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1 September 2010 Systematic Position and Origin of the Cretaceous Ammonoid Genus Takahashia
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Abstract

A second specimen of Takahashia eureka Matsumoto, 1984, from the lowest Cenomanian in the Hobetsu area of Hokkaido (Northern Japan), is described, and the diagnosis of the taxon is revised following a careful reexamination of the holotype. The presence of partially developed, minutely crinkled ribs on the shell implies that Takahashia had a close phylogenetic relationship with the long-ranging taxon Lytoceras (upper Sinemurian-Cenomanian), and we therefore assign it to the subfamily Lytoceratidae of the family Lytoceratidae. Evolution of Takahashia from Lytoceras supports the existence of a unique fauna in the North Pacific at the Albian-Cenomanian transition.

© by the Palaeontological Society of Japan
Yasunari Shigeta, René Hoffmann, and Masataka Izukura "Systematic Position and Origin of the Cretaceous Ammonoid Genus Takahashia," Paleontological Research 14(3), 196-201, (1 September 2010). https://doi.org/10.2517/1342-8144-14.3.196
Received: 5 January 2010; Accepted: 1 July 2010; Published: 1 September 2010
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