According to a Phys.org report, a large number of 40,000-year-old animal bones have been found in the third level of Spain’s Cueva Des-Cubierta by Enrique Baquedano of Madrid’s Regional Archaeology and Paleontology Museum and his colleagues.

In their paper published in the journal Nature Human Behavior, the group describes the site where the skulls were found, their condition and theories about why the skulls were placed in the cave.

The Cueva Des-Cubierta cave located in the Madrid Region of Spain was first discovered in 1978. Since that time, the remains of a Neanderthal child and tools made by Neanderthals have been found in the multilevel cave. The newly discovered bones include an assortment of large herbivore skulls that had been carefully removed from the animals’ bodies and modified with tools and sometimes fire, Baquedano said.

Most of the skulls belonged to bison or aurochs, which have horns; male deer with antlers; and two rhinoceroses. The researchers noted that the skulls would have provided little food, and may have been saved as hunting trophies, or could have served an unknown purpose.