The genus Priscacara is perhaps the most popular of the Green River fish fossils. A member of the Family Priscacaridae, the name Priscacara means "primitive head". Shaped rather like a sunfish, the genus sports sturdy, protective dorsal and anal spines. Among the two species, liops and serrata, serrata is uncommon. Liops is the smaller species, never exceeding 6 inches, whereas serrata have been found up to 14 inches. The genus went extinct at the end of the Miocene, and is thought by some to be related to the modern-day Cichildae.
About the Green River Formation: Class Actinopterygii, the ray-finned bony fishes, comprise almost half of all known species of vertebrates, some 20,000 extant species. There are numerous locations worldwide that are noted for wondrous preservation of bony fishes, and the Green River formation that covers some 25,000 square miles of SW Wyoming, west Colorado and east Utah is one of the premier examples. The formation is one of the largest lacustrine sedimentary accumulations in the world, and spans the period from 40 to 50 million years ago during the Eocene Epoch.
During the Eocene, based on the fossil record, the region was sub-tropical to temperate. Some 60 vertebrate taxa have been described from the formation, including crocodiles, boa constrictors, and birds, as well as abundant invertebrates and plants. The unusually excellent preservation of the Green River fish fossils is usually attributed to a combination of two factors: 1) a cold period during the Eocene that would have caused dead fish to sink faster due to a less inflated swim bladder; and 2) the great depth of the lakes and the consequent anoxic conditions that would have often prevented scavengers from disturbing the carcasses.
5.75" fish on 9.25x6.25 matrix
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