Japanese fossil forest could reconstruct Eurasian plants from late Miocene

The researchers thoroughly examined 137 stumps, 130 of which were recognized as fossil specimens of Wataria parvipora. 

“Wataria is a wood-fossil, recognized by its distinctive growth rings, abundant parenchyma rays, and lack of resin canals. In the 2000m2 fossil site, these stumps accounted for 95% of the tree remains, indicating that we discovered a forest predominantly of this species,” said Professor Toshihiro Yamada, who led this study.

The fossils were replete with preserved leaves 

The researchers discovered a bed of Byttneriophyllum tiliifolium leaves exquisitely preserved in the fossils. Plant fossils with leaves are scarce since the leaves detach easily from the plant over time. The authors add that this might sometimes result in distinct scientific names for leaves and stems — even if they belong to the same species. 

As per the statement, Byttneriophyllum is a member of the Malvaceae, or the mallows, which also include cotton, cocoa, and durian. Plants of the Malvaceae family were extensively dispersed over Eurasia from the Miocene to the Pliocene geological periods. 

The fossil reveals that Byttneriophyllum tiliifolium mostly dominated the ancient Wataria forest. 

“We found that 98% of the fossil leaves found at the site belonged to Byttneriophyllum, strongly indicating that they were shed from the parent trees. We could see that the leaves were deposited para autochthonously on the forest floor—they got fossilized where they fell,” Yamada elaborated. 

Before this study, other researchers discovered that the fossil fruit Banisteriaecarpum giganteum may be connected to Byttneriophyllum tiliifolium.

According to the researchers, further excavation efforts to find Banisteriaecarpum giganteum in Japan would aid in determining if these two are members of the same species. Moreover, it could help them fill in the gaps in species' taxonomic identification and ultimately locate "their place in the Tree of Life."

The results were published in the journal Scientific Reports.

Study Abstract:

Byttneriophyllum tiliifolium is a leaf fossil-species of the family Malvaceae that was distributed widely throughout Eurasia from the Miocene to the Pliocene. An affinity to some Malvadendrina subfamilies has been suggested for Byttneriophyllum-bearing plants, but remains to be clarified due to insufficient information on other organs. Here, we report an exceptional lower Miocene fossil locality in Japan where a monodominant forest of the wood fossil-species Wataria parvipora flourished. Notably, the forest floor was covered by a bed consisting almost exclusively of B. tiliifolium. We observed occurrence modes of B. tiliifoliumin this bed that confirmed that these leaves were deposited parautochthonously. These observations imply a biological connection between B. tiliifolium and W. parvipora. The wood and leaf characters together might narrow the affinity of Byttneriophyllum-bearing plants down to Helicterioideae within the Malvadendrina, although it is also possible that Byttneriophyllum-bearing plants constitutes an extinct lineage which is characterized by a combination of morphological traits found in several extant lineages. Our results suggest that Byttneriophyllum-bearing plants started to inhabit swamps no later than the end of the early Miocene when the global temperature was getting warmer.