CraigHyatt Posted May 15, 2016 Share Posted May 15, 2016 (edited) Specimens found in Eagle Pass Texas. This region is Upper Cretaceous. These specimens were all found on the ground or embedded at ground level. This level is about 2 or 3 m lower than the layers I've been working. It's mostly grey or yellow-grey clay and soft shale. These are all wider than the Sphenodiscus I found, so maybe Pachydiscus. Specimen 1 Specimen 2 Edited May 15, 2016 by CraigHyatt Info: Craig Hyatt, retired software/electrical engineer Experience: Beginner, fossil hunting less than a year Location: Eagle Pass, TX USA on the border with Mexico, hot dry desert Formation: Escondido, Marine, Upper Cretaceous Materials: Sandstone, Mudstone, Shale, Chert, Chalk Typical: Thalassinoides, Sphenodiscus, Exogyra, Inoceramus Reference: http://txfossils.com/Txfossils.html Link to comment Share on other sites More sharing options...
CraigHyatt Posted May 15, 2016 Author Share Posted May 15, 2016 Specimen 3 (may not be an ammonite, no sutures visible, but maybe some edge decoration) Specimen 4 (just a small fragment showing sutures) Info: Craig Hyatt, retired software/electrical engineer Experience: Beginner, fossil hunting less than a year Location: Eagle Pass, TX USA on the border with Mexico, hot dry desert Formation: Escondido, Marine, Upper Cretaceous Materials: Sandstone, Mudstone, Shale, Chert, Chalk Typical: Thalassinoides, Sphenodiscus, Exogyra, Inoceramus Reference: http://txfossils.com/Txfossils.html Link to comment Share on other sites More sharing options...
tmaier Posted May 15, 2016 Share Posted May 15, 2016 Looks like you are getting into the good stuff... =-) Link to comment Share on other sites More sharing options...
CraigHyatt Posted May 15, 2016 Author Share Posted May 15, 2016 Looks like you are getting into the good stuff... =-) Yeah. I spent the whole day on a walkabout looking for a better spot. As somebody on here mentioned to me, if you see a bunch of broken fossils lying around, chances are there's more good 'uns in the dirt. :-) Info: Craig Hyatt, retired software/electrical engineer Experience: Beginner, fossil hunting less than a year Location: Eagle Pass, TX USA on the border with Mexico, hot dry desert Formation: Escondido, Marine, Upper Cretaceous Materials: Sandstone, Mudstone, Shale, Chert, Chalk Typical: Thalassinoides, Sphenodiscus, Exogyra, Inoceramus Reference: http://txfossils.com/Txfossils.html Link to comment Share on other sites More sharing options...
JarrodB Posted May 15, 2016 Share Posted May 15, 2016 Nice find. Link to comment Share on other sites More sharing options...
JohnJ Posted May 16, 2016 Share Posted May 16, 2016 You're doin' great, Craig. The human mind has the ability to believe anything is true. - JJ Link to comment Share on other sites More sharing options...
Uncle Siphuncle Posted May 16, 2016 Share Posted May 16, 2016 (edited) Craig I think all your specimens are ammonites, probably Sphenodiscids. The sutured portion is the phragmocone and the living chamber lacks sutures. There are several species of Sphenodiscus noted in Texas, and I'm not sure if they are all still valid, but I recall reading about S. pleurisepta, S. lobatus, S. tirensis, and S. intermedius. I don't know all the diagnostics off the top of my head, but some may have subtle flank tubercles while others are smooth flanked. Also, the sharpness of the keel may vary between species. In my own collection, some of the larger specimens have sharp keels on the juvenile whorls, gradually becoming more rounded toward the living chamber. A related form from the Escondido is Coahuilites sheltoni. I've only found a few of these, but they have a wide, rounded venter and 2 rows of prominent tubercles. See images. Edited May 16, 2016 by Uncle Siphuncle 1 Grüße, Daniel A. Wöhr aus Südtexas "To the motivated go the spoils." Link to comment Share on other sites More sharing options...
Uncle Siphuncle Posted May 16, 2016 Share Posted May 16, 2016 Pachydiscus seems to have been on the way out in Escondido times, as I've only found a couple in South TX. You should be able to distinguish these easily from the other ammonites by the ribs. 1 Grüße, Daniel A. Wöhr aus Südtexas "To the motivated go the spoils." Link to comment Share on other sites More sharing options...
CraigHyatt Posted May 16, 2016 Author Share Posted May 16, 2016 (edited) On the subject of ammonite sutures, the first thing that popped into my mind when I saw them under my lens was "fractal". They look a lot like Mandelbrot set fractals. I checked online and, sure enough, found an article on the subject. Also, I know the chambers of the nautilus (and probably ammonites) are also self-similar fractals and the size grows in a ratio close to the Golden Ratio aka Phi ~ 1.618. Nature is amazing! http://n-e-r-v-o-u-s.com/blog/?p=1176 http://www.goldennumber.net/spirals/ Edited May 16, 2016 by CraigHyatt Info: Craig Hyatt, retired software/electrical engineer Experience: Beginner, fossil hunting less than a year Location: Eagle Pass, TX USA on the border with Mexico, hot dry desert Formation: Escondido, Marine, Upper Cretaceous Materials: Sandstone, Mudstone, Shale, Chert, Chalk Typical: Thalassinoides, Sphenodiscus, Exogyra, Inoceramus Reference: http://txfossils.com/Txfossils.html Link to comment Share on other sites More sharing options...
doushantuo Posted May 16, 2016 Share Posted May 16, 2016 (edited) https://www.researchgate.net/publication/281271224_Chapter_3_-_Ammonoid_Septa_and_Sutures http://palaeo-electronica.org/2011_1/136/136.pdf http://webpersonal.uma.es/~PPB/MathGeol.pdf https://www.kahaku.go.jp/research/researcher/papers/70487.pdf Of course there's more,this is just a sample.R.A.Hewitt,Oloriz*,Westermann are names that immediately come to my mind when someone says suture *look up his 'gate page,good stuff there on bathymetry and sutures Edited May 16, 2016 by doushantuo 1 Link to comment Share on other sites More sharing options...
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