CT scanner captures entire tusk of woolly mammoth

Researchers have, for the first time, successfully acquired CT images of an entire tusk of a woolly mammoth, according to a new “Images in Radiology” article published in the journal radiology. Researchers were able to perform a full scan of the tusk in its entirety—or in toto—using a recent clinical CT scanner. The new technology enables large-area imaging without having to perform multiple partial scans.

“Working with valuable fossils is challenging because it is important not to destroy or damage the specimen,” said the article’s lead author, Dr Baden, Switzerland. “Even though there are different imaging techniques for assessing the internal structure, it has not been possible to scan an entire tusk in toto without requiring fragmentation, or at least multiple scans that then had to be painstakingly pieced together.”

The extinct mammoth (Mammuthus primigenius) was the size of a modern-day African elephant and lived throughout Eurasia and North America. Most woolly mammoths became extinct at the end of the last Ice Age, and the last specimens lived around 6,000 years ago. They belong to the order Proboscidea, which includes modern-day elephants as well as other extinct mammoths, mastodons, and gomphotheres.

Mammoths were covered in fur and had small ears and a small tail to relieve frostbite. They also had tusks, which they used to scrape bark from trees, dig on the ground for food, and fight. Proboscidea tusks have allowed researchers to determine ages and identify specific life-changing events based on analysis of annual growth increments.

Newer CT scanners have larger gantries, which is the ring or cylinder in which a patient, or in this case the tusk, is placed. The introduction of larger portals now opens up the ability to scan larger objects that were previously not possible, noted Dr. Niemann.

The tusk examined by the researchers was found in central Switzerland and excavated by the Office for Monument Preservation and Archeology of the Canton of Zug. The tusk is 206 centimeters (cm) long overall – nearly 7 feet. It has a basal diameter (measurement at the base) of 16 cm – just over 6 inches. The overall diameter of the object – accounting for its helical or spiral curvature – is 80 cm, or just over 2.5 feet.

Tusks are primarily composed of two types of material: cementum, a substance similar to bone, and dentin, which underlies the cementum and makes up most of the tusk’s mass. Mammoth tusks are internally structured by annual increments of dentinal apposition that resemble stacked conical cups in longitudinal section (as opposed to transverse section). The first “cone” a mammoth produces forms the tip of the tusk, while the cone at the tusk base is the most recent, produced just before the animal dies. The cones in between are formed throughout the mammoth’s lifetime.

Using the larger gantry CT scanner, the researchers, in collaboration with the Institute for Evolutionary Medicine at the University of Zurich, were able to capture a clear image of the entire tusk interior.

“It was fascinating to see the internal structure of the mammoth tusk,” said Dr. Niemann.

The researchers found a total of 32 cones, leading to a minimum age of 32 years at the time of death. Although the mammoth tusk is well preserved, it lacks the tip, so the surviving estimate is slightly below the actual age of the animal at the time of death.

“Our mammoth died about 17,000 years ago at the age of about 32,” said Dr. Niemann.