Fossils on the Plaza?

So, once again, wandering about the Plaza, how can you go wrong?  Got some good shots of Brush Creek and the fountains, but the photo of the day was something I noticed on the way back to the truck.  One of the large boulders lining the walkway from the boulevard to the creek was loaded with fossils of marine life:  tube-worms, bivalves, gastopods, etc.  So, I thought, rather than the usual Plaza picts, this is alittle unusual: