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I have been doing more research on my unidentified Middle/Upper Coniacian heteromorph ammonite that I posted pictures and information on here, and with lots of papers and information from Keith Minor I think that I have narrowed it down to two ammonite genera, Neocrioceras and Pseudoxybeloceras. He sent lots of very helpful papers including Kennedy and Cobban's 1991 paper Coniacian ammonite faunas from the United States Western Interior. It includes pictures and information on 3 species of Neocrioceras and one species of Pseudoxybeloceras from the Coniacian Western Interior. Keith also emailed me some information that I will show here. At first I thought that my specimen could be Smedaliceras durhami which is so far known only from the Campanian Burditt Formation of south Texas. That was way out there and Keith didn't even consider that possibility because of how out there that suggestion was. Then I saw pictures on the internet of an Allocrioceras hazzardi specimen from Utah that did look similar to mine. The main problem with that theory is that A. hazzardi doesn't have lateral tubercles, so scratch that. It was after exchanging emails with Keith that I came to my aforementioned conclusion, that my specimen is either of the genera Neocrioceras or Pseudoxybeloceras. After studying Kennedy and Cobban 1991 a bit further it seems to me that Neocrioceras (Schlueterella) sp. most closely resembles my specimen. N. sp. has one set of lateral and ventral tubercles on both sides of the specimen respectively. The tubercles connect groups of 2-3 ribs. Between the tuberculate groups there are up to 6 finer non-tuberculate ribs. At first I said that on my specimen there were 7 non-tuberculate ribs between the tuberculate ones but on closer examination the tuberculate ribs come in groups like N. sp. with one tubercle connecting two ribs. In reality my specimen has 6 non-tuberculate ribs between each tuberculate group consisting of two ribs. The main difference that I notice is that my specimen has much weaker lateral tubercles than N. sp. Interestingly, Neocrioceras is not known from the Austin Chalk but there are a couple Pseudoxybeloceras specimens reported from the Santonian stage of the Austin Chalk in central Texas. The main reason why I don't think my specimen is Pseudoxybeloceras is because the species P. dispar, the only species of this genus reported from the Coniacian Western Interior in Kennedy and Cobban 1991, is quadrituberculate on every rib with no ribs being non-tuberculate. But I will say that I have not seen nor read any detailed descriptions of the Pseudoxybeloceras species found in the Austin Chalk so I still consider it a very possible candidate, though my specimen is considerably older. @Wrangellian, I know that you have experience with this genus from the Santonian. What do you think? In this post I also include 3 pictures of 2 different inoceramid specimens I found along with my heteromorph specimen. I sent Keith these pictures to help pin point my heteromorph's stratigraphic position in the Coniacian. Anyone have any ideas on what species they are? From what I am hearing from Keith my ammonite specimen could be a bit older than the Prionocycloceras gabrielense zone if these inoceramids are in the Magadiceramus subquadratus group. I will update this thread when I receive more information. Here are the edited relevant emails from my exchange with Keith: ______________________________ Keith Minor, February 17. Hi Heteromorph, According to Kennedy et al., Phlycticrioceras douvillei and P. oregonensis are junior synonyms of P. trinodosum. P. trinodosum has been found in several areas around the Cretaceous Tethys Sea. According to Walaszczyk, The Trinodosum Zone is middle Coniacian, which is consistent with the level that you are finding your specimens. Cremnoceramus ranges up into the middle Coniacian. However, I think that the clams that you have are probably Magadiceramus, probably M. subquadratus group. So the heteromorphs are slightly lower than the Prionocycloceras gabrielense's that you are finding, and your Texanitine could actually be Protexanites shoshonense, which would be about the right level. Also, I didn't put two and two together, but that big piece of a heteromorph that you showed me may actually be Neocrioceras, which doesn't have tubercles, or Pseudoxybeloceras, with small tubercles that fade on the body chamber. I hope this helps! Keith ______________________________ Heteromorph, February 22. Here are two websites with the pictures of the alleged Allocrioceras hazzardi specimen that I found pictures of online. The more I look at the pictures the less I think that the specimen is really A. hazzardi. I have never seen another A. hazzardi specimen that looks like it and all the descriptions that I have read on the species don't indicate this kind of variation. I now believe that it was misidentified, but I wonder what you think. http://www.ammonoid.com/coniacian.htm https://www.tonmo.com/threads/heteromorphs.11130/page-4#post-156740 So, do you have an opinion as to what species my specimen is? For me I am having trouble deciding between Pseudoxybeloceras (Pseudoxybeloceras) dispar or Neocrioceras sp. What I do know is that the alleged A. hazzardi specimen from Utah very much resembles mine. Thank you for all your help! ______________________________ Keith Minor, February 22. Hi Heteromorph, I see the images. Yes, that is definitely Allocrioceras hazzardi. It ranges from the Upper Turonian (Prionocyclus hyatti Zone) to the Upper Coniacian (Prionocycloceras gabrielense Zone). I don't know of any Santonian species. Hazzardi is probably the descendant of Allocrioceras annulatum from the Upper Cenomanian. Kennedy also described A. conlini, but I'm not sure that this is a separate species. I attached (as a Google Drive link) Kennedy's review of Eagle Ford ammonites (Texas). You can see that the ribs are all the same size in annulatum, but in hazzardi, the the spine-bearing ribs are bigger, and also hazzardi is a larger species. I double checked to see if Hamites and Anisoceras ranges up into the Coniacian, but they disappear in the Cenomanian (as far as I can tell), so these genera can be ruled out. However, Neocrioceras and Pseudoxybeloceras are genera that need to be considered. I have some papers on these, I think from South Africa. I'll find those when I have time. There's a couple of Pseudoxybeloceras specimens from the Austin Chalk from central Texas (Santonian). Kind regards, Keith Late Cenomanian and Turonian Ammonite faunas from north-east and central Texas ______________________________ P1 - Inoceramid oyster P2 - Same inoceramid oyster showing more clearly the perpendicular ribbing.
Heteromorph posted a topic in Fossil IDIn late February I went to a site in the Middle/Upper Santonian stage of the Bruceville Chalk Marl Formation, Austin Group, in Ellis county, Texas. While at the site I found a few inoceramids, possibly an anaptychus, and a chunk of rock that looks like it could have mollusk grazing traces on it. Then today I was organizing my collection and picked up the rock with the possible grazing traces. While I was handling the rock I happened to look at the bottom of it and spotted a small Squalicorax sp. tooth, my first tooth from the Santonian. It is 11 mm long and is pretty complete, with the left side of the root being exposed. I am not sure about the right side of the root, but it may still be there under the matrix. I have been trying to put it to a species. From looking through Welton and Farish’s book as well as elasmo.com the most likely candidates seem to be the two paleo-buckets S. “falcatus” and S. “kaupi,” and the species S. lindstormi. I am not terribly familiar with fossil shark teeth, so I am very curious what the more informed members of this forum can say about what species this could be. I am also wondering if the first picture could be of mollusk grazing traces. Would it be a good idea to try to prep it out further? And if so, what would a good strategy be with chalky/marly matrix? FIG 1: Possible mollusk grazing traces on the top of the rock. FIG 2. FIG 3.
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: Continued in next post...