The Haas Plesiosaur Fossil

Last Updated by Brian Gevik, Text provided by Darrel Nelson - Deadwood History Inc.Exhibits Director on
All Images Courtesy: Deadwood History Inc.

William Karl Haas  by Plesiosaur site excavation, 1934William Karl Haas (Charles Haas' son), by Plesiosaur site excavation, 1934


Area farmer and entrepreneur, Charles Haas, and his son, Arthur, were exploring for fossilized shark’s teeth one afternoon in 1934. They did not expect to see the bird-like skull protruding from a layer of Greenhorn Sandstone. Charles freed the skull and one flipper from the rock matrix and concluded he and his son had discovered a worthwhile specimen; that of a plesiosaur.

Arthur Haas with plesiosaur, 1934Arthur Haas with plesiosaur, 1934


The members of the Haas family were unaware of the exact identity of their discovery, but they immediately recognized its importance.  Charles and Arthur excavated and prepared major portions of the skeleton and consulted the available scientific literature of the day.  Charles pronounced the creature 'a curious mixture of fish, reptile, and bird'.  He then created a report regarding the find which was published by the Science Service Bureau in Washington, DC. 

Charles hoped to sell the fossil to a prominent museum for display, although none were willing to take on his find.   He then approached the newly built Adams Museum in Deadwood in order to donate the fossil.  Although he thought the fossil had national prominence, he was confident his donation to the Adams Museum would one day further tell the specimen’s story.

Haas Letter, 1940Haas Letter, 1940


Sixty years later, in 1996, that day came.  Then-director of the museum, Mary Kopco, agreed with the Haas family that restorative work was necessary on the fossil.  Dr. Gordon Bell with the South Dakota School of Mines and Technology in Rapid City began working with the fossil.  This work was continued by his student, Dr. Bruce Schumacher, who completed some of the restorations in a working paleontology exhibit at Disney World in Florida.  Slowly, Dr. Schumacher uncovered an incredible revelation—the fossil was a plesiosaur species previously unknown to science.



One key to this identification was the presence of ammonite imprints in the same rock layer. The appearance of various types of ammonites around the world is so common and consistent that they have been extensively mapped and are often used to date companion species. The specimen discovered by Charles Haas had characteristics out of sync with the established dating and several unexpected morphological features, causing Schumacher to suspect that this fossil was incredibly rare.

Comparison—Highlighting restorative work done on Plesiosaur skeletonComparison—Highlighting restorative work done on Plesiosaur skeleton


Plesiosaurs have a lineage dated with considerable certainty to an extended family tree of similar creatures.  The Adams Museum fossil exhibited transitional characteristics between several known species and these did not conform to the previous timeline. Dr. Schumacher was able to show, to the ever-vigilant paleontology community of scientists, that it was indeed unique. He had the privilege of naming the creature as a new species- Pahasapasaurus haasi, in honor of the Lakota term for the Black Hills and the Haas family.

Paleontologist Dr. Gordon Bell talking with Verne Haas, son of plesiosaur discoverer Charles HaasPaleontologist Dr. Gordon Bell talking with Verne Haas, son of plesiosaur discoverer Charles Haas


Today Pahasapasaurus haasi occupies a place of honor in its own exhibit case at the Adams Museum. Charles Haas’ descendants were major donors to the exhibit that highlights the plesiosaur and focuses on family-accessible educational displays.  

Plesiosaur Illustration by DHI Exhibits Director, Darrel NelsonPlesiosaur Illustration by DHI Exhibits Director, Darrel Nelson


Paleontologists have come to examine the specimen to verify Dr. Schumacher’s measurements and museum visitors continue to be awed by the size of the fossil. Illustrations depict Pahasapasaurus haasi in its fearsome glory, along with its discovery 95 million years later by a father and son in a South Dakota pasture and its ultimate restoration in a paleontology laboratory. No longer a secret, the fossil is one of the cornerstone artifacts in the rich collections of the Adams Museum.


For Teachers: Activity Idea

Learn more about Deadwood History Inc.

Dakota Midday Interview

Interview with Darrel Nelson, DHI Exhibits Director, and Bill Haas, grandson of the fossil's finder.

Host: Lori Walsh