This past week on Fossil Friday, I gave you a fossil from our Fossil Fan, Dan Coleman. Dan told us that he wasn't quite sure what it was, but he had some thoughts. You all had a lot of great guesses too.
Several people thought it was some sort of vertebrate--a fish- or reptile-like creature with dimpled skin. We got a couple votes for nautiloids, and even one vote for Nessie! But Ray Gildner got closest to what we think it is here in Fossil Land: stromatoporoids.
Dan says, "I think (over 80% sure) that it's a stromatoporoid, an extinct group of poriferans. The shape of it resembles that of a fish abdomen, but the pattern doesn't seem right for either Ostracoderm or Placoderm skin."
From the Milwaukee Public Museum:
"Stromatoporoids are an extinct group of sponges that formed a hard compact skeleton. Stromatoporoids lived only in seawater, and like modern sponges, they created currents to pump water in and out of their body, where they filtered out tiny food particles. The stromatoporoid skeleton, which was often quite large, generally had a dome-like form. Stromatoporoids were a major type of reef constructor."