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3D morphology of post mortem acrothoracican borings in Famennian heterocorals : a morphological diversification or a continuum ichnospecies?

Dworczak Patrycja G., Jarochowska Emilia, López Correa Matthias, Berkowski Błażej

Annales Societatis Geologorum Poloniae

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2022

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Vol. 92, No. 3

233--252

EN

Barnacle borings were found in six heterocoral skeletons. They are present as small (up to 2.9 mm long), slender, pouch-shaped borings with tapering, slit-like openings. The investigated borings were made by acrothoracican cirripedes, which mostly do not have a shell and bore into hard substrates to protect their “naked” bodies. The first occurrence of borings in skeletons of the heterocoral Oligophylloides Różkowska, 1969 from the Upper Devonian Tafilalt Platform was reported recently by Weyer in 2016. Here, the authors present the results of a detailed study of heterocoral remains with numerous acrothoracican borings from Jebel Bou Ifarherioun (Famennian, Anti-Atlas, Morocco). The borings were found on the basal part but also on broken branches and stems of the heterocoral corallum and occurred post mortem. There is no indication of a syn vivo coral-barnacle interaction with borings in tissue-covered areas. The authors used micro-CT scans to visualize the 3D morphology of the pits, their orientation, and distribution. Additionally, the 3D morphology of an assemblage of 75 pits was used to carry out ordination and cluster analyses, which showed that previously proposed ichnospecies may be a continuum of morphological variability. In the basis of measurements by the present authors, the studied borings do not fit any known ichnotaxa. The absence of bourrelets excludes the possibility that the borings studied belong to the ichnogenus Rogerella Saint-Seine, 1951. Hence, the results seem to contradict a synonymization that was proposed by Bromley and D’Alessandro (1987) and subsequent authors and leave room for further research and discussion on this topic. Although the inferred boring organism is a filter feeder and, thus, depends on currents, the authors did not find a preferential orientation of the borings. The samples considered here are the best-preserved Devonian barnacle borings to date.

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Entobia ichnofacies from the Middle Miocene carbonate succession of the northern Western Desert of Egypt

El-Hedeny M., El-Sabbagh A.

Annales Societatis Geologorum Poloniae

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2018

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Vol. 88, No. 1

1--19

EN

A bed of Middle Miocene (Serravallian) lagoonal facies with well-developed patch reefs is described from a section at the Siwa Oasis, northern Western Desert of Egypt. It is well-exposed in the middle Siwa Escarpment Member of the Marmarica Formation and displays remarkable bioerosion structures that show abundant ichnofossils. Nine ichnotaxa, belonging to four ichnogenera, were identified: two correspond to the clionaid sponge boring Entobia (E. laquea and E. ovula), five to the bivalve boring Gastrochaenolites (G. lapidicus, G. torpedo, G. cluniformis, G. hospitium and G. cf. orbicularis) and two to the annelid-worm boring Maeandropolydora (M. sulcans) and Trypanites (T. weisei). In addition, traces of the boring polychaete worm Caulostrepsis and the boring acrothoracican barnacle Rogerella were recorded. These ichnoassemblages have been assigned to the Entobia ichnofacies. The organisms bored into a hard, fully lithified carbonate substrate in a low-energy, shallow-marine environment. The ichnotaxa associations indicate water depths of a few metres (<10 m) and a very low sedimentation rate in a lagoonal setting during a Serravallian regressive cycle.

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A new etching trace from the Savignone Conglomerate (Oligocene), NW Italy, probably produced by limpet gastropods

Uchman A., Rattazzi B.

Acta Geologica Polonica

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2018

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Vol. 68, no. 4

651--662

EN

A new ichnogenus and ichnospecies (Solealites ovalis) of etching trace is preserved on the surfaces of clasts from the Savignone Conglomerate (Oligocene) in the Palaeogene Piemonte Basin in NW Italy. It is a shallow, oval depression with a central elevation, which was produced probably by limpet gastropods and served as their home scar, but other gastropods or even sea anemones are not excluded as the trace makers. The conglomerate is interpreted as a deposit of a fan delta, whose clasts have been bioeroded in an intertidal and shallow subtidal shore zone and redeposited to the deeper sea.

