I found a unique reddish colored 45mm thick fossil while on my walk yesterday. It is pentagon shaped. Longest distance is from side 6-4 and is 9cm. The dorsal side is darker than the ventral. Four of the sides are smooth. Side 6 has a smooth surface and is size of a quarter. Found in area of Pleistocene material. My guess was neural (4) from a tortoise. Based on drawing in Hulbert's book The Fossils Vertebrates of Florida (p. 122).
The thickness of this fossil is what is raising the question for me?
ID help is greatly appreciated.
SIDE 1
SIDE 2
SIDE 3
SIDE 4
SIDE 5
SIDE 6
SIDE 7