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KNIGHTIA FOSSIL FISH FOR SALE
More About Knightia
Knightia was a genus of clupeid (herring family) fish that lived in the Eocene, between 56 and 39 million years ago. They were small fish that swam in large schools into adulthood, a phenomenon that is not often observed in extant clupeid species. Their schools could reach rather large numbers that were sometimes killed all together, as evidenced through mass mortality plates. They were quite fragile and were susceptible to mass deaths if the water chemistry or temperature changed too drastically. This was largely offset by laying huge numbers of eggs: a classic tale of a high birth rate compensating for a large mortality rate!
Mass mortality layer of fossil Knightia.
Knightia’s importance to freshwater ecosystems is evident in its massive numbers throughout western Pacific Eocene deposits, but specifically within the Green River Formation. Experts typically have a solid number on the amount of fossil material discovered pertaining to a specific organism, but are at a complete loss trying to estimate the number of Knightia fossils that have been unearthed: specimens number in the millions. This speaks volumes to the species' prevalence!
Of all the fossils coming out of the Green River Formation, Knightia is absolutely the most prolific and is often the first fossil to come to mind when the formation is mentioned. Outside of the Green River Formation, Knightia has been found in lake and river deposits throughout Asia, particularly in China (K. yuyanga). This relationship is further evidence of a subcontinent that once connected North America and Asia.
Most Knightia fossils are dated to Eocene deposits (about 50 million years ago) where they died out towards the end of the epoch. Their order lives on through herrings, sardines, and shads, evolving over time out of freshwater environments and into marine or anadromous lifestyles.
Fun Fact - In 1987 the Wyoming state legislature designated the Knightia as the Wyoming state fossil.
What Did Knightia Eat And What Ate Them?
Knightia may be the most important fish to come out of the Green River Formation. This is because they were the most prolific primary consumer in the ecosystem. They were planktivorous and ate other producers like algae and diatoms. Much like any small schooling fish, they weren’t adverse to eating smaller fish or insects when opportunistic. Their large numbers were beneficial to all of the other fish, reptiles, birds, and mammals that sustained themselves on a healthy diet of Knightia by the mouthful. Knightia was a sort of linchpin in the aquatic ecosystems of the Green River Formation. Unfortunately for them, these fish were the epitome of the idea of eat to be eaten.
How Did Knightia Reproduce?
Paleontologists look to modern sardines that lay upwards of 200,000 eggs to conclude that Knightia may have lain in similar numbers. As with other fish, fry began their lives near shore and ventured outward to open water to feed in their massive schools. Unfortunately, other species that preyed upon Knightia, like Diplomystus, lived a reverse lifestyle that forced the larger individuals toward shore to feed on young fish. Most schooling fish will stay in humongous schools through adolescence before breaking into smaller schools, but this was not always the case with Knightia, which maintained enormous schools their entire lives.
Unlike Diplomystus, the other herring-esque species, Knightia had a rather rapid development from egg to adulthood. Knightia fossils show complete development of bones and vertebrae at every life stage, whereas many adult Diplomystus fossils are unearthed without complete development at the skeletal level.
Identifying Features
While there is some issue differentiating between Knightia and the other herring-like fish in the Green River Formation, Diplomystus, the greatest mix up is between the two Knightia species within the GRF. It seems a little too simple, but the primary (and indeed, the easiest) way to distinguish the two species is by the depths of their stomachs. While K. eoceana has the sleek body plan of modern herrings, K. alta has a distended stomach, almost as if they are in a constant state of pregnancy.
A Knightia alta showing its characteristic distended stomach.
References
Grande, Lance, A revision of the fossil genus Knightia, with a description of a new genus from the Green River Formation (Teleostei, Clupeidae). American Museum novitates ; no. 2731. 1982. New York, N.Y. : American Museum of Natural History.
Grande, Lance, The Lost World of Fossil Lake: Snapshots from Deep Time. 2013. The University of Chicago Press.
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