This is what Crick (1905) has to say on affinities:
"Whilst being most nearly related to such Eocene forms as Bayanoteuthis, and especially to Vasseuria, [it] forms a connecting link between these genera and the Cretaceous genus Belemnitella. Although only a single example is known, the form is so important that the writer proposes for it the name Styracoteuthis and, for its trivial designation, suggests the term orientalis."
Just to show that there's microstructure preserved here is a couple of photos of a roughly polished longitudinal section. Field of view in the first photo is 6 mm.
I see what Crick means about the similarities between Belemnitella and Styracoteuthis and here's a picture of an 8 cm Belemnitella (below) together with a Styracoteuthis.
So, is it a belemnite? Naef thought so and placed this form in "Familie: Belemnitidae BlaINV."
Donovan says "There is disagreement on what is the last belemnoid. There are genera which are intermediate between belemnoids and sepiids. I have placed Bayanoteuthis (Eocene), which probably had a rostrum of calcite, in the Belemnoidea. But Styracoteuthis (Eocene) whose rostrum has lost all the details of its internal structure through recrystallisation, was probably of aragonite .."
As can be seen above these specimens have not lost the details of the internal structure, though there is some recrystallisation. I've started to do a proper job of polishing the sections and will post some better images a bit later.
I'm told I should look for an example showing the protoconch. "A perforated first septum with a caecum entering the protoconch would implicate spirulid or sepiid affiliations, a closed first septum would prove that it is a belemnite."
Temperatures are down, so I'll go looking!
I never thought I would find myself doing microsurgery on an ancient squid, but challenged to look closely at the protoconchs of these Styracoteuthis fossils I've taken a scalpel to the attached juvenile (35 mm long as preserved). The phragmacone is recrystallized, but traces of septa can be seen. The exposed protoconch seems simple and cup-shaped.
I have just found this site. These fossils are very exciting and may give us an understanding of this strange group of belemnite-like coleoids. I would love to see them.
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