Previously unknown species of dolphins roamed the oceans 20 million years ago, including the sea that covered Switzerland, where hundreds of fossils from that time period have been discovered, researchers from the Institute said on Thursday. Institute of Paleontology of the University of Zurich.

After examining some 300 whale and dolphin fossils unearthed in Switzerland and dating from this period, the researchers identified two previously unknown species, the university said.

Combing through fragments of teeth, vertebrae and bone discovered in layers of marine sediment, paleontologists searched for the rarely found inner ear bones that help classify species.

"We have successfully identified two previously unknown families of dolphins in Switzerland," paleontologist Gabriel Aguirre said in the university statement.

Using computer-assisted microtomography, a 3D imaging technique, the researchers were able to reconstruct the soft tissue around the ear bones, creating 3D images of the appendages.

“It helped us to better analyze the auditory abilities of dolphins,” explained Aguirre.

In their study, published by the scientific site PeerJ, the researchers explain that they have established that the extinct species they have identified are related to sperm whales and dolphins living today.

Twenty million years ago, sharks, fish, dolphins and cetaceans thrived in the sea that covered Switzerland, whose shores were colonized by crustaceans, mussels and sea urchins.

A large amount of fossils have been discovered in the sedimentary layers known as the upper marine molasses.