1.82" Asaphiscus Wheeleri Trilobite - Utah

Here is a good-sized, 1.82" long Asaphiscus wheeleri trilobite from the Wheeler Shale of Utah. It was collected in the House Range and was cleaned under microscope using air abrasives. A really nice specimen with tight cheeks which is unusual for the species.

Asaphiscus wheeleri is a Cambrian carnivore that patrolled the offshore shelves, basins, and slopes of a warm equatorial ocean. Asaphiscus is representative of primitive trilobites belonging to the order of relatively large, ancient arthropods, Ptychopariida. Unlike some other Ptychoparids, Asaphiscus has eyes, making it a formidable predator. This extra visual sense would have adapted it well to hunting the Cambrian seas freshly teeming with diversity.

This trilobite hunted the Cambrian oceans from 513.0 mya to about 498.5 mya. It lived during a great evolutionary arms race at a time where the ocean was deepening and the sediments were deposited in a step-wise fashion toward shore. Where Asaphiscus wheeleri lived, the ocean was continually invading into Laurentia- a seemingly barren continental core of North America. In the sea, higher life was abundant and clawing for advantage.

Asaphiscus had the tough armor of the arthropod carapace to protect itself from things lurking in the basin clay. However, it was likely not a lurker and is described as a fast swimmer. It has a characteristic pygidium with a flat border. Many other trilobites of this time and environment also shared this adaption. One can imagine the purpose for this trait. Protection while the trilobite enrolled like a ball, or for streamlined speed to chase down prey?

These ancient carnivores are found in the Wheeler shale and Marjum Formations of western Utah. The Wheeler Shale, a remnant of an ancient embayment where the ocean intruded into Utah, is perched in the strikingly arid and steep terrain of the House Range. An oasis among the scrublands, the cold springs that pop from the fossiliferous limestones of the region are appreciated by fossil hunters.

Size ranges for Asaphiscus are half an inch to over 3 inches, with 1-2 inches being typical. Trilobites like modern day lobsters molted as they grew shedding their exoskeleton. About 80% of of the specimens collected in the wheeler shale tend to be molts. Molts are identifiable because they are missing thee "free cheeks" on the side of their heads. They are collected in the same quarries as the prolific Elrathia kingii but are less common and due to their thinner shell less likely to survive intact.
Asaphiscus wheeleri
Antelope Springs, House Range, Utah
Wheeler Shale
1.82" long on 3.1 x 1.9" rock
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