Colour banding in ammonoids

As you work your way into the puzzle, does it suddenly occur to you how old these creatures are? Just seeing the progress hit me that way.
 
Well it's easy to write 250 million years, but something else to relate that to our short lifespans.

That occasional flash of the imagination when you realise that this very nautilid, and this very ammonoid lived and swam in that ancient sea can be quite exciting. It's partly why I find the exceptionally preserved biotas (soft parts and all) so fascinating.

There's also something very interesting in these very early Triassic faunas to do with the emerging story of rapid rediversification of life after the great extinction.
 
Impressively precise!

Perhaps "old" will turn out to be the right adjective for the prolonged recovery story. The newer stuff (Oman, China) seems to be saying "much faster than we thought before". e.g. "the extraordinary extinction magnitude of the end-Permian event had surprisingly little effect on the duration of the lag phase."

Here's "the rock" this evening. The little ammonoid will soon be exposed.
 

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I doubt it would be marble. Marbles require great pressure and heat and most of the fossils would have been flattered. Also, the rock does not appear as crystalline as I would expect (although, I'm more familiar with marbles from the Grenville province). Limetsone would probably be my bet, with that strange milky texture being a result of the claning around the fossils. As far as I can tell from the photo...
 
That's right Stephanopod; the rock is a spar-cemented bivalve grainstone, the "Coquina Limestone" unit of Krystyn et al. 2003.

It does look a bit like marble though where I've worked away with the dremel tool.
 
That would be fun. Pity I've taken the pictures from any old angle.

So after a long day of work and a fun game of football I made a little progress with "the rock" (as I cooled down!) and am now heading out for the rest of the evening.

The little ammonoid will very soon be exposed enough to show Leo Krystyn for an ID.
 

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