January 2025: Toothed Whale

Romaleodelphis pollerspoecki Sánchez-Posada, Racicot, Ruf, Krings et Rössner, 2024

Skull

Neogene: Lower Miocene: Ebelsberg Formation, 22 million years

Area Traun-Pucking near Linz, Upper Austria (Austria)

Length 610 mm, breadth 310 mm

Toothed whales (Odontoceti) are mammals adapted to life in the water. From their ancestors 34 million years ago, they inherited streamlined bodies without hind limbs, front limbs modified into flippers, a triangular dorsal fin and the tail fluke, which made them fast swimmers. Today the group comprises more than 70 species, with body sizes ranging from 1.5 m (dolphins) to 20 m (sperm whales). They colonize all oceans and even rivers in Asia and South America. 

Over the course of 34 million years, toothed whales have also produced a large number of groups that are now extinct and only known as fossils. These include the skull shown here, which was recovered from 22-million-year-old rocks in Austria nearly 45 years ago, donated to the Bavarian State Collection in 1992, and has been the subject of extensive research over the last five years. 

We found that the skull belongs to a previously unknown genus and species of prehistoric dolphin, which we have formally described and named Romaleodelphis pollerspoecki. Twenty-two million years ago roamed the Paratethys, a shallow arm of the sea north of the Alps, together with many other organisms. Romaleodelphisalready possessed the typical, highly specialized skull anatomy of today’s toothed whales, i.e.,  significantly elongated jawbones and nasal openings moved far back onto the skull. The dentition extended over the entire length of the snout and consisted of 220-240 uniform, single-pointed teeth. 

A computed tomography scan has made it possible to assess also many of the internal features of the skull. This allowed most of the individual skull bones to be identified, and even the bony labyrinth of the inner ear to be reconstructed and measured in a digital 3D model. The shape of the inner ear indicates that Romaleodelphis was able to receive high-frequency signals, making it one of the oldest known toothed whales with a sense of hearing similar to that of the modern members of this group. These animals can communicate in frequency ranges that are beyond the hearing range of their predators. There may also be a connection with the development of the echolocation typical of toothed whales. It is unclear whether Romaleodelphis already possessed a fat organ, the so-called melon, which is important for echolocation. Because the skull is heavily flattened as a result of the burial and fossilization process, the presence of a depression between the root of the snout and the nostrils (wherethe melon is located in living toothed whales) cannot be confirmed.

This is not the first time that the skull of Romaleodelphis has been on display in the Munich paleontological museum. In fact, it was already presented as the fossil of the month in June 2012, albeit under the name Eoplatanista and with much less information about its anatomy. 

Gertrud Rössner and Michael Krings (SNSB-BSPG München), Catalina Sánchez-Posada (Bogotá, Colombia), Rachel Racicot and Irina Ruf (Senckenberg Forschungsinstitut und Naturmuseum Frankfurt a. Main)