Archive for the ‘Paleontology’ Category

Here is a rock that was presented to me in lab this week that I found interesting. It is a sample of the New Creek Limestone Formation found in western Virginia; also known as the Coeymans in New Jersey. It is a Devonian aged light gray, fossiliferous limestone, with very coarse grained calcite crystals. It is the fossils in the sample that I found most interesting. For some reason or another I have always been partial to crinoids. It might be because that was the first fossil I found on my own. With that said, the crinoid stem fossil found in this New Creek sample has retained its shape remarkably well, and it has a lot to do with diagenetic process of replacement. At some point during the process of this sediment becoming a rock the structure of the crinoid fossil (possibly aragonite) was replaced by calcite which is more stable. This process is sometimes called calcitization. If you look on the right half of the first picture below, you can make out the radial grooves in the fossil.

Mechanical pencil tip for scale.


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Whether they know it or not, this beautiful hotel in Barcelona has a 30 foot tall statue of an Archemedis Bryozoan; which is a shape that is immediately recognizable to those in the know.

International blog post #2 in the books.

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In part two of my Henson Creek fossil series on this blog I will be discussing Ostrea compressirosta. This bivalve is a member of the subclass Pteriomorpha like the Cucullaea Gigantea mentioned in my previous post, though this one adhered to the surface of the seafloor as opposed to burrowing into the sediment. Both were filter feeders that strained their nourishment from the water using a siphon.

O. Compressirosta ranges in age from the late Paleocene to the late Pliocene, but is found in Maryland only from 58.7 – 55.8 million years ago. Younger fossils have been found in Virginia, North Carolina, and Florida (I’ve heard a lot of people like to retire there, too).

This guy is also a member of the family Ostreidae, which are known as “true oysters” and the kind that we, as humans, like to dip in cocktail sauce. Unfortunately for us, we will never know what this particular oyster tastes like. Like all oysters, O. Compressirosta is monomyarian, meaning it has only one abductor scar from the muscle used to close the two shells. As you can see from the pictures below it also had irregular shell shape. The shell of this particular fossil would have been composed of calcite that weathered away leaving a sandstone cast like the C. Gigantea found in the same location. Oysters like these reproduce hermaphroditically, possessing both the larva and egg producing abilities sometimes switching between the two based on circumstance.

Try not to think about this post next time you are at Red Lobster. Sorry.

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A few years ago I took a Geology Field Studies class through NVCC. One of the trips we took led us to a creek in Maryland just off the Capital Beltway. I believe it was Henson Creek, but it has been awhile and the memory is a bit foggy. There was no path so we rolled up our pant legs and tromped through the creek, where the glauconitic quartz sandstone, Aquia Greenstone Formation, is exposed nicely. It wasn’t until we had walked in about 150 meters that it was brought to our attention we were walking all over these guys:

That is Cucullaea Gigantea, a now extinct bivalve from the Paleocene ranging in age from 58.7 – 55.8 million years old. These guys were infaunal suspension feeders, meaning they burrowed into the seafloor and strained their food from the water. By now the shell had completely eroded away, but what was left is a perfect mold of the interior composed of the greenstone. When this creature died a small opening was left so that sediments could fill in and later harden into rock. As time passed the more easily weatherable shell went away and all that remained was the more durable greenstone. C. Gigantea is about twice the size of its relatives such as Cucullaea recendens averaging about 8 – 14 cm in length, while C. Recendens averages 5 – 8 cm. Finding marine fossils in a Maryland creek bed also shows that it was once a marine environment. Along with a plethora of C. Gigantea fossils I also found some Ostrea compressirosta fossils, which I will talk about in a future post.

So, if you ever feel like going fossil hunting in the Washington DC area, Henson Creek in MD is bound to get you a handful of these guys

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