Steve O'Shea said:
OK, slightly composed. Phil, where are the fins?? Have any of these fossils had fins/fin imprints positioned anywhere?
Well, I have not seen any examples of Trachyteuthis
with fins, but then again I have only seen a couple of photos of this animal. Images are not easy to find.
I am sure fins must be present. Hopefully having finally sorted out this creatures' systematics, it transpires that the Upper Jurassic Trachyteuthis
is a member of the family Trachyteuthididae, which along with the Palaeololiginidae, make up the Mesoteuthina, a sub-order of the Vampyromorpha. These Mesoteuthids had some form of distinct gladius, though exactly how this differed from the Vampyromorphs I have yet to discover. (It may have been shovel-shaped).
They had eight arms of roughly equal lengths, and were a split from the Vampyromorphs sometime in the early Jurassic. They left no descendants and became an extinct family in the Cretaceous. Certainly the closely related Palaeololiginidae had fins, and example of which can be seen here
as did the Vampyromorphs, the stem group from which the Trachyteuthididae were derived in the early Jurassic.
Practically every source of information on these ancient 'squid' seems contradictory. It's giving me quite a headache.