However, the two most abundant vertebrate taxa of the formation provide crucial data about eco-evolutionary dynamics within a prehistoric ecosystem.
Fossil specimens of this stickleback form a time series spanning many generations over thousands of years, in which they can be observed developing a number of adaptations to their lake environment and diverging into two distinct ecotypes, exemplifying the rapid evolution that their modern relative, the three-spined stickleback, is well known for.
This suggests that following their colonization of the lake, the killifish may have driven the sticklebacks to extinction on a rapid timescale comparable to modern biological invasions.
[2] Uniquely, the paleofauna of the formation shares many elements with the native freshwater fauna found in lowlands along the Pacific Coast.
The rise of the mountains would have eventually cut off this water source, drying out the rivers and driving the ancestors of these fish to extinction.