Astephus antiquus (Leidy, 1873)

Taxonomy

Catfish

Kingdom: Animalia
Phylum: Chordata
Class: Actinopteri Cope 1871
Order: Siluriformes (sensu Chardon, 1968)
Family: Family ICTALURIDAE (sensu Lundberg, 1982 less tHypsidoris)
Genus: Astephus
Species: Astephus antiquus
Author Citation (Leidy, 1873)

Geological Time Scale

Eon: Phanerozoic
Era: Cenozoic
Period: Paleogene
Sub Period: None
Epoch: Eocene
International Age: Ypresian

Stratigraphy

Green River Formation
Laney Member

Provenance

Acquired by: Purchase/Trade

Dimensions

Length: 26 cm

Location

Currant Creek Ranch
Rock Springs
Wyoming
United States

• astephus antiquus
• eocene
• green river
• laney member
• rock springs
• tff-oilshale-ch1134

Comments

Astephus and Hypsidoris are both members of the Family Ictaluridae, native to North America. Green River catfish are easily recognized by their stout dorsal and pectoral spines, scale less bodies and broad skull. Ictalurid species have four pairs of barbels (or whiskers).  Like modern catfish, they possessed a vibration sensitive organ called the Weberian apparatus. The Weberian apparatus consists out of specialized vertebrae at the front of the spinal column which passed vibrations to the inner ear using the swim bladder as a resonance chamber. The structure essentially acts as an amplifier of sound waves that would otherwise be only slightly perceivable by the inner ear structure alone.

Normal size of Astephus is around 15cm and rarely exceeds 18cm, maximum total length is about 30cm. Hypsidoris seems to be in the same size range. The easiest way to distinguish Hypsidoris from Astephus is by counting anal fin rays; H. farsonensis has about 15 to 17 and A. antiquus has about 26. The diet of Green River catfish was probably similar to existing ictalurids consisting of plants, small fish, crayfish and mollusks. Astephus and Hypsidoris were probably bottom feeders. 

Astephus antiquus is unknown as a body fossil in the middle unit of Fossil Butte Member, and only one specimen has been found in all of Fossil Lake, although it is abundant in Lake Gosiute strata. The discovery of numerous and widespread fossil catfish in oil shale units of the Laney Member of the Eocene Green River Formation is evidence of aerobic conditions in the hypolimnic waters of ancient Lake Gosiute.

Hypsidoris farsonensis has only been found in Lake Gosiute deposits of the Green River Formation, east of Fossil Lake.

Revised Species Diagnosis from Grande & Lundberg 1988, p. 146: "An extinct genus of ictalurid catfish that differs from all other known ictalurids by the following combination of characters: lack of jawmuscle origin on the temporal region of the skull roof, the possession of villiform vomerine teeth, the possession of tooth plates lateral to the vomerine tooth plate, and the location of the cranial opening for the infraorbital canal in the sphenotic rather than the frontal. Admittedly none of these characters alone is unique to †Astephus, but the combination of all of them is. The genus appears to be unique among catfishes in having the ventral surface of the supraethmoid inclined sharply upward relative to the ventral surface of the vomer. No other characters apparently unique to the genus were discovered here."

Emended Species Diagnosis from Grande & Lundberg 1988, p. 147: "A species that differs from the only other known species recognized here (tA. antiquus) by the presence of a narrower vomerine tooth patch. Also, the median supraethmoid cleft appears to be deeper and the cranial fontanelles appear to be wider than in †A. antiquus (although the latter feature is possibly an artifact of preservation)."

Line drawing from Grande & Lundberg 1988, p. 151:

Identified by oilshale.

References:

Grande, L. and J. G. Lundberg. 1988. Revision and redescription of the genus Astephus (Siluriformes: Ictaluridae) with a discussion of its phylogenetic relationships. J. Vert. Paleont 8:139–171

Grande, L. 1987. Redescription of Hypsidoris farsonensis (Teleostei: Siluriformes), with a reassessment of its phylogenetic relationships. Journal of Vertebrate Paleontology 7:24–54.

Grande, L. and M. C. C. de Pinna. 1998. Description of a second species of the catfish Hypsidoris and a reevaluation of the genus and the family Hypsidoridae. Journal of Vertebrate Paleontology 18:451–474.