Why did the 3-meter-tall distant relatives of humans become extinct? New research finds that it was because of "poor diet"

A paleontologist once said that finding secrets in fossils is like solving Sherlock Holmes cases.

How to understand this sentence? Perhaps it means that with the help of fossils and modern analytical methods, scientists have the ability to travel through time and space and return to the "scene of the crime."

Among various "cases", "extinction cases" (extinction of organisms) always attract attention, such as the extinction of dinosaurs, which has always been the focus of everyone's attention. However, it is difficult to determine the specific cause of the extinction of a certain species, especially for some species with relatively little fossil evidence, such as the protagonist of today's article - Gigantopithecus brevis.

Recently, a team of scientists from China, Australia and the United States solved the mystery of the extinction of Gigantopithecus brevis, which lived in Guangxi, my country. The research results were published in the top international academic journal Nature.

What was the process of “solving the case” this time?

Why did the 3-meter-tall giant ape become extinct? It has always been a mystery

First, we need to get to know the "victim", who is the following:

Reconstruction of Gigantopithecus brevis (Image credit: Garcia / Joannes-Boyau)

The discovery of Gigantopithecus bu's story has many twists and turns:

In 1935, Dutch paleoanthropologist Konig found a tooth in a Chinese medicine shop in Hong Kong that looked very much like a human molar, but was almost twice as big as today's human teeth. After comparison, he believed that the tooth came from an ape. In honor of the Canadian anatomist Dassen, who named the Peking Man, he named the "owner" of the tooth Gigantopithecus.

For a long time after the name was given, people could not find the origin of Gigantopithecus. In 1955, Chinese scholar Pei Wenzhong discovered the tooth fossils of Gigantopithecus in a black cave in Daxin County during an investigation in Guangxi. From this, we finally knew that Gigantopithecus came from caves in southern China. Later, Chinese scientists discovered several caves in Guangxi, such as Liucheng Gigantopithecus Cave, which buried Gigantopithecus fossils (of course, fossils of many other species), and found a total of 4 mandibles and more than 2,000 teeth.

Karst landform landscape in Chongzuo, Guangxi (Photo by Zhang Yingqi)

Now we know that more than 2 million years ago, Gigantopithecus once lived in the karst area of ​​southern China. They can be said to be the largest primates ever on Earth, with an upright height of up to 3 meters and a maximum weight of up to 300 kilograms. (Do you remember King Kong in the movie?)

These giant beasts are not direct ancestors of humans, nor are they offshoots (close relatives) of humans. They are close relatives of orangutans that are now active in Southeast Asia, belonging to the subfamily Orangutan, and are only distant relatives of modern humans who belong to the subfamily Homo.

(Image source: Institute of Vertebrate Paleontology and Paleoanthropology)

But previous studies have shown that this distant relative died out before humans arrived in the area, and only about 2,000 teeth and four incomplete jaws have been found to prove their existence.

Other primates living in the same area at that time successfully adapted to the environment and reproduced, and its close relatives, the orangutans, have survived to this day. Why did Gigantopithecus become extinct?

It can be said that this question has always been an unsolved case in the discipline. Although the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences has conducted a systematic investigation in the area for more than 10 years and collected more fossil evidence of Gigantopithecus, the cause of the extinction of Gigantopithecus is still puzzling us due to the lack of targeted systematic dating and paleoenvironmental analysis with clear age ranges.

Multidisciplinary "investigation" to reconstruct the "crime scene" hundreds of thousands of years ago

The multiple decisive evidences that truly solved the mystery of Gigantopithecus' extinction came from a complex multidisciplinary comprehensive study.

The principle of the research does not seem to be "complex" and can be explained with a single picture: find fossils and deposits of plants and animals of the same period as the giant ape, determine their ages, reconstruct the ancient environment of the time based on this, and then reproduce the feeding behavior of the giant ape at that time, and draw a more complete ecological picture of the prosperous period, transitional phase, extinction window (the time period for the extinction of the species) of the giant ape's survival, and the post-extinction period, and finally deduce the reasons for their extinction.

