Thursday, October 10, 2013

Atractosteus from the Hell Creek

I feel a bit guilty. I found a gar specimen last year, in a soft sand, and I was afraid to prepare it. I had nightmares of thousands of bony scales floating loose in space. Well this week I finally took the plunge and started work. I've even been able to identify it to genus (I think). Let's start at the beginning.

June, 2012:
Hey look, a fossil! Toes for scale.
While prospecting in far western Harding County, SD for typical latest Cretaceous dinosaur fauna, Jacob and I climb a really high butte to GPS a Triceratops and see if it's on our landowner's property. No luck, it's a few dozen yards too far south. From up high we see a few very small low outcrops on our landowner's side of the fence that probably should be checked out. Jacob heads towards the pond, I trudge up to a sand blowout about 5 feet high at the most.
Scales in the field

The gar was just laying there in the flats. The scales caught my eye first, then I noticed the vertebrae, and the faint outline of a skull just barely coming to the surface.

Finishing the perimeter and consolidating
We treated the specimen like ones we dig up in Kansas: no need to expose any more, just find the perimeter. If you hit bone (or scales) just move on in a wider circle. The sand was so soft that we did all the work with mason's trowels. In about an hour or so, the site was perimetered.

Jacket's done!
I was fearful that no matter how good of a jacket we made, the thing in the loose sand would collapse out of it as we flipped the jacket, so I made the call to saturate the topside of the block with B-72 to harden it at least a bit. The hydrocal jacket was then applied directly to the rock, no separator being used. By lunchtime we had the jacket under control. Back in the lab, it sat under a workbench for over a year.

October 2013:
The specimen, now known as RMDRC 12-008, alternatively "ValDaGar" after my wife (plus it's really fun to shout), is brought out of storage. I figure it would be good to at least get the skull exposed, if it's there, before SVP. It'd suck to show up a second year in a row and tell researchers "no, we still haven't worked on it yet". After removing a few inches of sand (we dug deep JUST IN CASE) I finally hit something hard. Luckily it was bone, not the other side of the plaster jacket.

Here's where to start

Ok, I admit, it doesn't look pretty
Exposing the skull took surprisingly little time. I moved a bit further back to see if there was indeed articulated body. There was indeed. Every one of the hundreds of scales is getting prepared individually. I'll let the photos speak for themselves
Much better

The body slowly gets exposed

Side of face floated off a bit