A Murder of Tridenticeras

[Heteromorph]

On Friday my mother and I went to the same rock pile where she found this as of yet unidentified heteromorph ammonite exactly 5 weeks prior. We had been there multiple times since she found it but every trip was a bust because we had surface picked it as much as we could the first time. But within the last few days the pile had been turned up again when part of it was used to level a flat surface to pour a driveway. Because this site is so rich in rare heteromorphs I decided that it would be wise to hunt around it again. It had indeed been rejuvenated and the hunt was an hour well spent!

 

We had only been there a minute or two when I found my first Tridenticeras peramplum ammonite of the day. It was laying amongst the rocks used to level the ground a few feet away from the pile. It is only an external impression but very detailed. The ribs and tubercles are well defined all over the preserved specimen even on the tiny uppermost whorl as clearly shown in P1 - P3. This is the 9th T. peramplum specimen in my collection and the 2nd impression only specimen. It is also the second impression to preserve one of the whorls closest to the apex. It is in association with an inoceramid just above it. 

 

FIG 1 - FIG 6, Specimen 1:  Total shell height is 29mm, total shell diameter is 15mm. Ruler is in millimeters. 

 

FIG 1:  T. peramplum is trituberculate with the bottom two tubercles being closer together. 

 

FIG 2:

 

FIG 3:  This picture shows especially clearly the detail on the uppermost whorl. 

 

FIG 4: 

 

FIG 5:

 

FIG 6:

 

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[Heteromorph]

I was already pretty happy with my first find but my attention was still focused on finding more as we continued our search. About 2 or 3 minutes later I went on the other side of the pile and let out a bit of a happily surprised screech when I saw my second T. peramplum specimen of the day sitting rather precariously on a rock in the pile. This makes the first time that I have found more than one of this species in a day. It is a steinkern from a specimen that when complete was much larger than Specimen 1. It is far from complete and the bottom row of tubercles are mostly covered in matrix but is still a very welcome addition to my collection from this (normally) very rare taxa. It does have some unique charter about it in that the top cleanly separated from the base giving me a rare view of part of the dorsum. What is also very interesting is that some of the sutures appear to be preserved on this part of the dorsum though the are pretty indistinct. The sutures of this species are unknown to science so I always carefully study every specimen that I find to look for them. If those are some of the sutures on the dorsum then this is my first specimen to have them visible and the first specimen to have them visible from any collection that I know of. 

 

FIG 7 - FIG 13, Specimen 2:  Total shell height is 15mm, total shell diameter is 14mm. Ruler in millimeters. 

FIG 7:

 

FIG 8:  Note the possible sutures on the dorsum. Also note the oval shape of the specimen due to mild compression during fossilization

 

FIG 9:

 

FIG 10:

 

FIG 11:  Back of specimen. Part of it looks bleached for some reason. 

 

FIG 12:

 

FIG 13:

 

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[Heteromorph]

At this point it was, as they say in the world of crow memes, an attempted murder but within moments the full murder came to fruition. After I found Specimen 2 I put it in a safe place with Specimen 1 while we were continuing our search and walked back to the pile. Then within a few minutes my mother called me over to look at something. I went over there and she showed me a little oyster on a rock to be sure that is what it was. I confirmed its identity and then tossed it back onto the pile. As I was watching it land I quickly noticed that right next to where it landed there was something very peculiar. I immediately picked it up and in my hand was the third and final T. peramplum specimen of the day. I was absolutely elated! It is the most complete specimen of the day and the largest in diameter. Literally seconds before I threw the oyster onto the pile I was thinking that it would be just inexplicable if I found another specimen. 

 

FIG 14 - FIG 22, Specimen 3:  Total shell height is 27mm, total shell diameter is 19mm. Ruler in millimeters. 

 

FIG 14:

 

FIG 15:

 

FIG 16:  Angled side/bottom view.

 

FIG 17:

 

FIG 18:  Side of specimen. 

 

FIG 19:  Back of specimen with small inoceramid impression. 

 

FIG 20:

 

FIG 21:

 

FIG 22:  Top of specimen. Note the oval shape similar to Specimen 2. 

 

Continued in next post...

