The animal on the rock is a member of an extint taxon of ancient Arthropoda, called Trilobitomorpha. This belong to genus: Phacops. I take this photo with a SB-600 on the left side, tele-piloted by D70 pop-up flash. On the left you can see an Ammonite.
I used a Nikon D70 with a Sigma 70-300mm APO Macro Super II @ 195mm with a Sigma Macro lens. f/11; 1/100 sec; ISO 200
Postproduction with Adobe Camera RAW 3.4 and Adobe Photoshop CS2.
After taking a second look I'm bumping this to a six. Having something that once moved and is now a fossil definitely fits the challenge. The colors are warm and rich but the bright spot in the background is a distraction. This will be a nice addition to your portfolio when you clone out the bright spot (Darn basic editing rules).
Good colors. The thing with this image is that my eye keeps going to the only really sharp and bright part just left of center. And then it's hard for me to figure out what it is since there's not much detail in that part. Your title helps me understand that these are fossils. I think the dof is good but possible not on the right area within the image. The fossil to the left looks really interesting thanks to its spiral form.
As a geologist who studied paeleontology, I would say this is a trilobite fossil. If that is the case, then it would not be a life form from the Cretaceous period but more like the Cambrian, Ordovician, or Silurian.