Меловой период

Shigeta Y., Nishimura T. (2014) A new species of Anagaudryceras (Ammonoidea, Gaudryceratidae) from the lowest Maastrichtian of Hokkaido, Japan // Paleontological Research, vol. 18, no. 3, pp. 176–185, July 1, 2014
doi:10.2517/2014PR017

http://www.kahaku.go.jp/english/researc ... 223418.pdf