What’s Inside a Dinosaur Bone?

by Kevin Padian — (page 1 of 3)

Bones are the most abundant remains of dinosaurs that we have. And fortunately, they preserve a lot of information about how the animals lived. But to get at a lot of this information, you have to get inside the bones, on the microscopic level.

In 1994, some generous help from a UCMP donor and field volunteer, Dr. Jay Grimaldi, enabled the museum to renovate its facility for thin-sectioning hard tissues. With new tools and machines, we could now examine the daily growth lines that a snail lays down as it grows and changes its shell, and we could examine the vascular structures of ancient plant stems and the insides of fossil seeds. But most of the work that we’ve done in our lab is in sectioning the bones and teeth of ancient vertebrates. This work has given us great new insights on how these extinct animals grew, how they built their skeletons, what they ate, and how active they were.

The science of examining the tissue structures of organisms is called histology, and it has a long history at UCMP. Charles Camp, J.T. Gregory, and Frank Peabody were among the scientists who took thin-sections of the bones of fossil and recent animals to compare their structures. They started to build this collection in the 1940s, and their slides are still useful in our work today.

How do we make the thin-sections?
First we choose the tissue we want to sample, be it a shell, a plant part, or a bone or tooth. At least part of the specimen will be destroyed by this kind of operation, so usually we make a cast of it first. (After we’ve sectioned the specimen, we can indicate on the cast where the sections were taken.) Our preparators are so good at this that you can’t even tell what’s been cut after they restore and paint the original specimen. Once we cut out the piece we want to section, we embed it in an epoxy resin—much like superglue—and let it harden. This ensures that the specimen doesn’t crumble and fly apart when it’s sectioned. Then we attach it to a little arm that holds it against the edge of a small, diamond-tipped circular saw blade. This blade cuts slowly but surely through the bone, slicing the specimen like salami in any direction we need. We take these little slices and glue them to glass slides. At this point they’re too thick to let light

Thin-sections of bone are glued to slides, then ground further until translucent. (photo by Judy Scotchmoor)

through, so we grind them down on what look like little potter’s wheels fitted with discs of successively finer sandpaper, until we get the thinness we need. Then we put them under the microscope.