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Foss. Stud., Volume 2, Issue 2 (June 2024) – 2 articles

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18 pages, 27267 KiB  
Article
When Abnormality Becomes Perennial in a Reduced Population: The Case of Altudostephanus longicostis gen. et sp. nov. (Valanginian Ammonites, South-Eastern France)
by Didier Bert, Stéphane Bersac, Bernard Beltran and Léon Canut
Foss. Stud. 2024, 2(2), 92-109; https://doi.org/10.3390/fossils2020004 - 25 May 2024
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Abstract
The discovery of the new ammonite Altudostephanus longicostis gen. et sp. nov. around the lower/upper Valanginian boundary (Lower Cretaceous) with a true longitudinal ribs pattern oriented in the direction of coiling is reported here for the first time for the Cretaceous. This character [...] Read more.
The discovery of the new ammonite Altudostephanus longicostis gen. et sp. nov. around the lower/upper Valanginian boundary (Lower Cretaceous) with a true longitudinal ribs pattern oriented in the direction of coiling is reported here for the first time for the Cretaceous. This character rises questions as this type of ornamentation is mainly represented in the Paleozoic or old Mesozoic taxa. Its study shows that it is not a ‘shell accident’ and that it belongs to a particular lineage of Olcostephaninae, in a restricted geographical area and in a progenetic evolutionary context derived from Olcostephanus, which justifies the introduction of the new monophyletic genus Altudostephanus gen. nov. The discovery of a specimen of Passendorferia sp. (Oxfordian, Upper Jurassic) with the same pattern allows us to consider that this capacity could have a genetic cause. It seems that the fixation of this character, otherwise strongly recessive, in A. longicostis gen. et sp. nov. could take place thanks to a founder effect and the drastic numerical reduction in the population. The geological reference section PIG5 (Moriez area, South-Eastern France) is described, and the problem of the conservation of ‘pyritic’ s.l. ammonites is addressed with a proposed methodology allowing their long-term conservation. Full article
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15 pages, 4439 KiB  
Article
The Life and Death of Jamoytius kerwoodi White; A Silurian Jawless Nektonic Herbivore?
by Michael E. Brookfield
Foss. Stud. 2024, 2(2), 77-91; https://doi.org/10.3390/fossils2020003 - 9 Apr 2024
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Abstract
Jamoytius kerwoodi, is a primitive, eel-like jawless vertebrate found uniquely in an Early Silurian (Llandovery epoch; 444–433 Ma) horizon near Lesmahagow, Scotland. This species is a rare component of a low-diversity dominantly nektonic detritus-feeding and herbivorous fauna living over an anoxic bottom [...] Read more.
Jamoytius kerwoodi, is a primitive, eel-like jawless vertebrate found uniquely in an Early Silurian (Llandovery epoch; 444–433 Ma) horizon near Lesmahagow, Scotland. This species is a rare component of a low-diversity dominantly nektonic detritus-feeding and herbivorous fauna living over an anoxic bottom and is found at the transition from a marine-influenced, probably brackish-water, deep-water basin to a shallower-water, less saline and likely freshwater basin. In the absence of true teeth, Jamoytius was probably a detritivore or herbivore feeding on Dictyocaris. Jamoytius may have a common ancestor with living lampreys, especially as their ectoparasitic mode of life might have evolved from ancestral detritivores or herbivores. Full article
(This article belongs to the Topic Problems and Hypotheses in Palaeontology)
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