I_gotta_rock Posted July 31, 2016 Share Posted July 31, 2016 (edited) I found a whole shelf of these sand dollar urchins fused in sandstone on the edge of Coronado Island, in the San Diego Bay. Anyone have a clue how old they are? Edited July 31, 2016 by I_gotta_rock I refuse to give up my childish wonder at the world. Link to comment Share on other sites More sharing options...
CraigHyatt Posted July 31, 2016 Share Posted July 31, 2016 I found a whole shelf of these sand dollar urchins fused in sandstone on the edge of Coronado Island, in the San Diego Bay. Anyone have a clue how old they are? How long ago did you find them? (Just kidding. I have no idea.) Info: Craig Hyatt, retired software/electrical engineer Experience: Beginner, fossil hunting less than a year Location: Eagle Pass, TX USA on the border with Mexico, hot dry desert Formation: Escondido, Marine, Upper Cretaceous Materials: Sandstone, Mudstone, Shale, Chert, Chalk Typical: Thalassinoides, Sphenodiscus, Exogyra, Inoceramus Reference: http://txfossils.com/Txfossils.html Link to comment Share on other sites More sharing options...
I_gotta_rock Posted July 31, 2016 Author Share Posted July 31, 2016 Yeah, I wondered when I found them if they were something akin to vintage last week. In truth, I have specimens from two locations that really were something akin to vintage last week. One was in a very hard-water creek. A red maple leaf was still deteriorating while stuck to a rock, and the water made a perfect outline of a black mineral on a red-yellow stone that is completely fused to the rock! The other was in another spring, hundreds of miles away, that is so heavy in minerals that domes form at a rate of an inch a year. Leaves that fall on the domes are fossilized in a matter of weeks. Oddly enough, also red maple! I refuse to give up my childish wonder at the world. Link to comment Share on other sites More sharing options...
I_gotta_rock Posted July 31, 2016 Author Share Posted July 31, 2016 My mistake. Modern sad dollars do have a zillion rigid protrusions, if you meet them when they are alive. I miss-classified. I refuse to give up my childish wonder at the world. Link to comment Share on other sites More sharing options...
I_gotta_rock Posted July 31, 2016 Author Share Posted July 31, 2016 For the record, I looked up echinoid, because I couldn't remember where starfish fit in. Sand dollars are urchins, and are members of the echinoderm taxa. http://echinoblog.blogspot.com/2012/03/sand-dollars-are-sea-urchins-please.html I refuse to give up my childish wonder at the world. Link to comment Share on other sites More sharing options...
I_gotta_rock Posted July 31, 2016 Author Share Posted July 31, 2016 Bingo! I found it! I can dig online as well as in the dirt. See page 2. http://www.naturalhistorymag.com/partner/fossil-discoveries-in-downtown-san-diego?page=2 I refuse to give up my childish wonder at the world. Link to comment Share on other sites More sharing options...
BobWill Posted July 31, 2016 Share Posted July 31, 2016 (edited) Urchin is not a scientific name, just a common name. So is sand dollar but they are not the same thing. They are just one sub-order in one of the orders of the class that includes all urchins. The most obvious protuberances on sand dollars are tube feet and not referred to as spines. Spines are mostly for protection and tube feet are only for locomotion, feeding and respiration. Edited July 31, 2016 by BobWill 1 Link to comment Share on other sites More sharing options...
DPS Ammonite Posted July 31, 2016 Share Posted July 31, 2016 (edited) It is hard to tell what they are unless they are better exposed. There are fossiliferous formations in the San DIego area back to 75 million years ago in the Cretaceous. The modern looking sand dollars became common in the Eocene. I have yet to see any rock formations on Coronado. I suppose you might see some when digging for foundations. A large part of Coronado "Island" (actually a peninsula) was filled in with bay dredgings that could have come from any area formations. See these sites for more info on the fossils and geology: https://www.sandiego.gov/sites/default/files/legacy/planning/community/cpu/oldtownmidway/pdf/paleontological_resource_assessment_101413.pdf https://www.geocaching.com/geocache/GC23QEE_tourmaline-surfing-park-geology?guid=e079c303-f017-441f-97a9-50da321f7237 http://www.sandiegocounty.gov/dplu/docs/Paleo-Guidelines.pdf Edited July 31, 2016 by DPS Ammonite My goal is to leave no stone or fossil unturned. See my Arizona Paleontology Guide link The best single resource for Arizona paleontology anywhere. Link to comment Share on other sites More sharing options...
Oxytropidoceras Posted July 31, 2016 Share Posted July 31, 2016 (edited) I looked for the available geological maps of the "Coronado Island," San Diego Bay area at http://ngmdb.usgs.gov/maps/mapview/ . There I found: Kennedy, M.P., and Tan, S.S., 2008, Geologic map of the San Diego 30' x 60' quadrangle, California. Regional Geologic Map No. 3, California Geological Survey. http://ngmdb.usgs.gov/Prodesc/proddesc_84173.htm and http://www.quake.ca.gov/gmaps/RGM/sandiego/sandiego.html PDF file at ftp://ftp.consrv.ca.gov/pub/dmg/pubs/rgm/RGM_003/RGM3_San_Diego_2008_Plate1of2.pdf and ftp://ftp.consrv.ca.gov/pub/dmg/pubs/rgm/RGM_003/RGM3_San_Diego_2008_Plate2of2.pdf Pamphlet at ftp://ftp.consrv.ca.gov/pub/dmg/pubs/rgm/RGM_003/RGM3_San_Diego_2008_Pamphlet.pdf The map shows, Coronado Island as "Qop6," "Qmb," and "af." According to the map's pamphlet: af = artificial fill (late Holocene), "Deposits of fill resulting from human construction, mining, or quarrying activities; includes compacted engineered and non-compacted, non-engineered fill." Qmb = Marine beach deposits (late Holocene), "Unconsolidated beach deposits consisting mostly of fine and medium-grained sand." Qop6 = Old paralic deposits, Unit 6 (late to middle Pleistocene), "Poorly sorted, moderately permeable, reddish-brown, interfingered strand-line, beach, estuarine and colluvial deposits composed of siltstone, sandstone and conglomerate. Yours, Paul H. Edited July 31, 2016 by Oxytropidoceras Link to comment Share on other sites More sharing options...
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