Time: Early Middle Cambrian, (~525 million years ago)
is 70 mm long
Site: Comet Shale Member, Pioche Formation, Lincoln County, Nevada
This is the grasping arm of the “Terror Of The Cambrian”,
Anomalocaris, and it comes from the Comet Shale Member of the Pioche
Formation of Nevada. This deposit spans the transition of Early
to Middle Cambrian which saw the extinction of the Olenellid trilobites.
It is just younger than the comparable material from the Chengjiana
Biota of Yunnan Province, China and just older than the Burgess
Shale Fauna of Brithish Columbia, Canada. The members
of this group of enigmatic creatures are known from Asia, Australia,
Europe, and North America, and are thought by many to be closely
allied with the Arthropda, a position not held by all researchers.
The spiniferous grasping appendages are strongly suggestive of its
carnivorous habits; some trilobites from Utah have evidence of bite
marks that have been attributed to Anaomalocaris. The genus derives
its name from “anomalous shrimp” which was what the
describer thought the appendage was. The specimens from the Pioche
Formation are often somewhat faint. The specimen has been water
wet to heighten contrast, and I include a negative image of the
main slab to make it easier to see. Regardless, this is a rare specimen,
little seen outside of an academic collection.