Friday, September 11, 2015

Mandibles and scraps

I'm collecting pictures of all the mandible parts that we have found to date. A long time ago we found our first piece of mandible. This gave us the first clue that skull pieces would be found, even before the actual half-skull was found. Then we found an enigmatic piece which looks like an Ichthyosaur mandible piece, with a groove for tooth roots. I'm not sure now that is came from an Ichthyosaur since we have not found any other pieces like it. Here are pictures of both of them.

Here is the second definite mandible piece. It is split and the tooth roots are visible in the jawbone.

Latest, we have a more complete mandible in two pieces. One was excavated last year, the other piece a few weeks ago. They are both from the same bone, but were located in two blocks (block 1 and block 2) and were broken through when the blocks broke. This is the most complete fragment so far. It clearly shows that the front part of the jaw had teeth in sockets, but further toward the rear it transitioned to a grooved bone that may not have had teeth. Think of a horse, with cutting teeth in the front and molars in the rear separated by a vacant space. ( where the bit goes).  Other known thallatosaurs have weird tooth patterns so this is not surprising, I'd really like to find a whole lower jaw, or at least more toward the rear, but you get what you get on these beasts.

I wish you could see the detail in these teeth. They even have small pits in them. A retired dentist friend of mine ( Greg Gentry) from the NARG group says it's probably a case of the enamel wearing through and exposing the dentin, Since the dentin is softer, it wears away and forms a pit or depression. Anyway it's really cool and wonderful to think that these teeth were used 230 million years ago and were made the same way as current teeth, even though tey are reptile and our teeth are mammal.

 Last of all, I've been going through the back-log of bones removed from the block but not yet finished. This includes a lot of smaller fragments and backbones  - centrums. They don't tell us a lot scientifically so they have a lower priority, but we need to do them eventually. Here are a lot of rib fragments:

Ans here are a couple of centrums - the force-bearing part of the backbones. One of these is very unusual by being thin for it's diameter. We have one or two like this already. They both show the typical hourglass figure where the neural arch attached to them, so we know they are both from these thalattosaurs. 

Sincerely, Greg Carr

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