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Orodvician Period

The Ordovician fossil record contains a diversity of marine invertebrates, including graptolites, trilobites, brachiopods, and conodonts (early vertebrates). A typical marine community consisted of these animals, plus red and green algae, early fish, cephalopods, corals, crinoids, and gastropods. A drop in sea level may have contributed to the mass extinctions that characterized the end of the Ordovician, in which perhaps 60% of all marine invertebrate genera went extinct.

During the Ordovician Period in New Jersey, shallow seas gave way to deeper oceanic conditions. The shallow water limestone's and their reef-building organisms were replaced by dark colored shale's and mud stones and organisms typical of a deep-water environment. This change between environments is evident in the Valley and Ridge Province of northwestern New Jersey.