Chinanews.com, Beijing, November 11 (Reporter Sun Zifa) As we all know, the nose of mammals is mainly a respiratory and olfactory organ, but the proboscis represented by elephants is an exception - their long, soft and flexible snouts are also their important feeding organs.
According to the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences (Institute of Vertebrate Paleontology), the Chinese research team has recently conducted in-depth research on the diversity and evolution of the proboscis jaw and its co-evolution with the elephant trunk, revealing the feeding patterns of early elephants and the unique evolution of related organs.
Three-dimensional reconstruction model of a shovel-toothed elephant (Wang Yu/production). Courtesy of the Institute of Paleospine, Chinese Academy of Sciences
This important study on the co-evolution of the jaw and proboscis of proboscis was completed by Wang Shiqi and Deng Tao, researchers of the Institute of Paleovertebrate of the Chinese Academy of Sciences, Li Chunxiao, postdoctoral fellow of the University of Chinese Academy of Sciences, and Zhang Ji, professor of Huazhong University of Science and Technology, and the resulting paper was published online in the international academic journal "Electronic Journal - Life Science" (eLife) in the early morning of November 11, Beijing time.
Why do we need to do elephant trunk research?
According to the research team, elephants are the largest terrestrial mammals, and one of its most striking features is that it has a soft and flexible trunk, which is considered by experts in the mammalian encyclopedia to be the most sensitive organ in vertebrates, with at least 4,<> muscles and an extremely developed nervous system.
However, it is difficult to confirm the degree of development of the trunk of the ancestral group of elephants due to the lack of direct fossil evidence, but the academic community has long noticed that in the early stage of elephant evolution, including the Oligocene and Miocene, all kinds of elephants had extremely elongated mandibles and lower incisors, especially in the Early-Middle Miocene, the morphology of the lower jaw and lower incisors showed a high diversity.
Finite element mechanical analysis results and paleoecological environment reconstruction (Guo Xiaocong/drawing). Courtesy of the Institute of Paleospine, Chinese Academy of Sciences
How did elephants in this period use their jaws and lower incisors to feed? What is the role of the elephant's trunk in the feeding process? In the latest Miocene and Pliocene, the elongated jaws of elephants were unexpectedly shortened, what are the internal mechanisms of this legendary evolutionary process? There is no rational explanation for these important questions about the evolution and biological adaptation of the mandibular and proboscis of early elephants.
How was the latest research conducted?
The research team pointed out that previous studies have shown that as early as 1700 million to 1500 million years ago, during the Miocene climate suitable period, the star species of early elephants, shovel-toothed elephants with shovel-like jaws, had developed a feeding method of wrapping the trunk around the plant with the lower jaw cutting off the plant, which is the earliest evidence that the elephant trunk has achieved the function of curling the grip.
Based on this, the latest research has conducted a comparative study of the functional morphology of the three main types of long-jawed mastodons, namely shovel tooth elephant, chimer tooth and pig-sided tooth elephant, and found that their lower jaw morphology is different: the shovel tooth has a lower incisor that is wide and flat like a shovel, and the upper incisor teeth are short and curved downward, and there is no enamel band; The lower incisors of the incisor are club-shaped, the upper incisors are long, also curved downward, and have enamel bands; The anodont does not have lower incisors, but the mandibular symphysis is elongated and grooved, the upper incisors are stout and curved outwards upwards, and there is no enamel band.
In addition, their nose features are also different, compared to the other two types of early elephants, the nasal bone of the shovel-toothed elephant is the smallest, the structure around the nostril is the most complex, and even more evolved than the living elephant, these nose-related skeletal features indicate that the shovel-toothed elephant has a very well-developed trunk (the smaller the nasal bone, the more developed the trunk).
The relative abundance and enamel isotope values of three types of early-Miocene long-jawed elephants in northern China, as well as the fossil assemblages and corresponding biological ages of elephants at different sites (Source: Li Chunxiao). Courtesy of the Institute of Paleospine, Chinese Academy of Sciences
In order to further uncover the feeding and feeding patterns of these three elephants, the research team used a variety of research methods, including enamel carbon and oxygen stable isotope analysis and finite element mechanical analysis, to reconstruct the feeding behavior of these early elephants. The latter becomes a key means of restoring feeding patterns.
What are the key results of the study?
According to the research team, the results of their joint study have shown that shovel-toothed, pig-edged and chimeric tooth elephants have different feeding patterns and living environments:
The shovel-toothed elephant lives in a relatively open environment, and its lower jaw is only suitable for cutting plants that grow vertically, while the shovel-toothed elephant uses a flexible snout to hold the plant and then uses the lower jaw to cut horizontally, which is very efficient.
The elephant lives in a relatively closed environment and is suitable for cutting horizontal or oblique branches, which it uses to press the branches with the help of its nose and then cooperates with its jaw to complete the feeding.
The habitat of chimerodont is between or overlapping with both, and its feeding patterns are diverse, and it can be well adapted to woodland and grassland.
The phylogenetic position of the family Pornodontidae, Shovelodontidae and Chimerodontidae, as well as the comparison of the morphological characteristics of the jaw and nasal regions of the three elephants (Source: Li Chunxiao). Courtesy of the Institute of Paleospine, Chinese Academy of Sciences
The results of this study show that for early elephants, the elongated mandible and lower incisors are the main feeding organs, while the trunk is only used as an auxiliary tool, and the early elephants with different jaw morphologies have different ecological adaptability. As the ecological environment gradually became dry and cold, the shovel-toothed elephant was more able to adapt to the relatively open ecological environment and feed on herbaceous plants, which eventually promoted the development of trunk grasping function and flexibility.
What is the significance and impact of the results?
The research team concluded that the expansion of shoodonts into open habitats was terminated by extinction events including shovel-toothed elephants caused by the Tortona extreme heat event in the early Late Miocene, but the chicodonts continued to spread into the open habitats of the Late Miocene, and in the process of the evolution of the trunk to higher flexibility and stronger grasping function, the feeding function of the elephants was completely transferred to the proboscis, which eventually led to the shortening of the original feeding organs, the lower jaw and lower incisors. Therefore, the adaptability of feeding behavior in the open environment is the "catalyst" for the evolution of elephant trunk grasping function.
This study provides important evidence for understanding the evolutionary and ecological context of the trunk and jaw of elephants, an important taxon, and provides new insights into how proboscis adapts to the environment and how environmental changes shape the evolution of unique organs.
The latest research results on the evolution of the elephant trunk completed by Chinese scientists have also been highly recognized and evaluated by journal editors and international peer reviewers. According to them, this research integrates a variety of cutting-edge methods and provides very convincing results in multiple aspects such as ecomorphology, behavioral ecology, and co-evolutionary biology. The study is well-documented, beautifully illustrated, well documented and detailed, and the 3D models and animated videos are easy to understand, "which is of great significance for understanding the diversity of proboscis species and the co-evolution of feeding organs, and also provides a solid foundation for further exploration of life science and evolutionary biology." (ENDS)