An ancient relative of humans shows a surprisingly modern trait

January 16, 2019 by Jeff Grabmeier, The Ohio State University
The original Xujiayao fossil. Credit: Song Xing, Chinese Academy of Sciences

A relative of modern humans that lived at least 104,000 years ago in northern China showed evidence of dental growth and development very similar to that of people today, a new study found.

An international team of scientists performed the first systematic assessment of dental growth and in an East Asian archaic hominin fossil that is known as the Xujiayao juvenile.

The fossil is of a 6 1/2-year-old who lived between 104,000 and 248,000 years ago found at the Xujiayao site in northern China.

The researchers were surprised to find that in most ways, this child's dental development was very similar to what you would find in a child today, said Debbie Guatelli-Steinberg, co-author of the study and professor of anthropology at The Ohio State University.

"The Xujiayao juvenile is the oldest fossil found in east Asia that has dental development comparable to modern humans," Guatelli-Steinberg said.

"It may suggest that these archaic humans had a slow life history like modern humans, with a prolonged period of childhood dependency."

The study was published today (1-16-19) in the journal Science Advances.

Teeth provide some of the best data anthropologists have about the growth and development of our ancient ancestors, she said. That's because growth lines in retain a record of dental development.

Compared to our primate cousins, modern humans—including their teeth—take a long time to form and develop. Anthropologists believe this characteristic is associated with humans' longer periods of child dependency—how long a juvenile relies on support from a caregiver.

Among other techniques, the researchers used synchrotron X-ray imaging to look inside the fossil to see the internal structure of the teeth, including growth lines that revealed the rate of tooth development.

The results were surprising in part because so many other features of this hominin are not modern, such as the shape and thickness of the skull and the large size of the teeth, according to the researchers.

The buccal view of the Xujiayao incisor and canine showing the pattern of perikymata distribution. Credit: Song Xing and Paul Tafforeau
"We don't know exactly where this enigmatic East Asian hominin fits in human evolution," said Song Xing, lead author of the study, who is at the Chinese Academy of Sciences in Beijing.

"It has some affinities to archaic relatives like the Denisovans and Neanderthals with, as we found, some more modern features. It is a strange mosaic."

Using the growth lines in the teeth, the researchers estimated the death of the Xujiayao juvenile at about 6 1/2 years of age, said study co-author Mackie O'Hara, a graduate student in anthropology at Ohio State.

The first molar of this juvenile—what we call the 6-year-molar today—had erupted a few months before death and had started to wear a bit. The root was about three-quarters complete, similar to humans today.

"We found that this juvenile was growing up—at least dentally—according to a schedule similar to that of modern people," O'Hara said.

Another aspect that was similar to modern humans was the perikymata, which are the incremental growth lines that appear on the surface of the tooth.

"We found that the way these perikymata were distributed on the Xujiayao juvenile teeth was close to what we see in modern humans, and not to Neanderthals," Guatelli-Steinberg said.

The the Xujiayao maxilla (left) and three-dimensional (3D) reconstruction of the teeth (right). Credit: XING Song

Another interesting finding related to the long-period growth line, which is laid down about every eight days in modern humans.

"This juvenile had a 10-day rhythm, which you don't see very often in early hominins," she said. "Most of the early hominins had a shorter rhythm, closer to seven days. This is another aspect that is much more modern."

The one aspect of dental development in the Xujiayao juvenile that was not modern was the rate of growth in the roots of the teeth. Here, the juvenile showed relatively fast growth, compared to a slower growth in modern humans.

While the dental development of this juvenile suggested it had a slow life course similar to modern humans, Guatelli-Steinberg cautioned that we don't know what happens in later childhood in hominins like this one.

"It would be interesting to see if dental development in later childhood, such as the growth and development of third molars, was also similar to ," she said.

Explore further: Neanderthal teeth similar to modern teeth

More information: S. Xing el al., "First systematic assessment of dental growth and development in an archaic hominin (genus, Homo) from East Asia," Science Advances (2018). DOI: 10.1126/sciadv.aau0930 , advances.sciencemag.org/content/5/1/eaau0930

Related Stories

Neanderthal teeth similar to modern teeth

September 19, 2005

Columbus, Ohio, researchers say they've determined Neanderthal tooth development was similar to that of modern humans. The Ohio State University researchers said their findings suggest the maturation period of the two hominid ...

What dental remains from Homo naledi can tell us

September 13, 2017

Anthropologists just love to sink their teeth into a good mystery, and some recent research from NC State and Vassar College has done just that – by looking at what dental development in Homo naledi fossils can tell us ...

Recommended for you

6 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Ojorf
4.7 / 5 (3) Jan 17, 2019
...related to the long-period growth line, which is laid down about every eight days in modern humans


Finally!!!
Solid scientific evidence.
I allays knew weekends should be 3 days long.
Da Schneib
3 / 5 (2) Jan 17, 2019
Probably we couldn't tell much difference between these and us. Most likely we could interbreed with them, since it's proven we could with Neanderthals. It will be interesting to see what gets made of these over the next decade or two, if we can find more fossils.
granville583762
4.2 / 5 (5) Jan 17, 2019
Humans developed independently around the continents of this world

It is sad to think as this Childs teeth were growing he was about to die
but we would not know what we now know
as the puzzle
is
as this child lived 104,000 years ago in northern China
as this child is identical in comparison to modern humans
this Childs ancestor developing into modern humans
where ever humans were all over the world 104,000 years ago
104,000 years ago in Africa where this Childs ancestors roots lie
must also have been developing into modern humans
in each continent humans have distinctive characteristics
even as they were identically developing into modern humans
that 104,000 years old human remains in Africa of 6.5year olds with distinctive African characteristics
as they developed into modern humans

As there is theory also humans developed independently around the continents of this world
torbjorn_b_g_larsson
5 / 5 (4) Jan 17, 2019
Probably we couldn't tell much difference between these and us. Most likely we could interbreed with them, since it's proven we could with Neanderthals. It will be interesting to see what gets made of these over the next decade or two, if we can find more fossils.


We also could interbred with Denisovans and possibly at least one other lineage in Africa, as well as Denisovans likely interbred with an earlier split (such as [i]H. erectus[/i ] which was present in the area).

But here is a new candidate for fossil find in the area, a putative lineage of an ancient Neanderthal-Denisovan hybrid nearly as old as its two ancestral lineages: https://phys.org/...man.html .
Osiris1
5 / 5 (1) Jan 19, 2019
Guy with the tooth on the right played ice (age) hockey.
Whydening Gyre
1 / 5 (1) Jan 19, 2019
Guy with the tooth on the right played ice (age) hockey.

I wonder what politically incorrect names they would have had for their teams back then...

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.