ribstone

noun

1. A petroglyph in the form of an animal's rib cage.

   “Virtually all of the formal investigations of the Alberta ribstones have led to conclusions of great antiquity. Many of the ribstones are of quartzite, one of the hardest rocks known. These monoliths exhibit advanced erosion and deep patination.”

   “Most of the ribstones in Alberta are rounded humps, a bit like a buffalo itself, but there are some in Saskatchewan where the pattern of backbone, ribs, hoofs and pockmarks is inscribed on flat, almost triangular slabs.”