Brazilian researchers identify 400-million-year-old mollusk species in Paraná

In a paleontological site tucked into the Jardim Giana neighborhood of Ponta Grossa—a place locals call Curva 2, known since the 1980s for its abundance of fossils—researchers have identified a mollusk that swam in ancient seas 400 million years ago. The creature, named Actinopteria grahni, is a marine bivalve that predates dinosaurs by roughly 155 million years, making it a window into a world that existed long before the Mesozoic Era began.

The discovery emerged from the work of Elvio Pinto Bosetti, a professor at the State University of Ponta Grossa, and Kevin William Richter, a doctoral candidate in geography at the same institution. They published their findings in the journal Historical Biology on May 19th, capping roughly eighteen months of careful analysis. The species was named to honor Carl Yngve Grahn, a Swedish paleontologist who died in 2025 and whose contributions to similar research in Brazil—particularly his work on the Devonian Escarpment, a geological formation in Paraná—shaped the field.

The actual moment of discovery was almost accidental. Bosetti and Richter were searching for additional specimens of Actinopteria langei, a related mollusk from the same genus that had been found in the area before. Among roughly twenty samples of the known species, one specimen caught the attention of Sandro Marcelo Scheffler, a researcher from the National Museum at the Federal University of Rio de Janeiro, who was collaborating on the project. Scheffler recognized that this particular shell was different—something new.

What distinguished Actinopteria grahni from its cousin required close comparative work. The researchers, joined by Renato Ghilardi from São Paulo State University's Bauru campus, examined shell contours, the shape of the anterior auricle, the posterior expansion, and the radial ornamentation patterns. These morphological details, visible under careful analysis, revealed a species that had never been formally identified before. "Finding the species is luck, right?" Bosetti reflected. "We more or less know where to look, but finding a rare creature is luck."

The discovery opens two distinct paths forward. The immediate goal is to locate more shells of Actinopteria grahni at the same site. If successful, this would allow museums and paleontologists worldwide to reexamine fossils they may have collected and misidentified over the years, potentially revealing how widespread this species was in the ancient oceans. The second possibility is more pragmatic: understanding these ancient marine environments better can point researchers toward natural gas deposits. Bosetti noted that knowledge of where organic matter accumulated in these prehistoric seas offers clues to where oil and gas might be found today, potentially reducing exploration costs.

For now, the work stands as a reminder that even in well-known fossil sites, careful observation and collaboration can yield species unknown to science. A single shell, examined closely enough, can rewrite a small corner of Earth's deep history.