Monday, August 25, 2014

Making a Archival Cradle for Bernie's skull

I just got back from a two week fossil hunting trip including a week digging at the famous Como Bluff in Wyoming. I'll have more to say about that later. First, here's what I did immediately before the trip.

Part of preparing a fossil is preparing long-term storage for it. Fossils will badly deteriorate if rattled around loose in a drawer, many will break under their own weight, and all will get scratched if rubbed by other fossils. Bernie's skull will have to be protected for the long term (100+ years) by a rugged cradle of some sort.  I have followed a procedure developed by the Peabody Museum at Yale to make custom supportive cradles to protect it.

A link to the Society of Vertebrae Paleontology's Preparer's resources  can be found here:
 Resources for Preparers

And a specific link to the cradle technique is found here:
A Review of Vertebrate Fossil Support (and storage) Systems at the Yale Peabody Museum of Natural History

Using this technique, first I cut a piece of 3/4 inch plywood in an oversized outline of the skull. The edges are beveled to allow for easy pickup of the cradle and fossil. The oversized outline prevents the fossil from bumping into adjacent fossils (if they have similar cradles). The drywall screws projecting up into the plaster will hold it to the plywood since plaster and wood would otherwise separate in time.
I rolled out a piece of clay to act as the substitute for the eventual padding layer. I made the clay approximately 3 mm (1/8 inch) thick . 

Then I covered the skull with a separation layer. You can use thin cling wrap, but I chose aluminum foil as it would bridge the gaps in the skull nicely. 

Then I covered the aluminum foil with the clay where the future padding will go. This goes on the underside of the skull when it is on the cradle. For Bernie, I had to be careful that the cradle would not capture the fossils and keep it from being removed from the cradle. (It could not be re-entrant)

Here's the cradle base with the clay-wrapped skull. 

Then I put an additional layer of aluminum foil over the clay to prevent it from sticking to the plaster. 
 After mixing the plaster quickly, I put a large amount on the plywood, inserted the skull, and smoothed the outer edges. The plaster set quickly and I did this in two applications to give myself enough time. After hardening a few minuted I smoothed the outsides and trimmed the upper edge to be about 3 mm (1/8 inch) thick.

 Here is the cradle after the plaster has set and the aluminum foil and clay have been removed. For the moment I am using a layer of no-slip padding to keep the skull off the plaster. Eventually I'll have to get a longer-lasting plastic foam, probably made of Polyethylene. However, since the cradle is deep, I may decide to not glue the padding to the plaster and keep a replaceable foam padding.
 And here's the other side. It keeps the teeth up in the air so nothing touches them.
Hopefully this will last 100+ years, but I won't be around to see that. 
Sincerely, Greg Carr

Friday, August 8, 2014

Off with its - ?nose? and some dental work as well.

The skull preparation is coming down to the final lap. I decided to take off the nose and repair a large crack that evidently occurred when the skull was buried. I can tell this because the material in the crack is the same as the surrounding matrix. Cracks that occurred after the sand has become rock are filled with plain calcite.

To do this repair, I dug down deep through the crack (which was 2 - 4 mm wide) with a narrow bit from the #5 Paleotool (c) until the nose broke off the rest of the skull. I then cleaned up all the excess matrix from the surfaces of the break and fit it back together. This resulted in a very clean fit of the parts in the original configuration. In addition, it gives us a chance to see the cross-section of the jaw bone structure. This is really cool since we won't be able to cut across the bone and section it after it is officially classified as a new animal (known as the Holotype).

So here are pictures: The skull before repair, with a tennis ball standing in for the eyeball

Here is the skull with the pieces all cleaned up and fit back together. The fit of the parts is very clean. They are not glued back together yet as it's easier to do the final preparation on smaller pieces. So I'm just holding them together by hand in this picture. The curve of the jaw is a little more pronounced after it's in the original location.

A closeup of the break, partially excavated with the Paleotool
The inside (center line view) of the nose after removal
A closeup of the center line view of the main skull end after nose removal
The end-on view of the broken cross-section of the skull end. I'll have to do something else to get a proper depth-of-field view of the break.
And here is the broken end of the jaw fragment
Here's a little better view of the complicated bone structure immediately under the teeth. (Top left corner of the bone fragment)

Here's the inside of the nose after final cleaning. Note that there is a small tapered groove running from the tip of the nose back to the nasal passages and the naris (nostril holes) at the rear of this fragment. I believe this passage is used for expulsion of salt-laden water produced by specialized glands. These glands are found in marine iguanas and sea birds, and this physiological adaption allows them to live full time in the ocean and drink salt water. I bet this has never been seen before in such an old animal!
Here are the teeth after cleaning. You can see the broken-off roots of many more teeth, and some holes where teeth would have been. I don't know if these were broken before or after death. There was a large bone (coricoid) laying across the jaw where the teeth were broken and touching it. That could have helped break off the teeth, though there are no serious scratches on the coricoid. Perhaps it just nestled in the available space as the bones were packed together. I count t least 8 broken or missing teeth. The missing teeth  will give us a good chance to study the tooth root structure later
Here is the main jaw. These were some serious teeth - over 6 mm in diameter. Tennis ball in the orbit.
And here's the entire jaw looking down into the teeth row.
I only have about 4-5 hours left and the skull will be finished. Then I will build the archival cradle to hold it.
Sincerely, Greg Carr