Edited by oilshale
International Age: Ypresian
Green River Formation
Acquired by: Purchase/Trade
Erismatopterus is only known from Lake Gosiute and Lake Uinta deposits. It is one of the rarer Green River fish fossils, except in some mass mortality zones. Erismatopterus belongs together with its close relative Amphiplaga to the family Percopsidae within the order Percopsiformes.
Amphiplaga is best distinguished from Erismatopterus by its dorsal fin, which has three hard spines (the first one is very small) followed by 9 or 10 soft rays. Erismatopterus usually has two hard spines followed by 6 or 7 soft spines. Amphiplaga can reach up to 15cm with an average length of about 10cm while Erismatopterus does not exceed 12cm with an average length of about 5cm.
The Order Percopsiformes is a small order of North American freshwater fishes that includes three families: Amblyopsidae (cavefishes); Aphredoderidae (pirate perches); and Percopsidae (trout-perches). Closely related to neither trout nor perch, trout-perches have characteristics of both the trout and perch families. They exhibit characters of the salmonids, such as an adipose fin, cycloid scales, and soft fin rays, as well as characters of the percids, such as dorsal and anal fin spines, and ctenoid scales.
Trout-perch are generally silvery in appearance, often with a partially transparent appearance, and relatively large heads and eyes. They are small fish with weak fin spines, and an adipose fin similar to those of trouts. They feed on insects and small crustaceans.
Fossil percopsids are only known from North America, the current home of the extant genus Percopsis
E. D. Cope. 1877. A contribution to the knowledge of the ichthyological fauna of the Green River shales. Bulletin of the United States Geological and Geographical Survey 3(4):807-819
Grande, L. (1984): PALEONTOLOGY OF THE GREEN RIVER FORMATION, WITH A REVIEW OF THE FISH FAUNA. THE GEOLOGICAL SURVEY OF WYOMING, BULLETIN 63
Edited by oilshale