(Image source: Institute of Vertebrate Paleontology and Paleoanthropology)

The reason why it is called "complex" is that this research requires the collection of multidisciplinary samples and the use of multidisciplinary methods for testing and analysis. The people involved in the research include not only paleontologists, but also geologists and even rock climbing experts... Zhang Yingqi's research team from the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, cooperated with multiple scientific research teams from Australia, the United States and other places to show us a sad song of Gigantopithecus gradually disappearing in the long river of history.

Research methods used in this study (Photo provided by Pan Yue)

Step one: Collect samples, fly over cliffs, walk on walls, and explore caves.

Since 2015, Zhang Yingqi's research team has been conducting a "carpet-style" cave survey in Chongzuo, Guangxi, aiming to find more fossil clues related to Gigantopithecus. The team gradually explored and summarized the "cliff cave survey method" suitable for the karst peak forest and peak cluster landforms in Guangxi . The application of this method enables the research team to conduct cave surveys, assessments and excavations efficiently and systematically.

Survey of cliff caves and excavation scenes inside the caves (Photo credit: Zhang Yingqi)

In order to find more fossils, the research team will not choose caves that can be easily entered (the sites there have long been destroyed), but will look for caves on cliffs that are inaccessible to ordinary people. Only here may there be deposits and fossils that have not been destroyed by humans, such as this:

Source: Provided by Zhang Yingqi

Do you think "cliff-walking" is cool? Not really. If you're not careful, you might get stuck on the cliff...

After years of exploration, the research team, from a regional perspective, selected a total of 22 cave fossil sites discovered in Guangxi Zhuang Autonomous Region from 1999 to 2020 for systematic sample collection. The research covers 11 sites that produced Gigantopithecus fossils, as well as 11 later sites that did not produce Gigantopithecus fossils (as a control group for the previous 11 sites).

The second step is the detection and analysis stage.

The research team applied six independent dating techniques to fossil deposits and fossils themselves, obtaining a total of 157 radioactive dating results. These dating data were combined with the analysis results of eight aspects, including pollen, mammal groups, and tooth stable isotopes, trace elements, and micro-wear marks, to show us the causes and consequences of the extinction of Gigantopithecus. (Six Australian universities in the research team participated in the processing, testing and analysis of the samples.)

Research methods used in this study (Image source: Pan Yue)

1. Age determination to lock in the extinction window

In the huge data set of this study, the dating results are crucial. They are the starting point and cornerstone of the entire study. Revealing the exact cause of the extinction of a species is already a big challenge. Before that, only by determining the last time the species appeared in the fossil record can a clear time frame be established to reconstruct the paleoenvironment and restore the feeding behavior within this framework. On the contrary, without the support of reliable dating data, related research may be misled by wrong clues in the wrong time period.

The research team applied six independent dating techniques to fossil-bearing deposits and the fossils themselves, obtaining 157 radioactive dating results.

Luminescence dating measures the light-sensitive signals in the deposits that buried the Gigantopithecus fossils . It is the main dating technique used in this study, supplemented by the enamel system method (US) and the uranium-electron spin resonance method (US-ESR) for direct dating of Gigantopithecus tooth fossils. Direct dating of fossils can ensure that their age is corroborated by the luminescence dating results of the deposits that buried them.

In this way, a comprehensive and reliable timeline of Gigantopithecus extinction was constructed , and then based on Bayesian analysis, the extinction window was accurately locked in 295,000 to 215,000 years ago . In other words, the Gigantopithecus gradually became extinct during this period.

2. How did the environment change when the giant apes went extinct?

The research team reconstructed the environmental background that led to the ultimate extinction of Gigantopithecus through detailed analysis of pollen, charcoal, and mammalian populations.

The types of habitats reflected by the animal groups at different stages of the great apes’ survival (Image source: original paper)

The comprehensive analysis results show that 2.3 to 700,000 years ago was the heyday of Gigantopithecus, when woody plants accounted for a large proportion of the earth and the forests were lush; 700,000 to 295,000 years ago was their transition period, when the climate became more seasonal, the structure of forest communities began to change, the proportion of non-woody plants (such as ferns) gradually increased, and the environment began to become more diverse. Around 200,000 years ago was the late extinction period of Gigantopithecus, the forests degraded, the environment became more open and dry, and the grassland area increased significantly.

