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What do trilobites look when pulled out of the rock?


FossilSloth

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My main fossil collecting site is a Upper Pennsylvanian limestone roadcut that is rumored to have "some trilobites." I can find brachiopods galore but have never found a trilobite. What would it look like if I pulled a trilobite right out of the rock? Almost all of the brachiopods are found in a crumbly soft layer. Sometimes I can literally just pluck them out without tools. There are much harder layers present as well. Pic of the typical rock attached. Do I need to just split rocks in half until I find a cross section? 

IMG_2028.JPG

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As I haven't worked with this particular layer, take this with a grain of salt. If you are working the harder layers, it can be the case (but not always) that any fossils within the bedding plane will represent a structural weakness in the rock that can be exploited with a few firm strikes or taps along the edge. As I say, it isn't always the case as I've worked hard rock with high density that would cleave right through a trilobite. But, if that's the case, it isn't the end of the world if you get both pieces, prep them out at home, and glue the freed pieces back together.

 

If I were working that site, I'd keep my eyes open for weathered out pieces of the limestone in the talus. These might be easier to work, and would give you a better indication of what you might expect if you tackle the layer directly. Pennsylvanian trilobites are not terribly common, but if they are in the limestone layer, they might come out more robust than the flattened types one typically finds in shale.

 

But, even before tackling this tough task, do you have any documents on the stratigraphy? It might indicate what biota one can expect at each distinctive layer, usually attended with a description of the type of rock (for example, "argillaceous grey-brown shale, weathering to chips"). 

...How to Philosophize with a Hammer

 

 

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It sort of depends on what type of trilobite, what type of rock, preservation, ... etc. 

In the areas where I collect trilobites, the preservation varies quite widely.  Flattened, inflated, disarticulated, prone, enrolled or just pieces. 

Here is an example of what they can look like. 

None were prepped in these photos. Most are from shales. 

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    Tim    -  VETERAN SHALE SPLITTER

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With trilobites you need to be familiar with the geology to really know what to look for. As @Kane and @Fossildude19 said if you understand the rock then you'll know how the fossils will work with the rock and you'll be better prepared for extracting the fossil without harming it. I use a large wide chisel to extract fossils as a finer chisel sends a more concentrated shock wave through the rock which could damage the fossil. A wider chisel will disperse and even out the energy from your hammer swings and make for a cleaner break in the rock. Once again it depends on what type of rock your dealing with as some rock such as shale does an excellent job at preserving fossils whereas limestone might be a bit more difficult to work with. Typically your fossils will be embedded in sedimentary based rock such as shale, sandstone, etc. because the sediments are what preserved the fossil to begin with and for something to become fossilized it must be in an anaerobic environment void of oxygen so bacteria can't get to it and decompose the structure. I was meaning to send you a few trilobites but things keep coming up. I'll send you some E. rana's encased in shale so you'll have something to look at and work with.

Do or do not. There is no try. - Yoda

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@Fossildude19 raises a very good point. What species of trilobite are said to occur in this strata? That might set you up for knowing what to expect (if they were rollers, etc.). 

 

I forgot to add that inspecting the edges can also provide some guidance as to where to split. If you see something uncertain poking out, it might be a good plane to apply the chisel. When the edges show nothing, and you're presented with just a blank-faced block, tapping or striking around can reveal cracks that might suggest that structural weakness I spoke of earlier.

...How to Philosophize with a Hammer

 

 

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10 hours ago, Fossil-Hound said:

With trilobites you need to be familiar with the geology to really know what to look for. As @Kane and @Fossildude19 said if you understand the rock then you'll know how the fossils will work with the rock and you'll be better prepared for extracting the fossil without harming it. I use a large wide chisel to extract fossils as a finer chisel sends a more concentrated shock wave through the rock which could damage the fossil. A wider chisel will disperse and even out the energy from your hammer swings and make for a cleaner break in the rock. Once again it depends on what type of rock your dealing with as some rock such as shale does an excellent job at preserving fossils whereas limestone might be a bit more difficult to work with. Typically your fossils will be embedded in sedimentary based rock such as shale, sandstone, etc. because the sediments are what preserved the fossil to begin with and for something to become fossilized it must be in an anaerobic environment void of oxygen so bacteria can't get to it and decompose the structure. I was meaning to send you a few trilobites but things keep coming up. I'll send you some E. rana's encased in shale so you'll have something to look at and work with.

 

Thanks, man. I'm really looking forward to working on those. Trilobites really intrigue me, more so than most other fossils. 

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You may have to extract and split a lot of rock since trilobites were pretty rare by the time the Pennsylvanian age arrived. However, I've heard that they turn up pretty regularly at Jacksboro, a Pennsylvanian site in Texas and I recently found a very tiny one attached to a gastropod from the Pennsylvanian of western PA.

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Is it pretty much the farther back you go, the more trilobites there were? Because I do have Missippian, Devonian, and Cambrian limestone around me, too. 

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3 hours ago, FossilSloth said:

Is it pretty much the farther back you go, the more trilobites there were? Because I do have Missippian, Devonian, and Cambrian limestone around me, too. 

They died out once and for all at the end of the Permian. The prolificity doesn't just have to do with the geological age, but also the type of deposits. Whether deep sea, coastal, landslide induced, transported, etc. everything has an influence. Different types of fossils often tend to flock together like the birds for various reasons.

 

Greetings from the Lake of Constance. Roger

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6 hours ago, FossilSloth said:

Is it pretty much the farther back you go, the more trilobites there were? Because I do have Missippian, Devonian, and Cambrian limestone around me, too. 

Species diversity (which can often be correlated with occurrence) begins to drop off relatively early in the fossil record. The first image from H.B. Whittington's book on trilobites, reproduced from data in 1959, that gives an indication of diversity drop-off. The second from Levi-Setti's book.

 

 

triloccurrence.jpeg

triloccur.jpeg

...How to Philosophize with a Hammer

 

 

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