Jaw fossil shows hybrid trait of ancient and modern humans

Because of the lack of this characteristic, the scientists hypothesize that this early human was closely connected to older Middle Pleistocene species, most likely Homo erectus. 

This sort of hybrid morphological trait has reportedly never been observed in the skeleton remains of an East Asian Middle Pleistocene hominid. 

“The combination of both archaic and modern human features identified in the HLD 6 mandible is unexpected, given its late Middle Pleistocene age and differs from approximately contemporaneous Homo members such as Xujiayao, Penghu, and Xiahe,” mentioned the study. 

The findings suggest that modern human features may have first evolved among our ancestors some 300,000 years ago. 

The hybrid jawbone owner remains a mystery 

The researchers also retrieved a partial skull and a few leg bones from the same location. 

A deeper examination of the skull revealed that the facial bones are more similar to those of modern people than the jawbone. 

However, it has been difficult to determine which ancient species the entire skeleton belongs to. 

Reportedly, some of the mosaic morphologies were previously attributed to Denisovans. 

However, the presence of a unique mix of features seen in the Hualongdong specimen has added to the puzzle. 

The authors speculate that the remains may entirely belong to the third human lineage, which could be linked to Homo sapiens but not H. erectus or Denisovan.

In this case, the unidentified species had most likely had some evolutionary relationship with late Middle to Late Pleistocene hominins and shared some of their characteristics.

The findings were published in the Journal of Human Revolution.

Study abstract:

Excavations in Hualongdong (HLD), East China, have yielded abundant hominin fossils dated to 300 ka. There is a nearly complete mandible that fits well with a partial cranium, and together they compose the skull labeled as HLD 6. Thus far, detailed morphological description and comparisons of the mandible have not been conducted. Here we present a comprehensive morphological, metric, and geometric morphometric assessment of this mandible and compare it with both adult and immature specimens of Pleistocene hominins and recent modern humans. Results indicate that the HLD 6 mandible exhibits a mosaic morphological pattern characterized by a robust corpus and relatively gracile symphysis and ramus. The moderately developed mental trigone and a clear anterior mandibular incurvation of the HLD 6 mandible are reminiscent of Late Pleistocene hominin and recent modern human morphology. However, the weak expression of all these features indicates that this mandible does not possess a true chin. Moreover, a suite of archaic features that resemble those of Middle Pleistocene hominins includes pronounced alveolar planum, superior transverse torus, thick corpus, a pronounced endocondyloid crest, and a well-developed medial pterygoid tubercle. The geometric morphometric analysis further confirms the mosaic pattern of the HLD 6 mandible. The combination of both archaic and modern human features identified in the HLD 6 mandible is unexpected, given its late Middle Pleistocene age and differs from approximately contemporaneous Homo members such as Xujiayao, Penghu, and Xiahe. This mosaic pattern has never been recorded in late Middle Pleistocene hominin fossil assemblages in East Asia. The HLD 6 mandible provides further support for the high morphological diversity during late Middle Pleistocene hominin evolution. With these findings, it is possible that modern human morphologies are present as early as 300 ka and earlier than the emergence of modern humans in East Asia.