DATE2026.11.10 #Press Releases

Discovery of the World's Oldest “Brooding Snails” from a Dinosaur Excavation Site in Fukui

—Ovoviviparity and Diet 120 Million Years Ago: Miraculous Fossil Preservation Brought About by Wildfires—

Summary

A research group led by Dr. Taro Yoshimura, a Researcher at The University Museum, The University of Tokyo (at the time of the research: a doctoral student at the Graduate School of Science, The University of Tokyo), conducted a detailed analysis of a fossil assemblage of viviparid freshwater snails recovered from a dinosaur excavation site in the Lower Cretaceous Kitadani Formation of the Tetori Group (approximately 120 million years ago), located in Katsuyama City, Fukui Prefecture. As a result, they discovered numerous embryos preserved intact inside the mother shells, providing the first direct evidence from the Mesozoic fossil record of internal brooding via ovoviviparity, similar to that seen in extant viviparid snails. Furthermore, using micro-X-ray CT, the researchers revealed a developmental gradient corresponding to growth stages within the brood pouch and identified sexual dimorphism, in which females grew larger with more inflated shells. Additionally, analysis of digestive tract contents revealed a flexible, omnivorous diet combining grazing on attached algae, suspension feeding, and detritus feeding (feeding on organic sediment). Evidence was also found suggesting that they utilized the empty shells of contemporaneous large bivalves as shelters (or feeding sites on carcasses). Furthermore, the researchers elucidated why such extremely fragile embryonic shells, protoconchs, and gut organic matter remained intact in a freshwater environment where calcium carbonate readily dissolves: alkaline ash derived from frequent wildfires at that time flowed into rivers and lakes, thereby neutralizing and buffering the acidity of the water. These findings are groundbreaking in demonstrating that the sophisticated reproductive ecology and dietary adaptations of freshwater invertebrates date back to the age of dinosaurs, while also showing that wildfire deposits can create unique taphonomic preservation windows in inland aquatic environments.

Paleoecological reconstruction of the Kitadani Formation of the Tetori Group during the Early Cretaceous (approximately 120 million years ago)
Courtesy of Fukui Prefectural Dinosaur Museum / Illustration by Kohei Futaka

Journals

Journal name	Communications Biology
Title of paper	Exceptional preservation reveals the deep-time reproductive ecology and trophic breadth of Early Cretaceous viviparid gastropods