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Acorn barnacles (Crustacea, Thoracica, Balanomorpha) from the Eocene and Oligocene of the Isle of Wight and Hampshire (United Kingdom) and Manche, northern France

Gale Andrew Scott

Acta Geologica Polonica

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2021

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Vol. 71, no. 2

153--174

EN

Balanomorph cirripedes from the Eocene–Oligocene of the Hampshire Basin (United Kingdom) and the Middle Eocene of the Cotentin Peninsula, Manche (France) are described. A new genus, Vectibalanus, is founded, with the type species Balanus unguiformis J. de C. Sowerby, 1846; assigned to this are also Balanus erisma J. de C. Sowerby, 1846 and Vectibalanus mortoni sp. nov. In addition, a new species of Lophobalanus Zullo, 1984, L. fresvillensis sp. nov., is described. This is the first record of that genus from outside the eastern USA and the oldest species known to date. Cladistic analysis of 24 morphological characters suggests that Vectibalanus unguiformis is sister taxon to a group comprising the most derived balanomorph taxa, and thus represents an important transition in the evolution of the group, with the initiation of development of a complex parietal wall structure. Vectibalanus unguiformis was evidently adapted to low salinity habitats (10-30 ppt), and is the oldest known brackish water barnacle. The other species (V. erisma, V. mortoni sp. nov.) occupied more clearly marine environments (>30 ppt). Balanomorph barnacles appeared simultaneously in the Priabonian (Upper Eocene) of the Gulf and Atlantic seaboards of the USA and northwest Europe, which probably represents a northerly migration from Tethys.

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The miniature echinoid trace fossil Bichordites kuzunensis isp. nov. from early Oligocene prodelta sediments of the Mezardere Formation, Gokceada Island, NW Turkey

Demircan H., Uchman A.

Acta Geologica Polonica

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2012

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Vol. 62, no. 2

205-215

EN

The pascichnial trace fossil Bichordites kuzunensis isp. nov. occurs as an epichnial complex structure in early Oligocene prodelta sediments of the Thrace Basin in Gokceada Island, northwest Turkey. It displays characteristics of irregular echinoid burrows such as overall shape and a double meniscate filling with a chevron dorsal suture, in addition to the feature typical of the so far monospecific Bichordites Plaziat and Mahmoudi, 1988, that is a single central core around a single drainage tube. Its miniature size can be related to the small size of the tracemaker (ontogenic feature) or to its dwarfism in a stressed deltaic environment (palaeoecological feature). Its occurrence indicates a period of fully marine conditions during accumulation of the deltaic sediments of the Mezardere Formation.

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Kiss of death of a hunting fish : trace fossil Osculichnus labialis igen. et isp. nov. from late Eocene - early Oligocene prodelta sediments of the Mezardere Formation, Thrace Basin, NW Turkey

Demircan H., Uchman A.

Acta Geologica Polonica

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2010

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Vol. 60, no. 1

29-38

EN

The trace fossil Osculichnus labialis igen. et isp. nov. occurs as hypichnial pairs of uneven bilobate mounds in early Oligocene prodelta sediments of the Thrace Basin. Osculichnus is generally elliptical or crescentic in outline and has two lip-like lobes: a smaller and a larger one, which are separated by an undulate furrow. Herein, it is interpreted as a hunting trace (praedichnion) of a fish penetrating a surficial sand layer and into an underlying mud horizon. The fish hunted for small endobenthic bivalves and perhaps other invertebrates such as polychaetes. Penetration into surficial mud rather than sand resulted in poorly preserved variants of this trace fossil, whose median furrow is commonly not visible. The probability of fish trace makers is supported by experiments.