Dwarfed Ammonites, Shark Teeth, Brittlestar Fragments, and more: A Few Hours in the Grayson Marl Formation of North Texas

[Aidan Campos]

Here are some of my finds from spending a few hours on Wednesday, October 26th, in the Graysonites wacoense Zone of the Grayson Formation, Washita Group of north Texas (Early Cenomanian, ~97mya). This particular site exposes a micromorph layer full of thousands of tiny dwarfed Mariella bosquensis and M. rhacioformis ammonites plus a wealth of other taxa like various urchins, brittlestar fragments, shark teeth, many gastropods & pelecypods, etc. Those familiar with the Del Rio exposures of further south in central Texas (particularly the now closed-to-public Waco Pit in McLennan County), should recognize much of the fauna to be found at this site as it is laterally equivalent to those and faunally nearly identical, differing only slightly in the rarity of homomorph ammonites at this site vs further south, as well as slight differences in preservation/lithology. 
 

The following is just a fraction of what I found:

 

One of thousands of dwarfed Mariella bosquensis (Turrilitidae) ammonites: 

 

Cretalamna cf. catoxodon (Otodontidae) shark tooth, this species was first described from the Cenomanian of Western Australia by Siversson et al., 2015 where many species were split out of the broad C. appendiculata:

Goniophorus scotti (Saleniidae) sea urchin fragment: 

 

A tiny Stoliczkaia texana (Lyelliceratidae) ammonite: 

 

 

 

Arm fragments of Ophiura graysonensis (Ophiuridae), a brittlestar. I hope to find a complete specimen or at least a central disk at this site soon: 

 

 

 

 

 

Another Goniophorus scotti (Saleniidae): 

 

 

Some more dwarf Mariella bosquensis (Turrilitidae) ammonites: 

 

 

 

 

 

Found in just a few seconds of searching in one spot: 

 

Neithea texana (Neitheidae) scallop: 

 

Praescabrotrigonia emoryi (Pterotrigoniidae) clam: 

 

cf. Margarites (Margaritidae) gastropod: 

 

A very small Cymatoceras hilli (Cymatoceratidae) nautiloid: 

 

 

Imprints of the pellet-lined burrows of mud shrimp (the ichnogenus being Ophiomorpha). These almost certainly belong to Meticonaxius rhacheochir (Micheleidae) which is known from both the older Pawpaw Formation and the younger Britton Formation, the latter of which contains abundant identical Ophiomorpha which have been found with the bodies of M. rhacheochir preserved inside: 

 

 

Chondrites trace fossils: 

 

 

Bivalve shell fragment conglomerate slabs consisting mainly of Texigryphaea roemeri oyster and Neithea texana scallop fragments:

 

 

A mass of white nodules which I presume are likely fossilized rhodoliths, structures made up of the calcium carbonate secreted by coralline red algae which would freely roll around on the sea floor: 

 

Hundreds of Texigryphaea roemeri (Gryphaeidae) oysters: 

 

 

The layers above the micromorph zone abound with more typical Grayson Formation lithology & fauna, such as this Mariella rhacioformis (Turrilitidae) ammonite fragment. This species occurs in abundance in at the site in the more typical layers and occasionally as limonitic/pyritic micromorphs too: 

 

A portion of a typical non-dwarfed Mariella bosquensis (Turrilitidae) ammonite:

 

Protocardia texana (Cardiidae) clam: 

 

 

Edited October 31, 2022 by Aidan Campos

[Mikrogeophagus]

Really cool. Especially love the brittlestar parts and the urchins. That style of preservation is beautiful!

[deutscheben]

Those little fossils are so dang cute! Thank you for the detailed report and excellent photos.

[Jared C]

You trips reports are among the most informative I see on here. Keep 'em coming!

[Collector9658]

Sure looks like a lot of fun to spend a day collecting at. Glad I got to visit the Waco Pit years ago before it closed, that's too bad.

[Jeffrey P]

Excellent report, pics, and finds. Congratulations and thanks for sharing.

[PaleoPastels]

Wow even though those are just fragments, all of the ech finds and cephalopod finds are super cool!  I especially love part of the brittle star and I’d be over the moon to find something like that. I’d love to visit that area of Texas someday!  Taking notes on the species, Ive been on an invert fossil kick lately. 

 

Those mud crab trace fossils are also especially very interesting!