Another Trip to the Cannonball Formation (sharks, fish, and crabs)

[Thomas.Dodson]

I was eager to get out before the heatwave coming up so I made the visit to a couple new Cannonball sites the other day as well as property adjacent to where I collected the crabs this spring. I was expecting more good bivalve material from the first sites but I'm pretty happy with the results regardless. Sort of a continuation of this topic.

 

I tried a few cuts before working my way down to the area I found the concretions in before. The material in all was extremely fragmented. I still need to bust that concretion.

One of the inconspicuous cuts.

More fragments.

A worn Ophiomorpha?

I did find a worn Carcharias taurus tooth at this site which made it worth the stop.

Down in the familiar area I had immediate luck as the first concretion I busted had a shark tooth. It broke the tooth but the break is clean and should made for an easy repair.

Here's a crab (Camarocarcinus arnesoni) that was already split. This is the only split concretion I saw that contained a fossil. The white material obscures it a bit but the last one I prepped like this had the normal black color and carapace texture once I abraded away the white. This should clean up pretty nicely.

An example of a concretion.

Prickly pears, purple prairie coneflower, and prairie roses were all in bloom as well.

Concretions show variety in color, texture, and shape but there doesn't appear to be a correlation with any of these characteristics and which ones contain fossils.

The ratio of fossils to blanks was higher than last time but still not enough to warrant preparing the concretions directly. Got to split them all first and glue them back together as necessary. These two were blanks.

This pretty one was not.

Tiny (5 mm) fish vert.

Hard to see but the faint outline is probably a crab.

Otodus obliquus, a new species for me.

A gnarly piece of petrified wood, probably float material from somewhere.

Common Nighthawk eggs I believe.

 

 

 

[Thomas.Dodson]

 There seems to be decapod material attached to this which would be very exciting. 

Difficult to photograph.

Another crab cross section.

Worn scales.

Could be crab leg element.

Some concretions were too tough for the crack hammer in the field so they got the sledge at home.

This looks like just wood. Very variable centers of these concretions.

Another tooth.

Another crab. I tried to highlight the cross section on this one since they're difficult to see from photos.

There's an additional couple fish verts not pictured as well. A lot of these need time with preparation which I hope to get to soon. I'll post updates when I prepare them.

 

Lastly, I forgot to post these earlier. This float material comes from another roadcut. It appears to be Taylor Bed Silcrete, which caps the Dean Member of the Golden Valley Formation and is found as float material some distance from the outcrops at times. Wood and Equisetum is common in some pieces and farmers will use the natural hollows to thread wire and the like through to use as anchors for fences. Funny enough I was just researching this and other silcrete beds of North Dakota to try and determine the type of silcrete that the arrowhead I found the other week is.

[Fossilis Willis]

About 15 years ago I spent month or so working in Grand Forks area during a very rainy late spring. Between the humidity, mosquitoes and knee deep mud I swore that would be my last trip to North Dakota. But every time I read one your reports I reconsider. Love the crabs and shark teeth.

[bthemoose]

Great finds, especially the Otodus obliquus! I was actually just reading about Otodus from the Cannonball Formation the other day and wondering if anyone here had found any. Will you do any further prep on that one or leave it as is?

[Thomas.Dodson]

32 minutes ago, bthemoose said:

Great finds, especially the Otodus obliquus! I was actually just reading about Otodus from the Cannonball Formation the other day and wondering if anyone here had found any. Will you do any further prep on that one or leave it as is?

I haven't decided on that one yet but I'm leaning towards prepping it more since I'd like a lingual view. The problem is the root. It's visible on the current face but it's basically a trace, there doesn't appear to be substance. I might leave the root part as is in the concretion and remove the rock from the lingual side of the blade.

[jpc]

Nice....!  I read about Cannonball crabs decades ago and they have been on my bucket list ever since.  Meanwhile, I was in your state a few days ago.  Went to the museum in Dickinson.  Great museum.  

[Thomas.Dodson]

21 hours ago, jpc said:

Nice....!  I read about Cannonball crabs decades ago and they have been on my bucket list ever since.  Meanwhile, I was in your state a few days ago.  Went to the museum in Dickinson.  Great museum.  

It's been awhile since I've been to that museum but I always enjoyed it when I was younger.

 

Here's an update. Most of the crabs in this batch were pretty fragmented with chunks of carapace missing but there are a couple standouts.

 

The concretion in the first photo of the first post that I hadn't opened yet actually had a little crab.

 

Mostly complete cheliped tucked under the carapace for this one.

The concretion with the void had this piece. 1.2 cm. Sure looks like crab.

The one that was already exposed. It's unclear how much shell was missing from the start and how much was lost to weathering. The shape remains though. 2.5 cm long.

There's a lot of material going on underneath the carapace although it is very jumbled. Reverse side.

I've cleaned up the crab I prepped earlier this month as well. Mostly complete carapace.

It's too bad the Otodus obliquus was missing the tip but I was pleasantly surprised to the completeness of the cusps. The root was more separated from the matrix than I thought and wasn't difficult to prep.

The broken one had a complete root I prepped out.

And a rootless one.

 

[siteseer]

Carcharias taurus is a modern species known from late Miocene sites but the reported occurrences become more questionable earlier than that.  It's tough to identify a weathered crown unless you're happy with just "sand tiger."

 

It's great to see the Otodus tooth and crabs.  That second-to-last and last tooth are probably Striatolamia.  I once contacted Alan Cvancara and sent him some Paleocene fossils from Morocco and Maryland.  He responded by mailing me some of his publications.  Nice guy.

 

Jess

[Thomas.Dodson]

On 7/5/2021 at 4:55 PM, siteseer said:

Carcharias taurus is a modern species known from late Miocene sites but the reported occurrences become more questionable earlier than that.  It's tough to identify a weathered crown unless you're happy with just "sand tiger."

I'm aware of the controversy concerning pre-Miocene reports but I was just following Cvancara and Hoganson's classification. They assigned all ~2000 Cannonball Carcharias teeth from their study to Carcharias taurus. I'm sure there is some disagreement there. If you're interested in reading their justification I can send you a copy of the paper.

 

On 7/5/2021 at 4:55 PM, siteseer said:

That second-to-last and last tooth are probably Striatolamia.

That would be neat. I haven't had the time to go over them in detail but Striatolamia isn't mentioned in Cvancara and Hoganson's report.

 

I'm not sure this warrants another trip report so for now I'll add these here. I was at some other Cannonball sites today to mixed success but found another big tooth. This site was described as "loosely consolidated mudstone" but was more like just mud. It rained a lot last night so pounds and pounds of it stuck to my shoes.

This coral is pretty common at this site. I haven't looked it up yet. One of the gastropod spires should be identifiable.

A little too much of a puzzle for me.

Simple sandstone exposure. Not much free weathered but I took a gastropod and a couple of bivalves that need to be prepped out of sandstone blocks.

Never pass up an anthill.

Spot the Cannonball shark tooth.

From another roadcut site. This fragment might be identifiable.

Dosiniopsis deweyi, one of the species of bivalves that occurs in both the Fox Hills and the Cannonball. This is the first "complete" free weathered bivalve I collected out of the Cannonball.

Yucca flowers from another site.

The only fossil from this site was a little piece of Teredo petrified wood in a concretion.

 

Edited July 7, 2021 by Thomas.Dodson