The Opposite of Giant

Architeuthoceras

Architeuthis
Staff member
Moderator
#1
Pteroscaphites pisinnus, an ammonite that decided to bypass most of adolescence and go straight to maturity. Probably a small form of Scaphites whitfieldi, shown together in the second photo. It is not a baby Scaphites, both coil normally until reaching maturity when they grow the shaft and hook.
 

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neuropteris

GPO
Registered
#2
Ahhh - cute!

I do like Scaphites, a nice contrasting ammonite form to the ones we see commonly over here. I have found 1 scaphites in the chalk at a place called White Nothe on the South coast but the preservation in the chalk isn't as good as the ones you show and the others I've seen from the pierre shale.

Andy
 

Architeuthoceras

Architeuthis
Staff member
Moderator
#3
These are probably the most well preserved ammonites I find around here, at least the ones that have the most original shell preserved. Scaphites and Baculites are probably the most common ammonites in Cretaceous rocks in the Western Interior of the US and are used to correlate the Upper Cretaceous rocks. Luckily other forms are also found that also occur in Europe etc. and help correlate these rocks globally.

There is a "lineage" of Pteroscaphites in Late Turonian thru Middle Santonian rocks around here. However, the different species of Pteroscaphites have more in common with the associated species of Scaphites than they do with each other so they are probably dwarfs. And it is not just the Scaphites, dwarfs of other genera are being found and described.

For more information and a better explanation see; Landman, N. H. 1989. Iterative progenesis in Upper Cretaceous ammonites. Paleobiology 15(1), pp. 95-117.
 

Architeuthoceras

Architeuthis
Staff member
Moderator
#4
Heres More

W. J. Kennedy and W. A. Cobban, 1990, Cenomanian micromorphic ammonites from the Western Interior of the USA, Palaeontology 33 (2) pp.379-422


a (free?*) PDF from the Palaeontological Association on this page. 1969-1998 are available

*from their website:

Electronic access to back issues

Over the past few years the Association has been scanning back issues of the journal that are not marketed though our publicshers. These will be available online shortly, for free. Watch this space for developments.
 

Phil

Colossal Squid
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Registered
#5
Lovely Scaphites Kevin. I believe we get these in the local chalk here in East Kent too, not that I have ever seen one. Come to think of it, I've never found an ammonite in the chalk at all, merely collecting sea urchins and bivalves. Must try harder.

Thanks for the tip about the papers available from the Palaeontological Association. It seems most papers pre-1998 are fully available to download for free. I'll occasionally mine it for cephy papers and put links in the 'New Papers' thread. Thanks as ever!
 

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