Which animal is not two-legged?

29.01.2019 11:51

Long-necked dinosaurs rotated their forefeet to one side

Johannes Seiler Department 8 - University Communication
University of Bonn

Long-necked dinosaurs (sauropods) could align their front feet both forward and to the side. The position of the feet depended on the speed and the center of gravity of the animals. An international team of researchers used state-of-the-art methods to examine numerous sauropod footprints in Morocco at the foot of the Atlas Mountains. By comparing it with other traces of sauropods, the scientists determined how the long-necked animals moved forward. The results have now been published in the journal "Journal of Vertebrate Paleontology".

"Long-necked dinosaurs" (sauropods) were among the most successful herbivores of the Middle Ages - the age of the dinosaurs. Characteristic for this group were a barrel-shaped body on column-like legs and an extremely long neck that ended in a relatively small head. Long-necked dinosaurs existed between 210 and 66 million years ago - so they maintained their position on earth for a very long time. Their huge stature, with which they far surpassed other dinosaurs, also indicates their success.

The sauropods included the largest land animals in the history of the earth, some over 30 meters long and weighing up to 70 tons. "How exactly these giants moved is still unclear," says Jens Lallensack, paleontologist at the Institute for Geosciences and Meteorology at the University of Bonn. The joints in the legs were partly cartilaginous and therefore not fossilized - but bones alone only allow limited conclusions to be drawn about the sequence of movements.

Detective work with 3D computer analysis

However, the missing pieces of the puzzle can be reconstructed with the help of fossil footprints of the giants. An international team of researchers from Japan, Morocco and Germany under the direction of the University of Bonn has now investigated a special trace discovery site in Morocco at the foot of the Atlas Mountains. The site of the discovery consists of an area 54 by six meters in size, which was set vertically during the mountain formation and shows hundreds of individual step seals, some of which overlap. Some of these footprints could be assigned to a total of nine tracks (sequences of individual footsteps). "Working out individual tracks from this trampled mess of footprints was detective work and only possible through the analysis of high-resolution 3D models on the computer," says Dr. Oliver Wings from the central magazine for natural science collections at the Martin Luther University Halle-Wittenberg.

The researchers were amazed by the results: the tracks are extremely narrow - the right and left footprints are almost in line. The forefoot impressions are also not directed forward, as is typical for sauropod tracks, but point to the side - sometimes even diagonally backwards. Even more: the animals could switch between the two positions as required. "Humans are able to turn their palm down by crossing their ulna and radius," says Dr. Michael Buchwitz from the Museum of Natural History Magdeburg. In today's terrestrial vertebrates, however, this complicated movement is limited to mammals and chameleons. It was not possible with other animals, including dinosaurs. As a result, sauropods must have found another way of turning their forefoot forward.

How is the rotation of the forefoot to be explained?

How can the rotation of the forefoot in the sauropod tracks be explained? The key is probably in the thick layers of cartilage, which allowed great flexibility in the joints, especially in the shoulder. But why were the hands rotated outward at all? "Outward-facing hands with palms facing each other were the original state of the two-legged ancestors of the sauropods," explains Shinobu Ishigaki of the Okayama University of Science in Japan. The question should rather be why most sauropods turned their front feet forward - a movement that is anatomically difficult to achieve.

A statistical analysis of sauropod tracks from all over the world was able to provide important information: Apparently the animals tended to have outward-pointing front feet when the front leg was not used for active locomotion but only to carry their body weight. The front feet were often rotated further outwards when the animal was walking slowly and the center of mass of the body was far back. A forward-facing forefoot was only beneficial when the hands were also used to drive forward. It also shows that the external rotation of the forefoot was restricted to smaller individuals, while in larger animals it was mostly directed forward. It was apparently no longer possible for the large animals to straighten their forefoot to the side. "This loss of mobility was probably a direct result of the huge growth," says Lallensack.

Scientific contact:

Jens Lallensack
Institute for Geosciences and Meteorology
University of Bonn
Tel. 0151-19661028
Email: [email protected]

Original publication:

Jens N. Lallensack, Shinobu Ishigaki, Abdelouahed Lagnaoui, Michael Buchwitz, and Oliver Wings: Forelimb orientation and locomotion of sauropod dinosaurs: Insights from the Middle Jurassic Tafaytour tracksites (Argana Basin, Morocco), Journal of Vertebrate Paleontology, DOI: 10.1034 / 02724 .1512501

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