Dolphins are seen swimming at Evans Bay in Wellington, New Zealand, March 28, 2022. Photo:Xinhua

Previously unknown species of dolphin swam the oceans 20 million years ago, including in waters that covered Switzerland, today a land-locked country at the heart of Europe, researchers said Tuesday.

Back then, Switzerland was part of an island landscape, with its low-lying parts covered in ocean teeming with fish, sharks and dolphins, and with mussels and sea urchins lining the seabed.

After examining around 300 fossils of whales and dolphins found in Switzerland and dating from this period, researchers from Zurich University's paleontological institute discovered two previously unknown species, the university said.

Combing through fragments of teeth, vertebrae and bones found in layers of marine sediment, known as the Upper Marine Molasse, the researchers sought out the less commonly found bones from the inner ear, since they allow species to be classified.

"We managed to identify two families of dolphins previously unknown in Switzerland," paleontologist Gabriel Aguirre said in the statement.

Using micro-computed tomography, a 3D imaging technique, the researchers were able to reconstruct the softer organs around the hard ear bones, creating 3D models of the ears.

In the study, published on the PeerJ scientific publishing website, the researchers determined that the extinct animals are related to the sperm whales and ocean dolphins living today.

AFP