silurian period

In this week’s Trilobite Tuesday, we present a brief history of the ebb and flow of trilobite evolution. These amazing arthropods existed for nearly 300 million years of earth history, during which time they produced over 25,000 different scientifically recognized species. But the fact is that after presenting a dizzying array of species during the Cambrian, Ordovician and Silurian periods, by thetime the trilobite line reached the Devonian some 400 million years ago, their species count had dwindled down to a precious few. And by the time the Mississippian began, their was ostensibly only one order of trilobites left—the Proetids. Here is an attractive example of a “double” Ameropiltonia lauradanae from the Mississippian-age shale of Missouri. These proetids were among the last survivors of the noble trilobite lineage.

Learn much more on the Museum’s trilobite website


A fossil of Eurypterus remipes, a “sea scorpion” that lived during the Silurian Period (432-418 million years ago)  While they averaged about 6 inches long, one large individual has been discovered that was 4.3 feet in length.  The largest known species of Eurypterid could reach a monstrous size of 8 feet long.

All Eurypterus possessed paddles which they could use to swim but most likely walked as a primary means of locomotion.  They were most likely, exclusively marine animals with their fossils being found in shallow, intertidal environments.  Eurypterus is the state fossil of New York.

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The Blue Ridge Mountains

are a physiographic province of the larger Appalachian Mountains range. The mountain range starts at its southernmost portion in Georgia, then ends northward in Pennsylvania.
The Blue Ridge contains the highest mountains in eastern North America south of Baffin Island. About 125 peaks exceed 5,000 feet (1,500 m) in elevation. The highest peak in the Blue Ridge (and in the entire Appalachian chain) is Mt. Mitchell in North Carolina at 6,684 feet (2,037 m). Most of the rocks that form the Blue Ridge Mountains are ancient granitic charnockites, metamorphosed volcanic formations, and sedimentary limestones. The Blue Ridge Mountains began forming during the Silurian Period over 400 million years ago.
The English who settled colonial Virginia in the early 17th century recorded that the native Powhatan name for the Blue Ridge was Quirank. At the foot of the Blue Ridge, various tribes including the Siouan Manahoacs, the Iroquois, and the Shawnee hunted and fished.