PaleoLab

Project: Tyrannosaurus rex

skullRemarkably, the skull of the type specimen of Tyrannosaurus rex—arguably the most famous of all dinosaurs—had never been scientifically studied since its mounting. Shortly after the first skeleton of this large predator was collected by the famous dinosaur hunter Barnum Brown in 1902, its skull and skeleton were reconstructed for exhibit at the American Museum of Natural History in New York. The skeleton was sold to Carnegie Museum of Natural History in 1942. Click here to read about the history of our T. rex's journey from New York to Pittsburgh!

Unlike most dinosaur specimens on exhibit in Dinosaurs in Their Time, the skull of T. rex was, for the most part, sculpted out of plaster and contained only a few original bones and teeth. Later discoveries of more complete skulls of this dinosaur showed that this reconstruction was incorrect. Therefore, in 2003, the skull was carefully dismantled by experienced preparators to expose, clean, and conserve the original bones and teeth, which, for the first time, were studied by paleontologists. After this study was completed, the bones and teeth were inserted into a new skull reconstruction based on the more complete skulls of T. rex that have been discovered since 1902. The specimen was unveiled in 2008 in its new pose in Dinosaurs in Their Time.

Preparator's Journals

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April 28, 2008 - Allen
Here is a summary of what has happened over the last few years:

As described in the logs, the type skull was disassembled with all the fossil elements being cleaned and repaired. The fossil elements then went back into the collection as separate bones. Norm, Lauren, and I made molds of these elements and then casts. The type specimen casts were sent to the Museum of the Rockies where Michael Holland used cast elements from several of their specimens and the type specimen casts to reconstruct a complete skull. The skull that is on the type specimen is a composite of several tyrannosaurs including all the elements from the type specimen. Phil Fraley Productions-Pittsburgh painted the type cast skull, and Phil Fraley Productions-New Jersey mounted the type cast skull onto the type skeleton. All of the actual fossil skull elements for the type reside within the Carnegie Museum vertebrate paleontology collection.

October 21, 2003 - Amy
I finished cleaning the surangular today. As I mentioned last week, I had to leave some of the plaster on the bone because the bone would have fallen apart if I tried to remove it. The surangluar was the last bone that I had to work on of the T. rex skull, so this ends the preparation portion of the T. rex skull project. The next stage will be a scientific study by curator Hans Sues, PhD. Then the skull will be reassembled correctly by an outside contractor.

 

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actual bones

actual bones

actual bones

original rendition of the skull

October 14, 2003 - Amy
Today pretty much followed the same pattern as last Tuesday. This time I used the microjack # 4 airscribe to remove plaster from the surangular. It is one of the most delicate airscribes that we have. It did the job, but the work progressed very slowly. At about 4:00 a large crack started to radiate across the bone, so I slid the bone onto a board and carried it over to the fume hood where I squeezed Paleobond into the crack. I will probably not remove any more plaster from this bone, as I fear that it will fall apart on me. I’ll check with curator Hans Sues, who is the supervisor for this project, to see if he agrees.

October 7, 2003 - Amy
I continued removing plaster from the surangular today. It seemed like some of the plaster was glued to the bone, which made it very difficult to remove. At a certain point the entire bone seemed like it was going to fall apart, so I moved it to the fume hood and drizzled paleobond into the many cracks. I decided not to work on it any more today. Sometimes it is best to set one project aside for a while and to work on something else.

October 3, 2003 - Amy

skull
surangular

The Paleolab preparators received good news this week. The drier was installed on the air compressor and we can now use our airscribes again. Before the drier was installed, there was so much water in the airlines that we could not use our air tools for fear of having them jam up with rust. As a result we had to take projects to the basement lab when an airscribe was required.

I spent about an hour today working on the surangular bone. This bone is very delicate, so I was using the airscribe to remove plaster. I’d have to stop to apply glue periodically to keep it from crumbling into dust. The maxilla is finished. Norm helped me remove the last piece of iron rod.

I also trained Carol Hammer on the use of the microjack airscribe. She will work on removing rock from some vertebral spines of a very primitive amphibian, Platyhistrix, from the Lower Permian (about 290 million years ago) of New Mexico.

