Despite the scientific rigor of research, from time to time scientists may be amused by amusing and even absurd hypotheses. The witty study of the time is the fruit of the union of paleontologists and aerospace engineers, who simulated the snapping of the tail of large dinosaurs to see if the movement of the limb could break the sound barrier, creating a sonic boom. The object of study is sauropods, the large ancient long-necked reptiles.
Surprisingly, research in this field had already been done and defined that dinos could, yes, swing their tails faster than the speed of sound (Mach 1, which is 337 m/s or 1216 km/h) if they had a structure elongated at the end, like a cattle whip. The limb’s potential for defense against predators and in infighting within sauropod groups would then be much greater.
Calculating the tail speed
The idea, of course, was disputed by other paleontologists as seeming a bit far-fetched, which resulted in the current study. It focuses on diplodocids (Diplodocidae), group of sauropods that includes the famous Brontosaurs, with long, slender tails. Science, while accepting that they may have been used for defence, also points out that they could have been used primarily to counterbalance their long necks, probe the ground around them or as a stabilizer, a third leg, as in kangaroos.
The curiosity surrounding diplodocids also stems from their record, as they are among the longest creatures to ever walk the planet. As we have never found a complete tail, the researchers had to simulate its shape from what has already been found, combining 5 fossil remains from the sauropod group. The simulations then included soft tissue such as skin, tendons and ligaments, piling on top of the 80 vertebrae present in the tail alone. We humans have 33 in our entire bodies.
In the fossil record, we have only a few impressions of dinosaur skin and bones, with no trace of what would have been inside the soft tissues—this, too, had to be “guessed” on the basis of estimated reptilian anatomy. The thickness of the skin was calculated based on the dermis of crocodiles, modeling the mechanical deformation suffered by the tissues when the tail was swung and snapped in the whip effect.
Computer simulations linked the structure to an immobile modeled belt, weighing 1,446 kg and measuring 12 m in length. The skin, being complex with collagen fibers to give it elasticity, becomes almost completely brittle when placed under high stress, according to the scientists.
By calculating the properties of the soft tissues and the rotational movement of the tail, they discovered a more rigid limb than previously thought, taking advantage of the work of the tendons and musculature to avoid disarticulation of the vertebrae when putting the tail in motion. In the simulation, it ended up not breaking the sound barrier due to muscle friction in the vertebrae and aerodynamic resistance. If it exceeded the speed of sound, under these conditions, it would simply have broken.
Fast but not so much
The tip of the tail moved at speeds of 30 m/s, or 100 km/h, ten times slower than the speed of sound. In other words: too slow to create a sonic boom. A whip-shaped caudal structure cannot withstand the strain of moving at 340 m/s without breaking, regardless of whether it is made up of braided keratin filaments — like other dinosaur species —, 3-part skin segments and keratin or a mass of flesh like a flail. That’s even though the waist increased the movement of the tail.
Even without ultrasonic abilities, diplodocid tails could still have been used as an effective weapon against predators and rivals of the same species. At 30 m/s, the impact of a sauropod tail would be equivalent to the pressure exerted by a golf ball traveling at 315 km/h, which might not break bones or tear skin, but would certainly do damage to an opponent.
Source: Paleobiology
