An oddly shaped fossil in Hokkaido turned out to be a new species of ammonite, spiral-shaped marine creatures from ancient times, researchers said.
The newly identified ammonite, classified as a “heteromorph,” lived in the Cretaceous Period (145 million to 66 million years ago) and features a shell of an elongated silhouette.
A specimen of the same species had also been discovered in Wakayama Prefecture.
Daisuke Aiba, a chief researcher with the Fukada Geological Institute based in Tokyo’s Bunkyo Ward, was working for the Mikasa City Museum in Hokkaido when he came across an uncommonly shaped ammonite fossil in the repository of his workplace.
The Mikasa City Museum owns a collection of more than 4,000 fossil pieces, many of them ammonites. The fossil in question had long been preserved there without being identified.
“It just came to me, the moment I saw it, that it likely represents a new species,” Aiba, 36, said.
More fossils, however, would be required for closer research.
Using inscriptions on the museum’s fossil specimen labels as a clue, Aiba went on expeditions in northwestern Hokkaido between 2017 and 2023 and collected five more fossilized ammonites with similar features.
He also enlisted the help of fossil collectors and ended up gathering 13 individual ammonite specimens in Hokkaido.
After scrutinizing them, he described the fossils in a paper he published in August as representing Eubostrychoceras perplexum, a new species.
The ammonites of the species measure between 1 and 4 centimeters in shell height. They were all found in geological formations from the Santonian Age (86.3 million to 83.6 million years ago).
Comparison of the collected fossils showed that as nymphs, the ammonites of the species had straight shells. As they grew, they turned into tightly coiled shapes.
Aiba learned that a fossilized individual of the same species had also been found in Aridagawa, Wakayama Prefecture, and was preserved at the Wakayama Prefectural Museum of Natural History.
This showed the species was distributed outside Hokkaido as well.
“I hope to collect more fossilized specimens of the new species and their relatives to find out about their evolution path,” Aiba said.
AloJapan.com