September 30, 2003 - Amy
I have just about finished preparing the maxilla in the basement preparation lab. All that needs to be done is to cut off a piece of metal rod that is sticking out. I decided that the only safe way to remove plaster from the surangular is with an airscribe.  Using the hammer and chisel causes too many vibrations, which could potentially result in cracks forming in the very thin bone.

maxilla
maxilla (metal rod sticking out)

September 26, 2003 - Norm
Just got back from vacation. I’m finishing work on the squamosal. As you can see from the picture, there is still some fine work to be done on the specimen.

skull
plaster being chipped away

September 23, 2003 - Amy
The dentary is now finished. I spent today removing the last of the plaster from the surface of the bone. I also had to cut through a metal rod in order to remove it. This dentary has many more cracks in it than the right one did, and I filled them with Paleobond. I’ll spend the rest of the day working on the surangular.

iron beam
dentary

September 16, 2003 - Amy
Today was a tense day as my task was to separate the dentary and surangular, which I managed to do with 20 minutes left in the workday. It was difficult because the edges of the dentary and surangular where the two bones articulate are very thin and this region was covered by a considerable amount of plaster. I had to constantly check for cracks in the bones, especially along the edge of the surangular, and stabilize them with the Paleobond penetrant solution. This glue is designed to spread readily through and fill thin cracks, and it proved to be the perfect glue to handle the cracks that kept forming as I chipped the plaster away. So, all that remains of this project is to finish removing the remaining plaster from the isolated bones of T. rex skull and lower jaws.

 

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dentary and surangular

separation well under way

separation completed

September 9, 2003 - Amy
As you can see from the photograph, I was able to remove a lot of plaster today using my trusty hammer and chisels. The surangular bone seems to be much deeper than I anticipated. Yesterday I spent about an hour working in the basement preparation lab on the maxilla.

 

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back of lower jaw with iron exposed

lower jaw

who is this?

September 5, 2003 - Amy
I spent today using the hammer ad chisel to remove the plaster reconstruction of the angular bone in the left lower jaw in order to expose the underlying surangular bone. I found an amazing number of nails in the plaster reconstruction of the angular; in fact at one point it was bristling with nails. I also encountered a U-shaped metal rod that I will trace out and eventually remove.

 

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nails in lower jaw

U-shaped iron bar

September 4, 2003 - Norm
Work on the squamosal is just about done. I need to take it to the basement prep lab to use the air scribe for the finishing touches.

September 2, 2003 - Amy
It’s hard to believe that it is September already! We (Norm and I) moved the maxilla to the basement prep lab where I will continue working on it. I’ll be able to use the airscribe which is much more delicate than a hammer and chisel. Then, with the assistance of curator Dave Berman, we moved the surprisingly heavy left lower jaw up to the Paleolab. The lower jaw of T. rex is made up of seven bones. Of these, only the dentary and surangular are represented in the left jaw of our T. rex. The dentary is the tooth bearing bone whereas the surangular extends along the outer surface of the jaw from the dentary to the articular bone, which articulates with the skull.

 

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Dave and Amy

lower jaw

August 28, 2003 - Norm
Just about finished with the squamosal. If anybody out there needs nails I may be able to supply them for I find more buried in the plaster everyday.

skull
nails in plaster

August 27, 2003 - Norm
As I remove the plaster from the squamosal I seem to be running into an interesting amount of hardware. Can you pick  from the pictures three of the five items I’ve found. A nail, a screw, a staple, the kitchen sink , Jimmy Hoffa? We’ll have the answer next week.

 

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what is this?

the kitchen sink?

huh?

August 22, 2003 - Amy
It’s a little after lunchtime and I just finished removing the plaster from the dentary. I also squeezed some more paleobond into the cracks to help stabilize them. The dentary will be moved to the basement storeroom either today or Monday. I’ll spend the rest of the day removing plaster from the left lacrimal.

 

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dentary plaster free

lacrimal with some plaster remaining

August 20, 2003 - Norm
Back in Paleolab today I continued working on the squamosal. I removed the iron beam running across the bottom and a lot of the remaining plaster.

skull
iron beam removed

August 19, 2003 - Amy
I was able to free the dentary from the reconstructed portion of the lower jaw late yesterday. The remainder of Tuesday and all of today were spent removing a considerable amount of plaster from the inner portion of the dentary with a hammer and chisel. As usual, an iron rod had to be cut. This rod actually ran inside of a hollow portion of the front part of the bone.

skull
Amy holding plaster separated from dentary

August 18, 2003 - Amy
Norm and I brought up the right lower jaw from the basement storeroom this morning. Only one real bone in this jaw is the dentary, which is the tooth bearing bone. So far today, I have dug a trench between the bone of the dentary and the plaster reconstruction. Surprisingly, I’ve only encountered two metal rods. These will be cut through using the dremel tool and then the handsaw will be employed to free the dentary.

 

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removing dentary from lower jaw

exposing iron rods

August 12, 2003 - Amy
Today I was able to successfully separate the left maxilla and lacrimal. I continued chipping away the plaster and removed the two remaining iron rods that had extended along the midlength of the skull. Then I removed plaster to expose the dorsal (top) edge of the maxilla and lacrimal. Once this was done I was able to chip the plaster away from where the maxilla and lacrimal abutted each other. The next task was to dig a trench between the descending arm of the lacrimal and the maxilla. I encountered two metal rods which Norm cut with the dremel tool. Finally, after digging the trench for a while longer, the two bones cleanly separated from each other. The rest of the afternoon was spent chipping plaster off of the maxilla.

