What the inner ear of Europasaurus reveals about its life

Like its famous relative Brachiosaurus, Europasaurus belongs to the group of sauropod dinosaurs, which include the largest land-living animals that ever lived on Earth. Some representatives could attain body lengths of around 40 metres, possibly weighing up to 80 metric tons. However, Europasaurus holgeri was a comparatively small sauropod species with a body height of up to three metres.

Europasaurus, which lived about 154 million years ago on an island in modern-day Germany, constitutes the first dinosaur for which the evolutionary phenomenon of insular dwarfism was demonstrated: large island-dwelling animals become smaller over a number of generations. Possibly, Europasaurus represents the fossil counterpart to the recent Sumatran tiger and rhino, which are smaller than their closest relatives from the mainland.

Fossil skull remains of very young to fully-grown adults have been examined

For the study that has just been published, scientists from the universities of Greifswald and Vienna examined fossil braincase material of Europasaurus, belonging to different age stages: from very young and small individuals to adult ones. In order to learn more about these long extinct animals, the researchers reconstructed the cavities that once housed the brain and inner ears with the aid of micro-CT.

The part of the inner ear being responsible for hearing, the lagena or cochlea, turns out to be relatively long in Europasaurus. This suggests that these animals had a good sense of hearing, rendering intraspecific communication crucial and gregarious behavior likely.

Europasaurus was probably precocial

Another part of the inner ear is relevant for the sense of equilibrium and consists of three tiny arches. The scientists found that the inner ear cavities within very small specimens resemble the respective cavities of adults in form and size. "This supposes that very young individuals of Europasaurus strongly relied on the ability to equilibrate already. Some considered skull remains were so tiny (~2 cm) that they may belong to hatchlings, which renders the species precocial," says Sebastian Stumpf from the University of Vienna. Whereas some sauropods weighed several tens of tons more than their newly-hatched offspring (posing a lethal threat for the latter), the hatchlings of Europasaurus may have immediately followed the herd in some approximation.