THU 7 FEB 2019 04:28 PM
Scientists Analyze 100,000-Year-Old Child’s Teeth:
An ancient child with a mysterious evolutionary background represents the oldest known case of human like tooth growth in East Asia, researchers stated.
The child fossilized upper jaw contains seven teeth that were in the process of developing when the roughly 6½ year old youngster died at least 104,000 years ago and possibly more than 200,000 years back.
Using X rays to examine the teeth’s internal structure revealed that the 1st molar, which typically sprouts through the gums at around age 6 in kids today, had erupted a few months before death.
The root of that tooth was about 3-quarters complete, similar to the pace of development in modern human children. Other tooth roots discovered in the fossil grew more rapidly than those of modern youngsters.
But the ancient childs overall dental growth and development falls within the range observed among kids today, paleoanthropologist Song Xing of the Chinese Academy of Sciences in Beijing and her colleagues report online.
That human like rate of dental development suggests that the youngster belonged to an East Asian Homopopulation with a relatively long life span and an extended period of child care, the scientist speculate.
Those characteristics are associated with present day humans lengthy period of tooth growth. But it is hard to know where the childs remains, unearthed with other hominid fossils at a northern Chinese site called Xujiayao in the late 1970’s, fit in human evolution.
Identifying the Chinese fossils species is difficult because these finds have an unusual mix of features.
A thick brain case and large teeth most resemble traits of Neandertals and Homo erectus, 2 now-extinct members of the genus Homo. Yet the shapes of several cheek teeth look most like corresponding teeth of Homo sapiens.
Xing and colleagues suggest that it is also possible that the Xujiayao fossils come from Denisovans, an enigmatic East Asian population known mainly from ancient DNA .
Fossil and ancient DNA analysis suggest that all 4 Homo species lived in the region during the period that the childs fossil is dated to.
Regardless of species, the Xujiayao child provides the 1st peek at dental development in an ancient East Asian Homo population, says paleoanthropologist and study coauthor Debbie Guatelli-Steinberg of Ohio State University in Columbus.
“Modern humans develop slowly, and at least for the first 6½ years of life, the dentition of the Xujiayao individual suggests that it also developed slowly,” she says.
Lines that form in teeth at regular intervals during childhood mark enamel layers that accumulate daily and over longer period.
The Xujiayao childs age and dental growth rates were calculated by counting daily enamel layers. Intriguingly, a distinct growth line that forms about every 8 days in human childrens enamel materialized more slowly in the Xujiayao child’s teeth, about every ten days.
But it is hard to know from that one piece of evidence whether the ancient child matured even more slowly than youngsters today do, the scientist caution. The same growth line appears about every 7 days in other fossil hominids.
It is also not known whether the ancient child’s teeth would have continued to develop at a relatively slow, humanlike rate after age 6½. And it is unclear if the rest of the child’s skeleton matured gradually.
Because the species ID of the Xujiayao child is up for grabs, the significance of its slowed tooth growth is murky, says paleoanthropologist Tanya Smith of Griffith University in Nathan, Australia. Smith, who did not participate in the new study, investigate dental development in ancient hominids.
If the Chinese find belongs to H. sapiens, its dental growth rate and other tooth traits align with those of fossil H. sapiens from Israel and North Africa dating to as early as around 300,000 years back, Smith says.
H. sapiens, as well as H. erectus and Neandertals, display a wide range of sometimes overlapping dental traits and growth rates over time, she adds. That complicates classification efforts based on teeth alone.
Extracting DNA from the Chinese youngsters jaw or teeth would help to clarify its evolutionary standing. No such DNA retrieval attempts have yet been made, Guatelli-Steinberg says.