Milwaukee Public Museum

by Paul G. Hayes

EDITOR'S NOTE: This article is reprinted from LORE magazine, a benefit of museum membership. ©1996 Milwaukee Public Museum, Inc

Although he is popularly known as an expert in dinosaur extinction 65 million years ago in the Cretaceous Period, Peter Sheehan, curator of geology at the Milwaukee Public Museum (MPM), is more at home, literally, in the Silurian Period, which began about 425 million years ago.

He was born in Lockport, New York, which is underlain with Silurian dolomite. His doctor's thesis is about Silurian fossils from the Great Basin of Nevada and Utah. Now he works at a museum that stands over Silurian bedrock, whose fossils of undersea life comprise the core of the Museum's important paleontological collection.

Sheehan can't remember when he was not aware of "a wonderful natural history museum in Milwaukee." The word came to him from Grandfather Frank Dobrovolny, a German Baptist minister during the early years of this century.

Foreseeing and fearing the European wars, Dobrovolny made his way to western North Dakota where he took a parish. When his wife and two sons followed to Canada, the Rev. Dobrovolny came east to pick them up. "On his way, "Sheehan said, "he visited 'a wonderful German museum of natural history in Milwaukee.'"

It was the Milwaukee Public Museum, which had its beginnings in the old German-American Academy, where early curators labeled specimens with both their popular English and German names, but which was housed in the present Milwaukee Public Library building when Dobrovolny visited it.

"Even though my grandfather died before I could know him, I owe him a great debt for my being a scientist, 'Sheehan said. "It's clearly due to him and I never met him."

Dobrovolny was committed to the value of education for Ws eight children. All of them went to school and most earned Ph.D. degrees. They included two chemists, an inventor who helped develop radar, a medical doctor who worked on tropical diseases, a geologist, and a school teacher who married a paleontologist.

Sheehan's mother, Freda, went to nursing school in Niagara Falls, New York, where she met Joseph Sheehan, the oldest son of a big Irish family. Peter, their only child, was born in 1941.

When Sheehan was five, the family moved to Lodi, California, where he attended public schools. It was natural to attend the University of California in nearby Berkeley, where he majored in paleontology, earning his Bachelor's degree in 1965, his Master's in 1967 and Ws Ph.D. in 1971.

Sheehan's area of study focuses on the boundary marking the end of the Ordovician Period and the beginning of the Silurian. Both ages bear the evidence of shallow, warm seas, but the biological communities are sharply different. The boundary is distinct.

"In Mayville (50 miles northwest of Milwaukee) you can put your finger on it," Sheehan said.

Sheehan's studies shed light on the boundary as one of the five great extinction events that can be read in fossil records. They were caused by climate change, meteorite impacts or other events and at least 60% of living species -vanished.

"The climate changed," Sheehan said. "It cooled and glaciers formed." With water now in the form of ice, the seas receded and the habitat shrunk. "The glaciation probably lasted less than a million years," Sheehan said, "but that was enough for an estimated 60% loss of species."

After Berkeley, Sheehan spent a year in Sweden doing post-doctoral work, taught for a year at the University of Western Ontario, and served for several years as research professor at the University of Montreal. He met his wife, Carolyn, a native of Illinois, in Montreal where she was attending McGill University. Their son, Jesse, now is a college freshman studying music. Sheehan has three grown children by a former marriage and is a recent grandfather.

In 1977, Sheehan joined the Milwaukee Public Museum's geology staff, then led by Robert West. Sheehan first went to work learning the Milwaukee fossil collections and bringing them into usable form. The Museum, he said, has a good collection of Midwestern fossils, and is especially strong on the fossils of Silurian reefs.

Already an expert on extinction, Sheehan was fascinated by a new theory in the 1980s promoted by Luis and Walter Alvarez, father and son, that an asteroid crashing into Earth 65 million years ago may have caused the extinction of the dinosaurs.

Earlier, West had begun the Museum's popular "Dig-a-Dinosaur" program in which volunteer amateurs paid to hunt the western states for dinosaur remains. But the Museum's physical size prevented it from aspiring to a comprehensive collection of fossils as large as dinosaurs. Such collections can be assembled by the American Museum of Natural History in New York City and the Smithsonian Institution in Washington, D.C., but the Milwaukee museum's program was imperiled.

It was Sheehan's idea to collect not fossils but information. Museum staff trained the volunteers how to recognize fossil-bearing formations, identify species from bone fragments and keep accurate field notes. Scores of eager volunteers spent two-week sessions three times a summer for four years gathering information on the fossils they found in the Hell Creek formation of Montana and North Dakota, which contains the remains of the last dinosaurs to have lived.

The question was, did the dinosaurs die out gradually or did they vanish abruptly, suggesting a traumatic event like an asteroid impact. The data dug by the "Dig-a-Dinosaur" volunteers supports a sudden extinction. Published in Science magazine, the study went far to persuade paleontologists that an asteroid caused the extinction. The discovery of an asteroid crater the right size at the tight time has all but quelled the debate.