Up, Down, and Around the Taylor Marl

[Mikrogeophagus]

Because of the strong storms and sudden drop in temps over the past week, I decided to make a trip up north to Central Texas. I had been meaning to hang out with a couple of people in that region for awhile now, so I went ahead and organized a little itinerary of spots to hit in and around Austin. It had been just over a year since I last hunted alongside our resident Ptychodus expert, Lee (@LSCHNELLE), and I was long overdue on bringing him a few Christmas presents from North Texas. I also needed to take @Bill Thompson out to my Ozan echinoid honey hole (Lower Campanian), so he could score some of the unusual smushed varieties of urchins. At about 7 am, I picked up Bill from his car, and we carpooled the rest of the way while discussing the day's plans. Once we were near Austin, we got a call from Lee telling us that he'd need a ride. We were just in time to catch the exit, and soon all 3 of us were packed into my car, venturing to site 1 in the Lower Taylor Marl.

 

Unfortunately, it seemed Central Texas had not gotten quite as strong of rains as South Texas. The Ozan creek was still a bit mulmy which made it difficult to spot the small, flat echinoids we were looking for. The majority of the creek bed was unproductive (although there was probably plenty of fossils that were simply too hard to see), but we kept positive spirits until we reached the final gravel bar. I had previously found many urchins on the surfaces of large reworked shale blocks that collected at the creek's drop off. Because those blocks sat above water level, they had clean surfaces which made a close inspection very fruitful. One particular block yielded about 2.5 specimens of reddish-orange Allomma lindarae! This echinoid is extremely rare up in the NSR (where they are beautifully preserved with an inflated test), but they occur with much higher frequency down here. I handed them over to Bill for his own collection and forgot to snap a photo myself.

 

 

Grey Allomma lindarae from a past hunt

 

In addition to some shiny black echinoid spines, that was about the peak of excitement for our brief look into my site and soon we were back on the road.

 

Over the past year and a half, I've periodically been reading up on the Bergstrom Formation AKA Upper Taylor Marl (Middle Campanian). For a newbie like me, it's mysterious. Finding collections and past accounts of it online are few and far between. Still, the knowledge of what sorts of strange and awe-inspiring heteromorph ammonites existed within it gave me the drive to completely light up my phone map with potential construction sites. I gave Lee and Bill an initial warning that they were long shot localities, but thankfully they were both game to try our luck.

 

Driving up and down the rolling hills of shale geology felt like an expedition to the dark side of the moon. Outcrops of this part of the Taylor Marl, in contrast with the Ozan of Austin, are exceedingly rare and not many people get the luxury of observing them.

 

We pulled up to the first site. It looked really promising over satellite, but when we stepped foot on the overgrown lots, it was clear that we were a couple years too late. Other than some pretty bivalves, there was nothing much to offer.

 

As we got back into the car, Bill suggested we try a site he had hunted over 40 years ago that had the ammonites we were looking for. Since we were already in the area, me and Lee were both more than happy to give it a try. Eventually, we made it to the house of the landowner and watched Bill walk up to the door and work his magic. From our vantage point a couple dozen feet away, Lee and I had low expectations when the screen door remained closed and the initial conversation hadn't seemed very lively. Meanwhile, we had our own tangential conversations in the car that went on for a bit until we realized that, for some reason, we were still waiting in the car. We looked back at the house and it seemed that the mood of the exchange had brightened greatly. Pretty soon, Bill was walking back with a big smile across his face.

 

After some improvised parking, we found ourselves traversing across an expansive field. Perhaps due to the lack of trees, the wind had picked up and shouting was now a necessity. We navigated our way down a stair-step bank, dodging cow patties, and keeping our eyes fixed on some moderately-sized concretions in the creek bed. Upon reaching the bottom, I set my pack down and began getting my hammer out when I spotted the first jaw-dropper of the day:

 

Sproxybeloceras kimbroense

 

Courtesy of Lee

 

Literally less than a minute in, we were already on high alert. We knew this was the right spot. So we began to split up, hammering away at concretions and picking through the rubble.

 

I came across a huge segment of an ammonite that had some pretty sutures on the left side. We ended up having way too much stuff to take home and this specimen was given to the landowner.

