Ammonite or Gastropod ?

[drbush]

Hi friends, I went to Aruma formation area (Campanian-Maastrichrtian) to the North of Riyadh city and found this  small fossil , 26mm long by22mm What could it be? 

 

 

[Ludwigia]

I'm tending to see a gastropod here.

[Theroroth]

This is a good question, how does one distinguish between the two? - I am new to this, so would love to know.

[facehugger]

gastropod. I tend to look for features that distinguish ammonites - suture lines would fall under such criteria, I believe. 

[Ludwigia]

Ammonites, other than some heteromorph ones, normally have a horizontal spiral in one plane. Gastropods have a 3D spiral which winds either up or down. Your fossils appear to me to show the latter feature. There is a slight chance that these are heteromorph ammos, but as facehugger points out, suture lines cannot be seen.

[abyssunder]

Don't know what to say... 

Another possibility might be tube worm. 

[JohnJ]

@drbush 

 

Focused, close-up photos of the surface texture would be useful.

[RuMert]

Curled serpula or gastropod

[drbush]

[JohnJ]

Thank you, @drbush.  As others have mentioned, no Ammonoid suture lines are visible.

[drbush]