Could some sauropods literally "smack" opponents with their whip-like tails? The previous assumption that the rapid tips of the extensions could break the sound barrier is now contradicted by new computer simulations. Accordingly, the structures would not have withstood the loads at supersonic speeds. The giants probably accelerated the ends of their tails to around 100 kilometers per hour. With such blows, they could have beaten predators or conspecifics in competition, the researchers say.
A small head, a long neck, a barrel-shaped body and the end of the body formed a long tail - these are the hallmarks of the sauropod. These sometimes gigantic herbivores were exceptionally successful models of the dinosaur era: they spawned numerous subgroups and species, especially in the Jurassic period, which populated many parts of the world. Among them were the representatives of the diplodocids. She was distinguished by a particularly long tail that acts like a whip. This led to the suggestion that the animals might have used it in this way.
A gaudy hypothesis put to the test
The question also arose as to whether the acoustic effect known from whips could possibly occur: the crack occurs when the end is accelerated to supersonic speed by dynamic processes in the tapering structure. It then breaks the so-called sound barrier and there is a loud bang. A previous study, based on simulations, concluded that it seems possible that the diplodocid Apatosaurus louisae, up to about 26 meters long, could accelerate its tail end to more than the speed of sound of 340 meters per second. The idea of giants cracking whips was of course spectacular and so the hypothesis caused a stir – but also skepticism.
An international team of researchers has now re-examined the hypothesis of the loud dinosaur tail using more modern computer simulation processes and methods from engineering sciences. To do this, they simulated the movements of the tails of diplodocids using a model based on information from five fossil skeletons. The virtual dinosaur tail sits on a pelvic bone and consists of 82 elements that correspond to the vertebrae. In reality, the tail model would be over 12 meters long and weigh just under a ton and a half.
Rather only 100 kilometers per hour
"The project was quite a challenge because we had to tackle the problem with two methods that are normally used in aerospace engineering: multi-body simulation and estimation of the stress-bearing capacity of the materials," says lead author Simone Conti from NOVA- University of Lisbon. Using information about the durability of biological structures, the scientists were able to test whether their model tail would withstand the stress and move fast enough to produce a sonic boom. To do this, the base of the tail was moved in an arc, creating a whip-like movement.
As the researchers report, their results showed that the dinosaurs could not have cracked: the slender structures would not have withstood loads at such high speeds - they would have ruptured. The team then studied three different hypothetical one-meter-long structures attached to the end of the model's tail. They should mimic the end of a whip. The first structure consisted of three skin and keratin segments, the second of braided keratin threads, and the third of another possible tissue. The result: none of the structures could withstand the stress of moving at 340 meters per second.
Ultimately, the simulations showed that the diplodocids probably only accelerated their tail ends to maximum speeds of around 33 meters per second – around 100 kilometers per hour. "So although the tails of the diplodocids could not be moved fast enough to produce a sonic boom, it is likely that they could be used as defensive weapons or in combat with other diplodocids," says co-author Emanuel Tschopp from the University of Hamburg . Exactly how and for what purpose the giants used their long appendages is left to the imagination, according to the paleontologist.
Source: University of Hamburg, Scientific Reports, doi: 10.1038/s41598-022-21633-2