Bear Gulch Fossil Starfish with Many Legs

Lepidasterella montanensis

Phylum Echinodermata, Subphylum Asterozoa, Class Stelleroidea, Order Spinulosida, Family Heliathasteridae

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

Size: 105 mm by 95 mm across

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

LepidasterellaDescription: 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 a fine part/counterpart example of a many-armed starfish called Lepidasterella. At the time of its discovery some 25 years ago it was the only known many-armed starfish known from the time interval ranging from the Upper Devonian to the Lower Jurassic. The closest living relatives are the Sun Stars of the Family Solasteridae which are known as active and voracious predators. Sea Stars are one of the less commonly seen Paleozoic echinoderms, and thus poorly documented from the western United States, making this pair quite unique. Since Asterozoans typically begin to disarticulate soon after death, this one must have been buried quickly to be in such a fine state of preservation.

Reference: Journal of Paleontology May 1984 v. 58 no. 3 p. 843-851

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