Wednesday, February 22, 2012

Mastodon Tooth

At a Girl Scout Event we hosted here at the Museum on January, 21, 2012, an inquisitive young girl scout named Shannon asked me about a mastodon tooth we have displayed in our "Virginia's Underground" exhibit:

And since she was so curious, I promised her I'd blog about a mastodon tooth I repaired for the Museum--that particular tooth is not on display, but is housed in our Museum Collections and used for educational purposes--more below.

But, first, let's back up a bit:  What's a mastodon, you ask?  A mastodon is an extinct distant relative of mammoths (also extinct) and modern-day elephants.  Mastodons (this link takes you to a quick summary of prehistoric "elephants" provided by the University of Nebraska State Museum) were common in North America from about 37 million years ago to about 10,000 years ago.  From fossil evidence, we know mastodons had elephant-like stocky bodies, stood about 8-10 feet at the shoulder, and probably weighed up to 6 tons.  They had a low-domed forehead and curved upper tusks.  Mastodon teeth had blunt cone-shaped points or "cusps" that were used to eat twigs and leaves.  Mammoths on the other hand, had ridged teeth good for eating grasses.  Off the coast of Virginia, fishermen have been known to pull up mastodon teeth as far as 180 miles offshore!  Why so far out?  The coastline of Virginia has shifted over time due to changes in sea levels, which have changed many times during the course of geologic history.

So, back to the tooth:  several years ago I repaired a mastodon tooth that belongs to the Museum--it was in pretty bad shape as you can see from this photo:
It took me a few days, but I was able to piece it back together.  Often, fossil teeth are broken or incomplete as is this one.  In life, the tooth would have had long roots to anchor it into the mastodon's jaw like in the first photo above.  With the roots missing, this is what the tooth looks like from the underside:
This is what the repaired topside or chewing surface looks like:
I first learned to prepare fossils at the South Dakota School of Mines & Technology and later at the National Museum of Natural History, Smithsonian Institution, Washington, D.C.  One of the things I learned how to do was to prepare a latex mold of a fossil, then make a plaster cast using that mold.  I made a latex mold of this tooth by embedding it into a bed of clay, then coated the whole thing with a chemical to make the latex easier to peel off later:
I then applied several layers of latex rubber, letting the coats of latex dry before applying more.  I also embedded gauze strips into the wet latex to provide reinforcement to certain areas of the mold:
After all the latex had "cured" or dried completely, it looked like this:
Next, before I created a "mother mold" or "support mold" of plaster, I put down a barrier of plastic wrap to keep the plaster from sticking to the latex:
Then I constructed the "mother mold" of lightweight Hydrocal plaster, also reinforced with gauze, to give the latex mold some support:
After the plaster set completely, I flipped the whole thing over, removed the clay base, then removed the original tooth from the latex mold:
Here you see the original tooth, the latex mold and the "mother mold."  Eventually I used the latex mold to make several plaster of Paris replicas for the Museum--I even painted them to look like the original!
So, there you go, Shannon!  Thanks for asking such great questions--if you or anyone else has any more questions, feel free to post a comment.

For those of you that are local with children having completed grades 2 or 3 by June of 2012, I teach a summer kid's class called "More Than Dinosaurs"--please check our website for more details.  During this class, I teach a simpler, but very practical version of molding and casting using clay impression molds.

More "off the beaten path" in two weeks....

Cheers,
Lisa

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