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University of Iowa News Release


Dec. 1, 2006

UI Museum Of Natural History Finds Third Ice Age Sloth

For more than three years, students, staff and volunteers from the University of Iowa Museum of Natural History (MNH), the UI Department of Geoscience, the Department of Anthropology and the Office of the State Archaeologist have been excavating the bones of an SUV-sized Ice Age sloth from a site near Shenandoah, Iowa. In April 2006, the team announced the discovery of a juvenile sloth.

Today, the research team announced that diggers have unearthed the remains of a second juvenile sloth.

"We've found only one bone so far, but it's unmistakably a third sloth and unprecedented," said David Brenzel, curator of the UI Museum of Natural History.

"It's like winning the lottery-twice," added Holmes Semken, professor emeritus of geoscience and co-leader of the sloth expeditions.

The scapula, or shoulder blade, recovered on the early November dig has been confirmed as belonging to a very young individual of the same species previously recovered, almost certainly less than 1 year old, according to Greg McDonald, senior curator of natural history at the National Park Service in Denver, Colo. and the world's foremost giant sloth authority. "I never would have expected a second juvenile. We are in uncharted territory with this new discovery."

"This one is a real baby," according to Sarah Horgen, the MNH education and outreach coordinator who uncovered the fossil, noting that the bone is about two-thirds the size of the two juvenile scapulae previously found.

"I showed it to Holmes, and he got very quiet. I think he went into shock," she said. 

The team also recovered a complete hip bone and four or five ribs and vertebrae from the older juvenile and a half-dozen other bones or pieces still to be identified during the four-day dig. The site had previously yielded almost 90 bones from the adult and more than 30 bones of the older juvenile, both ranking as the second-most complete skeletons of their kind ever recovered and the first adult-juvenile combination ever found.

The discovery will force another rewrite of the grant proposal that Semken is preparing for the National Science Foundation (NSF) to fund analyses of the fossils.

"It's more important then ever that we try to prove this is a sloth family," said Semken, adding that he is assembling a team of university and national experts to assist in the work. "The potential window this opens into the family behavior of giant sloths is absolutely unique."

The proposed research has the potential to indicate the climate, local habitat, diet, dietary deficiencies, some diseases and possibly the migration patterns for the animals. Together, the three individual sloths may help establish parameters for determining the sex of adults, age of sexual maturity, growth rates and diet changes with age.

"This is truly a Rosetta Stone for understanding these rare and mysterious animals," said Semken.

Bob and Sonia Athen first discovered the sloth in the summer of 2001 behind their home, along West Tarkio Creek, which forms the border between their land and that owned by Dean and Loreta Tiemann of Lincoln, Neb. The Athens subsequently brought their specimens to Iowa City, where Semken identified them as the remains of a Megalonyx jeffersoni, the giant sloth discovered by and named in honor of Thomas Jefferson. Both families have been enthusiastic donors and participants in the excavations.

A dozen of the bones are currently on display in the lobby of Iowa Hall.  Additional information about the sloth digs and research can be found on the Museum of Natural History Web site at:

STORY SOURCE: University of Iowa News Services, 300 Plaza Centre One, Suite 371, Iowa City, Iowa 52242-2500.

CONTACTS: Research, Museum Curator David Brenzel, 319-335-0482,; Media, Gary Galluzzo, 319-384-0009,