Some sauropods may have been able to rear up on their hind legs, using their tail for support. A biomechanical model shows, however, that this posture was more accessible to relatively small species. The largest long-necked dinosaurs would have encountered too much stress on their bones and muscles.
Sauropods were quadrupedal herbivores, recognizable by their long necks and long tails. For a long time, paleontologists have wondered if they could rear up to reach higher vegetation, repel a rival, or defend themselves. Fossils do not allow direct observation of this behavior.
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To examine this question, researchers built digital models of several species. They estimated the stresses exerted on the femurs when the animal tilted backward. This method compares the likely strength of the bones to the forces induced by mass and posture.
The results show that size is not an advantage in this exercise. As mass increases, the hind limb bones must support considerable loads. Very large sauropods would therefore have had difficulty maintaining this position for long, even using the tail as a third point of support.
Conversely, some more compact species had a better-adapted anatomy. Their robust femurs and pelvis could distribute stress more effectively. The posture would nonetheless remain a biomechanical hypothesis, as it also depends on soft tissues that do not fossilize.
The authors do not conclude that all small sauropods reared up regularly. Rather, they indicate that this possibility varied according to size and morphology. The animal's diet, terrain, and age could also modify its ability to adopt this position.
This study reminds us that giant dinosaurs did not form a uniform group. Their behavior resulted from a balance between mass, skeleton, and muscles. Future models incorporating more anatomical elements could clarify which species actually used this posture in their environment.