Some long-necked dinosaurs may have had the ability to stand much more upright than their large bodies would indicate.
About 66 million years ago, two South American sauropods were able to stand up on their hind legs and remain there for relatively long periods of time, especially when they were young. This ability may help them reach higher leaves in trees, be more intimidating to predators, attract mates, and reproduce.
The dinosaurs are Uberabatitan from brazil neukensaurus The sauropods from Argentina were modest in size compared to the largest sauropods. Still, they were roughly equivalent to modern elephants. adult Uberabatitans It may have reached a length of 26 meters, making it the largest dinosaur known from Brazil.
New research suggests that their ability to stand upright decreased as they grew older. Young animals were able to support themselves well on their two legs, but adults probably experienced much greater strain 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 using engineering tools
To investigate how sauropods coped with the forces of standing upright, the researchers turned to computational techniques commonly used in engineering.
Their goal was to estimate the stress that gravity and body weight exerted on the femur as each dinosaur transferred its weight to its hind legs.
“Such small sauropods had a bone and muscle structure that allowed them to stand on their two hind legs more easily and for longer. Larger sauropods were probably able to stand as well, but the posture was not comfortable for short periods of time because it caused a lot of stress on the femur,” summarizes Julian Silva Junior, a postdoctoral researcher at the Faculty of Engineering of the State University of São Paulo (FEIS-UNESP) in Solteira, Brazil.
Silva Júnior is the study’s lead author. He conducted this research during his internship at the University of Tübingen, Germany, with a scholarship from FAPESP.
The research team created digital reconstructions of femur bones from seven species of sauropods. The dinosaurs selected represented a variety of evolutionary branches, body sizes, and anatomical features. Their models were made from fossils stored in natural history museums around the world.
Simulate upright force
The scientists used finite element analysis (FEA). It is a method of dividing a structure into many small sections and calculating how each part responds to pressure, weight, heat, and other forces. Engineers often use the same approach to test whether bridges, buildings, and machinery can withstand stress.
“Using this technique, we ran two simulations: one dealt with an external scenario, simulating forces coming from the outside in, in this case gravity and the animal’s own weight on the femur when the dinosaur was standing on its hind legs. The other analyzed an internal scenario, the forces exerted by the muscles on the femur,” explains Silva Junior.
By combining two simulations, the researchers estimated the total stress experienced by each species of femur.
The two South American sauropods had the lowest stress levels. one was a boy Uberabatitan Ribeiroi (Named after the Brazilian city of Uberaba, where it was discovered, and coincidentally Silva Junior’s hometown). The other is Neukensaurus australis (Found near the Neuquen River in Argentina).
Both lived during the Late Cretaceous period, about 66 million years ago.
Stronger bones gave smaller sauropods an advantage
Researchers found that these two species had particularly strong femurs. Their thicker, stronger bones were able to better distribute the forces created when the animal stands upright.
“They had stronger femurs, which allowed them to distribute stress better. The larger ones had very large muscles and even huge femurs, but they weren’t strong enough to support their weight. That doesn’t mean they couldn’t stand up, but they probably chose the best time to do so, because it must have been an uncomfortable position,” says the paleontologist.
Larger sauropods may still have been able to stand on their hind legs. However, simulations suggest that the pose could not be held as comfortably or for long.
adult Uberabatitan Perhaps some of you are facing the same problem. Although the juveniles examined in this study were fit to stand upright, fully grown animals would have carried much heavier weights. Its additional mass likely exposed it to levels of stress similar to those experienced by other giant sauropods.
Why sauropods may have stood on two legs
Standing upright may have provided several important benefits.
Sauropods were plant eaters, so by standing up on their hind legs, they may have been able to reach tall tree vegetation that was inaccessible to shorter animals. This posture may also have played a role in reproduction, by allowing males to mount females or perform visual displays to attract potential mates.
This pose may also have served as a defensive strategy. By lifting the front part of its body into the air, the sauropod would have appeared even larger and more threatening to approaching predators.
When supported by both hind legs and the tail, the animal would have formed a tripod posture. This means that the three points of contact help stabilize your body.
Important limitations of the study
The researchers note that their model did not include all the structures that would have influenced the way dinosaurs stood.
For example, the simulations do not account for cartilage, the flexible tissue that cushions joints and helps 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, the researchers speculated that cartilage plays a similar role across species. This means that this method is most useful for comparing dinosaurs to each other, rather than producing precise measurements for individual animals.
“The tools we use are very efficient at making comparisons, even if each answer is not exact. By comparing representatives of different lineages, we can get a fairly accurate picture of how these animals behaved millions of years ago,” say the researchers.
