| Zusammenfassung: | A fossil fish belonging to the genus Pungitius Costa was found in a siltstone of the Sterling Formation along the bank of Fox Creek at the head of Kachemak Bay, Kenai Peninsula, Alaska. The fossil bearing stratum is within and probably near the base of the approximate middle third of the Clamgulchian Stage exposed along Kachemak Bay. Plagioclase K-Ar dates of volcanic ash beds bracket this part of the section between 7.2 ± 0.6 MY and 6.9 ± 0.5 MY. The fossil specimen is well preserved and measures 72.5 mm from the tip of the premaxilla to the end of the body. The pelvic girdle of the fossil specimen possibly exhibits several unusual characteristics. The ascending branch of the pelvis appears to be absent, but may be represented by a mass of bone directed perpendicular to the anterior and posterior processes and ventrally. The pelvic girdle appears to be in place; thus, it is possible that this specimen had a reduced pelvic structure. However, the pelvic spine is long (9.6 mm). The presence of lateral plates, free dorsal spines and greatly expanded pelvic girdle with one spine and one soft fin ray restricts the specimen to the Gasterosteidae. The only stickleback genera with at least nine dorsal spines (nine are present in the fossil specimen) are Pungitius and Spinachia, and in the latter genus the body and particularly the snout are much more elongated than in the fossil specimen and the minimum number of dorsal spines is 14. Thus, this specimen clearly is a Pungitius, and represents the third fossil record of this genus. Sedimentologic and stratigraphic analyses of the Clamgulchian beds support the concept that these strata were deposited by meandering streams on a coastal lowland. The occurrence of the fossil specimen in siltstone suggests that it was deposited in a floodbasin environment. The geological data are consistent with the ecological tolerances of extant Pungitius populations. The large size of the fossil specimen and of its pelvic spine may indicate that it came from a population that was exposed to intense predation by vertebrates, possible absence of the ascending branch of the pelvis may indicate absence of such predation, but no other paleoecological information can be inferred from its osteology.
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