Abeliella 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 : 48-49

Abeliella Mägdefrau, 1937

Type ichnospecies

Abeliella riccioides Mägdefrau, 1937 , by subsequent designation in Häntzschel (1962).

Original diagnosis

n/a

Emended diagnosis

Strictly dichotomously branching boring system, running at or closely below the surface of osteic substrates. From a single point of entry, galleries of nearly constant diameter ramify without anastomosis and may show slight lateral widening towards the periphery of the trace.

Original description

Strictly dichotomously ramifying cavity system with an entrance at its “base”. Diameter of tunnels 4–8 µm. [Translated from German]

Remarks

Despite their minute size, these traces were already illustrated in detail in the mid-19 th century by Rose (1855) and Kölliker (1860) in transparent fossil fish scales (see reproduction of original figures in Fig. 17 A–B). Mägdefrau (1937) established two ichnospecies, A. riccioides and A. procera , both from fossil fish scales. Häntzschel (1975), in the second edition of the trace fossil volume of the Treatise on Invertebrate Paleontology, claimed that it was him in the first edition of the trace fossil volume of the Treatise ( Häntzschel 1962) who should be regarded as the first author of Abeliella , based on the assumption that the original description by Mägdefrau is to be considered a nomen nudum due to the missing designation of a type ichnospecies. However, the designation of a type ichnospecies only became a requirement in 2000 with the 4 th edition of the ICZN, and Mägdefrau’s original description is thus readily valid.

Unlike all other dendrinids, A. riccioides and A. procera are developed in phosphatic fossil fish scales, teeth, and jaw or skull elements, thus representing the only dendrinids observed to date in an osteic and not a calcareous substrate. A third ichnospecies, A. bellafurca Radtke et al., 2010 , was established from calcareous skeletal substrate. However, the principal substrate type is considered an important ichnotaxobase at the ichnogeneric level (e.g., Bertling et al. 2006; Höpner & Bertling 2017); thus, this conspicuous ichnospecies is better accommodated in a different ichnogenus. This decision is furthermore supported by the fact that unlike the other two ichnospecies of Abeliella , A. bellafurca is not strictly prostrate, but does develop a considerable vertical expansion in the central part of mature colonies, forming bundles of radiating galleries and thus bearing a close morphological (and biological) resemblance to the cyanobacterial ichnogenus Fascichnus Radtke, 1991 . Dichotomous branching is, although less pronounced, a common feature in several of the ichnospecies of Fascichnus and it thus seems most practical to transfer A. bellafurca to Fascichnus under the new combination Fascichnus bellafurcus .

Corrosion traces similar to Abeliella were described by Elsik (1966, 1971) in another type of substrate, the exine of fossil pollen and spores of Mississippian to Tertiary age. The latter traces have not been treated ichnotaxonomically as yet and should be grouped within a separate ichnogenus when acknowledging the substrate type as a primary ichnotaxobase (see above).

Figures

Fig. 17. Abeliella riccioides Mägdefrau, 1937. A–B. Early illustrations of this trace fossil by Rose (1855) and Kölliker (1860) based on observations of Cretaceous fish scales (reproduced from Rose 1855: pl. I, fig. 5 and Kölliker 1860: pl. XVI, fig. 14). C. Lectotype sample showing numerous specimens in a transparent Oligocene fish scale. D. Close-up of lectotype (arrow) and several paralectotypes, illustrating near-perfect bilateral symmetry of the traces. E. Surface SEM of a Cretaceous echodont tooth, showing the avoidance of tunnels as opposed to true anastomosis (reproduced from Underwood 1999: fig. 2a). F–H. Overview and close-ups of an unidentified Cretaceous fish tooth from the lower Campanian of Höver, Germany, illustrating typical increase in abundance towards the base.