Exceptional ancient DNA preservation and fibre remains of a Sasanian saltmine sheep mummy in Chehrābād, Iran

Abstract

Mummified remains have long attracted interest as a potential source of ancient DNA. However, mummification is a rare process that requires an anhydrous environment to rapidly dehydrate and preserve tissue before complete decomposition occurs. We present the whole-genome sequences (3.94 X) of an approximately 1600-year-old naturally mummified sheep recovered from Chehrābād, a salt mine in northwestern Iran. Comparative analyses of published ancient sequences revealed the remarkable DNA integrity of this mummy. Hallmarks of postmortem damage, fragmentation and hydrolytic deamination are substantially reduced, likely owing to the high salinity of this taphonomic environment. Metagenomic analyses reflect the profound influence of high-salt content on decomposition; its microbial profile is predominated by halophilic archaea and bacteria, possibly contributing to the remarkable preservation of the sample. Applying population genomic analyses, we find clustering of this sheep with Southwest Asian modern breeds, suggesting ancestry continuity. Genotyping of a locus influencing the woolly phenotype showed the presence of an ancestral ‘hairy’ allele, consistent with hair fibre imaging. This, along with derived alleles associated with the fat-tail phenotype, provides genetic evidence that Sasanian-period Iranians maintained specialized sheep flocks for different uses, with the ‘hairy’, ‘fat-tailed’-genotyped sheep likely kept by the rural community of Chehrābād's miners.

Adulis and the transshipment of baboons during classical antiquity

“…DNA of the mummified baboon shows postmortem damage, which is, however, relatively low compared to what can be expected for samples of similar age (Dabney, Meyer, et al, 2013, Kistler et al, 2017). Low frequencies of post mortem damage were observed for aDNA from mummified specimens and have been attributed to the water deprivation during the mummification process, which may prevent hydrolytic deamination (Rossi et al, 2021). Postmortem damage observed here is within the range previously reported for aDNA derived from Egyptian human mummies (Schuenemann et al, 2017) and a Iranian saltmine sheep mummy (Rossi et al, 2021), which supports the authentic origin of our ancient sequence data and tends to rule out the possibility of contamination with modern DNA.…”

Genetics of the phenotypic evolution in sheep: a molecular look at diversity-driving genes

“…Interestingly, when genotyping the hairy/woolly locus in a ~ 1600-year-old naturally mummified sheep found in a salt mine ( Chehrābād ) in northwestern Iran, the ancestral “hairy” allele (likely IRF2BP2 wt/wt or IRF2BP2 wt/asEIF2S2 ) was identified [ 152 ]. In addition, using scanning electron microscopic observations of the mummified hair fibers showed characteristics that are specific to sheep hair fibers of mouflon and medium-wool breeds.…”

“…In addition, using scanning electron microscopic observations of the mummified hair fibers showed characteristics that are specific to sheep hair fibers of mouflon and medium-wool breeds. This suggested that, during that ancient period, the herd was maintained for meat or milk production rather than wool extraction, and ovicaprids were destined to be used as food source for workers in that location [ 152 ]. This study highlighted the potentiality of using a locus for the phenotypic characterization of ancestral breeds using ancient DNA.…”

A Time to Sow, a Time to Reap: Modifications to Biological and Economic Rhythms in Southwest Asian Plant and Animal Domestication

“…A ca. 1600-year-old sheep mummy from a Sasanian salt mine in Chehrābād, Iran, was shown to be of the 'hairy' type by genetic and morphological analysis of exceptionally preserved mummified fiber remains [211]. This suggests that woolly sheep did not become a universal norm even in 1st millennium CE Southwest Asia, and that hairy breeds may have been used at this time for specialized milk and meat production.…”