Fossil site of the Western Water Half Musk. Photo courtesy of Institute of Paleovertebrate Vertebrate, Chinese Academy of Sciences
BEIJING, Sept. 18 (Xinhua) -- The horn is one of the most iconic structures of ruminants and one of the most important features of its identification classification. How did the horn originate and evolve? What are the features? Related research has long attracted the attention of the academic community.
At the site of Xishuigou in the Tabunbrook Basin in Gansu Province, a Sino-foreign cooperative team led by Chinese scientists found a new fossil of a more mysterious ruminant, the half-musk, about 20 million years ago, named "Xishui Half-Musk". This is the first time that a semi-musk fossil has been studied in detail in China, inferring that early ruminants had territorial behavior, which is expected to solve the mystery of the origin and evolution of ruminant horns.
This important research achievement paper on paleontological fossils was jointly completed by Deng Tao and Li Qiang, researchers of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, and Dr. Li Jiaokun of Nanjing University, and was recently published online in the international professional academic journal Linnaeus Journal of Zoology.
Territorial behavior and weight estimation of members of the early bovine family and the family Bovine. Photo courtesy of Institute of Paleovertebrate Vertebrate, Chinese Academy of Sciences
For the first time, skull appendages appear
Early ruminants were usually hornless , and horns gradually appeared later in the bovine family , giraffes , deer family , and forkhorn antelope. Recent genomics studies have shown that the horns on the heads of these ruminants may originate from the same cellular basis, but the histology and physiology of the horns between different families are very different, and the fossil types are also numerous, so whether the horns originate once or multiple times is still an unsolved problem.
Researcher Deng Tao, co-corresponding author of the paper, pointed out that this study has newly discovered the fossil material of Xishui hemimuthus and sorted out the systematic relationship between angular ruminants of different taxa, which is undoubtedly the key to solving the problem of angular origin.
Li Jiaokun, the first author of the paper, introduced that as a more mysterious class of ruminants, the previous fossil record of the semi-musk can only trace to scattered teeth, or stay on the fauna list. In January 2021, a systematic study of European hemimuth fossils was published confirming that hemimuth fossils are widely distributed in Western and Central Europe from the Late Early Miocene to the Miocene (about 20 million to 12 million years ago).
Chinese semi-musk fossils are currently found only in the Tapengbrook Basin in Gansu and Xiacao Bay in Sihong, Jiangsu Province. The semi-musk fossil material studied included a partially preserved skull, a relatively complete jaw and two partially preserved maxillas, which were collected in the Tabunbrook Basin in 1999, 2014 and 2015. As the first detailed study of a hemimuth fossil in China, the Sino-foreign cooperation team classified the fossil as a semi-musk genus based on the morphological characteristics of the buccal teeth of the fossil, and further established it as a new species of Xishui half musk based on the first appearance of horn-like skull appendages in the genus, including supraorbital bulge, preorbital bulge and thickened frontal bone.
Fossil buccal teeth of the Nishiwa half-musk. Photo courtesy of Institute of Paleovertebrate Vertebrate, Chinese Academy of Sciences
The effect is similar to the territorial behavior of the horns
Due to the lack of complete fossil materials and systematic studies for a long time, there are many controversies about the location of the semi-musk system, including being considered or attributed to the deer family, near the forkhorn antelope family, near the bovine family, and located within the musk family.
Deng Tao said that in this study of Xishui hemimuthus, the Sino-foreign cooperation team integrated the morphological characteristic matrix related to early ruminants that have been published so far, adopted the topological constraints of the latest genomics of ruminants, and used the maximum simplicity method for phylogenetic analysis to identify the semi-musk located in the basal position of the cattle family (bovine family and musk family).
In response to the question of what role the skull appendages of the Western water half musk are, the team demonstrated for the first time the ancillary structures developed on the half musk skull, showing that the west water half musk retains a supraorbital bulge, anterior orbital bulge, and a thickened frontal bone. Among them, the supraorbital bulge is located directly above the orbit and may be closely related to the horns of the ruminant; the preorbital bulge appears on the left and right sides of the skull, and this structure is also seen in early dinosaurs and protocornes, which is considered evidence of a lateral attack on the head; and the thickening of the frontal bone is most likely due to the adaptive support of the frontal bone during head impact.
Based on this, the research team speculates that the function of the skull appendages of the Western water half musk is most likely similar to the role of bull horns in territorial behavior.
To extrapolate the territorial behavior of early ruminants, the team also collected behavioral traits of living bovine and muskratidae, including living in territory all the time, showing temporary territoriality and non-territoriality during estrus or in special circumstances. Reconstructing ancestral traits based on phylogenetic relationships, the team concluded that members of the latest basal stem taxon, the bovine family and the general family of cattle, statistically significantly showed territoriality and had always lived in the territory.
Fossil skull of The Western Water Half Musk. Photo courtesy of Institute of Paleovertebrate Vertebrate, Chinese Academy of Sciences
Horns appear or increase the diversity of the total family of cattle
Regarding the origin of ruminant horns, there are currently two hypotheses of competing for mate weapons and metabolic feedback of foreguam fermented animals, the conjugal arms hypothesis refers to the larger ruminants who evolve horns to adapt to the open environment as weapons for competing for mates; the metabolic feedback hypothesis of foregut fermentation animals refers to the use of foregut fermented ruminants to cope with the increase of seasonal changes and evolve angles to balance the fluctuation of the proportion of weight and bone weight brought about by seasonality.
Deng Tao said that considering that the horns of ruminants are limited to the frontal top area, and that the early members of the bovine family and the family of cattle showed territoriality, the team believes that the hypothesis of competing for mate weapons may be more suitable to explain the origin and evolution of the horns of members of the family of cattle.
However, the team also pointed out that the weapons hypothesis may have problems such as "weight greater than 18 kilograms is not necessary for ruminants to have horns" and "in addition to competing for mates, the early evolution of horns may also be closely related to the competition for food resources" and so on.
System location of the West Water Half Musk. Photo courtesy of Institute of Paleovertebrate Vertebrate, Chinese Academy of Sciences
First of all, the real horns of the deer family and the horns of the forked horn family appeared later than the horns of the cattle family, giraffe family and the ancient deer family, and the climate was just before and after the Miocene climate suitable period, if the climatic environmental changes delayed the emergence of the horns of the deer family and the fork horn family, then the most likely way is to indirectly reduce the role of the horns by enriching plant resources.
Secondly, the early bovine and deer are all facultative plant eaters, that is, what plants can be touched will eat what food, if there is migration and proliferation, it is bound to cause uneven distribution of plant resources in the region, and territorial ruminants will compete and conflict with outsiders.
Therefore, before the appearance of horns, the way ruminants fought most likely depended on the advantage of weight, and the appearance of horns, bone- and hard, even if broken, would not be fatal, so that members of the bovine family of comparable size had a relatively more flexible and less costly way of fighting. "That is to say, the appearance of horns may provide opportunities and possibilities for the increase in the diversity of members of the bovine family who are close in size." Deng Tao said. (End)
Source: China News Network