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

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. primaevus represents one of the earliest known members of the genus Procambarus, a diverse and still-extant group of crayfish native to North America.