Cretaceous dicotyledonous fossil woods from Hokkaido, Japan, and early evolution of wood characters

Abstract

Fossil woods are abundant in the Cretaceous Yezo Group in Hokkaido, Japan. From 144 dicotyledonous wood samples, 14 species representing 10 genera were identified. All 14 species and four (Castanoradix, Frutecoxylon, Nishidaxylon, Sabiaceoxylon) of the 10 genera were new. Five genera (Icacinoxylon, Magnoliaceoxylon, Paraphyllanthoxylon, Plataninium and Ulminium) were already known from the Cretaceous and Tertiary, and one (Hamamelidoxylon) was known only from the Tertiary. Two specimens of Icacinoxylon kokubunii from the Albian (Lower Cretaceous) were the oldest records of dicotyledonous wood in Japan. The species distribution by age was: Albian: one species; Cenomanian: four species in four genera; Turonian: 10 species in eight genera; Coniacian: seven species in six genera; Santonian: eight species in seven genera. The study extended our knowledge of wood structural diversity among the early dicotyledons in the mid-Cretaceous in the northern hemisphere.