Cambrian Fossils Out of Place

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Cambrian rock layer is considered to be "Cambrian" because of the particular fossils it contains. But what does it mean when a rock layer designated as "Ordovician" contains distinctly Cambrian fossils? Paleontologists are facing that question after a recent find in North Africa.


Researchers in Morocco found fossils of Anomalocaris—a unique and until now characteristically "Cambrian" creature—in Ordovician rocks, which in some locations are positioned just above Cambrian strata. This evidently extinct animal belonged to a group of rather strange sea creatures classified as "anomalocaridids." One such marine animal was Hurdia, which had well-designed and fully-integrated body parts, including dual-function swimming flaps and gills.1 Despite their unusual appearance, no anomalocaridid looks like an evolutionary transition, and all of them look well-suited for aquatic life.