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First record of blister pearls in the oyster Hyotissa hyotis (Linné, 1758) from Pliocene deposits at Sidi Brahim, Lower Chelif Basin (north-west Algeria)

Khalili Rachid, Vinn Olev

Geologos

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2023

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Vol. 29, No. 3

167--172

EN

Fossil pearls are rare but important palaeoecological indicators in proving the former presence of parasites. A single right valve of Hyotissa hyotis from the Pliocene of Sidi Brahim shows numerous blister pearls inside the adductor muscle imprint. At the same locality, numerous shells with smooth adductor scars and without any blisters, have been collected. The structures in the studied valve can be assigned to blister pearls with high confidence due to their similarity to other Cenozoic pearls from Austria. The blister pearls likely formed as a reaction to parasite infestation. It is possible that some parasites especially targeted areas associated with the adductor muscles in the oyster genus Hyotissa, because similar blister pearls have previously been described in a congeneric species, H. squarrosa, from the Miocene of Austria.

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The late Cenomanian oyster Lopha staufferi (Bergquist, 1944) – the oldest ribbed oyster in the Upper Cretaceous of the Western Interior of the United States

Hook S. C., Cobban W. A.

Acta Geologica Polonica

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2016

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Vol. 66, no. 4

609--626

EN

Lopha staufferi (Bergquist, 1944) is a medium-sized, ribbed, Late Cretaceous oyster with a slightly curved axis and a zigzag commissure; it appears suddenly and conspicuously in upper Cenomanian rocks in the Western Interior Basin of the United States. At maturity, the ribs on both valves thicken into steep flanks that allow the oyster to increase interior volume without increasing its exterior footprint on the seafloor. Lopha staufferi is the first (earliest) ribbed oyster in the Late Cretaceous of the Western Interior, but has no ancestor in the basin. It disappears from the rock record as suddenly as it appeared, leaving no direct descendent in the basin. In the southern part of the basin where it is well constrained, L. staufferi is restricted stratigraphically to the upper Cenomanian Metoicoceras mosbyense Zone (= Dunveganoceras conditum Zone in the north). Lopha staufferi has an unusual paleogeographic distribution, occurring in only two, widely scattered areas in the basin. It has been found at several localities near the western shoreline of the Late Cretaceous Seaway in west-central New Mexico and adjacent Arizona, and in localities 1,900 km (1,200 mi) to the northeast near the eastern shoreline in northeastern Minnesota, but nowhere in between. In west-central New Mexico and adjacent Arizona, L. staufferi is a guide fossil to the Twowells Tongue of the Dakota Sandstone.

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Oyster-bioimmured ammonites from the Upper Albian of Annopol, Poland: stratigraphic and palaeobiogeographic implications

Machalski M., Kennedy W. J.

Acta Geologica Polonica

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2013

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Vol. 63, no. 4

545--554

EN

Ammonites Mortoniceras (Subschloenbachia) sp. are preserved as attachment scars on the oyster shells from the topmost portion of the Albian succession at Annopol, Poland. These oyster-bioimmured ammonites show a closest affinity to the representatives of Mortoniceras (Subschloenbachia) characteristic of the upper Upper Albian Mortoniceras perinflatum Zone. No ammonites indicative of the uppermost Albian–lowermost Cenomanian Praeschloenbachia briacensis Zone are recorded. Thus, the hiatus at the Albian–Cenomanian boundary at Annopol embraces the latter zone. The presence (and dominance) of Mortoniceras in the upper Upper Albian ammonite assemblage of Annopol suggests that the representatives of this Tethyan genus could migrate into the epicratonic areas of Poland directly from the Tethyan Realm, via the Lwów (Lviv) region.