Introduction
During a postdoctoral research project entitled "Jaw mechanism in carnivorous dinosaurs – function and variation of the intramandibular joint of theropods" Jørn H. Hurum’s main interest was with the tyrannosaurids. In the autumn of 1998, a nearly complete lower jaw of Tarbosaurus was prepared by a team consisting of Bjørn Lund, Hans Arne Nakrem, Øyvind Enger and Jørn H. Hurum from the Paleontological Museum, Oslo with help from Tomasz Sulej of the Institute of Paleobiology, Polish Academy of Sciences, Warsaw.
The preparation of the lower jaw was complicated because it was preserved together with the left side of the skull. The lower jaw was disarticulated from the skull and its constituent bones were separated. Silicone moulds of these were made during the 14 days spent in Poland after which Prof. Halszka Osmólska suggested the skull should be prepared in Oslo. This was a big challenge which we accepted without hesitation. For the past 8 years, Hurum had been working with specimens of small multituberculate mammal specimens from the Polish-Mongolian Expeditions. The change from the smallest vertebrates of the Gobi Desert to one of the largest, was a challenge in preparation techniques and logistics. A multituberculate has a skull size between 20 and 30 millimetres and the Tarbosaurus specimen has a skull length of 1,2 meters.
Tarbosaurus bataar
Tarbosaurus is a close relative of Tyrannosaurus rex and they were of similar size. While Tarbosaurus roamed in Mongolia, Tyrannosaurus was the king of the late Cretaceous in North America.
The specimen of Tarbosaurus prepared in Norway has the catalogue number ZPAL MgD-I/4. It was found in Nemegt, Gobi Desert, Mongolia by the Polish-Mongolian Expeditions led by Prof. Zofia Kielan-Jaworowska in 1965. The specimen was partly eroded and only the left leg, the hip and 13 vertebrae were collected. The remaining parts of the skeleton were collected in 1970. The right side of the skull is eroded away, and a few of the internal skull bones are missing.
Fig. 1. The skull still in a wooden crate before the removal of the lower jaw (photo: Jaroslaw Stolarski).
For us, the erosion of the skull was fortunate. Had it been a complete specimens, we would have never be allowed to prepare it as we did. Usually such a valuable specimen is only prepared from the outside. As it was, we took the skull apart bone by bone to reveal many new structures and this specimen is the first Tarbosaurus that can be studied both from the inside and outside.
Problems we want to solve during the study of this specimen:
- Some scientists believe that Tarbosaurus bataar and Tyrannosaurus rex are so much alike that the former belongs to Tyrannosaurus Only a detailed comparison of the two can solve this problem.
- Most scientists claim that the skull and lower jaw of tyrannosaurids were as loosely articulated as in varanoids and snakes today. This means that the flexibility allowed lateral flexion for increasing gape, or maybe it functioned to absorb, or soften, impact during biting.
- Some scientists claim that the robustness of the skull and lower jaws gave a rigid crushing bite.
We hope to solve these questions when the descriptions and comparisons are completed in 2001.
The preparation
The lower jaw was prepared in Poland in October 1998 and the skull was prepared in Norway in May 1999. A daily Internet diary documented the preparation of the skull while the remaining work was recorded more sporadically. This site was made for a Norwegian audience in 1999, and translated to English in April 2000.
Daily reports during the preparation, May 1999
May 3
May 4
May 5
May 6
May 7
May 8
May 10
May 11
May 12
May 13
May 14
May 18
Reports on the work with the specimen since the preparation
Photographing the bones
Silicone moulds of the bones
A peek into the brain
Back to Warsaw
Casting
The skull is assembled
Tarbosaurus on exhibit
The best view of the skull
Links
More about the Polish-Mongolian Expeditions http://www.paleo.pan.pl/museum/mongol.htm
More about Tyrannosaurus http://www.ucmp.berkeley.edu/trex/trexpo.html
About the Russian specimens of Tarbosaurus http://www.mathematical.com/dinotarbosaur.html
About the Tyrannosaurus "Sue" http://www.fmnh.org/sue/default_icam.htm
Dino links http://www-geology.ucdavis.edu/~GEL3/SHORTCH12.html
Paleontological museum home page
May 3 1999: The preparation starts
Photo of the skull after the removal of the lower jaw
Tomasz Sulej carefully removes the sediment covering the bones with an airscibe. Note the drawings of the specimen in the background. The preparation is very noisy.
May 4 1999: Breaking the skull in two!
The transport form Mongolia to Poland inflicted a large break just behind the tooth row which split the skull in two. We decided to break off the snout.
After a few hours of hard work the snout was loose.
May 5 1999: Starting to prepare the details
Jørn H. Hurum is seen preparing one of the small pieces before gluing them together.
Pieces removed from the skull are numbered and drawn on a large photograph of the skull. One surprise was the find of a large bivalve in sediment inside the skull.
May 6 1999: The teeth are prepared
Øyvind Enger, janitor at the Paleontological Museum, Oslo, is the project’s tooth specialist. He prepared specimens at night. The dentine is so fragile and the enamel so thin that this is the most exacting task of the whole project. One morning, at 3am, Enger used too much superglue on a tooth and glued his hand to the maxilla! He was stuck to a precious bone weighing about 6 kilos. He considered sleeping until help came. However he managed to use a debonder and could go home.
