Professor Toshihiro Yamada of Hokkaido University Graduate School has discovered two new species of seaweed from the Miocene period (approximately 1800 million years ago) in a stratum in Minamichita Town, Aichi Prefecture, which are the world's first fossils of such species.
Seaweed (monocotyledons that grow in the ocean) first appeared about 8100 million years ago. However, because seaweed decomposes easily, it is difficult for it to remain as fossils, and the formation process of the current blue carbon* ecosystem, which is considered essential for the stability of the global environment, remained unknown.
In the 1980s, a large number of fossils of deep-sea fish, sea urchins, sea lilies, starfish, crustaceans, etc. were discovered around Shizaki, Minamichita-cho, Chita-gun, Aichi Prefecture, and an illustrated catalog (Fossils of the Shizaki Group, compiled by the Tokai Fossil Research Group) was published in 1993. Many fossils were listed in the "Unclassifiable Fossils" category.
Professor Yamada, who has been a fossil enthusiast since childhood, had long thought that the fossil specimen was a "yarrow" ever since he first came across it as a high school student. However, when he recently looked back at the illustrated catalog, he realized that it was seaweed. He acquired two of the specimens from their owners, and further investigated the Shizaki Formation, obtaining one more seaweed specimen. Based on observations of morphological characteristics such as leaf shape, leaf sheath, and vein density, he reported one specimen as a new species, Morus kakimura, and the remaining two as a new genus and species, Aichiisohaguki.
These two species are thought to be the closest ancestors of Ryukyu Usugamo (Zangusa) and Thalassodendrone, which are the main species of seaweed in the tropical and subtropical regions today. In addition, fossils of bryozoans and oysters are attached to the leaves of Aichiisohaguki. This is the first time in the world that the prototype of the blue carbon ecosystem seen today in tropical and subtropical regions was formed by 2 million years ago.
The "Morizaka Group" is said to be a "treasure box of fossils" as "a layer where fossils of organisms with no fossil information can be obtained." It is expected that this will lead to progress in research on fossil fauna and elucidation of the history of shallow-water ecosystems.
Editor's note: Carbon absorbed and stored by marine organisms
Paper information:【Aquatic Botany】Seagrass fossils from the lower Miocene Morozaki Group in Aichi Prefecture, central Japan
