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Cretaceous-Period Ammonite Had Bizarre Shell

| Paleontology

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A new species of nostoceratid ammonite that lived during the Coniacian stage of the Cretaceous period has been identified from fossils found in Japan.

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Named Yezoceras elegans, the new ammonite species swam in the Cretaceous seas between 89 and 86 million years ago.

“This is the first species of the genus Yezoceras to be discovered in 44 years,” said lead author Dr. Daisuke Aiba and his colleagues from the Mikasa City Museum and Yokohama National University.

Yezoceras elegans belongs to the family Nostoceratidae, a diverse group of heteromorph ammonites known for the bizarre coiling of their shells.

The species had loosely coiled whorls, a wide umbilicus, and two prominent tubercle rows concentrated in the lower part of the whorls.

“Nostoceratidae includes more than 15 genera,” Dr. Aiba said.

“Many genera belonging to this family have basically helically coiled whorls, others have three-dimensionally meandered whorls.”

 

The fossilized shell of Yezoceras elegans. Image credit: Aiba et al., doi: 10.2517/2020PR008.

Dr. Aiba and co-authors found eight specimens of Yezoceras elegans in the Haboro area in Hokkaido, northern Japan.

They think that this and two other species in the genus, Yezoceras nodosum and Yezoceras miotuberculatum, were endemic to the northwestern Pacific region.

Yezoceras elegans might have originated from Yezoceras nodosum, judging from the stratigraphic correlation,” they said.

“The restricted occurrences of three Yezoceras species in Hokkaido suggest that the speciation of Yezoceras occurred in the northwestern Pacific realm during the Coniacian age.”

The discovery of Yezoceras elegans is reported in a paper in the journal Paleontological Research.

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Daisuke Aiba et al. 2021. A New Species of Yezoceras (Ammonoidea, Nostoceratidae) from the Coniacian in the Northwestern Pacific Realm. Paleontological Research 25 (1): 1-10; doi: 10.2517/2020PR008

 

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