News about the German “shrink dinosaur”

News about the German “shrink dinosaur”

With a length of only about six meters, Europasaurus was tiny compared to its gigantic relatives 154 million years ago. Illustration: © Davide Bonadonna

On a former island in what is now northern Germany, it had developed into a tiny creature: the Europasaurus is considered a case of island dwarfing among dinosaurs. Researchers have now found out something new about this special representative of the long-necked dinosaurs: the characteristics of the balance organ of the young animals suggest that they started life as precocial and then followed the herd. The paleontologists say that Europasaurs could probably also hear well and possibly communicated with each other.

When unusually small fossils of dinosaurs from the group of sauropods were discovered in a quarry on the northern edge of the Harz Mountains in 1998, it was initially assumed that they were a group of young animals. The long-necked dinosaur family is known to have produced the largest land vertebrates of all time: some sauropods grew to around 40 meters long and possibly weighed 80 tons. But then an examination of the fine structure of the bones discovered in the resin revealed that some of the specimens were fully grown in addition to juveniles. It finally became apparent that about 154 million years ago, a small relative of the brachiosaurs lived on an island in what is now northern Germany: Europasaurus holgeri was only about six meters long and weighed less than a ton.

Island gnomes looked in the head

It is assumed that the short stature was due to the phenomenon of so-called island dwarfing: Large animals sometimes become smaller on islands due to the limited food supply. There are various examples of this from the present and the past. On the islands of present-day Indonesia, for example, there were once pygmy elephants, which, measuring 90 centimeters at the shoulder, were hardly larger than a St. Bernard. In the case of Europasaurus, a sea-level rise in the Jurassic period probably led to the dinosaurs being isolated on an island and dwarfing there.

A research team from the Universities of Greifswald and Vienna has now devoted another study to this interesting species of sauropod. They used high-resolution computed tomography to examine skull remains from found individuals of different ages. As they explain, the reason for choosing this research approach was that there is hardly any other sauropod in the world that has more skull material from different ages. The focus of the study was the cavities where the dinosaurs' inner ears once sat. The paleontologists explain that conclusions about the characteristics of the former soft tissue were possible based on the bony structures.

Europasaurus was probably a precocial

As they report, the analyzes showed that the part of the inner ear responsible for hearing, the lagena or cochlea, was relatively long in Europasaurus. This feature suggests that Europasaurus had relatively good hearing, the scientists say. Exactly what it was used for remains unclear, but it could have played a role in the social behavior of the animals, which probably lived in herds: there could have been intraspecific communication, so the assumption is.

However, the clearest finding relates to the balance organ in the inner ear, which consists of three small semicircular canals. The researchers found housings for these vestibular organs in very small individuals, which already largely corresponded in shape and size to those of the adult animals. Some of the skull remains examined are so tiny that they may have come from hatchlings. "This shows that even very young individuals of Europasaurus were heavily dependent on their sense of balance," says senior author Sebastian Stumpf from the University of Vienna.

As the scientists explain, this provides an indication of the behavior of the animals after they were born: it stands to reason that Europasaurus was a so-called precocial. This is what animals are called in which the youngest already move independently and, in contrast to nest stools, do not grow up in one place. The study again proves that probably all sauropods were precocial. But in the case of Europasaurus, there could have been something special: Since the adults were not as gigantic as Brachiosaurus and Co, the Europasaurus juveniles could have migrated close to the group early on, according to the paleontologists.

Source: University of Vienna, Rheinische Friedrich-Wilhelms-Universität Bonn, specialist article: eLife, doi: 10.7554/eLife.82190

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