Long-necked dinosaurs from South America could easily stand on two legs, computational study shows

Sixty-six million years ago, two genera of long-necked, quadrupedal dinosaurs had an advantage over other sauropods: they could easily stand on their hind legs for extended periods. For example, this caused them to scare off potential predators and feed on leaves high up in trees.

The Brazilian Obra Betheton and the Argentinian Neucansaurus were about the size of a modern elephant. Although they were considered small for their group, it is estimated that adult obrabateans could reach 26 meters, making them the largest dinosaurs in Brazil. Because of their size, these sauropods could only stand for extended periods when they were young. This is the result of a study published in the journal paleontology. The study was conducted by researchers from Brazil, Germany and Argentina.

The scientists used a computational technique adopted in engineering. Their aim was to estimate the stress on the femur caused by gravity and the weight of sauropods when standing on their two hind legs.

“Smaller sauropods like them had a bone and muscle structure that allowed them to stand more easily and more easily on their two hind legs. Larger individuals were probably able to stand as well, but for a shorter period of time and with less comfort, since that position put a lot of stress on the femur.” Soltera, Brazil. Silva Janier is the first author of the study, which was conducted during an internship at the University of Tübingen in Germany.

The researchers digitally reconstructed the femurs of seven sauropods representing different evolutionary lineages, sizes and anatomical features for the group. The digital models were based on fossils found in natural history museum collections around the world.

Sauropod mimics of South America

The simulation was performed using finite element analysis (FEA), a computational technique that simulates how materials behave under conditions such as force and heat. For example, this technique is widely used in bridge design.

“Using this technique, we performed two simulations. One dealt with the external scenario, simulating the force coming from the outside. In this case, gravity and the animal’s own weight on the femur when the dinosaur stood on its hind legs. In the second, we analyzed the internal scenario, with the force that the muscle would exert on the femur,” Silvia Geo, “Sylvia Geo,” Silvia.

The sum of the two scenarios shows the amount of stress for each species. Two South American sauropods, a juvenile Obrabitaton ribeiroi (named after the Brazilian municipality of Obraba, where it was found, and, coincidentally, the hometown of Silva Janier) and Neucansaurus australis (found near the Nucon River in Argentina) showed the lowest levels. Both species lived during the Late Cretaceous period, about 66 million years ago.

“They had stronger femurs and could absorb stress better,” says the paleontologist. “The older ones had bigger muscles and even giant femurs, but not enough to support their weight. That doesn’t mean they couldn’t stand, but they probably chose the best time to do it, because it must have been a painful position.” They point out that adult Obrabatean individuals, unlike the juveniles analyzed in the study, probably had the same difficulty standing on their hind legs as other giant species.

This position would have been useful for feeding and reaching food in the higher parts of trees because sauropods were leaf eaters. It may also have been used for reproduction, allowing males to mount females and perform displays to attract mates. Finally, this can be useful for defense, making them appear larger to potential predators.

The authors note that the cartilage in these bones, which can dissipate stress quite effectively, was not taken into account. They also did not consider how the tail would assist the animal in the tripod position.

Furthermore, since cartilage was not examined in any of the seven specimens, it is assumed that its role was the same in all of them. “The tool we use is very effective for comparison, even if the answer is not exact for everyone. By comparing representatives of different lineages, we can get a fairly accurate picture of how these animals behaved millions of years ago,” says the researcher.