First Tetragramma! (with an insitu photo)

[Jared C]

As most of you should be able to easily tell, I know virtually nothing about invertebrates, despite the good potential my area has for them.

However, I was super fortunate the other day to find what ranks among my two best invertebrate finds: My first Tetragramma echinoid

 

While looking for flint nodules to knap, my step brother encountered a tiny little oasis of shale/clay in a vast sea of limestone. He wasn't immediately interested, but still mentioned it when he was talking about how he also found some solid, climbable boulders in the same area.

 

From the photo, I didn't have high hopes, but I still went anyway, mostly to check out the climbing potential there - though I brought some of my fossil collecting gear too. 

 

The area is mapped as Edwards Limestone, so I'm not sure what formation that little tongue of shale actually is - yet I was pleased to find that it was heavily fossiliferous, with many common invertebrates. Here's the entire exposure, shown below: the shadows make it hard to see, but there really is not much shale/clay visible under that limestone overhang anyway

 

 

 

With some inspection, I then saw this:

Isn't that a beautiful sight? While I didn't know the specifics of what I was seeing, I knew at least that it was a quality echinoid, and I was excited by its appearance.

 

It was in solid shape and was removed easily. Only after posting a photo or two on my Instagram story did I realize that it's more than just a nifty echinoid, when @facehugger mentioned that it might be a Tetragramma!

 

Here are some more photos of it when I got home:

 

Rarely does a fossil hunt of this nature end up this lucky for me - an uncommon genus in a microscopic exposure. Because of that, I thought it was worth posting about the whole trip!

 

Edited February 20, 2022 by Jared C
typos

[Ludwigia]

Congrats!!

[Creek - Don]

Nice.  Congrats on your first find!  I also found my first Tetragramma few weeks ago at the Central Texas Walnut Formation.   They are rare. 

[FossilNerd]

4 hours ago, Jared C said:

The area is mapped as Edwards Limestone, so I'm not sure what formation that little tongue of shale actually is

I wonder if the formation know as Edwards Limestone actually has shale layers in it.

 

 Many formations here have “Limestone” in the name because it dominates the formation, but other types of rock can be found in the formation (shale, mudstone, sandstone come to mind).

 

I know nothing of the Edwards Formation and little about the geology in your area, so I may be way off base, but food for thought. 
 

Great find by the way! I’d love to go Echi hunting in Texas!

[JohnJ]

Congrats, Jared.  You might have found an outlier of Comanche Peak formation.

 

 

[facehugger]

On 2/20/2022 at 3:49 PM, Creek - Don said:

Nice.  Congrats on your first find!  I also found my first Tetragramma few weeks ago at the Central Texas Walnut Formation.   They are rare. 

 

You found one of my spots, Don LOL

 

[Creek - Don]

2 hours ago, facehugger said:

 

You found one of my spots, Don LOL

 

Yeah, this spot was visible from the highway.  While I was at ths spot another fossil hunter stopped by and asked me to fossil hunt with him.  He was going further west to collect rocks.  He only stayed for 30 minutes or less.  I gave him some extra gastropod and echnioids since I had ton of them. 

[Jared C]

Came back to show that it cleaned up rather nicely, after a good vinegar soak and gentle scrub:

[JohnJ]

Vinegar should ONLY be used very sparingly on echinoid tests if you want to preserve tiny surface details.  Soaking an echinoid in acid can go wrong in many ways.  

[Jared C]

1 minute ago, JohnJ said:

Vinegar should ONLY be used very sparingly on echinoid tests if you want to preserve tiny surface details.  Soaking an echinoid in acid can go wrong in many ways.  

yikes! I should have checked before I plunged it. Thanks for the heads up, glad it's still in good shape. Is warm, soapy water and a soft brush usually the way to go then?

[facehugger]

I try to avoid soaking, but I will use a tooth brush dipped in vinegar to scrub away situ - @JohnJ is right, I have burnt up a few echs doing a soak in vinegar (thankfully, never burnt a tetra, though). 

 

Your tetra has a tiny associated spine! Super cool...

[JohnJ]

26 minutes ago, Jared C said:

 Is warm, soapy water and a soft brush usually the way to go then?

 

I think cleaning echinoids is an art based on many variables.  

 

Water and a denture brush is a good start.

[masonboro37]

Beauty!