This update covers November 15-16. The loose bone (the right postorbital) stuck in the antorbital fenestra was safely removed on the 15th. I needed a tool that was rigid, strong, small diameter, angled to a point on one end and had a very specific length, plus a very specific angled end on it. It needed a good “handle”. The space under the postorbital bone was such that a tapered tool would not do or fit. As these situations arise any preparator worth his salt will invent or modify a tool to work. Modifying a tool may work great, but then it may compromise its performance or safety later. So I tend not to modify tools for safety’s sake, but invent a single use throw away tool. In this case the choice was obvious- a paperclip modified to suit my needs. It worked great (for the 5 seconds I needed it), and cost nothing. It was needed to hook behind the bone and help lift it out. The postorbital will be fully prepared later. The tyrannosaur skull looks much better with the bone removed now.
Another thing I had to do was glue a paper-thin tiny piece of bone 2 X 1 mm back onto the palatine bone. I have seen many people try and pick such items up with tweezers only to have them: 1. get crushed in the tweezers jaws; 2. fall out onto the floor and get lost forever; or 3. the worst- they shoot (squirt) out of the tweezers jaws, flying directions and distances unknown. Impossible to find. What works for me is to put a small blob of glue on the main piece, then lick a finger tip, touch it to the small bone piece, then simply scrape it with a sharp knife blade onto the glue. From there it can easily be turned over (if needed) and moved into place. Once the glue is dry, excess can be cut away with a sharp scalpel blade.
At the end of the day on the 15th, a new bone was found that gave me hope of a major limb bone, but not enough was exposed to be sure. This morning more work was being done to expose this bone. It was determined to be a hadrosaur (duck-billed dinosaur) chevron; the slingshot-shaped bones on the underside of the tail. So that was disappointing. However, a little later, while digging around some more I found a major tyrannosaur limb bone and possibly another! We are certain we have the femur, but the other bones identity is presently unknown. It’s alignment is consistent with the fibula in a tyrannosaur in its “death pose” with the hind limbs pulled up towards the body. The femur is hollow and crushed so I am mixing 2-ton clear epoxy glue and pour this into the hollow spaces. This glue comes in a 2 barrelled syringe which dispenses the 2 part glue in a 50:50 ratio. It is squirted into a small mixing cup and thoroughly stirred with a wooden tongue depressor such as doctors use (but broken down to a more useful size). The glue is carefully poured in; sometime several batches are needed. I always leave extra glue in the mixing container to use as a gauge of what the glue is doing (is it setting properly?) inside the bone. For multiple batches, I number the mixing containers to see how one batch is curing compared to another. Bubbles rising in the glue are popped with a pin or sharp knife. Any glue that slops onto the bone surface is not wiped off (it will just smear), but allowed to set and is easily scraped off later.
I should also mention that I am keeping an eye of for any evidence of soft tissue preservation such as skin impressions, but nothing has been seen so far.
Late update: We can now confirm and femur AND articulated fibula on the Gorgosaurus, so a tibia is automatic, but what of the foot! There is enough room in the block for that too- fingers crossed.
Dave adds: This series has been going down very well so far and the preparation of fossils is something that gets very little attention. As a result there are, we suspect, quite a few questions ruminating in the minds of the readers and thought that a direct Q & A session might go down well. So if you have any questions about fossil preparation (on this specimen or in general) then add them here in this post. Darren and I will go over them and prepare some answers which will be posted next week. As ever more preparation updates to come soon.
All photos here and in the series are owned by Darren Tanke and the Royal Tyrrell Museum.