Sairocaris Paleozoic Phyllocarid Fossil from Heath Shale

Part and Counterpart

Sairocaris centurion

Phyllocarida, Archaeostraca, Sairocarididae

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

Size: Phyllocarid fossil is 105 mm long

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

Sairocaris centurion Paleozoic Phyllocarid 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 SairocarisMississippian times. Fine preservation of both fish and invertebrates is a hallmark of these deposits, presumably due to an anoxic depositional environment.

Sairocaris centurion Paleozoic Phyllocarid Fossil from Heath ShaleThis fossil is an example of the unusual Phyllocarid Sairocaris. I have included an interpretation of the specimen as it appeared in life (the limbs are not as yet known). The genus is also known from the older British Visean deposits, while its closest other relative is Kellibrooksia from Mazon Creek. The anteriormost portion is fainter than the rest because this part was the least mineralized.

click fossil pictures to enlarge

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