Historic Environment Scotland (HES) said the carvings – thought to be between 4,000 and 5,000 years old – were discovered inside Dunchraigaig Cairn in Kilmartin Glen, Argyll.
They are thought to date to the Neolithic or Early Bronze Age, and include images of deer.
Hamish Fenton, who has an archaeology background, found them by chance.
Kilmartin Glen is viewed as one of the most important concentration of Neolithic and Bronze Age remains in mainland Scotland.
Valuable as sources of meat, hides, and with bones and antlers used for a variety of tools, HES said deer would have been very important to local communities at the time.
bbc.co.uk/news/uk-scotland-57304921