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Discovering the unexpected in the Texas Turonian (March 2023)


Jared C

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Perhaps the most definitive, lasting project I've had during my short time in paleo is the excavation and study of a basal mosasaur skeleton my step brother and I found in September of 2021 (If you missed it, it's in my blogs on my profile). The site is on a fairly inconspicuous outcrop of the Eagle Ford formation, in a zone that's atypical for the upper eagle ford, as the rock itself is very condensed compared to what is usual for the upper kef. Notably, while Mosasaur material is very, very rare in the kef (kef is an abbreviation for the Eagle Ford formation), it pokes out with greater frequency here - I have found two other Isolated Mosasaur teeth there before. 

 

Both @LSCHNELLE, a geologist who is very familiar with the Eagle Ford, and a paleontologist that I'm working with have made this observation about this atypical site. Between the three of us, we weren't sure there was another exposure like it elsewhere. 

 

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Over spring break, I was in need of some good luck (after losing the transmission in my new car :DOH:), so, finding myself back using my parents car, I made a drive to spot I had scouted a year ago, expecting to see the massively steep Ozan exposure I had spotted from a distance before. 

 

Upon arrival, I was greeted with those gorgeous grey shales in all their glory. Upon closer inspection though, I was surprised to realize that things weren't as they seemed.

The shales were lighter than the Ozan, and physically much harder. I was suppressing exciting pangs of recognition for a few seconds, but it soon became very clear that this massive vertical exposure was an outcrop of that same lithologically atypical zone of the Eagle Ford that produced our Mosasaur. What's more, this site is many miles away, and mapped as a completely different geologic group. It appears that through upfaulting, a cross section of this zone shot through the layers of earth above it, standing as an Island of the Turonian in a sea of much younger rocks. 

 

One feature of the Eagle Ford (or any formation for that matter) is that the bulk of the rock is barren, only interrupted by small intervals of great fossiliferous accumulation. This stood to be true at this site as well, so I set about chasing those shelly lenses that caught my eye and changed my path of life over a year ago.

 

It didn't take long before I came to a shell lens a couple inches thick. One con of this site being a vertical cliff is that I can't peel slabs up as I can at its sister site, so I had to slowly chip into the lens, one piece at a time. Here are some finds that resulted:

 

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Small shark vertebra

 

 

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Fish vertebra

 

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An oddity, insitu in the middle of the shelly lens. Try your guess first

 

 

 

 

 

Upon removal:

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A really lovely Ptychodus tooth that I suspect is the unpublished species also found at our mosasaur site. Since the species has not been described yet, I can't fairly quote any exact morphological features to cement my ID, but I've seen enough by now to "know the look", and have had several of these teeth confirmed by Shawn Hamm. This tooth was one of the best fossils I could find to confirm the comparison to the atypical kef mosasaur site. 

 

Here's another view:

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Shortly after, I distracted myself from hammering out small chunks of the lens and took a peak under the one tiny 3D protrusion of the lens that there was. Under a ledge only a few inches wide sat a fossil that made my heart skip a beat:

 

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The tip had fallen off, likely from hammer vibrations since I chiseling not far away. But, undeterred, I extracted the slab and was met with an imperfect, though still beautiful sight.

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To find a mosasaur tooth after removing what was in total less than a gallon bag of slabs made for an exciting day. Though broken, a basal mosasaur is a basal mosasaur, who can complain? I was especially excited that this lightning fast find came from a new site - meaning there might just be what I'll happily nickname a "Kef mosasaur lens" that transcends beyond the boundaries of our original site. Any trip where you walk away pondering those things is a good one :) 

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