Lepidasterella
montanensis
Class Stelleroidea,
Order Spinulosida, Family Heliathasteridae
Geological
Time: Mississippian (~320 m.y.a.)
Size: Fossil
is 105 mm by 95 mm
Fossil Site:
Heath Shale Formation, Bear Gulch Limestone, Fergus County, Montana
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 a fine 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 one 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. This one is preserved on a massive
lens of matrix. The bicolor nature of the matrix is due to in-situ
weathering.
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