Upper Tithonian ammonites (Himalayitidae Spath, 1925 and Neocomitidae Salfeld, 1921) from Charens (Drôme, France)

Frau, Camille; Bulot, Luc G.; Wimbledon, William A.P.; Ifrim, Christina

doi:10.1515/geoca-2016-0034

Cited by 18 publications

(2 citation statements)

References 10 publications

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“…In any case, the presence of a form somehow comparable to Cordubiceras is particularily noteworthy, since this would be the rst possible record in central Italy of such a genus, which originally was known exclusively from southern Spain (Betic Cordillera: Olóriz & Tavera, 1979;Olóriz & Tavera, 1983;Tavera, 1985). In the literature it has been reported, albeit not described or gured, also in south-western France (Drôme: Frau et al, 2016). Other localities can be added only if one accepts this taxon as a senior synonim of Baeticoceras Geyssant, 1979 ( drawings by F. Venturi); b1, b2, b3) dorsal, ventral and lateral views of Volanoceras volanense (Oppel,…”

Section: Discussionmentioning

confidence: 99%

A Middle Tithonian ammonite faunula from the historical outcrop ofMonte Acuto (Cantiano, Umbro-Marchean Apennine, Italy)

Nannarone,

Bilotta

2024

Preprint

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The Middle Tihonian ammonite assemblage found in a single bank (with a total thickness of about 30 cm and subdivided in two beds), from the classic Monte Acuto outcrop originarily quoted in the second half of the nineteenth century, is here described. From the micritic matrix 20 ammonite specimens were extracted, belonging to 13 species, among which one, here dubitatively ascribed to Cordubiceras, was previously devoid of a formal designation and represents the first possible record of such a genus in central Italy. The fauna is dated to the Volanense Zone of the standard Mediterranean scheme.

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Section: Discussionmentioning

confidence: 99%

A Middle Tithonian ammonite faunula from the historical outcrop ofMonte Acuto (Cantiano, Umbro-Marchean Apennine, Italy)

Nannarone,

Bilotta

2024

Preprint

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“…During the Mesozoic, the Jurassic Perisphinctoidea provide the best-known examples of sexual dimorphism (e.g. Makowski 1962;Callomon 1963;Tintant 1963;Westermann 1964a, b;Elmi 1967;Schweigert 1997;Schweigert et al 2003Schweigert et al , 2007Parent et al 2008aParent et al , b, 2009Zatoń 2010;Frau et al 2015Frau et al , 2016. In this superfamily, the sexual dimorphism is most often expressed by distinct adult size and apertural modi cations.…”

Section: Introductionmentioning

confidence: 99%

Another Lesson From Beautiful Monsters: the Case of 'sex Reversals' in the Ammonoidea and Their Significance

Frau

Boursicot²

2021

Preprint

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Background: Expression of a sexual dimorphism is recognised in various fossil groups of molluscs such as the Ammonoidea, an extinct group of shelled cephalopods. During the Mesozoic, the best documented sexual dimorphic examples are seen in the Jurassic superfamily Perisphinctoidea. It is most usually expressed by distinct adult size and apertural modifications between the antidimorphs. Putative males (otherwise referred to as microconch) are small in size and develop lappets at the end of the shell while the females (macroconch) are larger and bear a simple peristome. Dubious cases are, however, known in that superfamily. They most often relate to taxonomic biases or lack of diagnostic characters, and some others expose ontogenetic anomalies illustrated by ‘sex reversals’ in the shell morphology and ornamentation. Results: The discovery of two specimens of the Callovian Aspidoceratidae Peltoceras athleta (Phillips), having both female and male features, questions the significance and causes of ‘sex reversals’ in the Ammonoidea. The two specimens have started with the macroconch ontogeny of Peltoceras athleta, and show an apparent change toward maleness in the adult, as illustrated by their rounded whorl section, ribs retroversion, fading of the tubercles and lappets typical of the microconchs. Few other cases of female-to-male ‘sex reversal’, as well as male-to-female ones, are known in the fossil record, all belonging to the Jurassic Perisphinctoidea (families Perisphinctidae or Aspidoceratidae). Since all Jurassic Perisphinctoidea are strictly gonochoristic, these ‘sex reversals’ are pathological in nature and are herein referred to as a new forma-type pathology: namely “forma hermaphrodita”.Conclusions: In the absence of any clear evidence of injury or parasitism, we hypothesize that such “forma hermaphrodita” individuals illustrate pathologic cases of intersexuality. Little is known about the ammonoid soft parts, and it is not possible to determine which internal sexual organs occur in specimen having both male and female external shell features. Abnormal feminisation and/or masculinisation also occur in modern cephalopods; the latter also grouping only gonochoric species. This phenomenon is similarly illustrated by a change in the adult body size and a mixing of both female and male structures. In that case, intersexuality is either advantageous in the population or caused sterility. The causes of intersexuality are not clearly established but environmental pollutants are evoked in modern cephalopods because they act as endocrine disrupters. ‘Sex reversals’ and/or non-functional reproductive abnormalities have also been caused by endocrine disrupters in various gonochoric gastropods species, but infestation, genetic abnormalities, temperature fluctuations or viruses are multiple causes which can stimulate or inhibit neural-endocrinal activity by direct gonadal influence, and ultimately lead to feminisation or masculinisation in fishes, isopods, crustaceans, and gastropods as well. Regardless of whether “forma hermaphrodita” is due to an exogenic or endogenic cause, the high frequency of intersex Perisphinctoidea in the Jurassic can be explained by the readily recognition of dimorphic pair, and the easy collection of large and sufficiently preserved fossil palaeopopulations in which intersex specimens have statistically more chance to be found.

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Jurassic integrative stratigraphy, biotas, and paleogeographical evolution of the Qinghai-Tibetan Plateau and its surrounding areas

Li,

Rao,

et al. 2024

Sci. China Earth Sci.

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Upper Tithonian ammonites (Himalayitidae Spath, 1925 and Neocomitidae Salfeld, 1921) from Charens (Drôme, France)

Cited by 18 publications

References 10 publications

A Middle Tithonian ammonite faunula from the historical outcrop ofMonte Acuto (Cantiano, Umbro-Marchean Apennine, Italy)

A Middle Tithonian ammonite faunula from the historical outcrop ofMonte Acuto (Cantiano, Umbro-Marchean Apennine, Italy)

Another Lesson From Beautiful Monsters: the Case of 'sex Reversals' in the Ammonoidea and Their Significance

Jurassic integrative stratigraphy, biotas, and paleogeographical evolution of the Qinghai-Tibetan Plateau and its surrounding areas

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