Sauropods, the long-necked giants of the dinosaur world, could orient their forefeet both forward and sideways, with the actual orientation depending on their speed and centre of mass, new research suggests.
A team from Germany, Morocco and Japan made the surprising discovery after using 3D computer analysis to investigate footprints found at the base of Morocco’s Atlas Mountains.
The results of the work, which was led by the University of Bonn in Germany, are reported in a paper published in the Journal of Vertebrate Palaeontology.
The vertical site shows hundreds of individual footprints, some of which overlap. Using high-res computer models the researchers assigned a part of these footprints to different trackways, and were amazed by the results.
The trackways are extremely narrow, with the right and left footprints almost in line, and 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 orientations as needed.
“People are able to turn their palms downwards by crossing the ulna and radius,” says Michael Buchwitz of the Museum für Naturkunde Magdeburg in Germany.
“However, this complicated movement is limited to mammals and chameleons in today’s terrestrial vertebrates.”
It was not possible in other animals, including dinosaurs, he says. Sauropods must therefore have found another way of turning the forefoot forwards.
The key, the researchers suggest, probably lies in the sauropods’ 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,” says Shinobu Ishigaki from the Okayama University of Science, Japan.
The question should therefore be why most sauropods turned their forefeet forwards – an anatomically difficult movement to implement.
One suggestion is that they tended to have outwardly directed forefeet when the foreleg was used only for carrying body weight, not active locomotion. 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, was a forefoot directed to the front advantageous.
The new research shows 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 Bonn’s Jens Lallensack.