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Rock Fossil Ocean Beach SF


dianahjerome

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Ive found this & other small fossils at ocean beach in San Francisco. Most look like sand dollars but this one has a foot w/clear metatarsals/phalanges & what looks like 3 vertabral columns or 3 portions of 1. Does anyone know what this is?

1483207264807.jpg

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this appears to be a well worn / broken piece of a sand dollar to me.

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Hi dianahjerome!

 

I also see a partial echinoid (sea urchin or sand dollar) in your specimen - see your image compared with a diagram that I found on the internet below:

 image022.jpg1483207264807.thumb.jpg.afd5fe91f47a895010fbfd097665e18d.jpg

red rectangle in the image of your specimen: ambulacrum

blue oval in the image of your specimen: interambulacrum

 

Cool find!!!

 

Monica

 

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The difference between the two types of echinoids lies in the symmetry/asymmetry . You could have an irregular echinoid, but considering the weathering status I would be not certain on this.

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dianahjerome

Thanks for the clarification about the bottom right pic!  ... I was more curious about the foot in the larger top picture & bottom left picture. Anyone have an idea of what the foot belonged to??

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The body cavity of a sand dollar is mostly void. I think these are the remains of the plates on the ventral side, or perhaps others that have been displaced. 

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Fossildude19

Welcome to the Forum. :)

 

I agree - it is a sand dollar/echinoid that has been crushed. 

Sorry, ... no foot bones there - those are plates from an echinoid, either the one on the other side, or a different one. 

I vote for the crushed one from the other side.

Regards,

 

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fifbrindacier

I agree both are worn and crushed echinoids, no foot bone here.

And, besides, welcome here :tff:

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Glad to see parts of these sand dollars are still showing up. I always liked the way the individual plate boundaries were outlined by the darker staining and the contrast between the lighter overall specimen and the darker enclosing matrix.

 

I actually collected pieces of them back in the 1970-80's! Thanks for the post--it brought back some good memories and some windy cold stormy winter memories of hunts when noone should be any where near the beach and eroding cliffs. Be careful!  

 

Continued hunting success!

Regards, Chris 

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It's a large sand dollar - the species is Scutellaster oregonensis. It's more common to find them on the beach than in situ within the cliff there. They erode out of the Plio-Pleistocene Merced Formation.

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