Fish Thyme (Time?)

I’ve been having some fun in the workshop the last month or so playing with and learning about how in the world to prepare and expose fossil fish from the Green River Formation of Wyoming. I bought five small samples of the most common fish found in this formation that are in small, flat slabs of limestone. The fish (and other seas animals) are found smashed flat in thin layers of stone that was fine sediment at the bottom of a huge inland lake. The samples I picked up at the Tucson Fossil Show last month are from the layer referred to as the “sandwich layer” and are the most common two types of fish they find – Knightia alta and Diplomystus dentatus.

Here’s a photo of the five plates I picked up with light pencil marks over the line of vertebrae along the spines of each. That gives beginners like me a reference mark of where to start picking away at the overlaying rock layer. If you hold one of these slabs up to the sunlight and move it around you can clearly detect the “bumps” in the surface of the stone that are the telltale sign that something is hidden underneath.

Maybe there’s a fish fossil in each of these five thin slabs of limestone?

With much trial and even more error I have been using a variety of tools and techniques to try to unlock these thin, fragile fossils from the overlaying limestone layers. It’s quite a trick. One picks or pries at the surface stone around the line of vertebrae trying our best to gently prod the stone up and off without damaging the paper thin layer of bones and flesh imprint left on the rock. It’s a trick I have absolutely not mastered (yet). Hence why I’m working with the most common, least expensive and least rare of this type fossil. And I’ve been having fun. Tiny picks, needles, small air scribe tools some, tooth brushes, air blowers, and our sand blasting cabinet (very carefully!) have all been tried. Just a hair too much pressure with a tool or too straight down at the piece and whoops, I damage it or loose a tiny bit of the fossil impression or bone.

Here are a few photos of two Knightia alta fish I’ve completed. Not great, but I’m having fun learning and isn’t that what it’s all about anyway.

You can see where I blew away the faint dark impression of fish bone and flesh on top and to the rear of this specimen. It’s hard! (And what’s that above his/her head? Might be a poop from another fish.)

Here’s the second one I prepared and cleaned up –

Did a little better on this one with less loss of bone material.

And a few photos of the third one I’m working on now. A couple in progress so you can see the development from nothing to something! I think this specimen is the Diplomystus dentatus variety. Also very common and a slightly larger fish with a slightly different fin pattern than the Knightia.

Following the pencil line which highlights the raised backbone of the fish.
Now the specimen is becoming more visible. The slab of stone is in reversed position from the first photo above. It’s coming around nicely and looks bigger than the first two.

And here’s the almost fully prepared piece. Complete with other things about; see the trail of poopoo(?) above its head. There are also some small items that showed on the obverse side that I went ahead and exposed for the practice. They are a full half an inch of stone below the surface where our fish friend came to rest – meaning these small deposits are from a very different date, older than our fish.

Almost done, but still trying to remove some stone between the visible ribs.
On the back of the same fish plate I saw two distinct bumps and both are evidence of … something?

And lastly, here’s the fully prepared specimen of Diplomystus – my first one! And see that I discovered a second fish as I cleaned around the mouth parts. Saw some more black bits so I cleaned more. Look what I found – a 2nd fish that was either being chased by the first OR (more likely) was caught up in the same event that killed the 1st one and they just settled on the bottom of the lake at the same time. Being chased and almost eaten by the 1st fish is a more exciting story, for sure!

Two fish, one small piece of limestone. I didn’t know the 2nd little fish was there until I did!