2.9" Fossil Crab (Potamon) Preserved in Travertine - Turkey
Travertine is a type of limestone that forms around mineral springs. It is often quarried for use as a building material, and that is how these crabs were discovered. They are found when hollow voids are cut into while sawing blocks of travertine. The travertine deposits in the Denizli Basin are Pleistocene in age, having been formed within the past 400,000 years.
A paper on these travertine preserved crabs can be found at the link below.
Unusual scaled preservation samples on freshwater decapods (Crustacea, Decapoda) from the Pleistocene (Late Cenozoic) of Turkey and Kazakistan