A Walk Among the Brachiopods

April 29, 2015

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Photographer: Robert L. Sheridan
Summary AuthorRobert L. SheridanApril 2015 Viewer's Choice

In the early Paleozoic Era, about 550 million years ago, complex soft-bodied invertebrates thrived in warm shallow seas. Sea and atmospheric carbon dioxide levels were high and the world was warm. Most of the proto-North America straddled the equator as the continent known as Laurentia ringed and penetrated by warm, shallow, sunlit oceans. This was a perfect habitat for evolution by trial and error. From an early confusion of soft-bodied marine invertebrates, hard parts began to develop, as the chemistry required to extract calcium from seawater evolved. This increased the survival of organisms that could put this chemistry to use. By the Ordovician Period, about 100 million years later, an array of reef-building, calcium-concentrating organisms had evolved, including species of sessile brachiopods, with two protective valves from the extinct Order Orthida.

Fast-forward 450 million years and some of this habitat is available for terrestrial hikers (top photo). Fossil Mountain in the Sevier Desert of southwest Utah’s Home Range is one such place. The uplifted and fractured remains of a massive, shallow reef are packed with reef-building Orthid brachiopods (bottom photo). Although bearing a superficial resemblance, brachiopods are not clams -- they evolved much later. The only place we can see Orthids today is in places like Fossil Mountain. A major extinction event, possibly related to global cooling with glaciation and falling sea levels during the Silurian period, meant the end for most brachiopods, including all Orthids.

Photo Details: Both - Camera Maker: Apple; Camera Model: iPhone 5s; Focal Length: 4.1mm (35mm equivalent: 30mm); Aperture: ƒ/2.2; Exposure Time: 0.0008 s (1/1208); ISO equiv: 32.