 

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separating lacrimal from maxilla

separating lacrimal from maxilla

Amy holding separated lacrimal

August 5, 2003 - Norm
Today I’m beginning to remove the overburden of plaster that covers the squamosal. I removed the iron bar running along the lower half with a hammer and chisel and pin vises of various sizes.

skull
iron bar and plaster being removed

July 30, 2003 - Norm

skull
final bone removed

Today Amy and I removed the last real bone from the back of the skull (squamosal). Now all the real bones are ready to be cleaned of the remaining plaster.

July 29, 2003 - Amy
Today we successfully removed the left maxilla and lacrimal. I had to finish digging the trench between the metal rod and the right maxilla and lacrimal. Then, Norm used the drywall saw and wire cutters to cut a thick metal wire running across the width of the skull. The next task was to cut a very thick iron rod that formed a support between the two maxillae. Norm used the dremel tool for cutting, while Allen Campbell, volunteer Jason Pardo, and I held the skull steady. The right and left halves of the remaining portion of the skull were easily separated after the rod was severed. I spent the rest of the day using a very small chisel and hammer to chip plaster away from the joined left maxilla and lacrimal.

 

 

Amy removing plaster

cutting skull

cutting ironwork with dremel tool

split skull; real bones

July 28, 2003 - Amy
The only real bones left in the front portion of the skull are the left maxilla (upper jaw bone) and lacrimal. To free these bones from the plaster reconstruction, Norm and I decided that first we should cut the skull roughly in half along its length. I began this process by using the hammer and chisel to dig a trench along the outer side of the outermost iron rod. After the trench was well underway, I began working on separating the right premaxilla (the other bone that makes up the upper jaw) from the right maxilla. I started to saw where the premaxilla and maxilla meet, but this wasn’t very productive. So then I tried using the hammer and chisel to remove some plaster between the maxilla and premaxilla. After about four taps with the hammer, both the right and left premaxilla separated cleanly from the respective maxillae.

 

 

premaxilla being removed

Amy removing premaxilla

premaxilla in sandbox

July 25, 2003 - Amy
Today we were able to free the lacrimal bone from the skull. First, I finished removing the plaster from the iron rod. It only extended part-way down the length of the skull, so I was able to lift it out instead of having to cut through it. I then used the hammer and chisel to dig a trench along the forwardly directed arm of the lacrimal. Then we used a drywall saw to cut through the trench. Next, with several of our volunteers holding the skull stable, Norm used the cast cutter to try to cut the lacrimal away from the upper jaw bone. He ran into another iron rod, so I had to use a hammer and chisel to free it. Fortunately the vibrations from using the hammer and chisel caused the lacrimal bone to separate cleanly from the surrounding plaster.

 

 

Amy, Norm and Jason removing lacrimal

using cast cutter

using hacksaw

lacrimal in sandbox

July 23, 2003 - Norm
I am continuing with the removal of the squamosal from the back half of the T. rex skull. Because the plaster in this area is very thick, I’ve been using the cast cutter and an electric drill to work through the plaster, along with a hammer and chisel. If all goes well, the next time I’m in Paleolab we should have the squamosal in hand.

skull
squamosal removal in progress

July 22, 2003 - Norm

skull
removing iron bar

Today using a hammer and chisel, pin vise, and cast cutter, I was able to remove the iron bar surrounding the large bone at the back of the skull (squamosal). Now, I should be able to remove the bone without cutting more than one iron bar. Today I am working on removing the squamosal bone from the T. rex skull.

July 22, 2003 – Amy
This bone looks like an upside-down L. The descending arm of the L forms a bony strut between the orbit (eye opening) and an opening in front of the orbit (anteorbital fenestra). The other arm of the L is directed toward the front of the skull.  I am using a hammer and chisel to chip the plaster away from the right outermost of four iron rods that extend the length of the top part of the skull. Then, with the help of Norm, I will cut the iron rod and remove it. Once the rod is out, I can dig a trench alongside the lacrimal to free it from the rest of the skull.

skull
removing ectopterygoid

July 15, 2003 - Norm
Piecing together the skull of a new dinosaur for the first time can be a complicated task. Sometimes mistakes can occur. When the skull of T. rex was initally reconstructed by American Museum of Natural History in the early 1900s, a bone called the right ectoptygoid was mistaken for the right postorbital bone and placed in the wrong location. Our new reconstruction restores the right ectoptygoid to its proper place.Today Amy Henrici and I removed the ectopterygoid that, according to Ken Carpenter’s paper on variation in T. rex skulls, “Osborn had erroneously used ... as a right postorbital in the reconstructed skull.” We were able to work around the supporting iron rods running through the skull, which made it less time consuming. Amy will now take this bone and remove the remaining plaster using an airscribe and pin vise.

