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Becky Barnes's blog

Osteoderm Fossils: More than Skin Deep

For most people, the first things they think about when they hear the word “fossil” are bones from some ancient creature. Considering the hard parts of animals fossilize more easily than the soft parts, they have good reason to think so. But did you know that skin can fossilize as well? It is rare, but with the right set of circumstances (the animal is buried quickly, and dries out), paleontologists can find patches of skin. Sometimes, like in the case of Dakota the Dinomummy (an Edmontosaurus on display in the ND Heritage Center & State Museum), paleontologists can find a LOT of skin.

Today, I’d like to write talk about something in between. It’s not a skeleton, but it is bone. And it’s not skin, but it helps shape and support the skin. It’s something called an osteoderm — literally “bone skin.” An osteoderm is a deposit of bone material found within the dermis (skin) of some animals, generally covered by a thicker keratin sheath (the same material that makes up your hair or fingernails). The keratin covering is generally called a “scute.” Different animals have evolved osteoderms, from lizards and frogs to dinosaurs. Rather than focus on an obscure group of animals, however, I’d like to use crocodiles as an example, since most people can visualize them a little easier.

Crocodilian leather with osteoderms

I just *happen* to have some crocodilian leather with osteoderms in place.

If you can imagine crocodile skin (or if you can’t, just look at the image above), it is made up of many square scales. Osteoderms are located under the largest of these scales/scutes. Most of the time when crocodile or alligator skin is harvested for use in the clothing industry, those bony plates are removed in order to insure flexible leather, so people don’t really get the chance to feel the natural armor. The scute is left behind, giving us the look of a large scale, without the backing of bone.

Osteoderms are one of my favorite pieces to find on a fossil dig. They’re small, compact, look like Swiss cheese on the top, and clean up well. In 2013, as we wandered through a fossil site after a rainstorm, I let my eyes wander. As my gaze travelled down one of the now-dry rivulets, I saw six squares of white. Fossils, when they sit out in sunlight for a while, may change color or become bleached. I blinked. Sure enough — I was looking at six little osteoderms all in a row!

Erosional rivulet with osteoderms

Erosional rivulet containing osteoderms bleached white from the sunlight.

Bleached osteoderm

Close-up of bleached osteoderm.

Another site we visit on occasion called Whiskey Creek contains dozens to hundreds of osteoderms. Some are small, and others the size of a large belt buckle. If you’re ever out with us when we find these, you may hear us say “scute” instead of “osteoderm.” This isn’t a slip of the tongue; yes, we know that it’s technically an osteoderm. It’s just more fun (and faster) to say scute than osteoderm. Scute scute scute!

Osteoderm in situ

Osteoderms in situ at Whiskey Creek. The smooth side faces inward, and the Swiss cheese side faces the outside of the animal.

Holding a piece of osteoderm

Mid-sized osteoderm, with hand for scale.

Designing a Museum Mural to Save Space: How a Paleontologist and Artist is Creating a 3-D Plesiosaur Exhibit

In October 2016 I wrote a “Year of the Plesiosaur” blog that showcased a chain of vertebrae from the neck of one of these Loch Ness-esque sea monsters. In a perfect world we would show the awesome size of this creature by hanging an entire cast of the skeleton (all 50 feet of it) in the Underwater World exhibit of the State Museum’s Adaptation Gallery: Geologic Time. However, we do not have the kind of space needed to facilitate that. What about hanging part of the cast instead? Even a portion of the 70-vertebrae-long neck is impressive to behold. As you enter Underwater World, there is a blank wall to the right of the mosasaur on display. We decided to paint the rest of the plesiosaur on the wall and have the cast neck and skull sticking out as a three-dimensional element.

Then the question was: what to paint? Do we paint a fleshed out creature and have the bones sticking out of the wall? Seems disconnected. How about a skeleton painted, and the 3D bones? Seems a little gruesome. What about an x-ray effect, with a fleshed out creature and the bones (real and painted) fading into obscurity? Perfect! What is the process now?

Sketch of Plesiosaur mural

Initial sketch for the mural.

We measured the wall at 106” wide. Then we picked up a painting canvas at 40” wide. Since I’m the artist for this mural project, I can paint in the comfort of my office instead of pretending to be Michelangelo for weeks on end. The plesiosaur was drafted in a few different poses, until we found one that fit what we wanted. We needed an underbelly view, since the animal will be above the viewer. Take into account light sources, so there are not strange shadows. Next calculate how much the painting will need to be enlarged into a wall mural to fit the space (265%). Then check the size of the last cast vertebra – 9.5” tall. So, at 265%, the last painted vertebra needs to be 3.6” tall in order to fit the expanded painting.

Water painted on Plesiosaur mural

Washes of blue acrylic get rid of the white void, and actually make it easier for me to concentrate.

Now it is time to paint. Redraw the critter on the canvas and rough out my lighting and shadows. I like to do an underpainting of acrylic first to get rid of the blank white of the canvas. Nothing is worse than a big white canvas staring at you. Acrylic dries fast, which is good and bad. Good because I can get a lot of color on fast. Bad because I’m terrible at going back and blending with established (i.e. already dry) colors.

Some bones have been painted onto the Plesiosaur mural

After layers of acrylic, the painting is just about ready for oil paints.

Once the underpainting is done, I start in with oil paints. Sadly I have an allergy to standard oils, but I’ve found a walnut-oil based paint that is low odor and is smooth like butter. The oils I can blend on palette, as well as on canvas. As of right now, the painting is almost done – I’m not going to show the final image, however, until our grand unveiling of the exhibit including the mural and cast neck and skull. So come by the museum on April 27 and you will be able to see the finished product!