ID Help -- From South Dakota

[DakotaBirder]

Any idea what this is? From today on the Buffalo Gap National Grasslands in South Dakota. First time I've come across something like this, with parallel structures running along the long direction and then converging to the center on both ends.

There's plenty of petrified wood in this area, some shell impressions and the like, but don't know what this is.

 

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[old digger]

Welcome to tnet!
Your item looks very much like a segment of a weathered cronoid stem.

 

[bone2stone]

It is heavily worn but it is from a rugose coral.
Cool the way it is worn.

Jess B.

 

[P.ALLEN]

Yeah it's a Cnidarian of sorts don't know the sp. offhand though, Crinoids have the orientation shifted like a stack of oreos.