Whale Fossils Reveal Their Secrets

The first whales appeared some 50 million years ago. Ankylorhiza tiedemani, an extinct species of dolphin with individuals measuring about 4.5 m, is believed to have lived 25 million years ago! A valuable discovery, the fossil provides important clues on the swimming adaptations of today’s whales.

In the article, researcher Robert Boessenecker of the College of Charleston in South Carolina and his team explain that mysticetes and odontocetes (including dolphins) have developed similar adaptations to achieve comparable swimming techniques. These changes occurred independently. Today there are two orders of cetaceans, namely odontocetes (toothed whales) and mysticetes (baleen whales). They have a common ancestor, but the following adaptive traits were not present originally: the shorter tail, the larger number of caudal vertebrae and the shorter humerus of the fins. The Ankylorhiza fossil shows that these evolutions took place in the two orders in parallel.

The researchers point out that these adaptations are quite unique. For example, they cannot be seen in the lineages of other marine mammals such as seals or sea lions.

Other fossils have also been analyzed. The study of the skulls of several species of whales is bringing major advances in the understanding of echolocation. Echolocation, a technique used to hunt prey, amongst other things, is a skill that toothed whales have been able to develop over thousands of years. It consists of emitting and receiving sounds to help the animals get a sense of their surroundings.

A study conducted by multiple researchers, including several from London’s Museum of Natural History, compared the skulls of 84 individuals of present-day cetacean species with those of 78 cetaceans of now-extinct races.

As for baleen whales, their skulls still show asymmetries, but to a lesser extent. Despite these characteristics, researchers still have serious doubts regarding their ability to have already been able to emit the ultrasound necessary for echolocation.

The process of considerably reducing these skull “deformities” required to capture ultrasound remains unclear to scientists. The team speculates that mysticetes skulls may yet undergo further modifications similar to those of toothed whales to improve echolocation abilities in future generations.

This fossil therefore provides insight into some of the many stages of evolution that have occurred over the span of more than 23 million years. The bones of this Ankylorhiza reveal the remarkable adaptability of these cetaceans.