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Showing results for tags 'phlycticrioceras trinodosum'.
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I found this Phlycticrioceras trinodosum heteromorph specimen in June of 2018 whilst hunting the middle/upper Coniacian Atco formation. It is the largest fragment of this species that I am aware of, having a whorl height of 51 mm as opposed to 47 mm of the largest fragment I've seen published. This genus is a bigger, rarer, and (mostly) younger cousin of Allocrioceras. I sent pictures of it to Keith Minor and he pointed out that there was also an echinoid sticking out of the specimen, something which I had totally missed! With much of the echinoid still stuck in the living chamber it is hard to get a definitive ID. But because it has such a shallow anterior ambulacra, which gives the anterior end a more smooth rather than definitive heart shape, he ruled out both Mecaster texanus and batensis. He suggested Micraster since the site has a strong European component in both the bivalve and ammonite faunas, and because the periproct side has the right shape. From finding other, although not as well preserved specimens that show similar morphology he appears to be right. I have yet to confirm this ID with Andrew Smith, but either way I think the piece is worth showing. And reading this thread got me thinking about how this could have happened and what effect it could have had on the echinoid's preservation. My thought is that because irregular echinoids lived and today still live most of their lives burrowing in the sediment it is unlikely that it would have crawled into the living chamber, but instead that it was blown into it post-mortem via currents that had dredged it out of the sediment. I already know that this site was a high energy environment from my other finds here so this seems the most likely possibility to me. But because of the fact there is still at least one spine still attached to the specimen it could not have been swept up from the sediment too long after death or all of its hairlike spines would have blown away. I do, however, find it interesting that it is positioned anterior first with its posterior towards the aperture, the position I would expect to see it in if it had indeed crawled into the shell. The specimen is also the best preserved echinoid from this site so far. Despite the ammonites being generally well preserved and not too crushed, most of the echinoids that I have from the site are terribly crushed, flakey, and often infested with rotting pyrite. I think being encapsulated in the chamber very much reduced those effects. Even though the ammonite and the echinoid are a bit crushed, the echinoid would have probably been worse off otherwise. The heteromorph fragment length is 70 mm and the whorl breadth, being a bit crushed, is 13 mm. I would think that this specimen, with its open planispiral coiling, would would have been at least over a foot in diameter when complete. It is the robust (female) morph of the species with a rib index of 5½. For comparison in Fig. 1 I pictured it with my most complete P. trinodosum specimen. From the part of the echinoid that is exposed I can measure 25 mm in length, 25 in width, and a thickness of 8 mm. I have also found abundant yet scattered fish remains at the site, so perhaps one day an ammonite-fish will come my way. But until then, anyone else got ammonite-echinoids to show? Fig. 1. Fig. 2.
Heteromorph posted a topic in Fossil IDAt a site where I have been finding heteromorphs, I have recently come across some vertebrate material. So far I have only found three vertebrate specimens; one bone fragment and two fish scales. I am hoping to get some information on their affinities. I am most interested in the fish scales, since it seems they would be the most easily identified. The site is in North Texas, the Austin Chalk group, Atco formation, upper Coniacian stage. For biostratigraphic reference, at this same site I have also found the ammonites Protexanites planatus, Phlycticrioceras trinodosum, Tridenticeras peramplum, Scaphites semicostatus, and Glyptoxoceras sp., among others. The bone (Figs 1-17) was found on Saturday the 14th of July. It is a small fragment from a more marly layer than the fish scales and most of the rare ammonites that I am finding are from, but still from the same site. The main part of it has 39 mm exposed length wise as shown in Figs 11-12 (some of it is still buried in the rock), and has a branch coming from the main part that is 22 mm long that forms a depressed canal structure in the rock (Fig. 14). The maximum thickness of the specimen that I can see is about 2 ½ mm. The branch begins to curve around when it meets the main part of the bone. The other end of the rock and the underside don't show much exposure of the bone except for a few bits poking through (Figs 16-17). I don’t know if the specimen came from a fish or some other vertebrate, but I would guess fish. If anyone can give more information on what kind of animal this came from and where this might have been located in the animal’s skeleton, that would be much appreciated. But I also know that due to its very fragmentary nature, a more definite identification may not be possible. The two fish scales (Figs 18-20) were both found on Friday the 27th of July over 100 yards from where the bone was found. These specimens are from a more chalky matrix than the bone, the same matrix that the rare ammonites are in. The first specimen (Figs 18-19) was found breaking open a large chunk of chalk. It is basically flawless and in excellent condition, and only has a little bit of obscuring matrix on the right side that could be prepped off. In the same chunk of rock that I cracked open to find this I also found a T. peramplum specimen. The fish scale is 5 ½ mm long by 5 ½ mm wide. The second fish scale I found (Fig. 20) was found within a few feet of the first one, possibly from the same fish specimen. It is a bit beat up and less complete than the first scale, but is larger from what I can see. It is 7 mm wide including the flatended area upon which the scale once was before it flaked away during excavation. The front part of it is still buried in the rock but could hopefully be prepped out. It is also in a chalky chunk of rock, not marly. I have noticed that these are less shiny than scales preserved in shales, though they still do glimmer a bit in direct light. They are also differently colored than most fish scales preserved in shales, with mine being on the red/brown spectrum while those in shale are usually black or dark gray. I am hoping that the distinctive symmetrical 7 way splitting shown on the first fish scale could narrow down the identification. I know that getting to the species or genus level could be very difficult, but could a family or order be at least possible? I have heard that identifying fish scales is challenging, but this paper indicates that it is not impossible. @oilshale, you’re a fishy guy (in a good way of course). Any ideas? Fig. 1.
