I had never heard the term osteoderm until this morning.
Osteoderms are bony deposits forming scales, plates or other structures in the dermal layers of the skin. Osteoderms are found in many groups of extant and extinct reptiles, including lizards, various groups of dinosaurs...The image above (credit Fritz Geller-Grimm), shows osteoderm on the skin of a Gila monster. What interested me was a report in the StarTribune about dinosaur osteoderms:
At the site in Madagascar, which was once a river, she and her colleagues found lots of osteoderms... she found that the adult osteoderm was hollow, while those from the younger skeletons were not.An osteoderm would obviously provide a non-weight-bearing site for calcium storage, but it's not clear to me if calcium could be selectively mobilized from one site while sparing others. But apparently crocodiles use their osteoderms for thermoregulation, so possibly dinosaurs could redirect blood flow to the osteoderms in times of mineral deficiency. Interesting theory.
"They weighed tens of tons," she said. "No way could they pull minerals from their limbs and still be able to walk. They would fracture their bones."