Fossil teeth offer new insights into human and primate history

A new window on human history has been opened by a global team of scientists who have discovered an innovative method to identify ancient seasonal climates using teeth.

Scientists have developed a new way to establish the role that ancient climates and seasonal behaviors played in the development of primates and humans, using microsamples of oxygen isotopes taken from fossilized teeth.

Professor Tanya Smith of Griffith University and David Green of Columbia University said in a Conversation article that, like trees growing outward and leaving growth rings, teeth grow in microscopic layers during l ‘childhood. Since climates and seasonal changes can change the width of growth rings, it is obvious that climates and changes in the body can also be seen in the growth layers of teeth.

Seasonal climates also influence body chemistry because the composition of oxygen isotopes in drinking water and food naturally varies in different climates. Heavier oxygen isotopes are more abundant in drinking water and food from dry, warm environments, while the reverse is true for water and food in humid, cool climates.

Micro-samples of fossilized tooth enamel can harvest the oxygen isotopes, which can remain stable for millions of years, locked inside these layers of growth to uncover the climates experienced by the animal when he was alive.

The study found that the composition of oxygen isotopes in teeth reveals details about seasonal rainfall, animal behavior and environmental conditions.

Smith said in a press release from Griffith University that the research is of great significance because seasonal changes in resource availability are thought to have influenced how species like great apes and modern humans evolved in the world. over time.

A thin slice of a 17 million year old Afropithecus tooth illuminated with polarized light reveals gradual growth (right to left). We microsampled oxygen isotopes weekly for more than three years, or 1148 days, in this tooth. Tanya M. Smith

The machine that makes it possible

The analysis of oxygen isotopes in teeth opens up a whole new branch of chronology for archaeologists. However, this comes with some challenges, including the fact that the growth layers of teeth are so small that the majority of chemical techniques cannot measure them.

This is where the High Resolution Sensitive Ion Microprobe (SHRIMP) comes in. The SHRIMP is a mass spectrometer, which was developed by the Australian National University, which can provide virtually non-destructive isotopic analysis of geological materials.

The researchers teamed up with ANU Emeritus Professor Ian Williams, a pioneer in the development of SHRIMP, to safely remove microscopic stains from fossilized teeth and measure the oxygen isotopes within. Climatic records in tooth enamel can be viewed with great precision because enamel has daily growth lines that can be seen in light microscopy.

What can teeth reveal

Using the fossilized teeth of ancient mammals from a 17 million year old site in Kenya, including Afropithecus turkanensis (a giant primate from the Miocene era), the study demonstrated that they were able to measure oxygen isotopes in these teeth to near -weekly accuracy.

The results showed that isotopes in tooth enamel can reflect human alterations to the terrain such as dams and record indications of historical weather events such as tornadoes, rain and hurricanes.

Additionally, records of a prolonged drought and an extreme rainfall event have been found in the monkeytooth growth layers that developed during the 1960s.

Additionally, the small-scale isotopic variation of teeth found in this study demonstrates that most previous studies of oxygen isotopes in teeth greatly underestimated the enormous seasonal variation in ancient landscapes.

Afropithecus Turkanensis

Following the result, the team compared the fossilized teeth to the teeth of modern primates across Africa with the fossil teeth of an Afropithecus and compared their results to their analysis of monkey teeth from the 1960s and old models of rainfall, which they simulated using state-of-the-art technologies. climate models. The results of the study suggest that over time, fossil apes experienced dry and wet seasons of varying intensity.

“The effects of climatic variations on early African apes are poorly understood because detailed records of seasonal variations from this early period – the Miocene – are rare,” Green noted.

“The isotope values ​​of Afropithecus and closely associated herbivores suggest that apes in this part of East Africa lived in seasonal forests or woodlands long before the origin of hominids.”

In an email to The Epoch Times, Smith said a number of 17-million-year-old land mammals have been observed alongside Afropithecus, including a type of prehistoric hippopotamus, giraffe, hyrax, rhinoceros and deer, including Anthracotheriidae, Giraffidae, Rhinocerotidae, Suidae and Titanohyracidae.

They also used samples from two types of prehistoric elephant species, Deinotheriidae and Gomphotheridae.

Smith said that although some mammals have no comparable modern species, the group of ancient animals analyzed includes species resembling giraffes, hippos and pigs.

Epoch Times Photo
Oxygen isotopes of Afropithecus teeth reveal wet and dry seasons that occurred 17 million years ago in East Africa. Daniel R. Green and Tanya M. Smith

The ancient climate explains the new characteristics of the first monkeys

The researchers noted that the new approach could also lead to a better understanding of the different characteristics of each species and the behavior of these creatures in their environment.

“We can see the impact of this seasonal climate on new anatomical features and behaviors of early apes,” Green said.

Meanwhile, Smith noted that more detailed data from ancient climates could better explain key features of early apes, such as unusual anterior tooth configurations and thick tooth enamel. She said these characteristics favor the consumption of hard foods, during seasons of drought or resource scarcity when foods that are easier to consume are not available.

“Another trait is their long and slow dental development, possibly related to a longer childhood, which has been suggested to allow more time for learning.”

“It would have been useful in more seasonal environments when foods follow complex spatial and temporal availability,” she said.

Analysis offers insight into human history

Over the past five years, Smith, Green, and Williams have been working on using this new form of analysis on human teeth to aid in the study of living and ancient humans.

In 2018, researchers provided an assessment of ancient seasonality using the teeth of Neanderthal children and currently they plan to sample African hominin teeth from the Turkana Basin in Kenya.

Smith said it’s possible to detect historic or prehistoric weather events if they persist for more than a few days using this new method. However, without another source of evidence such as a very good chronology of tree rings, she said it would be very difficult to link major droughts or storms to specific calendar years.

“We were able to identify droughts and storms in East Africa because we knew roughly when the primates grew up (i.e. the 1960s) and we could link our isotope data from oxygen to precipitation records.”

Lily Kelly


Lily Kelly is an Australian reporter for The Epoch Times, covering social issues, renewable energy, environment, health and science.

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