Ammonite ID

[Nimravis]

I am not an ammonite collector, but have a couple that I wanted to know if you could ID. I do not recall where I got them from, most likely from someone that I had given some Mazon Creek fossils too. If anyone could ID them, it would be appreciated.

 

[Ludwigia]

The first ammonite appears to belong to the family of the Perisphinctidae. The other two to the Ataxioceratidae. Sorry, I can't help you any further than that without any more information.

[Nimravis]

1 hour ago, Ludwigia said:

The first ammonite appears to belong to the family of the Perisphinctidae. The other two to the Ataxioceratidae. Sorry, I can't help you any further than that without any more information.

Thanks for getting back to me.

[(Julia)]

What makes them different?  Looking at them, I see differences only in maybe the amount of wear.  

[Ludwigia]

The Ataxioceratidae have what we call in German reoccurring "parabel" ribbing forms, which directly translated means parabola. These are the points on the ribbing where you can make out a "y" form. The ribs are more variable in form and direction and the splitting point lies deeper on the flank as with the Perisphinctidae. Their ribs also split in multiple forms before they carry on over the venter and are not just bipartite (splitting in two) as is always the case with the Perisphinctidae, whose ribs are much more straight and pronounced.