Basilemys Gets Plastered . . . Again

We haven’t posted for a while, but that doesn’t mean the work on our ancient tortoise has come to a standstill. For more than a month, Jim and Tylor have been piecing fragments of shell together and stabilizing the entire shell with glue in preparation for turning the big guy over.

Jim covered the shell with wet paper towels and then draped it with strips of burlap soaked in plaster, the same thing that was done to prepare Basilemys for his trip from the field to the lab many moons ago. The current plaster jacket is covering the exposed areas of shell and keeping everything intact while  Balisemys rests on his back for a while.

 

 

Once the tortoise was flipped, the rock began to separate itself from the shell and peeled off in one big section, revealing what was preserved on the bottom.  As you can see in the photo on the right (click on the image to enlarge it), there is a beautiful section of shell which is so well preserved that you can see the sutures between the plates and the pitted decoration.  The bottom shell is not as complete as the top, but that’s okay because it allows easier access to the bones lying between the top and bottom shells.

You might remember from previous installments that we have lots of unidentified bones that need further preparation, and you never know what new bones will be found. In the photo below, there is a smooth flat bone that still needs to be identified.  Any guesses?  If so, click on “Contact Us” under the About Us tab and let us know what you think.

 

 

We’ll be back when we have more to report.  Meanwhile, happy holidays to all!

 

Crime Show or Chess Game?

The plot thickens.  Take a look at this pile of bones.  (The view is from the front of the tortoise, looking down on it.) How does one make sense of it all?  Well, the bone outlined in green is either a humerus or a femur. (Bones may have shifted around a bit 75,000 years ago when Basilemys was unceremoniously  moved into his rock abode.) The bones outlined in purple are unidentified ones from previous weeks.  Blue outlines show pieces of shell.

This week as Jim started moving into the shell to work on a previously uncovered bone (the one circled in red, which is also not yet positively identified), he found two new bones below it. The bone peeking out (circled in yellow) from under the old mystery bone is one of the two new mystery bones.  The photo below shows them both circled in yellow.

 

This is still the front of the tortoise, but looking inside of it instead of over it.  Once again, the area outlined in blue is the shell.

Preparation is going to get more difficult with all these new bones inside of our tortoise.  To safely prepare an element, you must remove all the rock around it.  But when you have bones stacked on top of one another like we do with our tortoise, this can get a bit tricky. How can an element that’s attached to another element be prepared and gotten out of the way without damaging either one?

Next week the paleo team is going to spend time figuring out the answer to that question.  They will determine the order in which to remove the elements and figure out how to support the remaining ones after each piece is removed.

We hope to be back next week – depends on how long it takes to formulate the plan of attack.

 

A Big Revelation

This week Jim removed about 75 pounds of rock in no time flat (using the new angle grinder, of course) and exposed the rest of the preserved shell.  In this photo, he is cutting away at the base of the big block so it can be lifted off the shell.

All cut and ready to remove . . .

. . . and voila!  The rest of the preserved shell.

The paleontologists are now able to see how complete the shell is and are better able to interpret what they are seeing.  During the early stages of this journey, they thought they were uncovering the plastron (bottom shell) of Basilemys, but with this latest revelation, they realize they’ve actually been exposing the carapace (top shell).

Comparing our Basilemys to a more complete one helps us see how much of the shell we have.  The area outlined in red shows how much of the carapace is preserved in our tortoise.

Anatomy of a Carapace

The carapace is further broken down into sections.  In this photo, the colored outlines indicate the following:

• Blue is called the neuchal; it’s the rim of the shell where the tortoise’s head is.

• Red is one of the neurals that run down the center of the shell; they are the plates over the vertebra.

• Orange is one of the costals; these are plates that are fused with the ribs. The number of costals and the ornamentation on the shell help paleontologists distinguish between species of tortoises and turtles.

• Green is one of the marginals, which are the edges of the shell.

• Yellow is the pygal; it covers the posterior end of the backbone.

• Purple are the caudals, which are the parts of the shell farthest from the head.

Here is our specimen, which has the neuchal (blue), parts of 2 neurals (red), 3 to 4 costals (orange), and several marginals (green).  We are missing the pygal and the caudal sections of the shell.

This head-on photo of Basilemys shows how it is starting to look like a real tortoise!  The paleo team estimated that this tortoise was approximately 38 inches long by 32 inches wide, and the shell was about 4-6 inches thick.

Next week Jim will work on repairing the damaged portions of the shell and further exposing the skeletal elements of Basilemys. At some point after the shell is repaired, the entire specimen will be turned upside down and work will begin on the plastron.

Summer 2011 Newsletter

This issue of the newsletter talks about the growing beaver population in the Escalante watershed area,  “Bringing the Staircase to the Classroom” through Partners’ Education Outreach Program, and the 15th anniversary of the Monument’s creation.

Summer 2011 Newsletter

We’re Back!

What a difference the right tool makes.  This week LARGE sections of rock were removed from Basilemys’ shell, thanks to the new angle grinder purchased for the paleo lab.  In just one afternoon, a 12- to 15-inch area of shell was exposed.  If the same amount of rock had been removed using an air scribe (even the biggest one), it would have taken weeks!  The grinder will save the preparators lots of time as they work on Basilemys and on the many other specimens in the lab.

The angle grinder is equipped with a diamond blade and basically works like a hand-held concrete saw, but it allows more controlled cuts.  Here is GSENM Paleontologist Dr. Alan Titus using the angle grinder to make the initial cuts into the rock.

 

 

 

Next, Alan makes cross cuts to create square cutouts that are easily removed with a hammer and chisel, or an air scribe in more delicate areas.  (Note the change in color of Alan’s shirt and arms. It’s a dirty job but somebody has to do it, especially when there’s a new toy  . . . er um . . . tool to be tested.)

The before-and-after photos below show how much progress was made in one afternoon.  The checkerboard pattern in the “before” photo was done with an air scribe, which would have worked off enough rock so the hammer and chisel could be used . . . eventually.

 

One edge of the shell has a bit of damage (outlined in orange in the “after” photo). It may have been caused by water getting into a small crack in the rock and slightly eroding part of the shell, or it may have happened during the collection process.  Areas like this can be fixed, though, and when all are repaired, Basilemys will look mahvelous!