Fossil Information Sheet F004
Vertebrates are highly mobile organisms and characterised by internal skeletons - the oldest category of which are fish.
By the Silurnian period (439-408 million years ago) they occupied all water depths and as such fish fossils may be found in nearly all environments: streams, lakes and oceans.
As abundant as fish are they are surprisingly rare as whole fossils, the bony teeth of sharks fossilise well and are common in some environments, but other than that fish skeletons, being mostly cartilage, are so easily broken up after death that they make poor candidates for fossilisation.
They generally occur in shales especially marine black shale of freshwater lakes.
Whole fish are more common in lakes as they have been protected to a degree from excessive oxygen which causes decay.
In rare cases in certain limestones whole fish are preserved.
A very well know location for finding fossilised fish is
The Green River Formation
It is a tributary of the Colorado River where three separate basins exist around the Uinta Mountains of Northern Utah and south West Wyoming it is known as "Fossil Lake" because of the abundance of exceptional preserved fish fossils.
Typical examples of fish found in the Limestone at the Green River Formation are:
A fossil from the Green River Formation dating from the Eocene period.
An extinct fish from this same river formation.
A slender fish seldom exceeding 25cms in length feeding on astracods algal forms and smaller fish.
They themselves were included in the diets of larger fish.
Knightia is the state fossil emblem of Wyoming. Examples can also be found in Europe.
The plaque on display in the
includes two superb Knightia and 1 Priscacara approximately 50million years old from Green River Formation in Wyoming.