(East thing asked) Wang Shiqi: Why is the neck of a giraffe so long?
China News Agency, Beijing, June 3rd, Question: Wang Shiqi: Why is the neck of a giraffe so long?
China News Agency reporter Sun Zifa
On the African savannah and in many zoos, giraffes always stand out for their long necks.
Why do giraffes have such long necks?
How did the long neck evolve?
This topic of public curiosity has long attracted the attention of the academic community.
The international cooperation team, led by researchers Wang Shiqi and Deng Tao from the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, and Meng Jin, a visiting researcher at the institute and director of the Mammal Department of the American Museum of Natural History, recently passed the latest research on the discovery in Xinjiang, China, about 17 million years old. The former bizarre early giraffe fossil "Xiezhipanjiaolu" has been continuously studied in depth, and the two factors of giraffe courtship struggle and feeding pressure have been deeply combined, confirming that courtship competition is the direct driving force for the evolution of giraffe long necks.
This important research paper, which greatly promotes the cognition of the evolution of the giraffe's long neck through fossil evidence, was published online on June 3, Beijing time, in the internationally renowned academic journal "Science".
On the eve of publication, the first author and co-corresponding author of the paper, researcher Wang Shiqi, director of the Ancient Mammal Research Department of the Institute of Paleo-Spine of the Chinese Academy of Sciences, accepted an exclusive interview with China News Agency "Dongxiwen" to interpret the research results and popularize the "past and present" evolution of giraffe long necks.
The following is a summary of the interview transcript:
China News Agency reporter: Most ordinary people only pay attention to the peculiar neck shape of giraffes. What are the similarities and differences in the skeletal structure of the necks of mammals, including humans? What are the views on the evolution of its long neck in the academic world?
Wang Shiqi:
Although giraffes have only 7 cervical vertebrae like other mammals, the average length of each segment is more than 30 cm, and the total length can reach 2.5 meters, while cloven-hoofed species such as buffalo have a cervical vertebrae length of only about 5 cm. Is it the only living relative of the giraffe in the forests of Central Africa?
? Xing, the average length of each cervical vertebra is only more than 10 cm.
How the giraffe's neck becomes longer is a banner topic of evolutionary biology, and it has been the focus of research since the era of Lamarck and Darwin. come.
Although the two leaders have different understandings of the process of neck elongation in giraffes, the motivation for neck elongation is the need to eat leaves at high places, and neither of them doubts it.
In addition to feeding needs, other related factors have also received increasing attention and research.
With the deepening of the observation of giraffe behavior, scientists have further realized that the elegant long neck of giraffe is also a weapon of courtship competition between males. The longer the neck, the stronger the damage to the opponent.
Giraffes and tourists at Guangzhou Zoo in May 2020.
Photo by China News Agency reporter Chen Chuhong
In 1996, Robert Simmons of the University of Cape Town and Lue Scheepers of the Etosha Institute for the Environment in Namibia published an academic paper stating that the giraffe's long neck is not an advantage for feeding. Significantly, on the contrary, long necks are particularly beneficial for male giraffes to gain an advantage in courtship competition.
They believe that courtship competition is the first driving force for giraffes' long necks.
This view has sparked widespread debate in the academic community, with many supporters and opponents. The academic community especially expects the paleontology community to provide important fossil evidence to support or deny the theory that "courtship competition" drives the evolution of giraffes.
China News Agency reporter: What is the status of giraffe fossil discovery and research? How was the Xinjiang Xiezhi Panjiao deer fossil discovered and named? How to study the relationship between it and giraffe?
Wang Shiqi:
Fossil evidence is not an easy job. Giraffes have many different fossil relatives, but the first and so far only genus with long necks is Giraffe itself, whose fossil record is no earlier than the Pliocene 5 million years ago. .
Are the cervical vertebrae lengths of other fossil species of giraffes not proportional to those of living ones?
? X is longer.
Especially the mainstream Siva mammals in the giraffe family, not only do they have no long necks, but they have evolved to be as stout as cows, and their necks are relatively shorter rather than longer.
In the very perfect fossil record of the Cenozoic, there is currently no evidence for the intermediate state of giraffe neck elongation. It seems that the giraffe's long neck was suddenly produced in a short period of time.
At the same time, researchers have come to realize that in the fossils of giraffes, the diversity of head and horn shapes is far greater than that of the more diverse deer and bovid families.
