One of the odd fossils that I've found at the Ridgemont Quarry near Fort Erie, Ontario, Canada are these positive a negative specimens of an enigmatic fossil called Inocaulis plumosa
. It's been something of a mystery for a number of years and has been thought to be an algae or possibly a graptolite. Well there is a new paper coming out (in Alcheringa, the Journal of the Association of Australasian Palaeontologists) that states, based on new fossils from China, that it most certainly is a graptolite (possibly a dendroid or tuboid type).
I photographed the fossils wet to better show detail.
Graptolites were colonial animals that lived similar lives to a coral or bryozoan in that they filtered the water for food. Most were free floating but some did attach to the substrate. They are more closely related to vertebrates than invertebrates. The fossil does show some "hairy" extensions around the periphery of the body. This is only part of what was likely a larger group of animals. The specimen was found in the Bertie formation which is Silurian (Pridoli stage) in age.