The community of monstrous robbers of the dinosaur era has now gained another member: paleontologists present Llukalkan aliocranianus – the “terrifying one with the other skull”. The approximately five meter long predatory dinosaur belonged to the group of abelisaurs that were common in the south of the Cretaceous world. In addition to other special skull features, Llukalkan distinguished unusual structures in his hearing system. According to the scientists, he probably had particularly keen hearing, which distinguished him from co-existing relatives in his living space.
In the late Cretaceous the world of the predatory dinosaurs was divided into two domains: In the northern major continent Laurasia, especially the representatives of the tyrannosaurs had developed into the top predators. In southern Gondwana, however, the abelisaurs had taken on this role. Fossil finds show that various species of these two-legged dinosaurs roamed what is now Africa, India, Antarctica, Australia, and South America. Although their lines of development split up early on, the predators of the south resembled their “colleagues” in the north in many ways: the abelisaurs were five to nine meters long, had clawed hind legs, tiny stubby arms and terrifying teeth. In contrast to T. rex and Co, they had rather short skulls, some of which were characterized by combs and horns or at least by conspicuous cusp structures.
A new representative of the “southern predatory dinosaurs”
As the paleontologists around Federico Gianechini from the National University of San Luis report, the new representative of the abelisaurs also had a correspondingly “knobbly” appearance. Its remains were discovered in the Bajo-de-la-Carpa Formation in western Argentina and dated to be around 80 million years old. The fossil consists of an almost completely preserved skull with its sharp teeth. Based on size comparisons with other known fossils of representatives of the abelisaurs, the researchers conclude that the animal, presumably not yet fully grown, was about five meters long. Like these, the predatory dinosaur probably also wore huge claws on its powerful feet, with which it could stab its prey, as it were.
This abelisaur was big, fast and massively armed – making it one of the top predators in its habitat, say the scientists. They gave it the scientific name Llukalkan aliocranianus. It is made up of the native Mapuche word for “the terrifying one” and the Latin word for “other skull” – aliocranianus. The nickname refers to the detailed results of the investigations into the fossil. Accordingly, Llukalkan had a particularly short skull with special bulges and protrusions. The paleontologists say that his head resembled those of some of today’s iguanas.
Indication of sharp hearing
According to them, however, the most striking skull feature of the new dinosaur is an unusual area in the middle ear zone that has not been observed in any other abelisaur found to date. “This finding indicates a special hearing adjustment compared to other abelisaurs. Llukalkan probably had a particularly keen sense of hearing, ”says co-author Ariel Mendez of the Patagonian Institute of Geology and Paeontology in Puerto Madryn.
As the scientists explain, this finding sheds light on the evolution of species diversity among predatory dinosaurs at the end of the Cretaceous Period. Llukalkan apparently shared his habitat with at least one other relative: the remains of the abelisaur Viavenator exxoni were discovered only about 700 meters from his fossil. “This is important because it suggests that the diversity in these predatory dinosaurs was not only great overall, but also at the local level,” says Gianechini. Apparently, different adaptations – such as hearing abilities – made it possible for different large species of predatory dinosaur to coexist.
How Llukalkan lived, whom he hunted and what advantages his special hearing skills might have imparted to him remains unclear, but the fossil findings document pronounced adaptation processes, the researchers say. “These dinosaurs were still trying new evolutionary paths and diversifying quickly just before they disappeared in the great mass extinction at the end of the Cretaceous,” says Mendez. In this context, they are now hoping for more finds: “The new find indicates that even more representatives of the abelisaurs are waiting to be discovered. In any case, we will now look for more ways to gain more insight into their relationships with one another, ”Gianechini concludes.
Source: Taylor & Francis Group, technical article: Journal of Vertebrate Paleontology, doi: 10.1080 / 02724634.2020.1877151