May 7 1999: Turning the posterior part of the skull
The posterior part of the skull was cleaned for clay today. We used a box with soft material to protect the fragile inner side while we removed the burlap and plaster from the outside.
Some of the bones are now already finished. Here is the lacrimal bone.
May 8 1999: Mapping the bones
It is important to know exactly where all the removed fragments originally were. We are making photographs, notes and drawings of the bones.
The skull is now in many pieces.
May 10 1999: Only pieces
The skull is now broken into pieces. We put every fragment in a box with number corresponding to that on the maps. The big box contains the posterior part of the skull.
This attractive bone is the ectopterygoid, from the palate of Tarbosaurus.
May 11 1999: Unknown fragments
There were numerous skull fragments belonging to our specimen in the Warsaw collections. We took all of them to Norway and today is the big WHAT WHERE??? -day. During the day we found several important pieces among the fragments.
Only one piece is left with several bones articulated, we did not dare to break it apart.
May 12 1999: Cleaning the separate bones
The clay surrounding the skull is soluble in water, but we did not dare wash them as they were so fragile. One of the more robust bones, the jugal, was cleaned using water to remove a piece of the lacrimal attached.
Working late!
The jugal after the cleaning in water, here compared to the jugal of Allosaurus.
May 13 1999: The braincase
We believed that our specimen was so heavily eroded that the braincase was missing. But after two days of playing with the mystery bones we realized that it was present in pieces!! In the next exiting hours we puzzled together a complete braincase.
May 14 1999: the camera did not work….
Technical problems with the camera, no pictures from this day
May 18 1999: Putting the skull together again
This is a big day trying to assemble the skullbones. We are not missing much!
The skull from the inside
We are trying to fit in the braincase
The skull from the outside (premaxilla missing)
Tools and glue
Hand tools include small hammers, chisels, needles and brushes.
Mechanical tools include airscribe and an engraver tool.
The bones are more fragile than the sediment. This problem is solved by using large quantities of superglue to harden the bones.
The preparation team Øyvind Enger, Tomasz Sulej, Bjørn Lund og Jørn H. Hurum.
The music played during the work:
I love the dead - Alice Cooper
In the flesh - Pink Floyd
Coming Back to life - Pink Floyd
Death is not the end - Nick Cave and the Bad Seeds
Lovely creature - Nick Cave and the Bad Seeds
If I could turn back time - Cher
Heart of stone - Cher
Light at the museum - Wall of Voodoo
Groups:
T-rex
Dinosaur jr.
Barbie Bones
Grateful Dead
Photographing the bones, September 1999
The Museum photographer, Per Aas, photographed the separate bones from at least two views. Both black and white negatives and digital pictures were made.
A photo of the posterior part of the skull
Silicone moulds of the bones, October 1999
Silicone moulds were made of every bone. The bone was divided by cardboard into sectors before silicone was added.
A silicone mould of one of the pieces.
A peek into the brain, October 1999
Just before the material was returned to Poland we managed to get into the computer tomography (CT) laboratory at Ullevål Hospital. This was the oldest patient they ever had!
The braincase in the tomograph
Mona, head of the laboratory, helps us with the digital processing.
The first 3D pictures of the Tarbosaurus brain. The volume of the brain was 0.19 litres., less than a cup of coffee!
Back to Warsaw, October 1999
The skull packed for the long journey back to Warsaw. It is sad to say goodbye to this specimen we know so well.
Jens Jahren & Øyvind Enger
Casting, November 1999 to March 2000
When all the silicone moulds were completed, Bjørn Lund started to make casts of each bone. This is one of the most advanced moulds.
Every mould has been studied to find the best position for the casting holes. Casting material is poured through these holes.
The casting material is of the same consistency as yogurt and hardens within a few hours.
The skull is assembled, April 2000
The skull is colored to look like the original bones
Done !!!!
Tarbosaurus on exhibit, April 2000
We were asked by the IMAX Cinema in Oslo to mount a display for their opening of the film "T-rex 3D". We were offered the whole lobby as venue for an exhibit on tyrannosaurids and the evolution of birds. This was a great opportunity for us to explainthe Tarbosaurus project.
The skull was mounted on transparent plastic so it could be admired from both sides
The skull is glued onto the plastic sheet; we are quite nervous at this point.
When the lower jaw was mounted we took a deep breath and cleaned the plate for glue and fingerprints.
The exhibit is ready!
The best view of the skull, April 2000
The start: an ugly looking, broken skull in a wooden crate. The glue used 30 years ago has turned brown so that the skull is discolored. The skull is seen from the inside.
The end product: a magnificent skull of Tarbosaurus ready to be studied.
Seen from the outside, a model of premaxilla added.
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Publications from the project:
Hurum, J. H. & Currie, P. J. (in press): The crushing bite in
tyrannosaurids. Journal of Vertebrate Paleontology. 10 pp. 2 figures.
Describes the lower jaw in Tarbosaurus and Tyrannosaurus.
Sabath, K. & Hurum, J. H. (manuscript): The skull of Tarbosaurus bataar.
Acta Paleontologica Polonica (2001).