NicolaiT13 Posted May 16, 2018 Share Posted May 16, 2018 I found these today in southeastern Montana. I am located right on the edge of the Fort Union and Hell Creek formations. I am pretty sure the one on the left is an ammonite. What about the one on the right? Is that just a chunk of coral? Link to comment Share on other sites More sharing options...
Tidgy's Dad Posted May 16, 2018 Share Posted May 16, 2018 What's the scale of these, please? Not a coral, but could be a sponge. Life's Good! Tortoise Friend. Link to comment Share on other sites More sharing options...
NicolaiT13 Posted May 16, 2018 Author Share Posted May 16, 2018 Link to comment Share on other sites More sharing options...
FossilDAWG Posted May 16, 2018 Share Posted May 16, 2018 The spiral (ish) specimen on the left does not look like an ammonite to me, as it lacks any trace of suture lines. The one on the right is certainly not a coral, though it isn't clear to me what it actually is. The Hell Creek Formation is Cretaceous but of terrestrial origin. The Fort Union is Paleocene and also a terrestrial/fresh water deposit. Neither unit would be expected to produce marine fossils such as ammonites or corals, and corals are very rare anyway in the Western Interior Cretaceous. Don 4 Link to comment Share on other sites More sharing options...
Spongy Joe Posted May 16, 2018 Share Posted May 16, 2018 I reckon these are trace fossils - burrows of various sorts, with the sand around them cemented into the lumps. You can see small tubular structures in the middle of some of the features, which ought to be the original burrows. 1 Link to comment Share on other sites More sharing options...
NicolaiT13 Posted May 16, 2018 Author Share Posted May 16, 2018 Ok. I had to read up a little on trace fossils. Very interesting. I was finding perfectly cylindrical tubes at this site as well. I found other pieces similar to the one on the right above as well. I am still confused about the fossil on the left. Link to comment Share on other sites More sharing options...
Tidgy's Dad Posted May 16, 2018 Share Posted May 16, 2018 Some animals, some species of worm for example, make spiral burrows or tubes. This could be the preserved infilling of one of these. 1 Life's Good! Tortoise Friend. Link to comment Share on other sites More sharing options...
Spongy Joe Posted May 16, 2018 Share Posted May 16, 2018 Well, there are a couple of options for that. One is a coiled burrow, cutting through itself. The other is that it's all a cementation halo around the small vertical burrow in the centre. My bet is the latter. Well done on noticing the cylindrical ones as well - that certainly fits with the general interpretation. It's worth noting that trace fossils are extremely useful, when you're interested in the ecology of an assemblage, since they give you information on lots of things that are too squidgy to fossilise (except in rare places with freakish chemistry going on, like the Burgess Shale). 3 Link to comment Share on other sites More sharing options...
NicolaiT13 Posted May 16, 2018 Author Share Posted May 16, 2018 Thanks for the information. I appreciate it. Link to comment Share on other sites More sharing options...
jpc Posted May 16, 2018 Share Posted May 16, 2018 I think they are sandstone concretions/nodules. Much more common than burrows in both the Hell Creek and Ft Union. 4 Link to comment Share on other sites More sharing options...
Pemphix Posted May 16, 2018 Share Posted May 16, 2018 7 hours ago, jpc said: I think they are sandstone concretions/nodules. Much more common than burrows in both the Hell Creek and Ft Union. I think so too... Link to comment Share on other sites More sharing options...
Troodon Posted May 16, 2018 Share Posted May 16, 2018 See these in the hell Creek quite often. I agree with jpc. Link to comment Share on other sites More sharing options...
Ludwigia Posted May 16, 2018 Share Posted May 16, 2018 Although there is a remote possibility that the one on the left could be a gastropod mold. Greetings from the Lake of Constance. Roger http://www.steinkern.de/ Link to comment Share on other sites More sharing options...
jpc Posted May 16, 2018 Share Posted May 16, 2018 3 hours ago, Ludwigia said: Although there is a remote possibility that the one on the left could be a gastropod mold. It would be HUGE for the hell creek. Link to comment Share on other sites More sharing options...
Plax Posted May 16, 2018 Share Posted May 16, 2018 http://www.wyogeo.org/presentations/Marron Bingle-Davis Preservation of Underrepresented Freshwater Mollusks Hell Creek Formation of Montana.pdf just a google! I know nothing about the subject... Link to comment Share on other sites More sharing options...
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