Masanobu Yamamoto, Kath Ficken, Marianne Baas, Hendrik-Jan Bosch, and Jan W. de Leeuw. “Molecular Palaeontology of the Earliest Danian at Geulhemmerberg (the Netherlands)”. Netherlands Journal of Geosciences, vol. 75, Jan. 1996, pp. 255-67, https://njgjournal.nl/index.php/njg/article/view/12377.