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In defence of an iconic ichnogenus : Oichnus Bromley

Wisshak M., Kroh A., Bertling M., Knaust D., Nielsen J. K., Jagt J. W. M., Neumann C., Nielsen K. S. S.

Annales Societatis Geologorum Poloniae

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2015

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Vol. 85, No. 3

445--451

EN

By establishing the bioerosion ichnogenus Oichnus, Richard Bromley (1981) addressed ‘small round holes in shells’ and catalysed a series of still ongoing discussions on ichnotaxonomical principles. In a recent revision by Zonneveld and Gingras (2014), Oichnus was rejected, together with Tremichnus Brett, 1985 and Fossichnus Nielsen, Nielsen and Bromley, 2003, by means of subjective synonymisation with the presumed senior synonym Sedilichnus Müller, 1977. However, Sedilichnus is nomenclaturally unavailable, because it is an atelonym (conditionally proposed). In addition, reinvestigation of the type material of ‘Sedilichnus’ shows that it probably describes variably shaped oscula and thus is a genuine morphological character of the host sponge Prokaliapsisjanus, rather than a bioerosion trace fossil. The ichnogenera Oichnus and Tremichnus are re vised, leading to the synonymisation of Balticapunctum Rozhnov, 1989 with Tremichnus, and of Fossichnus with Oichnus. The refined ichnogeneric diagnoses return Oichnus to complete or incomplete bioerosive penetrations in calcareous skeletal substrates, commonly interpreted as praedichnia with or without signs of attachment, while Tremichnus (now including O. excavatus) exclusively refers to shallow pits passing into echinoderm skeletons that are interpreted as domichnia or fixichnia.

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Bioerosional ichnotaxa and the fossilization barrier

Bromley R. G., Nielsen K. S. S.

Annales Societatis Geologorum Poloniae

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2015

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Vol. 85, No. 3

453--455

EN

For the establishment of a new ichnogenus or ichnospecies, the type material shall be fossil, not unfossilized material. This is not always possible, because the transition between the two states, the fossilization barrier, is extremely vague defined. In most fossil material, this is not a problem. However, in the case of bioerosion structures (borings, rasping traces, attachment scars in hard substrates), the problem is serious. For example, when does a sponge boring in an oyster shell be come fossilized? The question arises when Recent and sub-Recent materials are considered. Two examples are discussed. (1) Microborings are described and named in foraminifera dredged from the sea floor. In this material, it is not possible to distinguish between “fossilized” and “unfossilized” foraminifera. Bioturbation and other processes may have mixed recently dead, Pleistocene and older foraminifera in the sea-floor sediments. (2) Small, characteristic borings are made by slipper limpets in pagurized gastropod shells. The structures would constitute a new ichnospecies of Oichnus, but these borings have not been found in “fossilized material” and the borings therefore remain nameless. Because bioerosion structures constitute “ready-made fossils”, it is suggested that the onset of fossilization be equated with the death of the bioeroding tracemaker.

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Epi- and endobionts on the late Silurian (early Pridoli) stromatoporoids from Saaremaa Island, Estonia

Vinn O., Wilson M. A.

Annales Societatis Geologorum Poloniae

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2012

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Vol. 82, No. 3

195--200

EN

A diverse sclerobiont community is described from the Kaugatuma Formation (lower Pridoli) of Saare- maa, Estonia. The stromatoporoid substrates studied here vary from low-domical to high-domical shapes. The community is numerically dominated by microconchids, which may have been characteristic of the sclerobiont fauna in the Pridoli of Baltica. Palaeoconchus aff. tenuis, Anticalyptraea calyptrata, Aulopora sp., sheet-like bryozoans, branching bryozoans, erect bryozoan holdfasts, rugosans, favositids, discoidal crinoid holdfasts, star- like crinoid holdfasts and sheet-like stromatoporoids encrust the domical stromatoporoids. Endobionts are repre- sented by embedded, symbiotic rugosans, Aulopora sp., and two rare borings Trypanites.