Why dinosaurs waved their tails – knowledge

The tails of two-legged dinosaurs not only formed a rigid counterweight to the head, but, according to new findings, played an important role in the sequence of movements. Similar to how pedestrians swing their arms when relaxed walking, the prehistoric lizards wagged the appendage of their rear to the side. Without a tail, the dinosaur would have cost 18 percent more muscle power to walk, writes a research team led by Australian biomechanic Peter Bishop in the specialist journal Science Advances.

With the help of computer simulations, the researchers examined the gait of the dinosaur species Coelophysis bauri. In the study, the up to three meters tall lizards are representative of the theropod group, which also includes representatives such as Tyrannosaurus rex and Velociraptor. It is characteristic of these carnivorous dinosaurs that they walked on two legs and had small front legs that were unsuitable for locomotion. They varied greatly in height, some measuring less than a meter, others up to 15 meters. Bishop’s team writes that getting around is key to understanding animals. Especially with regard to the evolution and the later extinction of the various theropods, bone finds and footprints alone provided an incomplete picture.

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The publication states that previous simulations were inadequate because body parts such as the neck, thorax, torso and tail were assumed to be rigid. This has been corrected in the paleontologists’ new computer model. To verify it, the researchers first used a living test object: a cockatiel. The flightless birds native to Central and South America share a common ancestor with the theropods.

Those who walk like on the catwalk have to compensate for the hip rotation

In the 3-D simulation, the hind legs of the chickens are described with 36 muscles each, for the activation of which an optimal value is calculated, as well as for the torques at the joints and for the coordinated accelerations. This resulted in a coherent cycle of movement. The simulation spat out a walking or running gait, which is equal to that of the real chicken, the scientists report.

The researchers then applied their model to Coelophysis, including the approximately 1.5 meter long tail of the dinosaur. The scientists also took into account that flightless theropods from the Triassic, to which Coelophysis belongs, put their feet in the middle or even crossed the center line while running, which is known from fossil footprints. With such a walkway on the catwalk, it is hardly surprising that the dinosaurs had to compensate for the twisting movements in their hips. In view of the short arms, the tail was used as an oar, as Bishop and colleagues were able to demonstrate with their simulation.

Theropods swung their tails to get more power for locomotion, and were anything but stiff hips. If they had the right hind leg in front, the tail swung to the left and vice versa on the other side. The same applies to the Olympic walkers in humans, except that Homo sapiens no longer has a tail. In order to convert the rotation of the hip at brisk speeds into a smooth gear, athletes therefore work a lot with their arms.

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