Some long-necked dinosaurs may have been far more capable of standing upright than their massive bodies would have suggested.
About 66 million years ago, two South American sauropods could stand on their hind legs and stay there for a relatively long time, especially when they were small. This ability may have helped them reach higher leaves in trees, make them more intimidating to predators, attract mates, or reproduce.
dinosaur, Uberabatitan from brazil and Newquensaurus From Argentina, were modest in size compared to the largest sauropods. Nevertheless, they were broadly comparable to modern elephants. Adult Uberabatitans They may have grown up to 26 meters long, making them the largest dinosaur known in Brazil.
New research shows that as they grew older, their ability to stand straight decreased. Younger animals were better able to support themselves on two legs, while adults probably experienced much greater stress due to their increased weight.
The findings come from a study supported by FAPESP and published in the journal paleontology. The international research team included scientists from Brazil, Germany and Argentina.
Testing dinosaur bones with engineering equipment
To investigate how sauropods handle the forces involved in standing upright, researchers turned to a computational method commonly used in engineering.
Their goal was to estimate how much stress gravity and body weight exerted on the femur, or thigh bone, when each dinosaur transferred its weight to its hind legs.
“Such small sauropods had a bone and muscle structure that allowed them to stand on both of their hind legs more easily and for longer periods of time. Larger ones were also probably able to stand, but for less time and with less rest, because this position placed too much stress on the femur,” summarizes Julian Silva Jr., a postdoctoral researcher at the School of Engineering of São Paulo State University (FEIS-UNESPR) in Ilha Soltera. Brazil.
Silva Jr. is the first author of the study. He conducted research during an internship at the University of Tübingen in Germany with a scholarship from FAPESP.
The team created digital reconstructions of the females of seven sauropod species. The dinosaurs selected represented different evolutionary branches, body sizes and physical characteristics. His models were created from fossils preserved in natural history museums around the world.
Imitating the powers of standing upright
The scientists used finite element analysis (FEA), a method that breaks a structure into several smaller sections and calculates how each part reacts to pressure, weight, heat or other forces. Engineers often use the same approach to test whether bridges, buildings, and machines can withstand the stress.
“Using this technique, we carried out two simulations. One dealt with the external scenario, simulating a force coming from the outside inward. In this case, when the dinosaur stood on its hind legs there was gravity and the animal’s own weight on the femur. In the other, we analyzed the internal scenario, the force that the muscles exerted on the femur,” explains Silva Jr.
By combining the two simulations, the researchers estimated the total stress experienced by the femurs of each species.
The lowest stress levels appeared in two South American sauropods. was a teenager Uberbatitan Ribeiroi (Named after the Brazilian municipality of Uberaba, where it was found, and coincidentally, Silva Jr.’s hometown). was the second Neuquensaurus australis (Found near Neuquén River in Argentina).
Both lived during the Late Cretaceous period, about 66 million years ago.
Strong bones gave small sauropods an edge
The researchers found that both species had particularly strong thighs. Their thicker, stronger bones were better able to dissipate the forces generated when the animals stood upright.
“They had stronger thighs and could better withstand stress. The bigger ones had much larger muscles and even huge thighs, but not enough to support their weight. This does not mean that they could not stand, but they probably chose the best time to do so, because it would have been an uncomfortable position,” says the paleontologist.
Larger sauropods may still have been able to rise on their hind legs. However, simulations show that they could not hold this posture as comfortably or for as long.
Adult Uberabatitan Individuals probably faced the same problem. Although the juveniles tested in the study were able to stand upright, fully grown animals could lift much more weight. That extra mass would likely have placed them under the levels of stress experienced by other giant sauropods.
Why could sauropods stand on two legs?
Standing straight could provide many important benefits.
Sauropods were plant-eaters, so standing on their hind legs may have helped them reach vegetation at tree heights that was unavailable to smaller animals. This posture may also play a role in reproduction by allowing males to mount females or perform visual displays to attract potential mates.
This posture may also serve as a defensive strategy. By raising the front of the body into the air, the sauropod would have appeared even larger and more dangerous to approaching predators.
When supported by both hind legs and tail, the animal would have formed a tripod stance, meaning that three points of contact helped to stabilize its body.
Important limitations of the study
The researchers note that their model did not include every structure that would have affected the way dinosaurs stood.
For example, the simulations did not account for cartilage, the flexible tissue that cushions joints and can help absorb and distribute stress. They also did not model the support provided by the tail when the dinosaur was in the tripod position.
Because cartilage was not analyzed in any of the seven specimens, researchers assumed it played a similar role in the species. This means that this method is most useful for comparing dinosaurs to each other, rather than generating precise measurements for each individual animal.
The researcher says, “The tool we use is very efficient for comparison, even if the answer is not exact for every one. By comparing representatives of different lineages, we can get a fairly accurate picture of how these animals behaved millions of years ago.”