50 million years old, Eocene-Era fossil fish comes from one of the world's famous Green River Formation in Wyoming. Amphiplaga is one of the rarer of the Green River fish fossils, making up some 1% of the total from Fossil Lake, its only known location. Named by the famous 19th Century paleontologist E.D. Cope, the name Amphiplaga is thought to mean "amiguous wound", pointing to the fact that the holotype specimen was headless. Shaped rather like a cross between a trout and a perch, the Percopsidae have colloquially termed “trout perches”. Fossil percopsids are only known from North America, the current home of the extant genus Percopsis. With a maximum total length of 150 mm and an average of 100 mm, this is an average-sized adult specimen of this rarely offered taxon.