fay_fay Posted July 24, 2017 Share Posted July 24, 2017 My daughter found this really cool fossil yesterday on Bolinas Lagoon. Any clues as to what it could be? We find lots of sand dollar fossils around here but this looks more like a bone from a large animal. It's about two inches in length & an inch wide. Very heavy. Link to comment Share on other sites More sharing options...
ynot Posted July 24, 2017 Share Posted July 24, 2017 Welcome to TFF! Sorry but this is not a fossil bone. It could be a borow cast (ichnofossil) or it could be a concretion (not fossil). Darwin said: " Man sprang from monkeys." Will Rogers said: " Some of them didn't spring far enough." My Fossil collection - My Mineral collection My favorite thread on TFF. Link to comment Share on other sites More sharing options...
FossilDudeCO Posted July 24, 2017 Share Posted July 24, 2017 @Boesse or @Harry Pristis are dugong rib sections known there? If not I like @ynot idea of a burrow or cast of some sort. Link to comment Share on other sites More sharing options...
fay_fay Posted July 24, 2017 Author Share Posted July 24, 2017 Thanks! Link to comment Share on other sites More sharing options...
Miocene_Mason Posted July 24, 2017 Share Posted July 24, 2017 I'd stick to concretion, remeinds me of a septerian nodule without the cracks. “...whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved.” ~ Charles Darwin Happy hunting, Mason Link to comment Share on other sites More sharing options...
fay_fay Posted July 24, 2017 Author Share Posted July 24, 2017 Here's some more loot from our morning walk. These are all sand dollar fossils from what we can see with our untrained eye. the second shot is one that I don't believe is a fossil but my boyfriend does. My hunch is fossils aren't generally that brittle (this broke easily when it dropped on the counter). I am sure this forum will clear this one up! I'll read up a bit more on ID'ing these things and see if we find anything else interesting during the next low tide. Link to comment Share on other sites More sharing options...
ynot Posted July 24, 2017 Share Posted July 24, 2017 They all look fossil to Me. Extant sand dollars tend to be white. and most fossils are brittle. Look in the rock at the head of the beach and You may find some whole ones in matrix (rock). 1 Darwin said: " Man sprang from monkeys." Will Rogers said: " Some of them didn't spring far enough." My Fossil collection - My Mineral collection My favorite thread on TFF. Link to comment Share on other sites More sharing options...
fay_fay Posted July 24, 2017 Author Share Posted July 24, 2017 Here's another one we're not sure about. We found most of these up at "the point", which I think is the spot Ynot is referring to. Link to comment Share on other sites More sharing options...
ynot Posted July 24, 2017 Share Posted July 24, 2017 Sorry but the last one does not look like a fossil. The head of the beach is the furthest away from the ocean, usually bordered by cliffs. The point is where the cliffs project out from the shore line. Darwin said: " Man sprang from monkeys." Will Rogers said: " Some of them didn't spring far enough." My Fossil collection - My Mineral collection My favorite thread on TFF. Link to comment Share on other sites More sharing options...
trisk Posted July 24, 2017 Share Posted July 24, 2017 https://californiafossils.org/2016/07/03/bolinas-lagoon/ has links to papers on the local geology that could be helpful. The complete sand dollar and bigger pieces appear to be dendrastrids. They're probably examples of the (still extant) species Dendraster excentricus. https://inverts.wallawalla.edu/Echinodermata/Class Echinoidea/Dendraster_excentricus.html has photos and diagnostic features. http://online.sfsu.edu/bholzman/courses/Fall02 projects/sandollar/sanddollar.html describes the evolutionary history. The last rock does appear to have a linear inclusion in the chipped edge, might be something there. A large number of small cone or ring-shaped structures are also visible on that surface in the full size photo, not sure if they're embedded or encrusting organisms. Can you take more photos of that side? Link to comment Share on other sites More sharing options...
Boesse Posted July 26, 2017 Share Posted July 26, 2017 So, not sure what the tube-shaped doodad is. However, I can shed light on the sand dollars: those are Scutellaster oregonensis which have eroded out of the Merced Fm., exposed on the west shore of Bolinas Lagoon. The Santa Cruz Mudstone is immediately west, and is the unit that produces whale bone. There are giant dugongids (Dusisiren dewana) from the Santa Cruz Mudstone but their ribs are the size of small whale mandibles (~10 cm in diameter) and not very common. I suspect that thing is a concretion. Link to comment Share on other sites More sharing options...
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