The Paleontology of North America

the Cambrian - 543 to 490 Million Years Ago

World Paleogeography: The supercontinent Pannotia had begun to break up as the Iapetus Ocean formed in between Laurentia (North America), Siberia, Baltica (North Europe), and Gondwana (South America, Australia, Africa, India, and Antarctica). Throughout the Cambrian, Siberia remained east of Laurentia, while Baltica was moving south of Siberia and southeast of Laurentia. Also moving south was Gondwana, the largest continent, which stretched from the Equator to the South Pole. North American Paleogeography: Fossil evidence tells us that Laurentia was centered on the Equator and rotated so that in present-day terms, Canada was east, instead of north, of the United States. As with most of the continents, the majority of North America was underwater throughout the Cambrian Period. Small landmasses in the central part of the continent shed sediment in this shallow sea. Farther out, away from this influx of sediment, shallow water limestones were deposited in a broad arc stretching from present-day Maine south to Texas and up to the Canadian Rockies. Beyond this region, deeper water deposits accumulated. Paleontology: Animals with hard skeletons first appeared in the Cambrian and the diversity of life on Earth increased very rapidly. Because most of the animal phyla first appear in the fossil record over such a short interval of time, people sometimes call this the "Cambrian Explosion." It was once thought that the Cambrian rocks contained the first and oldest fossils, but we now recognize that life has a history that begins about 3.5 billion years ago, near the beginning of the Precambrian. The shallow Cambrian seas contained the first trilobites and brachiopods, as well as archaeocyathids (early sponges) and a number of strange, early echinoderms. The Burgess Shale of western Canada is an exceptional site where we find fossils of many rarely preserved soft-bodied organisms, among them a possible chordate, Pikaia.

North America Today

Geologic activity over the last 490 million years has removed or covered up most of the Cambrian rocks of North America. Today, rocks of this age can be found below the surface in many places, and while many states have exposures of Cambrian rocks, they are generally smaller than exposures from other periods. Cambrian exposures can be found in areas like the Basin and Range (throughout the West), the Rocky and Appalachian Mountains, and in New England, as well as in Wisconsin and many other states.

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