Hello, I recently found what I believe is a fossil at an antique shop in central South Dakota. It was in with various rocks including granite, quartzite, sandstone, and even some petrified wood. I am a novice and only really know what I have read the past couple of weeks. So here is what I do know. The store owner was late seventies. Selling rocks his father had found in his farm many years ago near the Badlands in SD. This particular piece stuck out do to it's layers and pourous ends. It is 14"*6"*4.5". It is 15.6 lbs. I am just looking for any info or tips anyone may have for me to know more about what I'm looking at.