Monday, March 13, 2017

Time once again for Girl Scout "Thin...Bones?"

It seems like I have had a run of thin, delicate bones. Perhaps it's just the preservation in this part of the block, or perhaps they were all sorted here hydraulically. I also have a very long gastralia about ready to come out of the same location, almost 8 inches (200mm) long and 3/16" (3-4mm) wide. In any event, I have four bones that have really pushed my expertise in preparing very thin bones.
In the upper left, we have a quadrate. This bone is a link between the mandible (lower jaw) and the skull proper. The jaw articulates on the lower end of the quadrate. Then below it, lower left, is a possible fragment of skull, perhaps back by the quadrate. In the center we have most of the interclavicle (breastbone on humans). Finally, on the right is what I think is a thoracic rib (from the throat area). It has very unusual grooves in it. 

 All four of these have very thin sections, 1-2 mm thick. I have to be very patient and use lots of glue to keep them together. Above is and end-on view of the thinner sections.

 The quadrate is very unusual too. So far I have 3 entire quadrates and 1 or 2 partials. All 3 of the intact bones are very different in proportion from each other. There is a very robust bone (white 3D printed copy below). A second is almost the same proportions but has a much thinner structure, having only about 1/3 of the bone mass in life.  This new one is also different: it is smaller in one direction, but not so in the others. It is like it has been squished flatter. I don't think this is an artifact of preservation - the bone structure does not appear to be crushed. Here they are for comparison in the similar view:

 And here they are showing the significant different direction - only half the thickness.
So I really don't know what's going on - sexual dimorphism? Age differences? 
Anyway, they are soon to go up to Alaska. 
Sincerely, Greg Carr

Tuesday, March 7, 2017

Crocodile in the room

Something has been bugging me for quite a while about these bones - the gastralia in particular. We have two main sizes of gastroliths - some are about 1/8 inch diameter, some are about 1/4 inch diameter. A few are larger and smaller - I have one piece, length unknown (as it's not prepared yet) that appears to be about 3/8 inch diameter - if it's a gastralia. The smallest ones are about 1/16 inch in diameter - thickness of a toothpick. Here is a picture of the longest piece of large gastralia I have found, just uncovered today. The gastralia is the vertical bone across the center. It is about 1/4 inch in diameter (6mm), 165 mm long and had a curvature of 11mm. If we make the assumption that this bone is not too greatly distorted, it may reflect the diameter of the belly of the beast. By standard calculations a chord of a circle with these dimensions will have a diameter of about 630 mm, or almost exactly 2 foot across!  So these bigger beasties start rivaling existing crocodiles, larger than Komodo dragons. Unfortunately I cannot easily find the typical diameter of today's large reptiles, so I can't draw accurate comparisons.
Sincerely, Greg Carr

Monday, March 6, 2017

Two very interesting bones, and some so-so

Time keeps ticking away in the ol' quarry, and I keep taking out bones. I've gone back to block 2, the one the skull came out of, having mostly disposed of block 3. Block 3 is down to no visible bones so I thought I'd change. Block 2 still has over 30 bones showing on the surface, enough for a year's work or more.

I have sent off about 15 bones to Alaska, a whole mix. Two in the last shipment, and another currently here in Oregon, are worth mentioning. As 'the first shall be last', I'm commenting on the latest bone. It's an interclavicle (sternum or breastbone to us laymen). This is the first sternum we have found! These bones are "T" shaped, although one side of the top of the tee is broken off. The bone grain clearly shows the bone curve, and the center is very symmetrical and even has a great ridge running down the center. The bone is about 145 mm long, and the fin is very thin - about 2 mm thick at the end. And the bone was broken in many places with missing parts. So with many hours of work it is now close to what is was 230 million years ago.
Outside view .
 End view
 Inside view
We also have a nice limb bone. It is very solid, but the end was broken off before burial. So I think it is a good candidate for sectioning and a bone structure study. 

Now here is the most important news - we have found a osteoderm - a skin armor plate! It is nice shape, great rough surfaces, pits on the surface and everything you expect in this type of bone. And the rest of the story - no thalattosaurs have ever been found with osteoderms!!! This means one of two things: 1) We have the first thalattosaur with Osteoderms - or - 2) We have another species of Triassic Reptile in this mix of bones !!!  Either way, this is really great! 

The inside of the bone - rather smooth (at least in comparison to the other side). 

 The exterior side of the bone - rough and pitted.

 The very convoluted, very Rugose edge.
Sincerely, Greg Carr