July 12-13, 2003 - Yvonne
Norm (the head honcho on this project) assigned the rear portion of the skull as the next task.  My job this weekend was exploratory.  I again solidified the real bone with an ultra-thin glue.  Then I took out the magnets.  Using magnets, we can trace most of the rods beneath the plaster (thank goodness they didn’t use brass or aluminum!).  I started drawing on the skull.  Have to admit that was fun.  Yellow chalk for metal rods, white chalk for bone that was not visible from the other side.  I also marked possible cut sites. We wanted to make very conservative cuts, far from the bone. I started exploring the plaster around the bone, looking for the edges of the bones.  Some of the bone extended more than an inch behind plaster.  The more information we can gather before cutting, the safer the project will be for the specimen, and the less likely we will be to say OOPS!

July 9, 2003 - Norm
Today  we cut the skull into two parts. After consulting with Hans and Chris, it was decided that the best way to get at the real bones was to start by separating the back of the skull from the front and then taking the two real bones from the massive back of the skull, which would make working on them much more manageable. Yvonne and I were helped by Allen Campbell, while Ron and Mindy recorded the process. As can be seen from the pictures, the skull was built to last when it was assembled at the American Museum of Natural History. Iron rods run throughout the skull, and after we cut through the plaster with a cast cutter, we used a dremel tool with a metal cutting blade to get through the rods without causing any damaging vibrations to the original bones. It took most of a nerve-wracking day, but we were finally successful. Thanks to all for the help.

 

 

cutting back of
T. rex skull

back end of skull coming off

front of skull

July 3, 2003 - Norm
I was talking to Conservator Barb Hamann about various conservation techniques. She suggested that I try a magnet to find where in the plaster the iron supporting rods might be. I remembered that a former volunteer, Ralph Wells, a Westinghouse engineer, had given us a number of very strong magnets. I tried one and was able to trace where in the skull the rods were running.

skull
Preparator Yvonne Wilson applying hardener

July 2, 2003 - Yvonne

I tried to solidify the skull today. It has to be treated before we take it apart.  I used an ultra-thin glue to penetrate the cracks in the bone.  It often zips up into cracks that you didn’t even know were there.  Two curators, Norman, and I all discussed strategies for taking the skull apart.  Although it shouldn’t be that hard to remove the plaster, it still has to be planned in order to proceed smoothly.  Norman marked the skull in chalk where we plan to divide the skull initially.  Let’s hope we chose wisely.

July 1, 2003 - Norm

skull
L-R: Preparator Yvonne Wilson, Dept. Chair Chris Beard, Former Associate Director for Research and Collections Hans-Dieter Sues

Hans, Chris Beard, Yvonne and I had a meeting in Paleolab and decided that the best way to deconstruct the T. rex skull is to cut it in half with a cast cutter to separate the front and back halves of the skull. Yvonne spent part of the day using Paleobond penetrant to stabilize the bone, because in many places cracks can be seen.

June 20, 2003 - Norm
Mindy took some professional photos of me removing the iron work from the skull. She will try to take photos throughout the whole preparation process.

 

 

removing ironwork

applying hardener
(a kind of glue)

June 17, 2003 - Norm
Amy Henrici and I had a meeting in Paleolab with Hans-Dieter Sues. Hans suggested how to proceed with the preparation to remove the real bones from the parts that had been restored in plaster. Amy and I took the lower jaws to the Big Bone Room for safekeeping until they are ready to be worked on. I took some digital photos of the T. rex skull on its padded, circular table. This table, built specifically to handle a T. rex skull, is four feet in circumference with a capacity of 4,000 pounds. It rotates 360 degrees and has a hydraulic system that allows it be raised and lowered 12 inches. For additional support, preparators placed sandbags underneath parts of the skull. Such sandbags conform to the shape of the skull and help reduce stress on the fossilized material. Then I looked over some of the scientific literature gathered by Amy Henrici and Yvonne Wilson.

June 16, 2003 - Norm
Today we removed the type specimen of T. rex from the exhibit space in Dinosaur Hall. The exhibitions staff (Jim Senior, Bill May, Don Vojtko, Don Cromer) and I started by taking off the lower jaws from their iron work. After the lower jaws were safely removed, we all took hold of a section of the skull and carefully started to unscrew it from the threaded pipe on which it was balanced, removing the skull in the same way that you might twist the cap off a bottle. This required some not-so-dainty men to walk in circles on a very small platform in order to twist the skull from the pipe and then carry it to a waiting cart. The skull was then carefully wheeled into PaleoLab, the museum’s fossil preparation laboratory.The skull is now safely sitting in Paleolab, so miracles do happen.

 

 

lifting from base

on the cart

moving to PaleoLab

on table in lab

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