Amanda Maxwell

Jul 19th 2021

Two-Million-Year-Old Tooth Proteins Connect Orangutans With Ancient Apes

Not much is known about the family tree of the Gigantopithecus blacki, a giant hominid that lived around 2 million years ago. However, Nature reports that proteomic analysis of dental enamel in a fossil molar from one of these ancient apes links them as distant cousins to modern-day orangutans. Not only are these the oldest proteins ever analyzed, but the technique also opens the door to discovering more about our early ancestors, filling the missing links in the human family tree.

Enamel Protein Sequences Build the Family Tree

Fossils over a certain age usually don’t contain high-quality DNA, so in this study, the researchers used palaeoproteomics techniques to look instead at the ancient proteins contained in the tooth enamel. A EurekAlert press release describes how the team extracted proteins from a single molar that had been discovered from Chuifeng Cave in China. While DNA gives the genetic profile common to all cells, looking at the proteins shows the specific products of those genes in a particular tissue.

The team created protein profiles from the enamel samples, which they then compared with existing hominid proteomes in the database. This showed that the ancients apes were distant cousins of modern orangutans that diverged as part of the Miocene great ape radiation around 10 to 12 million years ago. The results also showed expression of alpha-2-HS-glycoprotein, according to the Nature report — an unusual finding that could explain the development of thick enamel crowns in the Gigantopithecus blacki molars.

Fossil Teeth Hold Surprising Riches

Before examining the enamel on the large fossil molar, not much was known about G. blacki apart from its possible size and weight. It lived between 300,000 and 2 million years ago in a tropical jungle area over southeast Asia. In this warm and humid climate, fossil records of bone rarely survive, but teeth are surprisingly robust.

A 2017 paper in The American Journal of Physical Anthropology describes how, in 1956, a Chinese farmer excavating a cave for manure for his fields dug up an enormous mandible or lower jawbone as well as numerous teeth. This finding helped researchers extrapolate the size of these ancient apes. BBC describes them as the largest primates ever on Earth, standing around three meters tall (just over nine feet) and weighing up to 500 kilograms (about 1,100 pounds).

Teeth hold a wealth of data for researchers, giving clues not only to the size of an animal but also to its diet and the way that it ate. In addition to the proteins uncovering the G. blacki family tree, the shape of the molars with their thick layer of enamel suggests that the apes ate bulky, fibrous plant materials. A 1990 paper in the Proceedings of the National Academy of Sciences reported scanning electron microscopy of the teeth, which showed evidence of the plant-based diet. The study found opal phytoliths on the tooth surfaces from silica deposits in plant cell walls.

Filling In Our Early Ancestor Missing Links

Palaeoproteomics could also help to fill in the missing links in the human family tree. Since our oldest ancestors also lived in warmer climates, ancient DNA is often badly degraded or not present at all. Being able to analyze the proteome in the fossils from our early ancestors could show how humans evolved.

The composition of teeth can also help scientists map out migration patterns in prehistory, giving valuable information on adaptation to climate change. Smithsonian Magazine reports how tooth composition can be used to map early human migration. Analyzing specific isotopes of the element strontium, which varies according to location, has been used to show when populations changed location, for example.

Fossilized dental plaque also shows what our ancient ancestors ate, revealing that being able to adapt to a greater variety of foods helped us move from jungle to savanna as the climate changed. This is one of the theories that explore why G. blacki became extinct. Their enormous size required large amounts of food, as National Geographic points out. As the tropical jungles vanished and turned into savannas, the ancient apes would not have been able to gather enough food to survive, and a lack of diversity in the diet meant they didn’t adapt.

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