On September 17, a team of Peruvian paleontologists unveiled a well-preserved fossil skeleton of the marine dolphin Lomacetus, estimated at 8 to 12 million years old and found in July in the arid Ocucaje Desert south of Lima, an area that was once part of the Pacific Ocean. The fossil measured about three and a half meters in length.
Researchers from Peru’s state Geological, Mining and Metallurgical Institute said the discovery helped them understand the geography of the past and how the coastline changed over millennia. “This finding gives us clear clues that the limits of the current coast were not always the same. Eight million years ago, the climate, the relief, and the coastline were completely different,” said geologist César Chacaltana, according to Exclsior. Over time, tectonic movements and climate changes transformed that ancient seabed into the current desert, where sand preserved the remains.
Lomacetus was a little-studied cetacean from the Miocene, a period that extended from 23 to 5 million years ago. The fossil adds to the limited knowledge about the genus, an extinct dolphin in the family Kentriodontidae, considered an intermediate group in the evolution of modern odontocetes. Researchers said the specimen shared characteristics with porpoises, or sea pigs, that still swim along the Peruvian coast. Although the first records of Lomacetus came from North America, its presence in the South Pacific suggested a wider distribution and raised questions about migratory routes and dispersion patterns during the Miocene.
According to the United States Geological Survey, the middle Miocene (15 to 11 million years ago) was marked by the Middle Miocene Climatic Optimum, which generated warmer and more stable conditions for marine life at mid and tropical latitudes, such as those of present-day Peru. That context favored diverse marine mammals, including cetaceans, sirenians, and sharks.
“We can now investigate how it moved, how it swam, what it ate, and how long it lived,” said paleontologist Mario Gamarra, according to Het Nieuwsblad. Millions of years ago, this area was a sea that functioned as a great natural hotel where different species came to reproduce. The geography, with mountains parallel to the coast, created unique conditions that favored marine life, said paleontologist Mario Urbina.
Peru’s Ocucaje Desert was regarded as a cemetery for ancient marine species and one of the most important paleontological sites in the world. The region hosted a marine ecosystem for about 45 million years, which helped explain its abundance of marine fossils. The area primarily belonged to the Pisco Formation, characterized by marine sediments from the Miocene and Pliocene.
Expeditions in Ocucaje uncovered fossils of four-legged dwarf whales, prehistoric sharks, giant turtles, and river dolphins. Earlier this year, a 9-million-year-old fossil of a great white shark relative was found in the Pisco basin. In April 2024, researchers from the Natural History Museum of the National University of San Marcos presented the fossilized skull of the largest known river dolphin, Pebanista yacuruna, also from Ocucaje and estimated at 16 million years old. That specimen, together with the Lomacetus, offered key evidence to reconstruct the ecological transition from marine to river cetaceans in South America.
The discovery of the Lomacetus added to a series of finds that established southern Peru as one of the most important paleontological deposits in South America. According to the institute’s records, more than 60 percent of the marine fossils found in Peru in the last two decades came from this region.
“These types of findings not only allow us to better understand the natural history of our country but also to understand how marine ecosystems responded to environmental changes over millions of years,” said Gamarra.
The Ocucaje Desert faces conservation challenges. Experts from the institute warned about vulnerability to fossil looting and informal urban expansion. In 2022, the creation of a protected paleontological zone was proposed with the Ministry of the Environment, but the project remained under evaluation.
The preparation of this article relied on a news-analysis system.