The giraffe skull is equipped with such a variety of horns, and what it means has also aroused the attention and thinking of the academic community.
It was also in 1996, the same year that courtship competition drives the evolution of giraffes' long necks, a team from the Institute of Paleontology of the Chinese Academy of Sciences discovered mysterious fossils in a stratum about 17 million years ago in the vast Gobi in the Ulungu River Basin in Xinjiang.
This is a fossilized skull of a large ruminant. The wall of the skull is abnormally thick. There is a huge disc covering the top of the head. There are four abnormally thick cervical vertebrae behind the skull. Among them, the first cervical vertebra The shape is particularly peculiar. In addition to the normal rotation function, an abnormally enlarged limit joint is also developed between the cervical vertebrae and the skull, and additional limit joints are also developed between the subsequent cervical vertebrae.
Unable to confirm the classification of the fossil, researchers have been calling it a "monster".
The working scene of researcher Wang Shiqi's field scientific investigation in the Gobi Desert in Xinjiang.
Photo courtesy of the interviewee
In subsequent field investigations, the team of the Institute of Paleo-Spine of the Chinese Academy of Sciences successively discovered dozens of similar "monster" specimens with varying degrees of completeness in the same period of strata in the Ulungu River Basin. Due to the special joints of its skull and cervical spine, research Some scholars believe that this is an animal that is extremely adapted to collision behavior, and further think that it may be related to some living animals (such as musk oxen, etc.) that have collision and courtship behavior in courtship competition, but beyond this consensus, " There has been no substantial progress in the study of "monster" fossils.
Beginning in 2015, I led a team to study and tackle these "monster" fossil specimens. For the first time in paleontology research, a high-speed dynamic simulation method was used. Sex is much higher than that of living animals such as musk ox that are adapted to head strikes, and it may also be the vertebrate that is most adapted to head strikes in the history of biological evolution.
Subsequently, through high-resolution computed tomography (CT) and 3D reconstruction of the structure of the "monster" inner ear, we found that the "monster" inner ear is completely different from the most likely bovine family previously thought, and also different from the deer family and musk family. etc., on the contrary, are consistent with the key characteristics of extant giraffes and confirmed by the European cooperative team with a large amount of data accumulation.
The initial finding that the "monster" belongs to the giraffe class makes it clear: the horn features already suggest giraffe-like properties, and it has a single horn that grows from the center of the parietal bone, which is found in the bovid, cervidae and pronghorn families. It has never happened before, but the horns of the giraffe and the shiwa beast grow on the parietal bone, and the giraffe has a single horn in the middle of the frontal bone.
Researcher Wang Shiqi introduced the fossils of "Xiezhi Panjiaolu" about 17 million years ago in his office.
Photo by China News Agency reporter Sun Zifa
With the discovery of a large number of "monster" tooth fossils, it has been proved from another perspective that it is a giraffe with a higher tooth crown.
On this basis, our team officially named the "monster" as "Xiezhi Panjiaolu", among which, Xiezhi is an ancient Chinese mythical beast with a single horn on the top of its head, which is considered to be a kind of unicorn. Since the Ming Dynasty, giraffes have been introduced to China, and people have called them unicorns.
China News Agency reporter: In addition to the conclusion that it belongs to the giraffe group, what important discoveries have been made in the evolution of the long neck?
Wang Shiqi:
Phylogenetic analysis shows that both the current giraffe and Xiezhipanjiao belong to the superfamily of giraffes. Their skulls and necks are very different in shape, but they are both related to male courtship struggles, and they both evolve in extreme directions.
By comparing the antler morphology of several major groups of ruminants, including giraffes, cattle, deer, and pronghorn, our team found that the diversity of giraffe antlers is much higher than that of other major groups, and the morphology is often extreme. This suggests that the courtship struggle of giraffes is more intense and diverse than other ruminants.
At the same time, giraffes and horned deer are both extreme fighters. In order to compete for the hearts of females, their males will not hesitate to develop some extreme weapons. Under the blessing of sexual selection, extreme behaviors have contributed to the evolution of various giraffe extremes in the history of evolution. Morphological evolution of the head and neck.
About 17 million years ago, the fossil ecological restoration of the "Xiezhi Panjiaolu" and the comparison map of the current giraffe.
