Long-necked dinosaurs rotated their forefeet to the side
Long-necked dinosaurs (sauropods) could orient their forefeet both forward and sideways. The orientation of their feet depended on the speed and centre of mass of the animals. An international team of researchers investigated numerous dinosaur footprints in Morocco at the foot of the Atlas Mountains using state-of-the-art methods. By comparing them with other sauropods tracks, the scientists determined how the long-necked animals moved forward. The results have now been published in the Journal of Vertebrate Paleontology.
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Well preserved footprints of the find site in Morocco with clearly visible claw impressions [Credit: The Society of Vertebrate Paleontology] |
Sauropods included the largest land animals in Earth history, some over 30 metres long and up to 70 tonnes in weight. "However, it is still unclear how exactly these giants moved," says Jens Lallensack, paleontologist at the Institute of Geosciences and Meteorology at the University of Bonn in Germany. The limb joints were partly cartilaginous and therefore not fossilised, allowing only limited conclusions about the range of movement.
Detective work with 3D computer analyses
The missing pieces of the puzzle, however, can be reconstructed with the help of fossil footprints of the giants. An international team of researchers from Japan, Morocco and Germany, led by the University of Bonn, has now investigated an unique track site in Morocco at the foot of the Atlas Mountains. The site consists of a surface of 54 x 6 metres which was vertically positioned during mountain formation and shows hundreds of individual footprints, some of which overlap.
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This is the complete surface of the track site in Morocco, which is 54 meters in length and contains hundreds of footprints [Credit: © The Society of Vertebrate Paleontology] |
The researchers were amazed by the results: the trackways are extremely narrow -- the right and left footprints are almost in line. Also, the forefoot impressions are not directed forwards, as is typical for sauropod tracks, but point to the side, and sometimes even obliquely backwards. Even more: The animals were able to switch between both orientations as needed.
How can the rotation of the forefoot be explained?
How can the rotation of the forefoot in the sauropod tracks be explained? The key probably lies in the mighty cartilage layers, which allowed great flexibility in the joints, especially in the shoulder. But why were the hands rotated outwards at all?
"Outwardly facing hands with opposing palms were the original condition in the bipedal ancestors of the sauropods," explains Shinobu Ishigaki of the Okayama University of Science, Japan. The question should therefore be why most sauropods turned their forefeet forwards -- an anatomically difficult movement to implement.
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Life reconstruction of the trackmaker, an early sauropod dinosaur [Credit: Darius Nau] |
Thus the forefeet were often rotated further outwards when the animal moved slowly and the centre of mass of the body was far back. Only if the hands were also used for the forward drive, a forefoot directed to the front was advantageous.
The analysis furthermore showed that the outer rotation of the forefeet was limited to smaller individuals, whereas in larger animals they were mostly directed forward. The large animals apparently could no longer rotate their forefeet sideways. "This loss of mobility was probably a direct result of their gigantism," says Lallensack.
Author: Jens Lallensack | Source: University of Bonn [January 29, 2019]
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