Rare Fossil Crayfish | Procambarus primaevus | Green River Formation | Wyoming

Procambarus primaevus Eocene (51.98 Million Years Ago) Green River Formation, Wyoming, USA   Specimen approx. size: 2.5" Matrix approx. size: 3.5" x 3.5" This crayfish has had very minimal restoration.   Procambarus primaevus is an extinct species of freshwater crayfish belonging to the family Cambaridae, known from the Eocene-aged Green River Formation of western North America, particularly from fossil deposits near Fossil Lake in Wyoming. Procambarus primaevus exhibits typical crayfish morphology with a segmented body divided into a cephalothorax and abdomen. Key anatomical features include: Carapace: Smooth and well-defined with a distinct rostrum. Chelipeds (claws): Prominent and relatively large, used likely for feeding and defense. Walking legs: Five pairs of pereiopods, as is typical of decapods. Abdomen: Clearly segmented with a fan-shaped tail (uropods and telson), aiding in rapid backward swimming. Size: Specimens generally range from 5 to 10 cm in length.   P. pr