Giant Dino Bone

What more can we learn about long-necked dinosaurs?

At least this: Macalester geology/biology professor Kristi Curry Roger and colleagues have found that Madagascar dinosaurs carried giant, hollow bones in their skin that may have helped them survive the harsh environments they inhabited. This discovery has shed new light on the anatomy and function of these bones in the biggest animals to ever walk on land. 

Curry Rogers is lead author of a paper published in a recent issue of Nature Communications about bizarre, gigantic bones that grow in the skin of Rapetosaurus, a species of huge plant-eating dinosaur from this Indian Ocean island nation. 

“This is the biggest osteoderm ever found for any backboned-animal,” says Curry Rogers. “The fact that it’s hollow debunks all sorts of ideas about how these bones functioned in long-necked dinosaurs.”   

Osteoderms—bones embedded within the skin—are common among reptiles and some mammals. They create the unique pattern on the backs of crocodiles, the armor body covering found on armadillos, and the distinctive plates of dinosaurs like Stegosaurus and Ankylosaurus.   

Among the long-necked dinosaurs called sauropods, osteoderms are found in one globally distributed subgroup—the Titanosauria.  For more than a century, paleontologists have been trying to determine how these weird bones were distributed in the skin of the long-necked titanosaurs and what they might have been used for. Were they for protection, as in armadillos and crocodiles? Were they for display? Could they have helped regulate body temperature? 

“Knowing something about the lives of these dinosaurs, particularly in the context of the drought-prone paleoenvironment they lived in, tells us that osteoderms may have been important for storing minerals, which allowed Rapetosaurus to survive the rough times,” says Curry Rogers. 

Instead of the hundreds of interlocking plates in living animals with osteoderms, Rapetosaurus had only a few osteoderms in its skin. This means that they were less likely to serve as protection or as body temperature regulators.   

“The discovery of these giant osteoderms provides new insights into what these bizarre structures may have done for the dinosaurs that had them,” says Curry Rogers. “It helps us clarify what these Madagascar dinosaurs looked like with their skin on. Our sample includes both adult and juvenile osteoderms, which tells us how the osteoderms changed over the lifespan of the dinosaur.”  

In the vicinity of the osteoderm, the skin of Rapetosaurus would have stretched, making it in places up to seven times as thick as an elephant’s skin. The bone also hollowed out over the course of the dinosaur’s lifespan, so even though it was massive, an osteoderm would’ve been fairly lightweight in adult dinosaurs.