Phareodus ([Fig. 21]) belongs to a family of fish, the Osteoglossidae, which began as marine forms and has since become a fresh-water family. At present, they are restricted to tropical rivers and lakes of South America, Africa, and Australia. In the past they had a much greater distribution, as its occurrence at Fossil Butte indicates, including North America. It is a deep-bodied fish with a large head. The anal and dorsal fins are close to the tail fins. The many sharp teeth in the mouth attest to the carnivorous habits of Phareodus.
The family Gonorhynchidae, the living sandfish of the Indo-Pacific area, is represented at Fossil Butte by Notogoneus ([Fig. 22]). Notogoneus is very long-bodied and quite slender. The body width does not vary much from head to tail, although narrowing does occur in the tail region. The tail fin is symmetrical, forming a good rudder. The anal, dorsal, pectoral, and pelvic fins are all small. The body is covered with small, elongate scales. Notogoneus was apparently a bottom feeder, living on small organisms picked off or out of the bottom of Fossil Lake.
The Recent catfish, Ameuirus, has also been found at Fossil Butte in the Green River shales. The form of the Eocene catfish was very much like the Recent one. The habits of the Eocene catfish were probably like those of the modern Ameuirus, i.e., adaptations to a scavenger-type existence.
Rather common in the sediments of Lake Gosiute, but not yet known from the Fossil Basin, is Erismatopterus, a member of the family Aphredederidae or pirate perches. This small, elongate fish has few distinguishing characters, the rounded front edge of the skull being most distinguishable.
Asineops is an Eocene relative of Erismatopterus and also one of the pirate perches. Asineops is, however, placed in a different family, the Asineopidae. Asineops, like Erismatopterus, is a rather plain-looking fish. The dorsal fin is long relative to the rest of the body. The body is slightly deeper behind the gills than elsewhere, giving Asineops a rather common appearance.
The Percidae, or perches, are represented at Fossil Butte by Mioplosus ([Fig. 23]). Mioplosus, as indicated by its well-developed teeth, was a carnivore that probably preyed on its piscine relatives in Fossil Lake. The large head blends in well with a strongly built, long body. The anal and dorsal fins are subequal in size and positioned opposite each other. The tail fin is large and fan-shaped. It is easily identified by the presence of two dorsal fins.
Fig. 21. A large Phareodus, fairly common in the Fossil Butte fish beds. Length of original, 54 cm. Collection of University of Wyoming.
Fig. 22. Notogoneus, a long, slender bottom-feeder, occasionally found at Fossil Butte. Length of original, 56 cm. Collection of University of Wyoming.