Ordovician Nautoloid?

[ashcraft]

Attached is a picture of a fossil from a lower ordovician deposit (Smithville). On the right is an operculum cover from a gastropod that is diagnostic from this formation. On the left is a nautilous? Any opinions?

Brent Ashcraft

[Guest solius symbiosus]

Very unusual.

This is a link to Early Ordovician cephalopods.

http://findarticles.com/p/articles/mi_qa37..._n21033147/pg_1

[geofossil]

Ordovician fossils can be very difficult to generalize about. We have some similar fauna but 'similar' can be deceptive using outward appearance.

The gastropod appear similar to an archaeogastropod like Ceratopia...but gastropod evolution goes in all types of morphology directions and it's difficult to know who is related to whom. there isn't really a definitive taxonomy of early Paleozoic gastropods. The groupings are a bit subjective.

The other specimen I'm taking a stab at in the dark. Ordovician nautiloids are difficultto classify without a good cross section, a look at the siphuncle and so on. Even then it gets dicey as a lot of the early publications are convoluted and specimens are shoe horned into families that may be artificial constructs. The coiled ones can be doubly difficult to I.D. as some coiled specimens ended after the coil and others kept going ....adding a straight series of chambers. Sometimes the coiled part is found and sometimes the straight section.

One ribbed type of coiled nautiloid found in Ordovician deposits is 'Lutuites '...it had a ribbed coil like your specimen but then grew a straight set of chambers.

[Guest solius symbiosus]

^I'm thinking in the lituitids, the septa was perpendicular across the thing. In his, the septa appear curved ... like some kind of goniatitic cephalopod. IDK, I don't know that much about cephalopods.