Miocene period fossil forest of Wataria found in Japan

An exquisitely preserved fossil forest from Japan provides missing links and helps reconstruct a whole Eurasia plant from the late Miocene epoch.

A well-preserved fossilized forest from the late Miocene epoch was found in Japan, near the Ota bridge on the Kiso river. (Photo: Toshihiro Yamada)

Complete plant fossils are seldom found as a single piece, as wood, leaves, flowers, fruits, seeds, or pollen detach easily from plants. This results in leaves and trunks having separate scientific names. Putting together the different parts to reveal the complete plant is like putting together a jigsaw puzzle. Connecting these dots and reconstructing plants is important to establish their taxonomic identity—their place in the Tree of Life.

Exposed riverbed from where the fossils were found. (Photo: Toshihiro Yamada)

A research group led by Professor Toshihiro Yamada from the Department of Earth and Planetary Sciences, Hokkaido University, found an exceptionally well-preserved fossil of a Wataria parvipora forest which was almost exclusively accompanied by fossils of Byttneriophyllum leaves. Their findings were published in the journal Scientific Reports.

Green area highlights the Mizunami group, a geological formation of which the Kani Basin, where the study site was located, is a part. (adapted from Nishino et al., Scientific Reports, June 22, 2023)

In 1994, the Kiso River (in Minokamo City, Gifu Prefecture) underwent a historic drought, in the process of which 400 in situ fossilized tree stumps surfaced. While most of the stumps have since been submerged, the team examined 137 stumps, of which 130 were identified as 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,” says Yamada.

Line drawing of one of the Byttneriophyllum tiliifolium leaves found abundantly in the fossil forest. (Nishino et al., Scientific Reports, June 22, 2023)

The team also found that the stumps were exclusively covered by a bed of one specific kind of leaf. Byttneriophyllum tiliifolium is a leaf-fossil species belonging to the mallow family (which includes cotton, cacao and durian). Fossils of this leaf were widely distributed throughout Eurasia during the Miocene and Pliocene epochs and the discovery of the Wataria fossil forest indicates that Byttneriophyllum tiliifolium are the leaves of Wataria.

Surface view of the fossil leaf Byttneriophyllum tiliifolium which was found abundantly in the fossil forest, indicating a strong link to Wataria parvipora.  (Nishino et al., Scientific Reports, June 22, 2023)

“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 paraautochthonously on the forest floor—they got fossilized where they fell,” Yamada elaborated.

Wataria parvipora showing annual rings. It is one of the characteristics that helped the scientists in identifying the wood-fossil. (Nishino et al., Scientific Reports, June 22, 2023)

Research by other groups has shown that the fossil fruit Banisteriaecarpum giganteum is related to Byttneriophyllum tiliifolium. Future research will focus on searching for Banisteriaecarpum giganteum in Japan, as this discovery would provide strong evidence that all three are part of the same species.

Original Article: Nishino Megumi, et al. An exceptionally well-preserved monodominant fossil forest of Wataria from the lower Miocene of Japan. Scientific Reports. June 22, 2023.
DOI: 10.1038/s41598-023-37211-z

Source: Press News

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