Need help to ID please

[Minskiyd]

Hello, I don’t know origin of this item but I got it in USA Colorado. Can someone please help 

thank you !!

[Harry Pristis]

For comparison:

 

[Fossildude19]

From Colorado, I think it might be more likely to be a baculite, rather than an Orthocone nautiloid.

[Ludwigia]

I agree with Tim.

[FossilDAWG]

I want to clarify the comments, as for someone new to fossil collecting there could be some confusion.  In a sense, both the answers you got are correct.  The fossil you have is a shell of a cephalopod, the class of molluscs that includes squid, octopuses, and the nautilus.  In this case the shell is straight, unlike the coiled nautilus.  Harry's diagram shows a straight-shelled (orthoconic) nautiloid, sort of like if you took a nautilus shell and straightened it out.  It is informative, because it shows the essential features of a cephalopod shell (divided into chambers, with a tube called a siphuncle running through the interior) and the live animal in a part of the shell called the living chamber, at the end.  Cephalopods evolved into a variety of groups.  The earliest to appear were nautiloids, which are characterized by simple divisions between the chambers (septa).  Where these septa meet the exterior part of the shell they form a line called the suture line, which in nautiloids is straight or has simple curves.  Later on a more advanced sort of cephalopod shell evolved, in which the septa are highly folded (which made them stronger), and so the suture line is very complex.  (Note that coiled nautiloids still exist).  These cephalopods with complex suture lines are ammonites; they diversified greatly through the Mesozoic but the went extinct at the end of the Cretaceous (or very shortly after that).  Your fossil is a type of straight-shelled ammonite, belonging to the genus Baculites, as Tim said.  In life it would have looked much like Harry's diagram, but with a more complex shell.  Several species of Baculites can be found in the Pierre Shale in Colorado and other Western states.  In order to identify yours to species, you would have to remove more rock so we could see whether or not it has folds or ribs, the exact cross-sectional shape, and the suture lines.  Even then these species are hard to ID.

 

Don

[Minskiyd]

Guys Thank You so so much!!! You are the best!!!