Abeliella riccioides Mägdefrau, 1937

Fig. 17

Abeliella riccioides Mägdefrau, 1937: 60, text-fig. 1, pl. V, fig. 1.

Without name – Rose 1855: 9, pl. I, fig. 5a–d. — Kölliker 1860: 228, pl. XVI, fig. 14. — Seward 1898: 127, fig. 27A (reproduced from Rose 1855). — Siverson 1993: 3, pl. 4, figs 1–2, 9–12.

Abeliella riccioides – Häntzschel 1962: W228, fig. 142-7 (reproduced from Mägdefrau 1937); 1975: W123, fig. 77-6 (reproduced from Mägdefrau 1937). — Underwood et al. 1999: 71, fig. 2a–d. — Buatois et al. 2017: 161, fig. 75G.

non Abiella sp. – Kutscher 1972: 27, figs 9–10 (= Talpina ramosa).

Original diagnosis

n/a

Emended diagnosis

Distinctly regular and bilateral symmetrical ramification pattern, strictly dichotomous and prostrate, with angle of bifurcations decreasing towards the periphery of the trace. Nearly constant tunnel diameter and only weakly widened gallery terminations.

Original description

In fossil fish scales, already Kölliker (1860) observed this very delicate and regular boring system, for which he holds a fungus responsible. These are star-shaped cavity systems (ca 0.25 mm in diameter) with a strictly dichotomous branching pattern. The peripheral terminations are weakly widened. Access to the tunnel system, which is oriented parallel to the surface in the interior of the scales, is located in the centre of the star. [Translated from German]

Supplementary description

Underwood et al. (1999) added the following observations and morphometrical data: “These borings have a distinctive radial pattern, with regular dichotomous bifurcations. The central point of the boring network is usually just below the surface of the substrate. Two, or more rarely three, initial branches contact the surface of the bone and thereafter stay as surface borings. The borings are either round or flattened in cross section and between 3 and 7 μm across, retaining a constant width throughout the network. These borings bifurcate at intervals of 20 to 40 μm, with each branch dichotomously bifurcating at a similar distance, giving a very regular pattern. On a flat substrate, the proximal bifurcations enclose angles of between 90 and 120 degrees, although the angle between the more distal branches of the boring tends to be more acute, down to about 30 degrees.” The size of the traces was measured in the holotype and from figures in Kölliker (1860) and Underwood et al. (1999) to range from 0.1 to 0.5 mm.

Type material, locality and horizon

Traces in fish scale from the Oligocene of Salbe, Germany, deposited in the collections of the Institut für Geowissenschaften und Geographie, Halle, Germany (MLU.Mäg1937.V.1). Because the fish scale contains numerous individuals of A. riccioides (syntypes), the complete and readily typical specimen shown in Fig. 17D (arrow) is hereby designated as the lectotype.