Exquisitely-Preserved Discoserra Mississippian Bear Gulch Fish Fossil
Part and Counterpart

Discoserra pectinodon

Class Actinoptergyii, Order Guildayichthyformes, Family Guildayichthyidae

Geological Time: Mississippian (~320 m.y.a.)

Size: Fish fossil is 62 mm long on a 185 mm by 95 mm and 150 mm by 120 mm matrix pair

Fossil Site: Heath Shale Formation, Bear Gulch Limestone, Fergus County, Montana

DiscoserraDescription: 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 fine specimen is a rare example of Gulidayichthyformes. The order and family was erected in 2000 to accommodate this unusual taxon which possesses an unusual mixture of primitive and modern characters in the skull bones. Note the detailed rhombic ganoid type scales and comb-like teeth. The species derives its name from the long teeth which presumably aided it in feeding, possibly on sponges. Overall, this is an exceptionally beautiful fish fossil and example of the type, rendered all the more desirable by the fact that both the part and counterpart examples are preserved.

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