The Salkhit calvarium belongs to a definitively, Anatomically Modern Human

In a paper published on the 30^th of January 2019, Devièse et al (2019), find that the Salkhit calvarium that I included in a post about the early, peopling of the Americas (see here), was that of an Anatomically Modern Human. 

Speculation had ranged from Asian Homo erectus, to Neanderthals, Denisovans, ‘archaic modern humans’ and finally AMH with some archaic features. Indeed, looking at the morphology, of the calvarium there were distinct similarities with specimens such as those from Petralona and Broken Hill, both assigned to Homo heidelbergensis, as the image below makes clear:

A quote from Coppens et al. (2006), that I used at the time highlights the problem of the species assignment from morphometrical data:

 “This preliminary study of a human skullcap discovered at Salkhit, Northeast Mongolia, in 2006, shows a mosaic of traits. Plesiomorphies can be seen on the frontal bone: developed brow ridges and a keeled squama. Apomorphies can be observed: high and back-located parietal eminences and absence of a sagittal keel. The skullcap seems to share also some features with Neanderthals that can be observed on the lower part of the frontal bone and in the nasal and orbital region such as a supratoral sulcus, a prominent glabella, prominent rounded lateral supraorbital margins, and a well-defined inward nasion. The comparison of the dimensions of the skullcap with those of skullcaps of a reference sample by multidimensional scaling analysis shows similarities with Neanderthals, Chinese Homo erectus and West/Far East Archaic Homo sapiens.”

Now all that speculation is at an end.

The authors applied a new, technique called compound-specific radiocarbon dating to find an accurate age for the fossil.

The authors used this alternative to conventional methods as the bones were heavily contaminated.

Samples are pre‐treated via high‐performance liquid chromatography (HPLC). This isolates the amino acid, hydroxyproline from bone collagen, thus enabling a purified bone‐specific fraction to then be radiocarbon dated by accelerator mass spectrometry (AMS).

The authors found the Salkhit calvarium to date between 34,950–33,900 Cal BP, or ca. 34,000BP.

The authors also carried out a mitochondrial DNA analysis of the Pleistocene hominin from Salkhit Mongolia.

In a stunning finding, considering its morphology and previous discussions about its species assignment, (based on morphological measurements), the Salkhit calvarium was found to: 

“The Salkhit mtDNA lineage was assigned to the modern human macro-haplogroup N.. Haplogroup N and M are the two basal mtDNA haplogroups shared among all present-day non-Africans. While the mosaic of archaic-like and modern human-like morphological traits have made the assignment of the fossil to Pleistocene hominin groups difficult, we thus show that the mtDNA of the Salkhit individual is of modern human origin. However, the sequence does not carry any substitutions characteristic of known sub-haplogroups inside the haplogroup N. A maximum parsimony analysis (subtree Fig. 5) assigns the Salkhit mtDNA to an uncharacterized lineage which branches off the root of haplogroup N.”

In other words, the Salkhit calvarium belongs to an individual with very basal mtDNA haplogroup N with no living descendants, or rather no living descendants, yet sampled. Its position with respect to the diversity of modern, human mtDNA, particularly macrohaplogroup N can be seen on their phylogeny tree:

Conclusion

The Salkhit specimen has given us a message: human morphological variation, especially that from early Homo sapiens, can extremely misleading. The variation in skull characteristics as we move backwards in time is much wider than previously recognised.

The assignment of, this specimen to AMH, thus raises some interesting questions regarding some other specimens from the region. A number of, other, skulls assigned variously to ‘archaic modern humans’, Denisovans and evolved Homo erectus such as the Dali, Maba and Jinniushan remains, should, in the light of this study, perhaps have their taxonomic status reconsidered.

References

Coppens, Y., et al., (2008). Discovery of an archaic Homo sapiens skullcap in Northeast Mongolia, Comptes Rendus Palevol 7(1), pp.51-60.

Devièse, T., Massilani, D., Yi, S., Comeskey, D., Nagel, S., Nickel, B., Ribechini, E., Lee, J., Tseveendorj, D., Gunchinsuren, B. and Meyer, M., 2019. Compound-specific radiocarbon dating and mitochondrial DNA analysis of the Pleistocene hominin from Salkhit Mongolia. Nature Communications, 10(1), p.274.