Fossil of a baby sea snail inside a mother’s shell discovered

Research teams from Academia Sinica and National Taiwan University have documented the first discovery of five species of freshwater molluscs in the Lower Pleistocene Tananwan Formation in northern Taiwan. This crucial discovery, which demonstrates that some lineages of present-day freshwater snails were established in Taiwan more than a million years ago, immediately establishes biogeographic links with East Asia.

The discovery includes only the second known global fossil evidence of a juvenile snail shell preserved within its mother’s shell, a rare find that reveals ancient viviparous (live birth) and nurturing behavior in these prehistoric snails. The research is published in the journal Geodiversity.

Dr Chien-Hsiang Lin of Academia Sinica, one of the study’s authors, said these were the oldest freshwater fossil organisms known in Taiwan. The research team compared fossil assemblages from Taiwan with those from East Asia and Japan, confirming the crucial role of the Taiwan Strait land bridge during ice ages. The land bridge acted as a key migratory corridor for freshwater species, highlighting its importance in the dispersal and evolution of East Asian species.

These ancient fossils provide a vital basis for comparison with modern freshwater ecosystems, now threatened by human destruction and invasive species, and serve as a solemn reminder of the need to cherish and maintain these fragile natural systems.

Dr. Chun-Hsiang Chang from the Department of Geology at the National Taiwan Museum of Natural Sciences said: “This study represents a significant advance in the understanding of Taiwan’s freshwater paleontology. While more than 99% of the island’s mollusc fossils are marine, the authors document the first well-described freshwater assemblage from the Early Pleistocene of the Tananwan Formation.

“Through integrated stratigraphic monitoring, detailed morphological analyses, and comparative taxonomy, the team establishes a solid framework for reconstructing the paleoecology of northern Taiwan. The discovery of juvenile shells within adult Sinotaia quadrata – only the second fossil evidence of viviparity among viviparids worldwide – provides a rare insight into ancient reproductive strategies.

“The biogeographic interpretation is equally remarkable: the early presence of S. quadrata in Taiwan implies an earlier faunal exchange with mainland East Asia, probably via recurrent Pleistocene landfall.

“By linking paleontology, stratigraphy, and island biogeography, this work goes beyond taxonomy to address broader evolutionary and environmental questions. It is a landmark contribution that fills a key gap in Taiwan’s Quaternary record and deepens our understanding of the evolution of freshwater biodiversity in the western Pacific.”