Fossil sand dollar, etc

[Vopros]

Hello

A few days ago I found a rock at Ocean Beach, San Francisco.

It attracted my attention because of a very small sand dollar it had in it.

At home I looked at it under a microscope.

Here's what I found:

https://c2.staticflickr.com/2/1585/25367346425_f7a063cdc2_o.jpg

https://c2.staticflickr.com/2/1553/25378945585_830affe649_o.jpg

https://c2.staticflickr.com/2/1600/25305546701_3eb81d77d9_o.jpg

https://c2.staticflickr.com/2/1608/25318128101_17cfc5b867_o.jpg

The shells other than sand dollar are only a few milometers in diameter. The sand dollar is 1.2 centimeter in diameter.

My questions are:

1. What shells there are in picture #2

2. What is there just below the upper left corner in the picture #3

3. What it is in picture #4

Thank you.

Edited March 1, 2016 by Vopros

[prem]

the little spirally shells are foraminifer shells...tiny, one-celled creatures that secrete the shell in a spiral pattern much like a miniature ammonite.

---Prem

[sseth]

Welcome to the forum. Great finds.

[jpc]

the little spirally shells are foraminifer shells...tiny, one-celled creatures that secrete the shell in a spiral pattern much like a miniature ammonite.

---Prem

yup, forams. Nice find.

[Vopros]

Thank you,

I also believe that some shells are ammonites, but I am not sure they could be found in the same deposit with sand dollars.

I asked USGS about that, and got response. The lady told me she was not an expert, but she believes that:

Ammonites were one of the many species that went extinct during the Cretaceous-Tertiary (K-T) extinction event, 66 million years ago.

From what I've read, sand dollars do not appear in the record until at least 65 million years ago, if not later. So no, it doesn't look like the two can be found in the same deposit. Of course, you could have a scenario where (millions of years ago) fossil ammonites were eroded out and redeposited along with live sand dollars, which were then fossilized in turn. But that probably wouldn't be common.

Edited March 1, 2016 by Vopros

[Raggedy Man]

http://www.marinespecies.org/foraminifera/photogallery.php?album=772

I was unable to look at 2, 3, 4, so I posted the link above for you. You should be able search pictures by morphology if not mistaken. It should help you identify your finds and if not, hopefully one of our knowledgeable members will chime with an ID.

Welcome to the forum!

Best regards,

Paul

Edited March 1, 2016 by Raggedy Man

[DPS Ammonite]

The USGS gal is right; sand dollars and ammonites did not coexist.

Assuming that you did not find a misplaced rock in San Francisco; it is probably part of the Pliocene/Pleistocene Merced Formation that occurs south of Fort Funston and into northern San Mateo County. Scutellaster interlineatum, a sand dollar occurs in the formation. See photo of 5 cm fossil. I can't tell what species you have unless more is exposed.

How big across are the spirally coiled shells that someone thought are forams? A size could help us determine if they are gastropods or forams. I have personally never seen any gastropods like that in the area.

Edited March 1, 2016 by DPS Ammonite

[Vopros]

The USGS gal is right; sand dollars and ammonites did not coexist.

Assuming that you did not find a misplaced rock in San Francisco; it is probably part of the Pliocene/Pleistocene Merced Formation that occurs south of Fort Funston and into northern San Mateo County. Scutellaster interlineatum, a sand dollar occurs in the formation. See photo of 5 cm fossil. I can't tell what species you have unless more is exposed.

How big across are the spirally coiled shells that someone thought are forams? A size could help us determine if they are gastropods or forams. I have personally never seen any gastropods like that in the area.

Well, as I mentioned above the shells other than the sand dollar are only a few milometers in diameter. The sand dollar is 1.2 centimeter in diameter. There are shells at the first picture close to the sand dollar. It is a good place to compare the sizes. There are also quite a few chitons and maybe some sea urchins there as well.

Also from this topic at this very forum http://www.thefossilforum.com/index.php?/topic/39117-ammonite-localities-in-sf/ it looks as ammonites could be found in SF.

But now I am even more interested to find out what this is

The full resolution is here: https://c2.staticflickr.com/2/1608/25318128101_17cfc5b867_o.jpg Thank you.

Edited March 1, 2016 by Vopros

[DPS Ammonite]

If the sand dollar is 1.2 cm then the spiral forams must be just under 1mm across, right?

The ammonites in northern most SF and the Golden Gate area occur in the slightly metamorphosed Jurassic and Cretaceous Franciscan greywackes that contain virtually no other fossils outside of isolation bivalves. The ammonites in the greywacke are much larger than the ones that you might think that you have and are also extremely rare. Only a handful have been found.

Your rocks might have been imported to help shore up the nearby Great Highway that is in danger of being washed away by the rising ocean and large waves.

Edited March 1, 2016 by DPS Ammonite

[Vopros]

If the sand dollar is 1.2 cm then the spiral forams must be just under 1mm across, right?The ammonites in northern most SF and the Golden Gate area occur in the slightly metamorphosed Jurassic and Cretaceous Franciscan greywackes that contain virtually no other fossils outside of isolation bivalves. The ammonites in the greywacke are much larger than the ones that you might think that you have and are also extremely rare. Only a handful have been found.Your rocks might have been imported to help shore up the nearby Great Highway that is in danger of being washed away by the rising ocean and large waves.

Well, I am not sure what shells these are(that is why I posted my questions here) , but ammonites are probably born small, and where there are big ammonites, there should be babies ones too, right?

About fossils at Ocean beach... During the years (much before Great Highway renovation) I have found quite a few sand dollars and other shells fossils at Ocean Beach. There are also petrified bones of whales or other Marine creatures, and nice concretions.

Even if the rock I found was imported, which I doubt it was, it still does not explain the presence of a sand dollar together with ammonites, if these are ammonites of course. Thank you.

[Auspex]

Except for the case of a consolidated reworked deposit, the coexistence in the same rock of sand dollars and ammonites cannot be.

[Vopros]

Except for the case of a consolidated reworked deposit, the coexistence in the same rock of sand dollars and ammonites cannot be.

I've got it, but what are the shells in picture 2 from my original post?

Besides, maybe I've made a new discovery :-)

[JohnJ]

You have not found baby ammonites. As others have said these are foraminifera, or "forams". They can look remarkably like ammonites.