The density of the embedded fragments, visible in the CT images, suggested that the material was compact cortical bone — the dense outer layer of a mammal’s skeleton, as opposed to the more porous trabecular bone that fills the interior of most bones.

This density was one of the first indicators that the embedded material was not part of the mastodon rib itself: the rib’s own cortical bone showed in the CT images as a relatively uniform layer surrounding the more open trabecular interior, while the embedded fragments were distributed through a channel that cut across this architecture.

The fragments were denser than the surrounding trabecular bone and had a different texture and geometry than the cortical layer.

But knowing that the embedded material was compact bone did not tell the researchers where that bone had come from.