ANALYSIS: Oh Snap! Dino-Era Croc Jaws Filled Many Roles
In the study, biologists examined how, as they evolved into larger forms, mammals developed bones with joints that fit into each other more exactly, a trait known as congruence. By fitting together better, the mammal bones reduced the possibility of stresses in unexpected parts of the joint. However, at the same time, the mammals developed thinner cartilage pads between their bones.
The study's authors suggested there may have been a limit where the benefits of increasingly congruent bones proved insufficient without thick cartilage cushions. At that point, the mammals couldn't evolve any larger because their joints may have lacked the physical ability to deal with the gigantic mammals' weights.
Millions of years before mammals hit this size ceiling, the long-necked dinos may have avoided the limit by keeping a thick layer of cartilage between their leg bones. As the sauropods grew larger, their cartilage pads grew along with them and continued to cover a larger surface of the knee joints. These larger cartilage pads could expand evenly across the bone joint and spread out the tremendous weight of the sauropods.