A tooth from a Neanderthal child who lived 120,000 years ago suggests that our cousin species began cutting their baby teeth at 4 months – earlier than for the average modern human
24 November 2021
The first estimate for when a milk front tooth erupted from the gum in the upper jaw of a Neanderthal child is revealing new information about the development of our extinct cousins. The young owner of the deciduous tooth – sometimes known as a baby tooth – lived in what is now Krapina, Croatia, about 120,000 years ago, and the tooth may have emerged sooner after birth than we expect for our own species – from around 4 months of age rather than from about 7 months.
Front teeth, or incisors, are generally the first to erupt from the gum. They enable infants to start eating harder foods. Until now, very little was known about how milk teeth developed in Neanderthal children.
“Milk teeth are a unique window on the prenatal life and early childhood of past populations. They grow as part of a developing organism. So, we can use teeth to get information on the growth rates of children,” says Alessia Nava at the University of Kent, UK.
Nava and her colleagues used high-energy X-rays to take three-dimensional pictures of the Neanderthal tooth, from the white top part of the tooth called the crown, down to a small part of the tooth root.
A tooth’s crown is made of enamel. In the enamel of milk teeth, there is a faint mark called the neonatal line below which there is enamel produced before the baby was born and above which lies enamel laid down postnatally.
Enamel is deposited by cells in a daily cycle, which gives it a pattern of stripes called cross-striations. The distance between adjacent stripes represents the amount of tooth growth in a day.
“As cells are laying down the enamel, they produce a slightly less mineralised substance every 24 hours, producing cross-striations. They’re our fundamental way of establishing the time [between birth and tooth eruption],” says Patrick Mahoney, also at the University of Kent, and a lead author of the study.
The team used these growth lines to assess how well-developed the incisor was at birth, and how much post-birth developmental time was required before it was mature enough to emerge. The group then checked the estimate by analysing a jawbone from a Neanderthal that carries three teeth that were about to erupt at the time the Neanderthal died.
The team estimates that Neanderthals began to cut their milk teeth between around 4 months to nearly 8 months after birth. Modern human milk teeth typically emerge later, between around 7 and 10 months of age.
The single Neanderthal baby tooth provided additional information that also pointed towards early eruption. By looking at the thickness of its daily enamel layers – and the thickness of dentin layers in the root that are also deposited daily – the team concludes that both the enamel and dentin grew at rates higher than those for modern humans, indicating that the tooth would have completed its development sooner.
The team says earlier tooth eruption may have enabled Neanderthal babies to eat harder foods at a younger age than is the case for modern human babies. This could have helped young Neanderthals meet the energy needs of their brains, which are thought to have been slightly larger than modern human brains.
“This study is of great interest because these are the first baby teeth to emerge into the mouth, giving us some indication of how fast Neanderthal babies needed to start processing solid foods,” says Debra Guatelli-Steinberg at the Ohio State University.
Journal reference: Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2021.2079
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