[Heteromorph]

It was a very successful day afield! I hope to have many more like them as the development the pile is in continues to expose more rock. And though Friday's specimens are beautiful, my favorite specimen of this species was found by my mother in September in the same development but at a different exposure of rock. The bottom whorl is missing but other than that it is in very pristine condition. It even shows a few of the finer, non-tuberculate ribs that run between the tuberculate ones in well preserved specimens. It also has the apex preserved and is the 3rd specimen in my collection to have that.  It is the most complete specimen in my collection and as far as I know in any collection and is the largest (possibly second largest, not completely sure) in diameter in my collection if you are counting the impression of the missing bottom whorl. It doesn't have any visible sutures, but that is goal of mine.

 

FIG 23 - FIG 36, Specimen 4:  Total shell height is 43mm, total shell diameter is 19mm. Ruler in millimeters. Found in September of 2017 by my mother.

 

FIG 23:

 

FIG 24:  Different light angle but same camera angle as FIG 23.

 

FIG 25:

 

FIG 26:

 

FIG 27:

 

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[Heteromorph]

FIG 28:

 

FIG 29:

 

FIG 30:

 

FIG 31:

 

FIG 32:

 

FIG 33:

 

FIG 34:

 

That is it for T. peramplum. I found more interesting ammonites and inoceramids that day but because of schedule constraints that will have to wait for Tuesday or Wednesday. 

[Tidgy's Dad]

A great day out for you. 

Very exciting read and super finds. 

Thanks for sharing. 

[Phevo]

10 hours ago, Heteromorph said:

On Friday my mother and I went to the same rock pile where she found this as of yet unidentified heteromorph ammonite exactly 5 weeks prior. We had been there multiple times since she found it but every trip was a bust because we had surface picked it as much as we could the first time. But within the last few days the pile had been turned up again when part of it was used to level a flat surface to pour a driveway. Because this site is so rich in rare heteromorphs I decided that it would be wise to hunt around it again. It had indeed been rejuvenated and the hunt was an hour well spent!

 

We had only been there a minute or two when I found my first Tridenticeras peramplum ammonite of the day. It was laying amongst the rocks used to level the ground a few feet away from the pile. It is only an external impression but very detailed. The ribs and tubercles are well defined all over the preserved specimen even on the tiny uppermost whorl as clearly shown in P1 - P3. This is the 9th T. peramplum specimen in my collection and the 2nd impression only specimen. It is also the second impression to preserve one of the whorls closest to the apex. It is in association with an inoceramid just above it. 

 

 

Over here where I am from the external molds are more valued than the internal molds, because you can make a cast in silicone which will hold alot more detail than an internal mold

 

Very nice specimens, I know how hard mollusc material is to come by in chalk ;P

 

 

[Peat Burns]

Great finds.  I bet those are hard to "prep out".  Have you ever tried to expose more?  I did on a Eopachydiscus mold/cast once.  It was somewhat "sticky", but I was able to expose some more of it (the central whorls were filled with matrix).

[Monica]

Beautiful ammonites!!!  And you can tell your mom that I am  because of the little specimen that she found! 

[Heteromorph]

On 3/4/2018 at 8:13 PM, Tidgy's Dad said:

A great day out for you. 

Very exciting read and super finds. 

Thanks for sharing. 

Thank you very much! I plan to post some more photos of my interesting finds from Friday soon.

  

On 3/5/2018 at 3:07 AM, Phevo said:

 

Over here where I am from the external molds are more valued than the internal molds, because you can make a cast in silicone which will hold alot more detail than an internal mold

 

Very nice specimens, I know how hard mollusc material is to come by in chalk ;P

 

 

Thanks! I suppose that would be the case more with gastropods than with ammonites. The ammonite steinkerns that I find in the Austin Chalk are very detailed when preservation is good. 

 

On 3/5/2018 at 6:05 PM, Peat Burns said:

Great finds.  I bet those are hard to "prep out".  Have you ever tried to expose more?  I did on a Eopachydiscus mold/cast once.  It was somewhat "sticky", but I was able to expose some more of it (the central whorls were filled with matrix).

Thanks! Sorry it took me a while to respond. So far I have only tried to prep one T. peramplum ammonite specimen. I found it in October and tried to prepare it with dental picks and well placed drops of vinegar and made a bit of progress by getting some small matrix chunks off. But then I chickened out and stopped before I did any damage which was probably a good decision since my preparation skills are quite minimal. 

