Dinosaurs probably also beat up their own kind with their tails
Ankylosaurs had tail clubs with which they could strike powerfully. Researchers previously assumed that they used them as a weapon to defend themselves against the T. rex, for example. A fossil now shows injuries that indicate something else.
In prehistoric comics or movies, ankylosaurs often fend off attacking tyrannosaurs with their bony tail clubs. In fact, they didn’t just teach T. rex to fear: the armored dinosaurs may also use their iconic tail clubs to beat up unwelcome fellow species, reports a research team in the specialist magazine “BiologyLetters“.
A 76-million-year-old specimen of the species Zuul crurivastator was examined. The name “zul‘ goes back to a dog-like monster of the same name in a 1984 Ghostbusters film that, like the dinosaur, has a short, rounded snout and prominent horns behind its eyes. “Crurivastator” is a nod to the notion that the tail club was used to smash the legs of two-legged tyrannosaurs.
Fossil remains of one such animal were found years ago in the Judith River Formation in Montana. Its tail was about ten feet long and had sharp spikes on the sides. The back half was stiff, and the tip was encased in huge bony lumps that formed a massive, hammer-like weapon. In addition, the hardy herbivore bore rows of spikes along its flanks, which were armored with bone plates.
The well-preserved specimen had some spines broken off on both sides near the hips – tips missing and bone and horn sheath healed to a blunter form, as shown by Victoria Arbor of the Royal BC Museum in Victoria (Canada), Lindsay Zanno of the North Carolina Museum of Natural Sciences in Raleigh (USA) and David Evans from the Royal Ontario Museum (ROM) in Toronto (Canada).
The injuries were caused by a blow from another Zuul’s massive tail club, not a charging predator like one tyrannosaurs, as the team suspects based on location and pattern of injuries. Ankylosaurs may have fought for social and territorial dominance, or for females.
In addition to other indications, this is supported by the fact that the largest and most pointed spines in Zuul were on the flanks – and predatory dinosaurs would therefore hardly have attacked these places in particular. In the case of injuries inflicted by tyrannosaurs, a random distribution is to be expected, especially on the back or in the vulnerable neck area.
Nowadays specialized animal weapons like the antlers of deer and the horns of antelopes usually used to fight members of the same species over mates or territory, researchers at Arbor say. The tail clubs of the ankylosaurs could also possibly have been such sexually selected structures and were used primarily for intraspecific fights – with the clubs always being swung into the opponent’s flanks in a ritualized manner, similar to the flank thrust of bison or the blow to the neck giraffes.
While in ankylosaurs it was the force of the blow, in diplodocids – large, herbivorous dinosaurs with long necks and tails – it is the immense speed of the tail beat, which is presumed because of the whip-like resemblance, that fascinates researchers. According to earlier assumptions, the end of the tail could beat faster than the speed of sound (1236 kilometers per hour/343 meters per second) and produce a sonic boom. Scientists now contradict this in a paper published in the specialist magazine “Scientific Reports“ presented modeling study.
The team led by Simone Conti from the NOVA School of Science and Technology in Caparica (Portugal) also came up with remarkable values: The diplodocids whipped up to 33 meters per second (more than 100 kilometers per hour, km/h) with their whips long, thin tails.
Fast whipping useful against predators
The used model of an Apatosaurus tail is over 12 meters long, weighs 1446 kilograms and consists of 82 cylinders representing vertebrae and are attached to an immovable hip bone base, the researchers explain. Tests on it showed that there was no way the tail could reach 340 meters per second – it would have broken before then, skin and soft tissue torn. Even with hypothetically possibly existing extensions of the tail tip similar to those of a bullwhip, the load at the tip would have been too great at the speed of sound, further tests showed.
Conti’s team concludes that no diplodocid has ever produced a sonic boom – but the rapid whipping was probably useful for defense against predators or for fighting with other diplodocids. At 30 meters per second, the pressure exerted on impact by the tail end piece is equivalent to that of an 88 meters per second (315 km/h) golf ball or a 57 meters per second (205 km/h) volleyball. No bones break and skin does not tear, but the blow is quite painful.
However, there are several other theories as to the use of the long Diplodocid tails with their narrow and light end part: The function as a “third leg” during the two-legged standing posture is one of them, as a counterweight to the long neck, as a noise-producing structure or as a kind of tactile organ spatial perception. However, Conti and his colleagues are convinced that the anatomical structure is the best indication of its use as a whip for defence.
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