Description: The Bear Gulch Limestone is a deposit of some 70 square km in extent and 30 m in depth that has been a source of one of the most diverse assemblages of fossil fish with some 110 species having been described over the past 30 years. Most were new to science, and provided a unique view of the marine environment of Mississippian times. Fine preservation of both fish and invertebrates is a hallmark of these deposits, presumably due to an anoxic depositional environment. This specimen is known as a salp, a planktonic tunicate that moves through the water column by pumping water through its gelatinous body. This pumped water is strained for the phytoplankton contained. While salps appear morphologically similar to jellyfish, they are actually most closely related to the vertebrates. Their rudimentary nervous system is thought to have been the precursor to the more complex one in vertebrates of today.