Argentine researchers double invertebrate fossil record in Patagonia, discover 16-million-year-old snail species

In the Patagonian valley of Bryn Gwyn, where whitish sediments hold the geological memory of sixteen to twenty-one million years, a team of Argentine researchers has fundamentally expanded what we know about the ancient seas that once covered the southern tip of the continent. The scientists at the Patagonian Institute of Geology and Paleontology, working methodically through four years of fieldwork and laboratory analysis between 2021 and 2024, have doubled the documented invertebrate fossil record at one of Argentina's most significant paleontological sites—and in doing so, they have uncovered a species of sea snail that rewrites the evolutionary timeline of its entire genus.

The location itself carries weight in the history of Argentine science. Bryn Gwyn, a name borrowed from Welsh meaning "white hill," has been known to geologists and paleontologists for more than a century. The site's fame rested almost entirely on its vertebrate fossils—the teeth of sharks, the bones of whales and dolphins—specimens dramatic enough to capture the attention of local residents and tourists alike. But the invertebrates, the smaller creatures that formed the true foundation of those ancient ecosystems, had been largely overlooked, dismissed as scientifically unglamorous and difficult to study systematically. The new research, led by scientists including Damián Pérez, Mariel Ferrari, Nicolás Farroni, Aylén Allende Mosquera, and José Cuitiño, changed that entirely.

The team identified twenty-seven distinct taxonomic groups at Bryn Gwyn—a doubling of the previously known diversity. Among these were oysters, sea urchins, crabs, and two major groups of marine invertebrates, brachiopods and scaphopods, that had never before been documented in sediments of this age in the region. But the most striking discovery was a new species of carnivorous sea snail, formally named Buccinanops halleri in honor of geologist Miguel Haller. The genus Buccinanops is common in the waters off Argentina today, easily observed crawling along the coasts near Puerto Madryn and Puerto Pirámides. Yet its fossil record was nearly nonexistent—only a handful of specimens dating back a few thousand years had ever been found. The discovery of Buccinanops halleri in sediments dated to fifteen to sixteen million years ago represents the oldest known record of the entire lineage, pushing back the evolutionary history of this genus by millions of years.

What makes the discovery scientifically significant is not merely its age but its distinctiveness. The ancient snail bears a particular ornamentation—fine circular lines etched across its shell—that does not appear in any living species of Buccinanops today. This detail, visible to the naked eye in photographs, provided the crucial clue that the researchers were looking at something genuinely new, something that had evolved and then disappeared from the fossil record, leaving only its modern descendants to inhabit the Patagonian seas. Pérez explained to journalists that this ornamental difference was the key that unlocked the species' identity and significance.

The broader context of these findings reveals something equally important about the world sixteen million years ago. The Mioceno epoch, to which the Gaiman Formation belongs, represents the last great warm period in Earth's history before the planet entered a prolonged cooling trend and the ice ages began. The Patagonian seas of that time were somewhat warmer than they are today, and the fauna that inhabited them—the complete ecological networks that the researchers have now begun to reconstruct—shared characteristics with marine communities found in other Patagonian formations, in Santa Cruz province and southern Chubut. This suggests that vast regions of southern Argentina experienced similar environmental conditions, shaped by the same rise in sea level that occurred during the early Mioceno.

The work also reflects a broader shift in how paleontology is conducted in Argentina. Twenty years ago, the field was smaller, more fragmented. Now, with more researchers in place and a growing emphasis on interdisciplinary collaboration, scientists can ask more complete questions about ancient ecosystems. They can move beyond cataloging the spectacular finds—the whale bones, the shark teeth—and instead reconstruct the entire web of life that surrounded those larger creatures. Pérez emphasized that this kind of research is never the work of a single person but rather the product of a coordinated team, each member contributing specialized expertise.

Patagonia itself stands as one of the world's most important fossil repositories, a place where continuous rock sequences preserve nearly two hundred million years of geological history, from the first dinosaurs to the present day. The new findings from Bryn Gwyn add another layer of detail to that vast archive, filling in gaps that had gone unnoticed for generations. As researchers continue to examine the invertebrate fauna of the Mioceno, they will be able to compare what they find in Patagonia with marine communities from other regions—the south of Brazil, other parts of the continent—and build an increasingly precise picture of how life organized itself in the ancient seas before the world grew cold.