Tomatticus Posted August 26 Share Posted August 26 Can anyone help identify the fossil found in this pebble found on the beach Nr Newhaven? 1 Link to post Share on other sites
connorp Posted August 26 Share Posted August 26 No. Looks like an echinoderm of some sort. 1 3 Link to post Share on other sites
Rockwood Posted August 26 Share Posted August 26 That's a partial internal mold of an echinoid (sea urchin). The shape to the right is a cross sectional view of one of the spines that would have articulated with the external side. 2 4 Link to post Share on other sites
Tidgy's Dad Posted August 26 Share Posted August 26 (edited) Yes, partial regular sea-urchin test. Probably a cidarid. The circular areas are where the spines would have been attached. I must confess that when I was a child and saw my first one of these, my first thought was also octopus. Edited August 26 by Tidgy's Dad 3 3 Link to post Share on other sites
Rockwood Posted August 26 Share Posted August 26 30 minutes ago, Tidgy's Dad said: I must confess that when I was a child and saw my first one of these, my first thought was also octopus. Sucker (s) ! 6 Link to post Share on other sites
Tidgy's Dad Posted August 26 Share Posted August 26 5 minutes ago, Rockwood said: Sucker (s) ! An 'armless mistake. 7 Link to post Share on other sites
Tomatticus Posted August 26 Author Share Posted August 26 49 minutes ago, Rockwood said: Sucker (s) ! Link to post Share on other sites
Tomatticus Posted August 26 Author Share Posted August 26 Thanks all. That makes total sense. I have other fossils from the same area that are, I believe, the external bits. Will post when I get the opportunity. Link to post Share on other sites
Rockwood Posted August 28 Share Posted August 28 Okay, I really feel like I should clean up a mess that I made in this identification. I don't want faulty information being seen as what novices might take to be correct. @Tidgy's Dad correctly identified the post. I believe my calling it a mold fossil is incorrect, and that it should probably be pointed out that this is actually the inside of a body fossil. 1 Link to post Share on other sites
Carl Posted August 29 Share Posted August 29 20 hours ago, Rockwood said: Okay, I really feel like I should clean up a mess that I made in this identification. I don't want faulty information being seen as what novices might take to be correct. @Tidgy's Dad correctly identified the post. I believe my calling it a mold fossil is incorrect, and that it should probably be pointed out that this is actually the inside of a body fossil. I actually agree that it is a mold. But I'm seeing an external mold rather than an internal one. Echinoderms certainly present confusing and wonderful fossils. 2 Link to post Share on other sites
Bobby Rico Posted August 29 Share Posted August 29 (edited) I think It is a mold of tuberculated interambulacral plate , well I think that’s what you call this bit of Echinoderms. Edited August 29 by Bobby Rico Link to post Share on other sites
Rockwood Posted August 29 Share Posted August 29 (edited) 1 hour ago, Carl said: I actually agree that it is a mold. But I'm seeing an external mold rather than an internal one. Echinoderms certainly present confusing and wonderful fossils. So you see it as being convex ? Oh. You're saying the body isn't there. I have trouble with the stereom being molded that way, but mold was my first impression. Edited August 29 by Rockwood Link to post Share on other sites
Carl Posted August 31 Share Posted August 31 On 8/29/2023 at 10:03 AM, Rockwood said: So you see it as being convex ? Oh. You're saying the body isn't there. I have trouble with the stereom being molded that way, but mold was my first impression. I see the impression as a concave mold of the external surface of the test. I don't think you'd see that level of tubercle detail from an internal mold of the test. But am I seeing it wrong? 1 Link to post Share on other sites
Rockwood Posted August 31 Share Posted August 31 5 minutes ago, Carl said: I see the impression as a concave mold of the external surface of the test. I don't think you'd see that level of tubercle detail from an internal mold of the test. But am I seeing it wrong? You probably have it right. Could it be a pressure shadow that makes this appear to me as a body fossil ? It just looks too complex to be a mold. Link to post Share on other sites
Carl Posted August 31 Share Posted August 31 1 minute ago, Rockwood said: You probably have it right. Could it be a pressure shadow that makes this appear to me as a body fossil ? It just looks too complex to be a mold. Not sure I follow: What's a "pressure shadow" and why would it be too complex? And either way, it's a body fossil as it preserves the morphology of a body part. Link to post Share on other sites
Fossildude19 Posted August 31 Share Posted August 31 Sometimes, the high contrast can fool our eyes into seeing things as a cast, when actually it is a mold. This photo of one of my gastropods can sometimes look like an inflated (convex) gastropod, but is actually a very detailed imprint (concave) of one. 2 Link to post Share on other sites
Mark Kmiecik Posted August 31 Share Posted August 31 You mean like this: 1 Link to post Share on other sites
Bobby Rico Posted August 31 Share Posted August 31 Maybe this may help ?Prionocidaris from Kent. 3 Link to post Share on other sites
Rockwood Posted August 31 Share Posted August 31 5 hours ago, Carl said: Not sure I follow: What's a "pressure shadow" and why would it be too complex? And either way, it's a body fossil as it preserves the morphology of a body part. https://en.wikipedia.org/wiki/Pressure_shadow It just looks like it has more depth than it should. A mold would have contours, but no real dimension. Link to post Share on other sites
Mahnmut Posted August 31 Share Posted August 31 Hello together. As far as I understand chert fossils, they form by a chemical process, silica falling out of solution. This can preserve very fine detail. And other than the classical technical version of mold-making where a shape is pressed into a pliable mass like clay (or sand or...) no relevant pressure is involved. Neither is north sea chert usually subject to much diagenetic deformation as far as I know, so I would not expect pressure shadows in this context. I agree this is a highly detailed negative of the outer surface of something like a cidarid. There are no tuberkels or anti-tuberkels on the inner surface. I do not know if here the original calcitic test got dissolved in the process, or got replaced by silica and separated from its counterpart mechanically. Best Regards, J 1 1 Link to post Share on other sites
Carl Posted September 1 Share Posted September 1 17 hours ago, Rockwood said: https://en.wikipedia.org/wiki/Pressure_shadow It just looks like it has more depth than it should. A mold would have contours, but no real dimension. I think I understand pressure shadow now - thanks for that. But most mold fossils need no pressure as I think the word is being interpreted. If something is buried gently in fine sediment there wouldn't really be an pressure to speak of until it was well-buried, and the detail can be extremely high res. 1 Link to post Share on other sites
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