 

Huge ammonite fragment

 

The next ammonite was a huge, distorted Sphenodiscus. This fossil is so strange. It's as if the ammonite was melted and bent into some strange form. On the same concretion, the surfaces contains all sorts of various inclusions. The most interesting is a pile of associated chondrichthyan vertebrae.

 

An inner whorl of Sphenodiscus sp. that seems to have migrated laterally.

 

Another portion of the Sphenodiscus sp.

 

A pile of chondrichthyan vertebrae and some Micrabacia sp. coral

 

Lee came back with a HUGE Baculites texanus fragment that was larger than any Baculites I'd ever seen. Hopefully he'll post a pic of it!

 

As I was walking back from looking at the B. texanus, I stumbled upon a concretion with a particularly shiny gastropod on top. Wondering if any other cool things might be present on the underside, I yanked the whole thing out of the ground. Well... there was something cool underneath...

 

Didymoceras binodosum

 

After cleaning: Didymoceras binodosum

 

The combination of Didymoceras, grassy landscapes, and wind had me feeling like I'd woken up in the Pierre Shale of South Dakota!

 

Nestled within the heavily crystallized center of one concretion was another example of D. binodosum. The crystals are made up of barite (BaSO4) which has a yellow-green coloration under light.

 

Didymoceras binodosum and barite crystals

 

Everyone had a knockout day and we each had several bags filled with concretions. Carrying all of it back to the car was a tough, but happy exercise. I honestly didn't get to see everything the others found because we bagged up so quickly. After stopping by the owner's house once more, we continued on to one last spot to wrap up the day.

 

Bergstrom nautiloid

 

S. kimbroense. Lee gifted the bottom right one which has some iridescence.

 

Scattered spatangoid plates

 

I asked Lee prior to the trip about visiting his South Bosque site so I could collect some micro matrix in order to find a better specimen of that ?Galeocorax/?Galeorhinus. He gave Bill a bit of a tour and spark notes summary on the Eagle Ford geology in Central Texas. Even though I'd had the privilege of hearing all before, it was nice to hear it again and pick up stuff I hadn't last time. The place looked very different compared to 2 years ago. Such is expected for these creeks as each flood alters them so drastically.

 

We didn't want to spend too much time, so we picked around hash layers only just a little. One slab I lifted revealed a moderately-sized Ptychodus tooth. I tried to wiggle it, but for some reason it didn't budge. Lee was also watching as I moved another slab and revealed a second tooth very close by. Now I noticed that the two black structures lacked the ridges of Ptychodus. Maybe they were phosphatic nodules? Their close proximity made me dig a little further down. 

 

Now it was obviously a shark tooth root, and a big on at that! Lee snapped a quick photo during my excitement.

 

Shark tooth root

 

I thought this surely had to be a Cretodus. I tried to carefully remove it, and slowly more was exposed. Sadly, I split the crown off, but it wasn't much of an issue as I had b72 at home. As I pulled it out, I excitedly announced "Cretodus"! But, after a closer look, I didn't see any crown ornamentation. No- instead I saw a super thick lingual neck which shot off alarm bells that it could be the elusive Cardabiodon!

 

The Middle Turonian Kamp Ranch of North Texas is said by Siversson to commonly hold the large-toothed shark, Cardabiodon venator. Much of the South Bosque is slightly older, being in the Early Turonian. From the Early Turonian Watino of Alberta, a similar Cardabiodon tooth to mine was found and labeled Cardabiodon. aff. ricki. A subsequent paper established that the Watino specimen could be an intermediate form between the older Cardabiodon ricki and younger C. venator. I think that might also be true for this tooth. The highly localized labial foramina suggested an affinity for C. venator, but the well-developed cusplets and more gracile cusp morphology suggest close proximity to C. ricki. So, I'll just stick with this tooth being C. aff. ricki.

 

 

C. aff. ricki labial view with highly localized circular labial foramina along the basal edge of the crown root boundary. C. ricki has a more sporadic and dispersed pattern of foramina.

 

C. aff. ricki, Ptychodus anonymus, and Squalicorax sp.

 

A monster shark tooth is the perfect way to end a day in my book!

 

Thanks for reading

[Shaun-DFW Fossils]

Amazing discoveries, I got excited just seeing what you uncovered! Thanks for sharing!

