Knightia is at the bottom of the predatory food chain in the Green River Shales of Wyoming, USA. Going back over 50 million years and covering an exposure area of about 2,5000 miles to a thickness of about 2000 feet, these rocks are full of fossil fish. This specimen is 5cm long and it is difficult to determine whether it is Knightia oceana or Knightia alta, the two most common species that make up about 95% of fossil fish finds in this part of the world.
Many of these specimens are damaged or distorted when the rock is fractured. In this one, the jaw and lower head is damaged. There is also fragments of another fish below its belly. This is typical of many specimens that are sold as beginners collection specimens for a few pence.
However, with so many fossils available there is a good chance that one will be complete. This is a specimen of Knightia alta and the fish is preserved in its entirety, showing the skeleton and soft tissues, fins and jaws, all in their original position as the fossil was preserved. This wealth of fresh water herrings has allowed study of the population dynamics and ecology of these fossil fish, which show that they were living in a world that is essentially the same as the world we are living in today (without the impact of human activity).