Fossil ID help!

[courtmccutch]

I found this about 20 years ago while playing in a mound of dirt that my Grandpa had dug when building his new house. The location was near a creek in north, central Arkansas. His house is also near the Buffalo river in Searcy County, Arkansas, US. 
 

The measurements are 5 inches long (12.7 centimeters), 2 1/2 inches wide (6.35 centimeters) 

 

I’ve been hanging on to this since I was a kid. I’d be grateful to receive any help identifying what I have!

[Darktooth]

I am not 100% sure but it looks like it could be a Mammoth tooth that is missing the enamel.

Wait for others to chime in.

[M Harvey]

1 hour ago, Darktooth said:

I am not 100% sure but it looks like it could be a Mammoth tooth that is missing the enamel.

Wait for others to chime in.

I was thinking the same thing.

[Carl]

My initial knee-jerk response was mammoth tooth, too, but it falls quite short when all the photos are reviewed. The best I can guess is that it's an orthocone naautiloid, but that's not a perfect match either.

[Mark Kmiecik]

Way too much going on in too many different directions to be a nautiloid.