 

The matrix is actually pretty easy to deal with but to get any matrix off of the specimen I have to get at the angle right with the pick to pry small chunks of it off. Hopfully with time and better tools I can improve my preparation. 

 

Here are pictures of the specimen before I tried to prepare it. The pictures below are what it looks like now. Thankfully I never touched the specimen with my pick so it is fine but the area around it is quite messy looking. Do you or anyone else have advice on how to clean up around the specimen?

 

 

FIG 35.

 

FIG 36.

 

FIG 37.

 

On 3/6/2018 at 4:49 AM, Monica said:

Beautiful ammonites!!!  And you can tell your mom that I am  because of the little specimen that she found! 

Thanks! I did! 

[Peat Burns]

@Heteromorph if you don't have a pneumatic air scribe, you can get an electric engraver to clean up the prep marks around the specimen.  I bought one at the hardware store for $14.  You can lightly oscillate back and forth to remove the pick marks.  A dremel with sanding bit can smooth it out even better (or even carefully applied sandpaper).  Hope this helps. I know those can be tough based on my experience prepping my Eopachydiscus 

[ynot]

Nice finds, congratulations!

[Heteromorph]

So here my other notable finds from Friday, March 2.

 

Figures 38 - 40 are of an ammonite that is too fragmentary and buried in matrix to easily identify, but it could be of the genera Protexanites or Prionocycloceras, perhaps Prionocycloceras gabrielense. What I find very interesting is the almost spine like nature of the tubercle shown in FIG 38. While its tip has broken off its full impression is still there allowing the original extent of the tubercle to be seen. All the Protexanites specimens and Prionocycloceras specimens that I have found have prominent tubercles, especially Prionocycloceras, but not this pronounced. Also notice the smoother area below the ammonite in FIG 38. I have found this before on or near other specimens but I am not sure what it is. Probably some kind of calcite formation. 

 

FIG 38 - FIG 40, Specimen 5. 

 

FIG 38.

 

FIG 39: Side view showing length of fragment. 

 

FIG 40: Ventral view showing what appears to be a keel which would be indicative of Prionocycloceras. 

 

Figures 41 - 47 are of a few interesting inoceramid specimens from the site. I have noticed a trend with the inoceramids at this site that may or may not have something to do with the quality and quantity of the heteromorphs that I find there, which is that I have found many more inoceramids with both valves still articulated than at any of my other sites. From just this pile and the immediate area around it I have found 3 articulated inoceramid specimens including the specimen below, not to mention many other well preserved non-articulated valves. This is just a guess but could that indicate a low energy depositional environment, perhaps a low area with less wave action and turbulence? That could possibly account for the quality of the specimens since they were not getting knocked around the sea bottom and the quantity since if it was a low area the ammonite shells would tend to sink into it. Just a theory. Maybe I am just noticing things that I usually don't.

 

FIG 41- FIG 44, Specimen 6.

 

FIG 41.

 

FIG 42.

 

FIG 43.

 

FIG 44.

 

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[Heteromorph]

FIG 45, Specimen 7: Single and well preserved inoceramid valve. Notice the baculite fragment at the top of the picture. 

 

FIG 45.

 

FIG 46 - FIG 47, Specimen 8: Large inoceramid hinge fragment. 

FIG 46: Notice the chalk seam cutting through it which shows that the it broke before fossilization.  

 

FIG 47.

 

FIG 48, Specimen 9: Rudist from Edwards formation Matrix brought in for check dam. 

 

FIG 48.

 

FIG 49, Specimen 10: Chondrodonta oyster from the Edwards formation.

 

FIG 49.

 

 

That's it!

[KimTexan]

I had some Mariella heteromorphs with similar material around them. I got a drill bit, I think it was just one for stone, and I drilled holes 1/4 to 1/2 inch away from specimen through the rock all the way around the specimen to help remove larger chunks more quickly. Then I used my diamond tip bits with my Dremel to remove the matrix between drill holes. Poor man’s (girl’s in this cas) method. I can’t afford to buy a pneumatic setup. So I make due with what I have.

If the rock is really hard it doesn’t work well, but if it is just Chalk it does pretty well.