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Showing results for tags 'micrasteridae'.
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Hi, Some weeks ago, I found those spatangoid echinoids in my usual Upper campanian/Lower Maastrichtian hunting zone of SE of Pyrenees: I think they fit well with Diplodetus brevistella, as shown in http://www.echinologia.com/galeries/micrasteridae/index.html#diplodetus But, I found no other references of Diplodetus in the Pyrenees, and hardly in distant zones of Spain, which makes me doubt (Diplodetus is a genus mostly found in Northern Europe)
I found this Phlycticrioceras trinodosum heteromorph specimen in June of 2018 whilst hunting the middle/upper Coniacian Atco formation. It is the largest fragment of this species that I am aware of, having a whorl height of 51 mm as opposed to 47 mm of the largest fragment I've seen published. This genus is a bigger, rarer, and (mostly) younger cousin of Allocrioceras. I sent pictures of it to Keith Minor and he pointed out that there was also an echinoid sticking out of the specimen, something which I had totally missed! With much of the echinoid still stuck in the living chamber it is hard to get a definitive ID. But because it has such a shallow anterior ambulacra, which gives the anterior end a more smooth rather than definitive heart shape, he ruled out both Mecaster texanus and batensis. He suggested Micraster since the site has a strong European component in both the bivalve and ammonite faunas, and because the periproct side has the right shape. From finding other, although not as well preserved specimens that show similar morphology he appears to be right. I have yet to confirm this ID with Andrew Smith, but either way I think the piece is worth showing. And reading this thread got me thinking about how this could have happened and what effect it could have had on the echinoid's preservation. My thought is that because irregular echinoids lived and today still live most of their lives burrowing in the sediment it is unlikely that it would have crawled into the living chamber, but instead that it was blown into it post-mortem via currents that had dredged it out of the sediment. I already know that this site was a high energy environment from my other finds here so this seems the most likely possibility to me. But because of the fact there is still at least one spine still attached to the specimen it could not have been swept up from the sediment too long after death or all of its hairlike spines would have blown away. I do, however, find it interesting that it is positioned anterior first with its posterior towards the aperture, the position I would expect to see it in if it had indeed crawled into the shell. The specimen is also the best preserved echinoid from this site so far. Despite the ammonites being generally well preserved and not too crushed, most of the echinoids that I have from the site are terribly crushed, flakey, and often infested with rotting pyrite. I think being encapsulated in the chamber very much reduced those effects. Even though the ammonite and the echinoid are a bit crushed, the echinoid would have probably been worse off otherwise. The heteromorph fragment length is 70 mm and the whorl breadth, being a bit crushed, is 13 mm. I would think that this specimen, with its open planispiral coiling, would would have been at least over a foot in diameter when complete. It is the robust (female) morph of the species with a rib index of 5½. For comparison in Fig. 1 I pictured it with my most complete P. trinodosum specimen. From the part of the echinoid that is exposed I can measure 25 mm in length, 25 in width, and a thickness of 8 mm. I have also found abundant yet scattered fish remains at the site, so perhaps one day an ammonite-fish will come my way. But until then, anyone else got ammonite-echinoids to show? Fig. 1. Fig. 2.