The team of geneticists and archaeologists from Ireland, France, Iran, Germany, and Austria have been able to sequence DNA from a mummified 1600-year-old sheep. The sheep was found in an ancient Iranian salt mine known as Chehrābād. The specimen is highly interesting for archaeologists because it reveals sheep husbandry practices of the ancient Near East.
The specimen also underlines how natural mummification can impact DNA degradation. The salt mine of Chehrābād is known to preserve biological material and is the same location where the “Salt Men” were recovered. The new discovery has confirmed that the natural mummification process known as desiccation, where water is removed from a corpse preserving soft tissues that would otherwise degrade, can also preserve animal remains.
The researchers were led by geneticists from Trinity College Dublin and were able to extract DNA from a small cutting of mummified skin from a sheep leg recovered in the mine. Typically, ancient DNA is degraded and fragmented. However, the team found the sheep mummy DNA was extremely well preserved with longer fragment links and less damage typically associated with ancient specimens. The group attributes the preservation to the mummification process at the salt mine, which provides ideal conditions for preserving animal tissues and DNA.
The influence of the salt mine was also noted in the microorganisms present in the skin of the sheep leg. Salt-loving archaea and bacteria dominated the microbial profile and could have contributed to the preservation of the tissue. The mummified remains are genetically similar to modern sheep breeds in the region, suggesting there’s been a continuity of ancestry of sheep in Iran since at least 1600 years ago.
The team also investigated the sheep DNA preservation to look for genes associated with a woolly fleece and fat tail, which are two important economic traits in sheep. Some wild sheep are characterized by a hairy coat that is much different from the woolly coats seen in many domestic sheep today. Fat tail sheep are common in Asia and Africa where they are used for cooking.