In March of this year I found a heteromorphic ammonite that has had me curious ever since. So yesterday I finally sent an email about it to a local ammonite expert, Ron Morin, who is associated with the Dallas Paleontological Society. I had a correspondence with him in May of this year as it related to him identifying my Phlycticrioceras trinodosum heteromorphic ammonite which I recently added to 'Collections'. That's when I first talked to him. Then at the Dallas Paleontological Society's Fossil Mania event in October, I was talking to Roger Farish about my unidentified ammonite. He recommended that I contact him again for identification. Here is the email and the pictures that I sent him yesterday. I will post an update to this thread when he responds, which from my experience might be weeks. I have edited it to remove any slightly sensitive information like my name and more specific location information (I'm paranoid), as well as to fix any grammatical errors and to add relevant reference designations in between the < and > symbols: "Hello! I am Heteromorph, the one who contacted you to identify my Phlycticrioceras trinodosum specimen in May of this year, and I was wondering if you could help me identify another heteromorphic ammonite from the Upper Coniacian stage of the Austin Chalk. This specimen was found on March 23 of this year in a creek in Ellis county. It is, in fact, within half a mile of where I found the last specimen that I sent to you for identification. The stratigraphy of this area is the Atco member of the Austin Chalk, Prionocycloceras gabrielense zone. My problem is that even though it resembles P. trinodosum, there are differences that would make me reluctant to indenify it as such. To date, I have not found one like it. It is similar to P. trinodosum in that the whorl section is compressed, it has ventral tubercles, and it has an open planispiral shape. But it also has 3 key differences that make me think it is either a different species or it is very pathological. I list these below. First and foremost, the main difference is the lack of any ventrolateral tubercles, which are one of the defining characteristics of P. trinodosum. On both the specimen itself and its negative, it appears to be free of any ventrolateral tubercles. The only tubercles that I can see are the ventral tubercles which are something that P. trinodosum has as well. Second, the ribs are shaped differently than P. trinodosum. While P. trinodosum has rectiradiate ribs, this specimen has ribs which are rectiradiate until about half way up from the umbilicus, at which point it bends. Due to the fragmentary nature of this specimen, I have a hard time determining whether it bends abapically or adapically. Third, the ribs are more costate on this specimen than any of the twelve P. trinodosum specimens that I have found in the Austin Chalk. It has a rib index of 7, while the most costate specimen that I have found and know for sure is a P. trinodosum specimen only has a rib index of 5. While this is not unheard of for this species, with specimens of this species having rib indexes of up to 8 (Emerson et al. 1994), yet from my experience it is apparently very unusual for this part of the Austin Chalk. The closest thing that I have seen to my specimen is illustrated on Plate 11, fig 2 of Young, 1963 (as P. sp. cfr. douvillei), the similarity being the fact that they both have rib indexes of 7. After that, though, the similarity ends in that P. sp cfr. P. douvillei still has ventrolateral tubercles and rectiradiate ribs. I also found a very small P. trinodosum negative in the same creek just a few feet away. It has ventrolateral tubercles and a rib index of 4. The ribs are rectiradiate. A photo of it is not attached here. My specimen is 87mm long including its negative and has a whorl height of 34½mm. The oval whorl section is compressed like P. trinodosum. It is shown first in the attached photo DSCN5355. Aside from the specimen in question, for reference I have also attached photos of two P. trinodosum specimens that I have found. They are both from within 5 miles of the creek site, so they are on roughly the same stratigraphic level. What I am calling P1 is shown first in the attached photo DSCN5281 <F13> in comparison with the specimen in question. P1's negative is shown first in the attached photo DSCN5394 <22>. The positive is 69mm long when both pieces of it are measured together but 53mm when just measuring the largest piece. It has a whorl height of 31mm and a whorl breadth of 9mm. Rib index of 4. It was found within a quarter of a mile of the creek site. Because it is has just a slightly shorter whorl section to the specimen in question it is a good comparison piece. The specimen which I am calling P2 is shown in the attached photo DSCN5361 <F27>. It is only a negative but I am attaching a picture of it here because it is the specimen that I referenced earlier with a rib index of 5. It is 23mm long and has a whorl height of 15mm. It was found about 4-5 miles to the south-west of the creek site. For reference, here is a post I made about the P. trinodosum specimen that I sent you a picture of in May. I thank you very much for your help in advance. Sincerely, Heteromorph" I have given an alphanumerical designation to each picture for ease of reference. I guess it is probably kinda silly to have so many pictures that this is necessary. If this is stupid, than I extent my apologies to the Mods. I will patiently receive correction. Thank you to everyone in advance. F1 F2 F3 F4