, Porrentruy, Bern and Basel were consulted, apparently none of which houses the material in question, which thus needs to be considered as currently lost. Considering these circumstances, unfortunately there appears no feasible way forward but to regard Étallon’s dendrinids as nomina dubia, altogether.

The first extant relatives of Dendrina were observed in bivalve shells from the Golfe de Gascogne off the French coast and elsewhere by Fischer (1875), who established the ichnotaxon Dendrina europaea. This dendrinian is herein classified within Nododendrina as N. europaea comb. nov.

Mägdefrau (1937), in his important review on endolithic bioerosion traces “Lebensspuren fossiler ‘Bohr’ –Organismen”, established four ichnospecies of Dendrina, including the widely used D. belemniticola, thereby finally formalising the second original Quenstedt (1849) dendrinian (see above). The very small D. incomposita is herein addressed as Nododendrina incomposita comb. nov., and Mägdefrau’s D. minor is synonymised with it. Dendrina anomala is considered a new combination under Calcideletrix, another one of Mägdefrau’s (1937) ichnogenera.

Based on an SEM analysis of epoxy-resin casts, Hofmann (1996) refined the diagnosis of Dendrina and, following a splitter approach, disregarded D. dendrina and D. belemniticola while establishing a series of morphologically very similar new ichnospecies of Dendrina. Most of these are herein considered as a reflection of the ontogeny and the morphological variability of the former two ichnospecies and thus as their junior synonyms. Another one of Hofmann’s dendrinids, i.e., D. brachiopodicola, is herein synonymised with Calcideletrix flexuosa Mägdefrau, 1937. In the same year, Plewes (1996) attempted to establish D. ordoplana, which is, however, also morphologically reminiscent of D. dendrina, and apart from that was never formally published, creating a nomen nudum.

In conclusion, among the 22 ichnospecies originally erected under the umbrella of the ichnogenus Dendrina, merely three of them remain nomenclaturally robust and morphologically sufficiently distinctive (i.e., their geometry cannot be explained by ontogenetic stages of the same ichnospecies or by differences in the substrate) to be considered ichnotaxonomically distinct and valid. These are D. dendrina (Morris, 1851), D. belemniticola Mägdefrau, 1937 and D. lacerata Hofmann, 1996. Two further original ichnospecies of Dendrina are now grouped within Calcideletrix and Nododendrina (see above). Dendrina is distinguished from all other Dendrinidae by its tubular inlet tunnel, leading to the centre of a radiating rosette of constant thickness and with peripheral branches not tapering to fine terminations.

An invalid junior homonym, Dendrina Costa in Fornasini, 1898, was established for a foraminiferan. No substitute name was proposed and, according to Loeblich & Tappan (1964), the genus is presently considered synonymous with Cibicidoides Thalmann, 1939. In the botanical nomenclature, Dendrina was established by Fries (1832) as a valid homonym with two species (D. flava and D. pulla) of ascomycete fungi.