From the album: Harding Sandstone
Chondrichthyan? denticles
Tezakia hardingensis
Harding Sandstone, Canyon City, CO, USA
These are possible Ordovician Chrondrichthyan (class of cartilaginous fish including sharks) denticles, if true, these would be the earliest known.
Described by Andreev et al. (2015) and Sansom et al. (1996)
^Andreev et al. (2015)