It is obvious that ankylosaurs were able to defend themselves: the animals had a spiky shell and a long tail with a club-like tip, which not least could scare off predators. The well-known Tyrannosaurus Rex, for example, should have feared for his shins in an attack: “Zuul crurivastator” is what ankylosaurs are called today, which means something like “leg destroyer”. The animals themselves had fairly short legs, four to six meters in length, lived between 166 and 66 million years ago, and they only ate plants. But they were probably not peaceful. On the contrary.
Scientists from the Royal Ontario Museum in Toronto and the North Carolina Museum of Natural Sciences in Raleigh, USA, have now examined a particularly well-preserved fossil more closely; The team led by evolutionary biologist and paleontologist Victoria Arbor is now reporting on their results in the journal BiologyLetters. The dinosaurs therefore rarely used their club-like tails to defend against carnivores, but mainly against their own kind.
fossils of ankylosaurs have been discovered on different continents, the specimen examined now comes from Montana, USA. The bodies of the animals were covered by bone plates of different sizes, so-called osteoderms. He wore large spikes on his sides. On this fossil, however, these tips were missing on both sides near the hips. In addition, underlying osteoderms were fractured and healed at various stages. Apparently the Zuul had suffered repeated blows to this spot over a long period of time.
The injuries indicate a complex social behavior.
Who struck? According to the researchers, it wasn’t really a large predatory dinosaur. A tyrannosaurus, for example, would have left randomly distributed injuries all over the body, but especially on the back – after all, the predator was significantly larger – and on the comparatively vulnerable neck. Instead, however, the injuries were well within reach of other ankylosaurid tail clubs, according to the study. These were not flexible enough to hit the back of another ankylosaur. The animals could only strike from the side.
For the researchers, this indicates a complex social behavior of the ankylosaurs. Injuries always in the same places speak for a ritualized fighting behavior. The scientists speculate about ranking fights and possibly also a rutting season during which the animals attacked competitors. The ankylosaurs hit each other’s flanks with their tail clubs.
Whether there were once differences between the clubs of males and females is unclear. Based on the fossil, it is difficult to determine the sex of the examined “Zuul crurivastator”. But the evolution of these clubs was less affected by how well they protected against predatory dinosaurs, Victoria Arbor and her team believe. In that case, for example, it would have been useful if the clubs had grown larger over the course of evolution – because the dominant carnivorous dinosaurs also increased in size. But apparently something else was decisive: namely, how effectively other ankylosaurs could be chased away with the clubs.