Drawing by Wang Yu and Guo Xiaocong
Further analysis of the ecological environment of the Xiezhi Panjiao deer and the ecological niche it occupies found that the earth was in a warm period at that time, and the forest was dense in general. However, in the Xinjiang region where the Xiezhi Panjiao deer lived, the Qinghai-Tibet Plateau in the south was rapidly uplifting. , blocking the transmission of water vapor, making this area drier than other regions.
Enamel stable isotopes suggest that the Xiezhipanhorn deer live in open grasslands and may migrate seasonally.
For animals at that time, the barren grassland environment was not as comfortable as the forest environment, and the fierce fighting behavior of Xiezhi and Panjiao deer may be related to the pressure brought by the living environment.
At the beginning of the appearance of the present giraffe, it also encountered an environment similar to the Xiezhi and Panjiao deer: about 7 million years ago, the East African plateau also changed from a forest environment to an open grassland, and the environment on which ancient giraffes lived gradually disappeared, prompting them to have to. Adapt to new changes.
When the present genus Giraffe appeared 5 million years ago, giraffes with taller bodies may have developed a way of attacking competitors by shaking their necks and heads during this period. Through this extreme fighting method, the blessing of sexual selection The giraffe's neck lengthened rapidly within 2 million years and became the current giraffe genus, thus effectively occupying a relatively marginal but highly rewarding ecological niche for feeding on high leaves.
China News Agency reporter: The research paper on the fossils of Xiezhi Panjiao deer has been published in a top international journal. What is the significance of this achievement?
Wang Shiqi:
The discovery of the Xiezhi Panhorn deer fossil provides important fossil evidence for unraveling the evolutionary mystery of the giraffe's long neck.
Among the fossils of the giraffe family, the shape of the head, neck and horn is very diverse.
The giraffe's long neck with small antlers, and the sturdy neck with disc-shaped horns of the Xiezhi, are just two extreme examples, both of which are related to the way males fight in courtship: both giraffes and antlers They are extreme fighters whose extreme behavior, under the auspices of sexual selection, promotes extreme morphological evolution in giraffes.
Looking back at the entire evolutionary history of giraffes, at the beginning of evolution, the ecological status of giraffes was more marginalized than those of the bovid family, which seems to predetermine their evolutionary path: marginalized ecological positioning promotes extreme intraspecific Courtship competition, and extreme courtship competition promotes extreme morphological evolution.
This is enough to cause the academic community to think more deeply about the evolution direction, strategies and results of species.
The study of the Xiezhi Panjiao deer, a species with a similar pedigree, a similar evolutionary environment, and the same evolutionary strategy as the giraffe, has greatly promoted our understanding of the details of the giraffe's neck evolution. Although there are still many details that cannot be fully understood, However, the study of the fossils of the Xiezhi Panjiao deer has opened a new window for obtaining this secret.
If you want to ask whether the long necks of giraffes are for food or sex?
Our latest research gives the answer: Eating may be an outcome, and sex may be a pathway to that outcome.
The important thing is that each species must find its own place in the ecological environment in order to survive in a challenging world.
(Finish)
Interviewee Profile:
Photo by China News Agency reporter Sun Zifa
Wang Shiqi, young paleontologist, director and researcher of the Paleomammal Research Office of the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, doctoral tutor of the University of Chinese Academy of Sciences.
Mainly engaged in the systematic evolution of Cenozoic large mammals and the Cenozoic biostratigraphy in East Asia, focusing on the major scientific issue that the uplift of the Qinghai-Tibet Plateau caused the aridification of inland Asia to become the evolutionary center of the open fauna in the northern hemisphere.
Important research achievements that have been completed include: discovery of the driving force and ecological factors of the specific evolution of the head and neck of giraffes (such as the evolution of long necks); proposing the differentiation and ecological radiation of feeding methods in early elephants, and the change of feeding organs from the mandible to the proboscis The evolutionary process of transfer; proposed that the Qinghai-Tibet Plateau and inland Central Asia were the evolutionary centers of the subfamily Ophia, and found important fossil evidence; proposed the theory of the heterochronic evolution of sex of large ungulates.
He has presided over and is carrying out a number of scientific research projects such as the strategic pilot science and technology special sub-project of the Chinese Academy of Sciences, the basic special sub-project of the Ministry of Science and Technology, and the major project sub-project of the National Natural Science Foundation of China, and has published nearly 100 professional academic papers.