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AK hiker

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I have studying ammonite anatomy and nomenclature as well as the local geology where I have been hiking. Today I rough prepared several ammonites and feel like I can make an educated attempt to name 2 of 3 that I worked on. I am reasonably certain they are from member three of the Matanuska Formation in the Talkeetna Mountains. I have shared some pictures of where I found one on the snow at the bottom of an avalanche so pictures of that one first as it is new to me. In my effort to learn these will describe why I believe it is Gaudryceras tenailiratum; wide umbilicus, course ribs, rounded venter, pattern of major rib separated with repeating pattern of secondary ribs, the ribs are asymmetrical with the anterior side sloping in concave slope and the slopes abruptly. I did not prepare the back side as it was a double and left the mold from the other ammonite as I think it pretty cool.

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The next one also is ribbed and I believe is Neophylloceras ramosum and base that decision on the pictures from the Gological Survey Professional Paper 432 as well as the description. I have seen these one many times and have a few in the garden. I found that prepping them I have become quite attached as it takes time and learn the morphology as cleaning the fossil. This one had several shells in the matrix and I left a portion of one.

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Will make another post for the third ammonite

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Thanks in advance for any helpl!!!

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This is an ammonite I found several years ago and would like to know what it is. Being smooth there are many that occur in the Matanuska Formation so not as simple for me to look at pictures and descriptions to determine what type it is. I thought it could be from the Pachydiscus or Pseudophyllites genus but I do not know how to make the determination on this one. It is the thickest one relative to its diameter of any ammonite I have seen. I have left the back side unprepared  as the fossil stands on its own with the flat natural base and it started to crack when I tried to remove the matrix on the backside. Again THANKS for any help. 

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I agree with Gaudryceras tenailiratum for the first one.  I think Gaudryceras denmanense also occurs in Alaska but the ribs on that species are less dense but more pronounced.

Neophylloceras ramosum is a good ID for the second specimen.  There is another species of Neophylloceras in the area so I will have to look up the differences.  On a technical note, I think Neophylloceras is considered to be a subgenus of Hypophylloceras these days, so the name would be Hypophylloceras (Neophylloceras) ramosum.

Finally I agree that it is not always easy to tell the smooth ammonites apart but the lack of any ribs, the whorl shape, and the proportional size of the umbilicus is consistent with Pseudophyllites indra.  You could try to trace out the suture line to be sure.  In the Nanaimo Group on Vancouver Island Pseudophyllites is also different in that the shell is usually preserved as a light brown material, different from the white or iridescent shell of the Pachydiscus or Canadoceras specimens, but that is a taphonomic feature that results from the structure of the shell and it may not be consistent in other localities.

@fossisle and @Wrangellian are familiar with the Nanaimp Group ammonites and they may be able to say more.

 

These are very nice fossils indeed!  :wub: :wub: :wub:

 

Don

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On 7/6/2020 at 3:21 AM, FossilDAWG said:

I agree with Gaudryceras tenailiratum for the first one.  I think Gaudryceras denmanense also occurs in Alaska but the ribs on that species are less dense but more pronounced.

Neophylloceras ramosum is a good ID for the second specimen.  There is another species of Neophylloceras in the area so I will have to look up the differences.  On a technical note, I think Neophylloceras is considered to be a subgenus of Hypophylloceras these days, so the name would be Hypophylloceras (Neophylloceras) ramosum.

Finally I agree that it is not always easy to tell the smooth ammonites apart but the lack of any ribs, the whorl shape, and the proportional size of the umbilicus is consistent with Pseudophyllites indra.  You could try to trace out the suture line to be sure.  In the Nanaimo Group on Vancouver Island Pseudophyllites is also different in that the shell is usually preserved as a light brown material, different from the white or iridescent shell of the Pachydiscus or Canadoceras specimens, but that is a taphonomic feature that results from the structure of the shell and it may not be consistent in other localities.

@fossisle and @Wrangellian are familiar with the Nanaimp Group ammonites and they may be able to say more.

 

These are very nice fossils indeed!  :wub: :wub: :wub:

 

Don

Thank you very much! I have been wanting to put names on the fossils I have been seeing for some time now and wanted to learn so did not ask for an ID before I had some basis to understand them. I'm on my third ammonite book now with which is helping me to make sense of the scientific papers but have a long way to go with the geology here in Alaska as it is very complicated with the numerous terrains that make up Alaska. So a pair of Hypophylloceras (Neophylloceras) ramosum on my desk to ponder. Thanks again.

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Edited by AK hiker
Correct spelling
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Very nice ammonites AK hiker, FossilDAWG(Don) is correct for the first 2. But our Nanaimo Group Pseudophyllites are more inflated with a smaller umbilicus.

This may be a smooth Pachydiscus or Anapachydiscus in my opinion

Rick

Cephalopods rule!!

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Will do my homework and trace out the suture line and report my findings for the last one. 

Thanks for your input.

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Have reviewed the suture line diagrams and compared to sutures that are visible on the ammonite in question. The match is Anapachydiscus nelchinenisis, in my inexperienced assessment. This is the only one that has suture lines with acute architecture of what was reported in the formation. The physical description also matches. Thanks. IMG_4388.jpg.85b782ea4d39dd6c44cb25454a8dc784.jpg

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