Eutrephoceras species?

Discussion in 'ID Requests' started by nwn, Jun 28, 2010.

  1. nwn

    nwn Larval Mass Registered

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    Nautiloid size : 4.1cm X 3.7cm (1.61" X 1.46")
    Origin : Fall River county, South Dakota, USA

    I looked through the websites recommended by some very kind fossil collectors. However, identifying an Eutrephoceras still a difficult task for me even with references; they all look pretty much the same, ie. E.elegans and E.dekayi. Here's some link to Eutrephoceras references that I mentioned.
    E.elegans http://www.wmnh.com/wmima29.htm
    E.dekayi 1: http://www.yale.edu/ypmip/taxon/ceph/30394.html
    E.dekayi 2: http://www.clemson.edu/public/geomu...phalopods/nautiloid_eutrephoceras_dekayi.html

    Both of the E.dekayi seems a little different from its suture but they are the same species; i'm confused :shock: and I still had a few Eutrephoceras to be identified.

    Can someone tell me what species is this nautiloid? Many thanks to those who contribute~:notworth:
     

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  2. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    :welcome: to TONMO nwn

    Your specimen looks like E. dekayi to me. I will look in Ammonites and other Cephalopods of the Pierre Seaway when I get home and see if I can verify that ID (you should get a copy if you do a lot of collecting in SD :sly:).

    If those are the sutures visible on the specimen from Yale, I don't think it is a E. dekayi as Eutrephoceras sutures are relatively straight.
     
  3. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    According to the previous referenced book the location of the siphuncle is the primary means of ID;

    E. alcesence: central to dorsocentral, Shell large

    E. dekayi: 1/4 to 1/3 distance from dorsum to venter, shell depressed

    E. "elegans" nebrascensis: 1/3 distance from venter to dorsum

    E. montanensis (variety of dekayi?): central, shell compressed

    They consider E. elegans a Cenomanian, European species, not present in the western interior US.

    Any sign of the siphuncle on your specimen?
     
  4. nwn

    nwn Larval Mass Registered

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    Geez, that's a lot of useful information, thanks Kevin! :notworth: This probably the best site ever with all information I needed. Internet is my only resource to collect fossils and information since I never have the chance to collect fossils at the site.
    Before this, I had difficulties to choose a book among dozens of books, I will get the book you recommended.Thanks!

    After studying from several sources, the nautiloid from Yale is Eutrephoceras dekayi variety of mortonese :heee:

    Well, too bad that I could not see any sipuncle sign on my nautiloid. I got another big Eutrephoceras, but neither of them show their siphuncle.

    Another interesting about the Eutrephoceras is that the small ones had bulge suture on the dorsum(hope i used the correct word:lol:), but not on the large ones.
     
  5. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    If you do get that book, there are some good cross section drawings of Eutrephoceras, so perhaps you could get a better feel for the ID from them.

    Good luck. :smile:
     
  6. nwn

    nwn Larval Mass Registered

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    After getting it's height to width ratio, I suspect that nautiloid to be a Eutrephoceras dekayi. But the width does not seems right, it is rather narrower
     
  7. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    With any fossil there is probably some degree of intraspecific variation, so there may be slight differences from one specimen to another, and none may match the type exactly. There may also be some temporal variation or some population variation. Someone may look at the nautiloids from the Cretaceous western interior of the US and split them up into several more species or even several more genera than are currently recognized, or someone may lump them all into less taxa than currently recognized. With only one specimen to look at, and very little stratigraphic control, getting an exact ID will be a crap shoot at best. 8-)
    Your best bet will be to get as close to one of the described species as you can with the available literature and data. Then as more information is received and studied you can refine the ID... then wait for someone to have a different idea or more data and change everything. Happens to me all the time, kinda makes it fun! :sly:
     

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