Neanderthals' faces different from humans

Neanderthals, who appeared about 200,000 years ago, are quite distinct from modern humans in the manner in which their faces grow, a new study has found.
Researchers at New York University's College of Dentistry (NYUCD) have for the first time described the developmental processes that differentiate Neanderthal facial skeletons from those of modern humans.
They set out to understand the morphological processes that distinguish Neanderthals' faces from modern humans' - a potentially important factor in understanding the process of evolution from archaic to modern humans.
Bone is formed through a process of bone deposition by osteoblasts (bone-forming cells) and resorption by osteoclast (bone-absorbing) cells, which break down bone.

In humans, the outermost layer of bone in the face consists of large resorptive fields, but in Neanderthals, the opposite is true - in the outermost layer of bone, there is extensive bone deposition.
The researchers studied several well-preserved Neanderthal child skulls unearthed in 1926 in the British territory of Gibraltar and from the La Quina site in southwestern France.

They used an electron microscope and a portable confocal microscope to map for the first time the bone-cell growth processes (resorption and deposition) that had taken place in the outer layer of the facial skeletons of young Neanderthals.
"Cellular processes relating to growth are preserved on the bones," said Timothy Bromage of NYUCD's Department of Biomaterials.

"Resorption can be seen as crater-like structures - called lacunae - on the bone surface, whereas layers of osteoblast deposits have a relatively smooth appearance," he added.
The study found that in Neanderthals, facial bone-growth remodelling - the process by which bone is deposited and reabsorbed, forming and shaping the adult skeleton - contributed to the development of a projecting (prognathic) maxilla (upper jawbone) because of extensive deposits by osteoblasts without a compensatory resorption - a process they shared with ancient hominins.
This process is in stark contrast to that in human children, whose faces grow with a counter-balance action mediated by resorption taking place especially in the lower part of the face, leading to a flatter jaw relative to Neanderthals.

"This is an important piece of the puzzle of evolution," said Rodrigo Lacruz, professor at NYUCD.
"Some have thought that Neanderthals and humans should not be considered distinct branches of the human family tree. However, our findings, based upon facial growth patterns, indicate they are indeed sufficiently distinct from one another," she added.
Neanderthals share with older African hominins a similar facial growth pattern, researchers said.
The findings were published in the journal Nature Communications.