Triassic Coleoids

Hajar

Haliphron Atlanticus
Registered
#1
Does anybody know anything about Triassic coleoids such as the attached Atractites? There are two in the slab, the larger being 95 mm long. At the top is a chambered orthocone (Michelinoceras). These are from the Middle Triassic Prida Formation of Nevada.

From the outside they look like belemnites, but I polished a partial specimen and see that it is totally recrystallized (originally aragonite?).
 

Attachments

Hajar

Haliphron Atlanticus
Registered
#5
The link doesn't seem to work. The paper is: Atractites guards from the Early Jurassic of New Zealand, A. B. Challinor, Department of Earth Sciences, University of Waikato, Hamilton, New Zealand. Online publication date: 30 March 2010.

"Guards extensively recrystallised, composed of interlocking calcite crystals. Concentric lamellar and poorly defined radial structures remain visible on unprepared transverse surfaces and are faintly visible on a polished transverse section."
"No remnant of the phragmocone is preserved."
"The crushed nature of C1384 may indicate that the guard was poorly calcified in life, perhaps partly or largely organic (Jeletzky 1966), although some authors suggest it was aragonitic (Doyle 1990).."
 

willsquish

Blue Ring
Supporter
#8
Could you post a link to the inaccessible papers you'd like to see? I too have been wondering at the difference between aulacocerids and belemnitids and I have university access to many literature sources for now.
 

Architeuthoceras

Architeuthis
Staff member
Moderator
#9
I think Hajar linked to most of the papers I saw on a search. I did read a paper recently that removed Hematites from the Aulocoerida, I'll try to remember where I read that... An updated treatise like article would sure help with classification of these Coleoids. :confused:
 

Hajar

Haliphron Atlanticus
Registered
#10
Many thanks willsquish. One paper I would very much like to see is related to the Michelinoceras in that specimen, rather than the Atractites and that's Mehl 1984.

Was this your paper on Hematites Kevin?
 

Hajar

Haliphron Atlanticus
Registered
#14
Yes, they do look a lot like both the older Hematites and also the much younger Vasseuria. What do you think the grooves and ridges were for?
 

Members online