2.1" Xiphosurida Arthropod (Pos/Neg) - Horseshoe Crab Ancestor

This is a rare, Lower Ordovician arthropod which would be a member of order Xiphosurida. Xiphosurida is believed to be a very ancient ancestor or at least closely related to the modern day horseshoe crab. It comes from the Upper Fezouata Formation near Zagora, Morocco.

This specimen is 2.1" long including the telson (tail spine) and has a beautiful orange/red coloration due to the oxidation of iron pyrite. Both the positive and negative impression are included.

Horseshoe crabs are arthropods of the Family Limulidae, Order Xiphosura. They evolved during the Ordovician Period, about 450 million years ago. The oldest fossil was found in Manitoba, Canada and was 445 million years old. Though some species of horseshoe crab have become extinct, there are four species alive today.

Horseshoe crabs have described as looking like round nose battle tanks, but at least one group of researchers thought one fossil found in Idaho looked like Darth Vader. They have a shell that covers their entire body except for the tail, two small eyes on top of the shell with 6 others around the edges of the shell and a thin tail sticking out the back. Living Horseshoe crabs are grey, green and brown. Horseshoe crabs are more closely related to spiders than to true crabs. Like spiders, horseshoe crabs do not have mandibles for grinding food, instead they have two appendages for moving food into the mouth.

Horseshoe crab fossils have been found world wide, Siberia, Lebanon, Spain, Morocco, Canada and the US. The oldest fossil Horseshoe Crab was found in Manitoba, Canada, Vaderlimulus (Darth Vader) was found in Idaho. Solnhofen Germany produces most of the commercially available Horseshoe Crab fossils.
Unidentified Xiphosurida
Zagora, Morocco
Upper Fezouata Formation
2.1" long including spine
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