Ceph ? Non ceph - the mystery object !

Architeuthoceras said:
Great finds! 8) Are the guards usually found separated from the phragmocones? The belemnites over here very rarely have any portion of the phragmocone preserved, at least the ones I find :frown:

stay calm big Kevin, your time will come, this was my 1st.
thx for putting on such a good show guys, you all passed except Phil (nice pic) who has to answer this additional point before receiving his commendation.
I've not read up on phragmocone construction as yet, so what exactly is the cone of concentric rings that has been preserved eh ? I dunno.

Keef
 
I'm not Phil, but i'll answer anyway. :shock: Phil told me, so he still gets his commendation.

The Phragmocone of a shelled cephalopod is made up of air (or gas) chambers separated by the septa. Usually when the phragmocone of a belemnite gets fossilized, the chambers are filled with detritus or infilled with calcite. when and if the shell material desolves you are left with a series of concentric conical segments. The contact of the septa with the shell wall forms the suture. Belemnite sutures are straight, so you get the concentric cones, ammonoid sutures are complex, and the shell is usually coiled so the phragmocone is preserved as a coiled series of complex ended segments. :smile:
 
Mystery Object

In answer to Kevins question about Belemnite/Phragmocone combos - I can only ocmment on what I've found on the Coast but the rock sequence they are found in certainly seems to be a factor - in the Grey Shale where mine and AndyS's pictured beasties came from, associated Belemnite Guards and Phragmocones are very common whereas in the slightly younger Alum Shales they are less so (though Belemnite guards are abundant and phragmocones are also still present). I've also found lots of Belemnite guards in the Cretaceous age Speeton Clay from further south but these generally seem to have a void where the phragmocone was. Basically I don't know why they occur so frequently in the Grey Shale - might be due to conditions during fossilisation or the species of Belemnite involved?

Andy
 
Yep, I've never found a belemnite phragmocone yet down at Folkestone. The type we get down there are Neohibolites, Albian Cretaceous, and somewhat boringly are the smallest known form of belemnite, as far as I know. The guards are exceptionally well preserved and lie completely free of the clay matrix; they can be collected by the dozen in the beach shingle. The phragmocone being delicate in nature has no sturdy rock to support it and is completely worn away; a pity, though the socket it fitted into is often well preserved.

I wonder if Neohibolites is a catch-all genus? Although the guards are all about the same length, about 30mm or so, there is a great variation in the shape of the tip of the guard. Some are pointed, some conical, some rounded. Odd.

:belemnit:
 
Phil said:
I wonder if Neohibolites is a catch-all genus? Although the guards are all about the same length, about 30mm or so, there is a great variation in the shape of the tip of the guard. Some are pointed, some conical, some rounded. Odd.

could possibly be the Si, GSi, GTi models of the same species ? maybe not
 
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