Changes in the environment will inevitably lead to changes in the giant ape's "diet".

3. From prosperity to decline, they ate worse and worse

Although it is somewhat unbelievable, dental tissue does contain rich information related to the feeding behavior of species, which can help us deeply understand their ability to adapt to the environment, the diversity of their food resources, the regularity of their feeding behavior, etc.

The team conducted trace element and microwear texture analysis on the giant ape's teeth.

According to previous studies, trace elements deposited in teeth can indicate the diversity of food available to animals . If clear bands of strontium (Sr) and barium (Ba) appear in the enamel, it proves that the food available to animals is not only abundant but also diverse, while if obvious bands of lead appear, it proves that animals drink water regularly. The texture of microwear marks in the enamel depends on the type of food in the animal's diet .

The research team found that during the prosperous period, Gigantopithecus showed multiple clear synchronous Sr/Ca and Ba/Ca bands in its enamel and dentine, but they turned into less obvious diffuse bands when approaching the extinction window. In addition, obvious lead bands can be seen in the teeth of Gigantopithecus during the prosperous period, but they became less obvious during the extinction window. The results of microwear analysis also showed that Gigantopithecus had obvious differences in diet during the prosperous period and when approaching the extinction window.

The truth of the case: The "picky" giant ape died in a changing environment

The results of this comprehensive study show that Gigantopithecus became extinct between 295,000 and 215,000 years ago, much earlier than previously thought, and that it flourished in forests with abundant and diverse food resources between 2.3 million and 700,000 years ago.

Between 700,000 and 600,000 years ago, the structure of forest communities began to change as seasonality increased and the environment became more diverse.

At this time, the "eating problem" of Gigantopithecus became more and more serious.

The data set contains the changes over time (time unit: ka millennium) (picture from the original text)

Gigantopithecus preferred food resources mainly from woody plants, such as leaves, flowers, and fruits. After the reduction of forests, they will inevitably face a shortage of food. The alternative foods they rely on are some high-fiber and low-nutrition foods, which greatly reduces the diversity of their food.

Despite this, their bodies became larger and more cumbersome, and their geographical range of feeding activities was greatly reduced. As a result, their populations faced long-term survival pressures and continued to shrink, eventually leading to extinction. However, the orangutans, close relatives of Gigantopithecus, became smaller and more flexible as their living conditions changed, and also changed their feeding behavior and habitat preferences, thus being able to survive the environmental changes.

The enlightenment of Gigantopithecus brucei to us

Orangutans can be considered "people who know the times" and have more flexible survival strategies and can quickly adapt to changes in the environment. However, Gigantopithecus is more like a "maverick" who has reached the end of his rope and is unwilling to go with the flow. Perhaps it was this stubbornness and conservatism that led to its demise.

Reconstruction of the life scene of the great ape (Photo credit: Garcia / Joannes-Boyau)

Due to the lack of skull and postcranial fossil evidence, we still know very little about this large distant relative. Do they live in trees or on the ground? What kind of displacement behavior do they adopt? What position do they occupy on the phylogenetic tree? Why do their body shapes change? To answer many questions like these, we have to wait for the discovery of more key fossil evidence in the future.

As the sixth mass extinction looms, it is imperative that we understand why species go extinct. As the story of Gigantopithecus extinction shows, exploring the causes of past unresolved extinction events will provide new starting points and insights for our understanding of the resilience of primates in the past and in the future, as well as the fate of other large animals .

Paper information: Researcher Zhang Yingqi is the co-first author and co-corresponding author of the paper, and Pan Yue, a graduate student from the Institute of Vertebrate Paleontology and Paleoanthropology, is the co-author. This research was funded by the Australian Research Council and the Chinese Academy of Sciences. Mr. Cui Qingwu from Beijing Cave Exploration provided professional technical support such as SRT and rock climbing to the scientific research team during the field expedition.

Written by: Zhang Wentao

Reviewed by: Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences

This article is from the "Science Academy" public account. Please indicate the source of the public account when reprinting.