A Day of Micromorph Ammonites, Shark Teeth, and Urchins in the Grayson Marl Formation of North Texas

[Aidan Campos]

Here are just some of my finds from a day spent in the Graysonites wacoense Zone, Grayson Marl Formation, Washita Group of north Texas (Lower Cenomanian, ~97mya) last Sunday, November 13th. This is my second visit to the site, which is equivalent to and faunally almost identical to the Del Rio micromorph exposures of further south, today only present at a couple sites in the DFW area. 
 

Starting off with the first find which happened to be my first complete (sans spines and Aristotle’s lantern of course), and largest Goniophorus scotti (Goniophoridae) urchin: 

 

Parasmilia graysonensis (Caryophyliidae) coral

 

A beautiful little Haimirichia amonensis (Haimirichiidae) shark tooth: 

Ex-situ photo of the H. amonensis: 

 

A couple more Goniophorus scotti (Goniophoridae) urchins: 

 

 

Coenholectypus nanus (Holectypidae) urchin:

 

Crushed C. nanus:

 

The most abundant fossil to be found, progenic dwarf Mariella bosquensis (Turrilitidae) ammonites: 

 

 

 

Progenic dwarf Mariella rhacioformis (Turrilitidae) ammonite with distinctive strong ribbing:

 

A very tiny Goniophorus scotti (Goniophoridae) urchin: 

 

 

Turritella irrorata (Turritellidae) gastropod:

 

Two teeth of Squalicorax sp. nov. (Anacoracidae), an undescribed shark from the Grayson/Del Rio Fm. of Texas: 

 

 

 

Second specimen:

 

Progenic dwarf Mariella bosquensis (Turrilitidae) ammonite: 

 

And another nice Goniophorus scotti (Goniophoridae) urchin to finish it off:

 

 

Edited November 20, 2022 by Aidan Campos

[JohnJ]

Very nice finds, Aidan!

[Ludwigia]

Great finds and they won't take up much space either!

[sixgill pete]

Amazing Aidan. I really love the Goniophorus

[FossilNerd]

Awesome finds! Those echinoids are little beauties. 

[Nimravis]

These are great finds, gotta love the small stuff.

[historianmichael]

Nice finds Aidan. You have been making great work searching the the North Texas Grayson micromorphs

[Ironhead42]

These are some of my favorite fossils! Looks like a great trip!

[GPayton]

It never ceases to amaze me how the exact same member of a formation like the Grayson can produce different species even just an hour's drive in a different direction. Here in Waco the infamous (and now unfortunately closed) shale pit produces Cretalamna teeth like nobody's business, but I've only found about three Sqaulicorax teeth in the over 20 times I've visited it, alongside just a single Goniophorus - despite lots of diligent searching for more! 

The first shark tooth you showed a picture of that you called Haimirichia amonensis I had always known as Carcharias amonensis. Did the species recently get assigned to a new genus? I know the Del Rio sharks are really under-described so I wouldn't be surprised if it had.

Great finds! You've made me want to take a break from exploring the Eagle Ford and get back to looking in the Grayson again! 

Edited November 21, 2022 by GPayton

[Aidan Campos]

1 hour ago, GPayton said:

The first shark tooth you showed a picture of that you called Haimirichia amonensis I had always known as Carcharias amonensis. Did the species recently get assigned to a new genus?

Indeed this species was moved quite recently in Vullo et al., 2016 which erected the genus Haimirichia and family Haimirichiidae based on an outstanding articulated specimen from Morocco: “The new material provides crucial anatomical data for this taxon, such as head shape, cranial structure, tooth formula, organization of the ampullary system and type of vertebra. Based on these features, this short-snouted, broad-headed shark is confirmed as a member of Lamniformes but is clearly not assignable to any of the known living and fossil genera, and is thus described as Haimirichia amonensis gen. nov. Moreover, this unique set of features, including several autapomorphies, differs sufficiently from those of odontaspidids and other lamniform families (both living and extinct) that it requires the erection of the family Haimirichiidae fam. nov. The articulated specimen of H. amonensis reveals a novel ecomorphological specialization within the Lamniformes, adding to the high disparity observed within this order. During the Cenomanian, H. amonensis was a common, widely distributed species that likely had a lifestyle similar to that of some living medium-sized coastal pelagic carcharhiniform sharks with a comparable overall morphology, such as the whitetip reef shark Triaenodon obesus.”

 

- Vullo, Romain & Guinot, Guillaume & Barbe, Gérard. (2016). The first articulated specimen of the Cretaceous mackerel shark Haimirichia amonensis gen. nov. (Haimirichiidae fam. nov.) reveals a novel ecomorphological adaptation within the Lamniformes (Elasmobranchii). Journal of Systematic Palaeontology. 14. 10.1080/14772019.2015.1137983.

Edited November 21, 2022 by Aidan Campos

[RuMert]

Impressive finds and diverse too. I usually saw nothing but teeth in Cenomanian