[Ludwigia]

Great finds! I just love those heteromorphs, but that tooth is also nothing to sneeze at.

[Kohler Palaeontology]

Very nice finds !  that's a nice shark tooth.

[historianmichael]

Nice finds! You have a habit of exploring the rare stuff of the Late Cretaceous of Texas. I’m quite envious.
 

Your coiled ammonite from the Bergstrom Formation is Placenticeras. Sphenodiscus does not occur until the Maastrichtian, while Placenticeras lived in the Campanian.  

[FossilDAWG]

That would be a dream trip for me.  Those heteromorphs are fantastic!   
Don

[Fossildude19]

Excellent report and finds!

Thanks for taking us along for the ride!

[Jeffrey P]

Congratulations. I too am super impressed by your heteromorph ammonite finds. The shark teeth and echinoid are also way cool. Thanks for sharing. 

[LSCHNELLE]

It's hard to say what an amazing day that was especially in the Bergstrom member of the upper Taylor Marl. That had been also a dream of mine since 5 years ago. But getting landowner access is not a gift that I have acquired. And I also enjoyed showing off one of the Eagle Ford areas that I have great knowledge of. And that was a joy seeing Tyler finding some nice shark teeth during our brief visit. As requested, here are photos of that giant baculites (180 mm long)! It was probably my best find there.

Edited September 10 by LSCHNELLE
Added information.

[LSCHNELLE]

One more low quality shot from the field an of a red colored in situ Allomma lindarae from Tyler's spot.

[Jared C]

Amazing report!

I’ve been interested in the Bergstrom before as well, only recently finding one good exposure. Unfortunately, I think it was too low in the section and didn’t have the alluring concretion zone I so hoped for. Yours is an impressive escapade and I will be using this report to better nail down the types of concretions to watch out for!

Also, it’s amazing to me how you can make a single daytrip to the South Bosque and come away with a shark I’ve never seen in the upper eagle ford after hunting it for 3 years.
At that- I'm not even sure I’ve ever even heard of a Texas occurrence of Cardabiodon, online or anything.  

Awesome report and can’t wait to see more from you!

 

[PFOOLEY]

[Mikrogeophagus]

6 hours ago, historianmichael said:

Your coiled ammonite from the Bergstrom Formation is Placenticeras. Sphenodiscus does not occur until the Maastrichtian, while Placenticeras lived in the Campanian.

Thank you for the correction! I know very little on ammonites, so this quick Maastrichtian vs Campanian rule will be helpful in the future

 

3 hours ago, LSCHNELLE said:

Wow! I didn't see those sutures up close in the field, but now that it's so clear here I must say they are extraordinary!

 

58 minutes ago, Jared C said:

I’ve been interested in the Bergstrom before as well, only recently finding one good exposure. Unfortunately, I think it was too low in the section and didn’t have the alluring concretion zone I so hoped for. Yours is an impressive escapade and I will be using this report to better nail down the types of concretions to watch out for!

Once you see the concretions, they are unmistakable! Their whiteness really contrasts against the dark shales. Most of the area is private land which makes searching difficult, but it seems the outer Austin area has had so much population growth that construction is really ramping up. Would not be surprised at all if one of those developments hit the concretionary layer or something else entirely! 

 

1 hour ago, Jared C said:

Also, it’s amazing to me how you can make a single daytrip to the South Bosque and come away with a shark I’ve never seen in the upper eagle ford after hunting it for 3 years.
At that- I'm not even sure I’ve ever even heard of a Texas occurrence of Cardabiodon, online or anything.

Yes it is a very odd and newish shark that I think is underreported because Texas collectors are likely to quickly write it off as Cretoxyrhina or Cretodus. Siversson only mentioned in passing (10.5281/zenodo.13549022) that they occur "commonly" in the "Kamp Range" (typo of Kamp Ranch) of NE TX (I only have like 3 lateroposteriors of C. venator). I think I have seen some online from amateurs that are supposedly out of Late Cenomanian deposits in North TX which would make me think that they could possibly be in the Bouldin Flags of Central TX as well. Definitely worth it for everyone to go through their bigger teeth and compare them to Cardabiodon and Dwardius!