Medieval scribes filled volumes called bestiaries with illustrations and descriptions of fantastic creatures. The manuscripts containing representations of these animals also depended on a menagerie of beasts: The covers of these and other volumes were fashioned from the skins of calves, goats, sheep, deer, pigs and, in some macabre instances, humans.

Most of these hides were shorn before they were turned into book bindings. But one set of medieval manuscripts from northeastern France has a peculiar finish: Its weathered covers are covered in clumps of hair.

“These books are too rough and far too hairy to be calfskin,” said Matthew Collins, a bioarchaeologist at the University of Copenhagen and Cambridge University and an author of the new study. But identifying the source of the shaggy leather has proved difficult.

While these furry tomes would seem at home in Hogwarts library, they were originally made in the scriptorium of Clairvaux Abbey, a hub for an order of Catholic monks, the Cistercians. The abbey, founded in 1115 in the Champagne-Ardenne region of France, was home to one of the largest monastic libraries in medieval Europe.

Some 1,450 volumes of the abbey’s extensive corpus survive. Roughly half of these manuscripts remain in their fragile, original bindings. Many were bound during the 12th and 13th centuries in the Romanesque style, which placed the parchment between wooden boards fastened with thread and cord.

At Clairvaux Abbey, these Romanesque books were often housed inside a secondary cover that was bristled with fur. Traditionally, this unshorn leather was thought to be made from boars or deer. However, the hair follicles on some of the manuscripts do not match the fur of either mammal.