North Texas Jaunt - Ammonites, Echinoids and More!

[JamieLynn]

I took a little trip up to Eureka Springs Arkansas and figured I'd get a little quick hunting in along the way....because North Texas is, as we say, a "bit of a drive" (which means anywhere from 3-6 hours, with "fairly close" being anything under 3 hours.....).  I scouted out a few locations and contacted a friend who gave me a few more locations and it's amazing what you can find in 20 minutes when you are motivated by temperatures around 106 F. It really makes you not want to be out for terribly long.  Plus, my husband was waiting patiently in the car with the windows down and I didn't want  him to melt.  

 

But I stumbled upon a couple of nice patches of Texas Cretaceous that I initially thought were Del Rio/Grayson Formation, but I am now convinced are Duck Creek Formation. The first spot yielded my best preserved (large) ammonite I've collected so far.....most ammonites need some prep work to get the inner whorls clean, but this one came out of the ground...just like this!  (The micro ammonites which I usually collect are much cleaner, typically)

 

 

Cleaned up it looks like THIS. Nice suture patterns visible. I think it is a Mortoniceras nodosa. It's 4 inches.

 

I also found a Mortoniceras cf. ootatoorensis, but it is going to need some prep work.

 

A few feet over was a lovely little Pliotoxaster whitei echinoid.

 

Just a little busted test, but overall, a real beauty. 1  1/4 inch

 

 

 

 

 

 

I was very confident that these were Duck Creek formation (what is shown on the Texas Geo Map for this area) but when I checked on another site directly across the road - it seemed to be a VERY different ecosystem....no large ammonites, no heart urchins, but more of the small oysters (Plicatulas) and other fauna that I associate with the Grayson formation, and pretty quickly I found a little Goniophorus echinoid that i KNOW is found in the Del Rio/Grayson formation. But right next to it was a big Bivalve Trigonia that I had not ever seen in the Del Rio! So I was confused. 

Getting home and looking through the HGMS book, the trigonia is a Scabrotrigonia which indeed, is found in the Duck Creek formation and apparently, to my surprise, so is Goniophorus echinoids! So okay, I'm up Duck Creek WITH a paddle.....metaphorically.

 

LOVE these little Goniophorus scotti  Big one is 3/8 inch.

 

The Scabrotrigonia emoryi :  1 inch

 

I also found a very small pyritized ammonite and an even smaller fish vert. But again, it was VERY hot and so that concluded my 20 minutes of fossil hunting! 

a pretty little Neithea texana 

 

So I collected a little bit of matrix from another site a bit off the road and it yielded some very nice little micro finds which helped to confirm my Duck Creek idea with this little Scaphites bosquensis (at least that is what I am fairly positive it is). 

 

 

I also had a chance to stop in at Post Oak Creek, but that will be another post! 

The weather has turned for the better here and the Austin Paleo Society has their Lake Texoma Field Trip planned for this month, so I may just be making my way back up to North Texas ..... fingers crossed! 

 

 

 

 

[old bones]

Good haul for so short a time! I love the echinoids.

[Mikrogeophagus]

Wow those are some epic scores! Definitely worth the hunting trip I'd say!

 

Grayson vs Duck Creek is pretty hard to figure out. Like you said Goniophorus pops up in both so that isn't much help. However, I think your site might actually be Grayson like you originally thought. Your heart urchin looks like Hemiaster calvini as opposed to Pliotoxaster whitei. H. calvini is the most common urchin, after Goniophorus scotti, out of the Grayson. The Duck Creek more commonly has Macraster spp. and Holaster simplex to my knowledge. Your ammonite also looks a little Grayson-y, but that is less substantial evidence. Of course pyritic micromorphs pop up in both with similar preservations so that doesn't contribute to the verdict.

 

Excited to see some sharks teeth from POC. And good luck in the future with Texoma!

[JamieLynn]

@Mikrogeophagus well now you've thrown a wrench in my gears....hahahah!!! It's that Trigonia that has me really leaning toward Duck Creek as I have not seen any trigonias in the Grayson. But I trust your assessment of the H. calvini over Pliotoxaster. I have a really hard time with the spatangoids narrowing them down except by formation. What would set a calvini apart from a plio?  And there is a possibility it's BOTH Grayson and Duck Creek, because they were at two different sites, even if they were close by.

[Mikrogeophagus]

For Trigonias, I have seen a good handful come out of the Grayson with a reddish coloration (preservation is extremely variable in the Grayson, so I'm sure other areas could be diff colors).

 

I am a bit out of my depths in trying to describe urchin anatomy, but I'll give it a try. I only really have an overall perception of what H. calvini looks like. Keep in mind I know basically 0 terminology . For reference, here are some photos of P. whitei that I collected on a DPS trip to the Goodland about 2 years ago:

 

 

I'd say P. whitei has shallower and less sharply defined petals. The petals as a whole seem to be situated farther anteriorly and take up less percentage of the surface on P. whitei. The anterior outline of P. whitei seems more inflated and the posterior extends farther posteriorly. H. calvini is proportionally taller (like a grape) whereas P. whitei is more squat (like a smushed grape).

 

Perhaps @JohnJ or another urchin person can come on here and make a better informed judgement than I.

 

 

 

 

[JamieLynn]

@Mikrogeophagus - I will get out some of my Plios and have a good comparison look at them tomorrow.