Tuesday, December 17, 2013

Jaw Fragments and Shoulder Girdle

Jaw Fragments and Shoulder Girdle

We have for your viewing pleasure a couple of unrelated items. Back in July I posted about a jaw fragment with teeth that we found. We now have a second jaw fragment, with tooth sockets. These two jaws are not from the same type of animal. In one, the teeth are in separate sockets  - called "Thecodont". The other, the teeth (now missing) are in a groove with equal sides - called "Aulacodont".

The Aulacodont is most typical in Ichthyosaurs except for the Triassic varieties of Shonisaurus and Cysbospondylus which are Theocodont. The giant amphibians have teeth that are in individual sockets - Theocodont. So who's jaws do we have above? 

The skull we have, amphibian, has teeth present but the details of the jaw are not clear since they haven't been prepared yet. The teeth in the jaw look like the teeth in the picture above.  So I'm betting the jaw fragment with teeth belong to the amphibian, and the jaw with the groove is from the Ichthyosaur. This contradicts my posting of July 26th where I thought we had the Ichthyosaur jaw. We keep learning new things and finding new bones all the time with this specimen! 

As a second item, we have now fully prepared what looks like a Scapula. Previously we had two bones that I believed to be Coracoids. We also have a humerus, or upper arm bone. We can fit all four bones together as they would have been in life. This scapula is thick at the part where all three bones fit together (the Glenoid Process) where the limb rotates. Otherwise, it is very thin about 1-3mm thick. This bone required a full plaster backing to complete the preparation. It came out very nicely - a great bone!. 

 We are still missing the clavicles (collar bones) but one bone is a strong candidate. 
We'll have it out in a couple of days so we should be able to see if it really is a clavicle. 

Friday, December 6, 2013

Humerus, Femur and Scapula

Quick posting - Humerus and Femur and Scapula

I have finished preparing a second upper (proximal) limb bone. Back in the spring I prepared out what I considere to be a Humerus based on one wide end. I now have a second bone that is the same shape, only a little smaller. It also is a mirror image, so it probably came from the other side of the body. I think we have a Humerus (larger bone) and a matched Femur (smaller bone) from the same animal. Both bones have hollow ends, indicating they both came from a subadult animal. The simplest explanation is that we have fore and hind limb bones from one animal. The other explanations (a pathological specimen or bones from two individuals) are always possible but not probable. Here's the pictures (camera didn't focus too well):

I also have the first Scapula removed from the large block and being finished. The front side has all the matrix removed, and the back side has most of it removed. Since it is a very thin bone (about 2mm in places) it would break badly when removing the last of the backside matrix. So I've coated it with Latex and bedded it on a plaster backing. This will provide enough support to remove the remaining matrix. I should have it done next week or two. I used this same technique while preparing a coracoid and it worked really well. I promise to post pictures of the scapula, the humerus and the two coracoids together when they are all done so we have a size comparison. 

Merry Christmas one and all. 
Sincerely, Greg Carr