The sail-backed Spinosaurus from Africa is one of the best-known dinosaurs in popular culture. Its large size and semi-aquatic lifestyle sets it apart from other predatory dinosaurs. Unfortunately, their patchy fossil record hides so many secrets about Spinosaurus and its close cousins, collectively known as spinosaurs.
But a broken leg bone, a tibia, from Araripe Basin in northeastern Brazil might reveal more about this elusive family of dinosaurs. The two continents may now be an ocean apart, but these separated cousins are a reminder of a time when the two landmasses were joined back in the Early Cretaceous Period. Though incomplete, this particular fossil tells an interesting story about South American spinosaurs.
First of all, a slice of this bone reveals that the animal was heavy-boned. The wall of the bone has thickened, leaving very little gap in the middle that’s typical of land-dwelling dinosaurs. Such adaptation is commonly found in other terrestrial animals that went back to live in shallow waters such as manatees, platypuses, and marine sloths. It is expected that the extra density prevents the animal from floating at the surface like ducks — or even us humans— when it’s not actively trying to dive.