Malcolmt Posted November 24, 2013 Share Posted November 24, 2013 (edited) I just thought I would upload a picture of a very large doublure that I have been prepping from St. Mary's cement quarry in Bowmanville Ontario, Canada. This is a fairly well recognized site that has produced some amazing specimens over the years. Unfortunately for us collectors they only open it up to us one day per year, generally in October. There were at least 4 of us from the forum there this year. I did find a number of relatively complete isotelus that day but in hindsight I think this is likely the only piece that will stay in my own collection. (Pirahna, if you are reading this and have any good article on isotelus doublure, they would be greatly appreciated. I have been trying to find a good picture or diagram of a complete one from isotelus.) The picture is an incomplete doublure from an isotelus latus. (originally I had thought I. gigas but Kevin has pointed out what I think is a better identification) The doublure extends around the underside outer margin of the cephalon and is visible in the ventral view of a trilobite. In some trilobites the hypostome is attached to the doublure to provide structural stability to the feeding apparatus. What you can see is approximately 170 mm wide or about 7 inches, that's a Canadian quarter by the way which is basically the same size as a US one. Based on this I would estimate the minimum length of the trilo to be 12 inches perhaps even a bit bigger. You can see the terracing on the bottom surface quite clearly. The piece is not completely prepped at this point as I still need to clean up the tool marks. Prepping was via airscribe and dolomite air abrasion. Here is a link to a good paper on isotelus hypostomes http://www.academia.edu/213012/The_function_of_forks_Isotelus-type_hypostomes_and_trilobite_feeding Edited November 27, 2013 by Malcolmt Link to comment Share on other sites More sharing options...
Bev Posted November 25, 2013 Share Posted November 25, 2013 BEAUTIFUL! Thanks for posting! The more I learn, I realize the less I know. BluffCountryFossils.NET Fossil Adventure Blog Go to my Gallery for images of Fossil Jewelry, Sculpture & Crafts Pinned Posts: Beginner's Guide to Fossil Hunting * Geologic Formation Maps Link to comment Share on other sites More sharing options...
TMNH Posted November 25, 2013 Share Posted November 25, 2013 Nice find! Big ones are always exciting! Link to comment Share on other sites More sharing options...
Jed '06 Posted November 25, 2013 Share Posted November 25, 2013 Wow, you do have some Big Ones up there Malcolm! Very nice! Link to comment Share on other sites More sharing options...
Fossildude19 Posted November 25, 2013 Share Posted November 25, 2013 That's a monster, Malcolm! Thanks for posting it. Regards, Tim - VETERAN SHALE SPLITTER VFOTM --- APRIL - 2015 __________________________________________________ "In every walk with nature one receives far more than he seeks." John Muir ~ ~ ~ ~ ><))))( *> About Me Link to comment Share on other sites More sharing options...
erose Posted November 26, 2013 Share Posted November 26, 2013 That is a very interesting specimen. Sometimes fragments are worth collecting just for their size or level of preservation. Many years ago I found a huge hypostome in the Ordovician rocks near my childhood home. I figured out it was from an Isotelus cf. maximus. Then I found some reference material and determined it was probably from a good 14-16 inch specimen when complete. Large fragments of those bugs are scattered and common throughout the Cincinnatian Series. If that is I. gigas it was a big one. Link to comment Share on other sites More sharing options...
Northern Sharks Posted November 27, 2013 Share Posted November 27, 2013 I think that it is more likely from an Isotelus latus based on the size, location and more rounded outline than found on I.gigas. I have a pic/drawing showing the complete ventral anatomy for I.gigas that I will send you later on tonite There's no limit to what you can accomplish when you're supposed to be doing something else Link to comment Share on other sites More sharing options...
Malcolmt Posted November 27, 2013 Author Share Posted November 27, 2013 Kevin, I think I agree that it is a isotelus latus doubure. According to Marc Behrendt Generally, to tentatively identify the large Ontario Isotelus, 2 features should be observed. If the cephalon and pygidium are rounded with long genal spines--Isotelus maximus*; with blunt or no genal spines--Isotelus latus*. If the cephalon and pygidium are triangular with genal spines, odds are it is an Isotelus mafritzi, with no genal spines, odds are it is an Isotelus gigas*. There are other rarer species present, but this is a simple method to establish what Isotelus species you probably have. * indicates this species can exceed 10 inches (25 cm) in length. Link to comment Share on other sites More sharing options...
PennyT. Posted November 27, 2013 Share Posted November 27, 2013 Malcom, congratulations! I'd sure remember that "anniversary" and go to the quarry each year. Here is a photo from most complete one I've found and a photo another Forum member sent me. But I'm sure Piranha or someone else will have better resources to share with you. It does give you an idea of what a whole one would look like, however. *Mine is Isotelus iowensis. Penny http://www.thefossilforum.com/uploads/monthly_03_2013/post-4301-0-58410700-1364168000_thumb.jpg http://www.thefossilforum.com/uploads/monthly_03_2013/post-6808-0-97783100-1364167037_thumb.jpg Link to comment Share on other sites More sharing options...
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