Wednesday, 30 November 2011

A Giant Madagascan Dinosaur Had The Largest Osteoderms Ever

A CT scan of the Rapetosaurus osteoderm (bottom) and a size
 comparison between the dinosaur , a human and the osteoderm
The skins of reptiles are some of the most highly prized on Earth. Crocodile leather was particularly desirable because of its scaly texture and variety of color; now Crocodilians have protected status. Yet not all characteristics of reptile skin come from the color and size of the creature's scales. When examined closely, the presence of small nodules is revealed. These are placed at regular intervals all over the creature, creating an astonishingly beautiful texture.

They are produced by small pieces of bone which lie just under the skin. These structures, called osteoderms, are vital to reptiles. First and foremost, they keep the skin taut; secondly, they give it strength. Yet they have other uses. Crocodiles can raise and lower their osteoderms rapidly to change the temperature of their bodies. We know that dinosaurs and other such prehistoric reptiles also possessed these bony structures; all armoured groups, such as the ankylosaurids or stegosaurids possessed osteoderms.

The only non-armored group were the titanosaurs, the last giant sauropods on Earth. Yet the discovery of a truly massive osteoderm suggests they may have had another function. What is more, the bone belongs to a rather unlikely dinosaur, Rapetosaurus, and was discovered in late Cretaceous formation by a team of palaeontologists, led by Professor Kristina Curry Rogers from Macalester College. Sediments around the fossils show that the creature lived in an environment which suffered long droughts for part of the year.

The team believe that the osteoderms may have helped Rapetosaurus to survive in the harsh ecosystem.  They also discovered more remains: two skeletons, one of an adult and one of a juvenile, alongside osteoderms belonging to each. They found that Rapetosaurus possessed very few of these structures. Therefore they would be useless for patterning or temperature control as a great many would be needed to achieve these effects.

The juvenile osteoderms were solid. However it seems that, as the creature matured, the structures became hollow. This led to the conclusion that they were a means of storing nutrients and minerals. This idea was backed up by the fact that titanosaurs laid dozens of football-sized eggs. Crocodiles also do this and re-absorb the minerals in the eggshells by eating them and storing them in their osteoderms. Studies such as these are useful, as they allow us to recreate the life of the dinosaurs and their habitats.