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Why are pyrite fossils small?


Alexander D.G

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Alexander D.G

Hey everyone,

I've been wondering why pyrite fossils are almost always small compared to others of the same species. does it have anything to do with the way the fossil is formed or is it something else entirely?

thanks in advance!

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I don't know if that is always the case. I've found pyritized goniatites that are fairly plump for their kind, and long nautiloids in the Billings Fm shale that get up to a healthy size. Another recent find of mine was an almost completely pyritized and enrolled trilobite (Greenops widderensis) that is the same size of an average non-pyritized specimen. 

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Alexander D.G

Thanks for your insight, i have only ever seen small ones they do seem te be a lot more common than the big ones like most fossils.

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It could have something to do with the amount of iron and sulfur available in the formation.

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Maybe in some areas there's a form of preservation bias where small shells are crushed in the fossilization process while bigger, thicker shells survive but when pyritization occurs it may give extra strength to smaller specimens?

Just a wild idea! :D

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The Amateur Paleontologist

I saw in a book about British dinosaurs (Lomax & Tamura 2014) an illustrated reference to a fairly large theropod femur from Charmouth (Dorset) which was heavily pyritised :)

Also someone from London's NHM 'Dinosaur Lab' posted a few weeks ago on Twitter a picture of another pyritised theropod limb bone from Charmouth.. 

5bf8411d50ec0_ScreenShot2018-11-23at19_03_02.png.81f7d8cb15a1986e49b1e2c90a3bcdc2.png

 

-Christian

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I agree. In many cases, I've seen them come out pretty small. For example, in the Arkona Fm, even the trilobites there are pretty tiny! I would speculate that smaller pyritized fossils might be a preservation bias given that larger pyrite replacement usually leads to higher probability of disintegration by oxidation. It also depends on the depositional environment, too, as many of these are preserved in anoxic conditions. And then it also depends on location, whether subtidal or offshore, which does play a factor in size of fauna in the water column, as well as the "movement of the mud."

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Alexander D.G
6 minutes ago, The Amateur Paleontologist said:

I saw in a book about British dinosaurs (Lomax & Tamura 2014) an illustrated reference to a fairly large theropod femur from Charmouth (Dorset) which was heavily pyritised :)

Also someone from London's NHM 'Dinosaur Lab' posted a few weeks ago on Twitter a picture of another pyritised theropod limb bone from Charmouth.. 

5bf8411d50ec0_ScreenShot2018-11-23at19_03_02.png.81f7d8cb15a1986e49b1e2c90a3bcdc2.png

 

-Christian

Never seen a pyritised bone before, that looks amazing!

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I was just thinking I have more small specimens of the same species of ammonites than I do large specimens. So is it just mater of larger specimen are more rare? 

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And on that topic of muddy, stormy bottoms, this lovely article on the Arkona I referenced above. The primary author teaches at the same uni as me, and you have the legendary Carlton Brett and the equally notable Topor brothers. It does elaborate on shell concentrations. 

 

Tsujita, C. et al. (2006). Evidence of high frequency storm disturbance in the middle Devonian Arkona shale, Southwestern Ontario. Journal of Taphonomy (4)2: 49-68. LINK

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1 minute ago, Kane said:

And on that topic muddy, stormy bottoms,

Not in perlite company Kane please.:)

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Just now, Bobby Rico said:

Not in perlite company Kane please.:)

:hearty-laugh:I honestly hadn't made the (obvious) connection! :P 

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