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A new exhibition, "Corridor of Time: Cretaceous and Paleocene Prehistoric Life," at the Heritage Center, the state museum in Bismarck, North Dakota, includes includes fossil discoveries by Chapin Professor of Geology J. Mark Erickson, who has been conducting research and leading groups of St. Lawrence students to conduct digs in the area since 1972.

Erickson has been an advisor to the museum during its planning. The exhibition, which opened to the public December 9, includes 25-foot-long murals of Cretaceous and Paleocene life reconstructions, accurately depicting the flora, fauna and geology of central North Dakota just before and just after the episode of dinosaur extinction that marks the boundary between the Mesozoic and Cenozoic Eras of geologic time. Many of the fossils discovered by Erickson and St. Lawrence researchers are portrayed or are included as specimens within the new exhibit, as well as in the marine Cretaceous exhibit that was unveiled previously.

Erickson was first to recognize the paleogeographic feature known as the Dakota Isthmus, a land bridge that joined the eastern and western subcontinents of North America 66.5 million years ago after the continent had been split down the middle by a major seaway for 40 million years. More than 30 St. Lawrence students have participated in studies of fossil invertebrates, vertebrates and plants of the Fox Hills Formation, sediments of which were laid down as shoreline and beach deposits on the Isthmus. Erickson and his students have been the first to describe and name many of these organisms over the years, while some remain to be described. The exhibit is based on much of this work and on numerous studies of the overlying Hell Creek Formation that have been made by North Dakota Survey geologists in the past 20 years.

During the continuing discovery process renowned photographer Mark Klett '74, a student of Erickson's, described the Linton Member, then a newly defined sedimentary unit of the Fox Hills Formation that was part of the Dakota Isthmus coastal setting. In 2003, Daniel Peppe '02 described the fossil leaves from that member at an international paleobotanical conference in Argentina, a major addition to knowledge of Late Cretaceous plants of North Dakota. The plants provide information about ancient temperature and rainfall amounts on the Isthmus, whereas studies of the oxygen isotopes by Scott Carpenter '85 corroborate mild temperate ocean temperatures of the Fox Hills Sea.

Fossils for the 55-million-year-old Paleocene portion of the exhibit have been discovered through the efforts of geologists from the North Dakota Geological Survey with whom Erickson has worked over the years. State Geologist Ed Murphy and John Hoganson, the Survey's paleontologist, have encouraged collaboration of St. Lawrence students in the excavation and preparation of numerous specimens of freshwater turtles, crocodiles, champsosaurs, petrified stumps, clams, snails and leaves from several sites in the badlands and the Missouri River Valley of North Dakota. Since 1993, Hoganson and Erickson have often worked together at excavation sites of fossil turtles, crocodiles and petrified trees, as well as at the Johnsrud Paleontology Lab of the North Dakota Geological Survey, where students learned how to clean, recover and prepare fossils of many types. That collaboration has also provided materials for the new Corridor of Time exhibit.

The last St. Lawrence geology field expedition to North Dakota will take place in June of 2007, when another group of students will make both scientific and cultural discoveries of their own among the buttes of the badlands and flood plains of the Missouri River Valley.

More information: Science at St. Lawrence

The North Dakota Heritage Center Web site

Posted: December 7, 2006

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