This Specimen has been sold.
3.5" Hoekaspis Trilobite - Bolivia
This is a very unusual trilobite, a Hoekaspis yahuari from Bolivia. It's preserved inside an insanely hard concretion that was broken open. Very few Hoekaspis retain their free cheeks like this example. This comes out of an old collection we recently purchased, so we have only one other specimen available besides this one.
Trilobites were a very diverse group of extinct marine arthropods. They first appeared in the fossil record in the Early Cambrian (521 million years ago) and went extinct during the Permian mass extinction (250 million years ago). They were one of the most successful of the early animals on our planet with over 25k described species, filling nearly every evolutionary niche. Due in large part to a hard exoskeleton (shell), they left a excellent fossil record.